Academic literature on the topic 'Lizard Sex'

AbstractStomach flushing is one of the proposed techniques to study lizard diets. Apparently, it is ranged, together with direct observation and faecal analysis, as a non-harmful method for dietary studies. Some works explored the usefullness of stomach flushing, but we lack information about its effect on lizard's survival probabilities. In this paper we studied the effect of stomach flushing in an urban population of the rainbow lizard (Agama agama) from Calabar (Nigeria). During a period of five months of 2010, 147 lizards were noosed, sexed and individually marked. One group of lizards was stomach flushed only once, whereas the rest of lizards were not flushed. The flushed sample of lizards showed a lower survival than non-flushed lizards of all sex and age classes. In this study, the pictured diet from stomach flushing was very similar to results obtained with a faecal analysis of the same lizard population. Thus, both methods seem to be reliable to study the diet of the rainbow lizard. However, our results indicate that stomach flushing increases the probability of mortality (or at least emigration rates) in all age and sex classes, precluding its extensive use as a method to study lizard's diets.

Abstract The sand lizard (Lacerta agilis) is a common species in Europe that inhabits a wide range of habitats, including anthropogenic environments. It is a frequent carrier of common ticks (Ixodes ricinus), which poses a severe threat to the lizards’ health. We determined the living space used by lizards in a rapidly changing environment and ascertained the number of parasitic ticks found throughout the reptile’s active season. We conducted telemetry research on a dynamically developing housing estate located on the outskirts of the city of Zielona Góra (western Poland) in 2016-2017. We obtained data from 16 adult lizards, from which we collected 2529 ticks. Using generalized linear models (GLMs), we determined the relationships among the number of transmitted parasites, size of occupied areas (minimum convex polygon, MCP), the weight of lizards, and sex of lizards. Results indicated that the number of ticks was negatively correlated with lizard body mass, but positively correlated with home range. Sex was not significantly associated with the number of ticks. Additionally, the parasite load was lower during the lizard’s non-breeding season than during the breeding season and was lower for males than for females during the non-breeding season. Males have larger home ranges than females.

SUMMARYSex ratio theory usually predicts an equilibrium sex ratio and equal proportions of males and females in a population, including the progenitors of the reproductive cells of protozoans. This proposal was tested with three species of malarial parasites of lizards, Plasmodium mexicanum of the western fence lizard, and P. agamae and P. giganteum of the African rainbow lizard, using single samples from naturally infected lizards, repeated samples from free-ranging lizards (P. mexicanum only), and repeated samples from laboratory maintained animals. Macrogametocytes were usually more abundant than microgametocytes, and were slightly larger, revealing a typically greater investment of resources by the progenitors of female reproductive cells. However, the proportion of microgametocytes varied among the three species and among infections within each species of Plasmodium. The sex ratio of gametocytes often remained constant within infections followed over time even if the absolute number of gametocytes was changing. However, the equilibrium sex ratio of gametocytes varied among those infections that had an unchanging microgametocyte proportion. Thus, although an equilibrium sex ratio apparently occurs for most infections, there appears to be no characteristic proportion of microgametocytes for any of the species. Potential explanations for this conflict with theory are presented.

Lizards represent unique model organisms in the study of sex determination and sex chromosome evolution. Among tetrapods, they are characterized by an unparalleled diversity of sex determination systems, including temperature-dependent sex determination (TSD) and genetic sex determination (GSD) under either male or female heterogamety. Sex chromosome systems are also extremely variable in lizards. They include simple (XY and ZW) and multiple (X1X2Y and Z1Z2W) sex chromosome systems and encompass all the different hypothesized stages of diversification of heterogametic chromosomes, from homomorphic to heteromorphic and completely heterochromatic sex chromosomes. The co-occurrence of TSD, GSD and different sex chromosome systems also characterizes different lizard taxa, which represent ideal models to study the emergence and the evolutionary drivers of sex reversal and sex chromosome turnover. In this review, we present a synthesis of general genome and karyotype features of non-snakes squamates and discuss the main theories and evidences on the evolution and diversification of their different sex determination and sex chromosome systems. We here provide a systematic assessment of the available data on lizard sex chromosome systems and an overview of the main cytogenetic and molecular methods used for their identification, using a qualitative and quantitative approach.

Dietary resource partitioning among age-sex classes of Agama agama (Squamata: Agamidae) assessed by fecal pellet analysis. Dietary analysis is critical to understand the ecological roles of lizards, especially of species of Agama that are colonizing continents and islands from which they were previously absent. The foraging habits of four groups—viz., adult females, adult males, and young and juveniles (of both sexes)—of Agama agama in Nigeria were observed to assess the diet of the lizards and the contribution of the diet to separating age-sex classes. The claim that fying arthropods are less likely to be eaten by lizards was tested, and the hypothesis of dietary opportunism was explored. Sets (3–5 pellets) of 1453 fecal pellets collected during a 2-yr period were linked to individual lizards. Multivariate discriminant analysis of individual food items showed 61% lizards were correctly classifed to age-sex. However, items pooled into composite food groups, yielded fewer (43%) correctly classifed lizards. Cluster Analysis indicated that individual foods were less common (46.3%) to lizard classes than composite foods (76.1%). Thus, lizard age-sex classes are better differentiated when prey item is identifed at the lowest possible taxonomic level. Overall, arthropods are the largest, composite food for all lizard classes but, the relative amounts of different arthropod taxa varies signifcantly, and is highest for Diptera. Other foods include plants, seeds, and non-arthropod animal material. Differing coeffcients of variation accentuate dietary disparities within classes. Proportions of most individual and composite diet items differ signifcantly by month, season, and study site. Although consumed by lizards, no traces of white mold were found in the feces; this underscores the value of combining fecal analysis with surveillance of foraging habits of Agama agama.

Squamate reptiles show high diversity in sex determination ranging from environmental sex determination to genotypic sex determination with varying degrees of differentiation of sex chromosomes. Unfortunately, we lack even basic information on sex determination mode in several lineages of squamates, which prevents full understanding of their diversity and evolution of sex determination. One of the reptilian lineages with missing information on sex determination is the family Gerrhosauridae, commonly known as the plated lizards. Several species of gerrhosaurids have been studied in the past by conventional cytogenetic methods, but sex-specific differences were not identified. In this study, we applied both conventional and molecular cytogenetic methods to metaphases from both sexes of the Peters’ keeled plated lizard (<i>Tracheloptychus petersi</i>). We identified accumulations of rDNA loci in a pair of microchromosomes in metaphases from males, but only in a single microchromosome in females. The restriction of the observed heterozygosity to females suggests a putative ZZ/ZW system of sex chromosomes, which represents the first report of sex chromosomes in a gerrhosaurid lizard. The lack of sex-specific signals in all other cytogenetic methods implies that the sex chromosomes of <i>T. petersi</i> are poorly differentiated in sequence content.

Predation risk influences decision making, escape behaviour, and resource use. Risk assessment and behavioural responses to predation can depend on demographic and environmental factors. We studied the escape behaviour of the long-nosed leopard lizard (Gambelia wislizenii) when approached by a human predator (= “simulated predator”), analysing flight initiation distance (FID) and flight distance (FD) relative to demographic and environmental variables. Starting distance (SD) of the simulated predator and orientation of prey lizards relative to the simulated predator influenced FID, but body size of the prey lizard did not. Sex interacted with SD to affect FID. Females lengthened their FIDs as SD increased, while male FID was unrelated to SD. Flight distance increased with increasing SD. Gambelia wislizenii’s ecological role as an ambush predator may explain their escape behaviour; reproductive status potentially affected the interaction between sex and SD.

The purpose of this study was to analyse selected factors determining the level of infestation of Ixodes ricinus ticks on Lacerta agilis and Zootoca vivipara lizards found in Central Europe. Both environmental factors (habitats within protected areas and areas transformed as a result of human activity) as well as morphological factors (age, sex and size of lizards, location of ticks on the lizard’s body) were assessed. We found that the age and size of a lizard played a significant role in the level of infestation, but this depended on the species and habitat. Females of both species differed significantly in their level of tick infestation; females of L. agilis had lower infection than Z. vivipara. In contrast, there was no difference in levels of infection between juveniles and males of the different species. We also found that the impact of body size changed in the different habitats: the number of ticks increased with body size in natural areas only. In addition, more frequently ticks were found in the front groin area (336 individuals) and forelimbs (202), less often on the neck (12) and never in the hind groin area. These differences might be because it is easier to infest a larger individual than a smaller one, and areas of the front of the lizard might be more accessible whilst foraging. This study provides additional information about tick infestation that may be relevant to the conservation of the species of lizards.

Abstract There are a remarkable variety of sex determination systems among different animal taxa. In most animals, sex is determined chromosomally. Although in an increasing number of animals sex determination has been found to be influenced primarily by the environment. Species with genotypic sex determination (GSD) have their sex determined at the time of fertilization, by genetic factors alone and those with environmental sex determination (ESD) have their sex determined by environmental factors that act after fertilization. Temperature-dependent Sex Determination (TSD), whereby the sex of the developing embryos depends on the temperature at which they develop is widespread in oviparous reptiles and occurs in all crocodilians, marine turtles and tuatara examined to date and is common in many freshwater turtles and lizards. SECTION ONE Temperature-dependent sex determination (TSD) was never expected to occur in viviparous reptiles, as thermoregulation by pregnant females would result in relatively stable gestation temperatures. Temperature-dependent sex determination and viviparity goes against all the basic assumptions that TSD occurs in oviparous reptiles where temperatures within a nest vary widely. However, skewed sex ratios as a result of incubation temperature indicated the possibility of TSD in the viviparous lizard Eulamprus tympanum. In my first experiments I show the first recorded case of a viviparous reptile with TSD. The developing embryos of the viviparous skink E. tympanum are subject to TSD, with gestation temperature having a highly significant effect on sex and warmer temperatures giving rise to male offspring (Chapter 1). Sex is fully determined at the time of birth and can be differentiated histologically into testes or ovaries (Chapter 2). The morphology and histological characteristics of the gonads of neonatal E. tympanum resulting from the treatment temperatures described in chapter 1 illustrate that sex in E. tympanum is easily distinguished at the time of birth and corresponds with the presence or absence of hemipenes. Males are histologically characterised by an elongated gonad consisting of seminiferous tubules with either no cortical epithelium or, if present at all, in a very thin band. If they are present, M�llerian ducts, showing signs of degeneration, are attached to the kidney by a shortened mesosalpinx. Females are histologically characterised by an irregularly shaped gonad consisting of a thick cortical epithelium that occasionally contains oocytes. The M�llerian ducts are obvious structures attached to the kidney by a fibrous mesosalpinx. The presence or absence of hemipenes is a reliable technique for determining sex in newborn E. tympanum. Sex determination is easiest to perform on neonates within the first few days of birth as hemipenes become increasingly difficult to evert as neonates age, however, with practice they are easily identified without full eversion. SECTION TWO The thermal biology of E. tympanum in the field is restricted by both the thermal properties of their habitat (Chapter 3) and behavioural modifications when faced with a predation threat (Chapter 4). The available temperatures in the field suggest that TSD is biologically relevant in the species and not just a laboratory artefact; E. tympanum can attain mean selected temperatures achieved in the laboratory but the proportion of time at the temperature is restricted. Females actively thermoregulate in the field, although they are restricted in their efficiency of thermoregulation by environmental constraints, for example, microhabitat structure, weather conditions, predator avoidance and social ranking. The highly territorial nature and high densities of E. tympanum present in Kanangra Boyd National Park potentially force less dominant individuals into less favourable habitats that are significantly cooler. An important point is that gravid females in more favourable habitats in the period encompassing the middle third of development (the assumed sex determining period) are selecting higher temperatures, with lower variance and have greater thermoregulatory efficiency than during the rest of pregnancy, therefore, thermoregulating more precisely during this thermosensitive period (Chapter 3). Chemosensory cues provide important information on the risk of predation. Hence, chemoreception is a common mechanism used by many species to detect the presence of, and subsequently respond to, a potential predator. The perceived risk of predation may force retreat to sub-optimal conditions, forcing a trade-off between the risk of predation and the ability to acquire resources. The basking regime maintained by gravid female E. tympanum, can directly alter sex ratios of offspring produced through temperature-dependent sex determination (Chapter 1). The avoidance of predator scents may restrict basking ability and in turn alter the sex of offspring produced. I measured responsiveness to chemical cues using tongue flicks as an indicator of chemical discrimination in females of different reproductive condition. I then measured activity and basking behaviour of gravid and non-gravid females in experimental enclosures in the presence of various chemical stimuli to determine if basking opportunity is compromised by the presence of a predator scent. Females respond differently depending upon reproductive condition, with gravid females responding most significantly to a predator scent. Activity, basking frequency, and time spent in the open (basking duration) are significantly reduced in gravid females in the presence of a predator stimulus. Under laboratory conditions, gravid females modify their behaviour and forego the opportunity to bask when there is a perceived predation risk (Chapter 4). SECTION THREE As female viviparous reptiles can regulate the temperature of the embryo by maternal temperature selection (Chapter 1), the occurrence of TSD in E. tympanum opens the possibility for females to select the sex of offspring. Reproducing females may benefit by facultatively adjusting their investment into sons over daughters or vice versa, in response to population wide shifts in adult sex ratios. Female E. tympanum, can manipulate the sex of their offspring in response to sex imbalances in the population using temperature-dependent sex determination (Chapter 5). When adult males are scarce, females produce male-biased litters and when adult males are common, females produce female-biased litters. The cues used by a female to assess the adult population are not known, but presumably depends upon the female�s experience throughout the breeding season and is the subject of further investigation (Chapter 6). The maternal manipulation of offspring sex ratio in E. tympanum suggests a selective advantage of temperature-dependent sex determination. Any facultative sex ratio response needs to recognise the scarcity of one sex in order to overproduce that sex in the next generation; offspring sex ratio will vary inversely with adult sex ratio. Maternal sex allocation in E. tympanum is linked with population (or adult) sex ratio (Chapter 5), and one of the mechanisms by which females recognise an imbalance may be linked to visual recognition of males (Chapter 6). Females maintained throughout pregnancy without any male stimulus produce entirely male offspring (Chapter 5). In contrast females exposed to male stimulus produce both sexes (Chapter 5). Females respond differently to varying degrees of male stimulus and visual recognition of males in a population may be more important than chemoreception. In the absence of visual cues, females produce more male offspring, even when chemosensory cues are present (Chapter 6). The study system presented here offers many advantages over oviparous species with TSD, due to E. tympanum being relatively short lived and fast maturing. Thus, the fitness consequences over multiple generations as a result of gestation can be investigated. Viviparity allows maternal control of embryonic temperature during gestation and a means of maternal sex allocation. Until now the maternal side of TSD and sex allocation has been where the mother deposits her eggs and the allocation of sex steroid hormones at oviposition, both of which have been difficult to study. The work presented and the study system itself should inspire great interest in TSD and viviparous reptiles.

Thesis (Ph. D.)--University of Sydney, 2004.
Title from title screen (viewed 5 May 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Biological Sciences, Faculty of Science. Degree awarded 2004; thesis submitted 2003. Appendices contains published articles co-authored by Robert. Includes bibliographical references. Also available in print form.

Reptiles exhibit marked diversity in sex-determining mechanisms. Many species exhibit genotypic sex determination (GSD) with male heterogamety (XX females/XY males), others have GSD with female heterogamety (ZW females/ZZ males), and still others exhibit temperature-dependent sex determination (TSD). The distribution of these mechanisms throughout the reptile phylogeny implies evolutionary lability in sex determination, and in some lineages there has been a number of transitions between GSD and TSD. Despite this diversity, GSD and TSD have traditionally been viewed as mutually-exclusive mechanisms of sex determination in reptiles, since there is little evidence for their co-occurrence. Considerable empirical and theoretical effort has been directed towards understanding the adaptive significance of TSD in reptiles. In comparison, there has been little focus on understanding how evolutionary transitions between GSD and TSD occur at a genetic and mechanistic level. I addressed this question by applying both empirical and theoretical approaches to investigate interaction of genotypic and temperature influences in the sex determination of two endemic species of Australian lizards. The three-lined skink, Bassiana duperreyi, has XX/XY chromosomal sex determination, yet a previous investigation reported a significant male bias in the sex ratio of eggs incubated at low temperatures. To enable an explicit test for temperature induced sex reversal in this species, a 185 bp Y chromosome marker was isolated by Amplified Fragment Length Polymorphism (AFLP) analysis. The marker was subsequently converted into a duplex PCR assay that co-amplified a 185 bp (or 92 bp) Y chromosome fragment and a 356 bp fragment of the single-copy nuclear gene C-mos (from both sexes) as a positive control. The accuracy of the PCR sex assay was tested on 78 individuals for which sex reversal was not expected. PCR genotype and sex phenotype were concordant for 96% of the animals. This is one of the very few sex tests developed for a reptile, and the first report of Y chromosome sequence from a reptile. The PCR assay was subsequently applied to genotype hatchlings from both cool (16-7.5C) and warm (22-7.5C) cyclical incubation temperature treatments, and identified sex reversal in 15% of genotypically female (XX) embryos (n=26) from the cool treatment, but no sex reversal in eggs from the warmer treatment (n=35). Thus, low incubation temperatures can over-ride genotypic sex determination in B. duperreyi, indicating that GSD and TSD co-occur in this species. The Central bearded dragon, Pogona vitticeps (Agamidae), has ZZ/ZW chromosomal sex determination, and is a member of a lizard family in which GSD and TSD are both widespread, indicating evolutionary lability in sex determination. AFLP analysis was applied to isolate homologous Z and W chromosome-linked markers (71 bp and 72 bp, respectively) from this species. The AFLP sequences were subsequently extended into larger genomic fragments by a reiterated genome walking procedure, producing three non-overlapping contigs of 1.7 kb, 2.2 kb and 4.5 kb. The latter two fragments were verified as distinct, homologous Z/W chromosome fragments by PCR analyses. An amplified 3 kb fragment of the 4.5 kb contig was physically mapped to metaphase spreads, identifying the W microchromosome, and for the first time in this species, the Z microchromosome. PCR analyses indicated the presence of homologous sequences in other Australian agamid species, including both GSD and TSD species. The isolated sequences should therefore prove useful as a comparative genomic tool for investigating the genomic changes that have occurred in evolutionary transitions between sexdetermining mechanisms in agamids, by enabling the identification of chromosomes in TSD species that are homologous to the sex chromosomes of P. vitticeps. The isolated sequences were further converted into a duplex DNA sex assay that co-amplified a 224 bp W chromosome fragment and a 963 bp positive control fragment in both sexes. This PCR assay diagnosed chromosomal sex in three Pogona species, but was not effective outside the genus. Incubation treatment of P. vitticeps eggs revealed a strong and increasing female bias at high constant temperatures (34-36C), but an unbiased sex ratio between 22-32C. Hatchlings from three clutches split between 28C and 34 or 36C incubation treatments were genotyped with the W chromosome AFLP marker. At 28C, the sex ratio was 1:1 but the high temperature treatments produced 2 males and 33 females. All but one of the 30 lizards (97%) incubated at 28C had concordant sex phenotype and genotype, but only 18 of 35 animals (51%) from the high temperature treatment were concordant. All discordant animals were genotypic males (ZZ) that developed as females. Thus, temperature and genotypic influences can interact to determine sex in P. vitticeps. These empirical findings for B. duperreyi and P. vitticeps were extended into a novel theory for the evolution of sex-determining mechanisms in reptiles, working within the framework that species with temperature-induced reversal of chromosomal sex determination are a window to transitional stages of evolution between GSD and TSD. A model was derived from the observation that in both lizards, an extreme of incubation temperature causes sex reversal of the homogametic genotype. In this model, the strength of a genetic regulatory signal for sex determination must exceed a threshold for development of the homogametic sex to occur (male in Pogona, female in Bassiana). The strength of this signal is also temperature-sensitive, so diminishes at extremes of temperature. Simulation modelling demonstrated that increasing the relative magnitude of the threshold for sexual development can cause evolutionary transitions between GSD and TSD. Even more remarkably, decreasing the relative magnitude of the threshold value causes an evolutionary transition between female and male heterogametic GSD. Quantitative adjustment of a single model parameter (the threshold value) thus charts a continuous evolutionary pathway between the three principal mechanisms of sex determination in reptiles (XX/XY-ZZ/ZW-TSD), which were previously considered to be qualitatively distinct mechanisms. The experimental demonstration of temperature-induced reversal of chromosomal sex determination in both B. duperreyi and P. vitticeps presents a challenge to the traditional view that reptilian sex determination is strictly dichotomous (GSD or TSD), and suggests instead that sex determination in reptiles consists of a continuum of systems of interaction between genotypic and temperature influences. Simulation modelling provided solid theoretical support for this proposition, demonstrating that transitions along this continuum are effected simply through shifts in the mean population value for the sex-determining threshold, without requiring substantial genotypic innovation. An important implication of this theory is that transitions between XX/XY and ZZ/ZW modes of GSD may retain the same sex chromosome pair, and the same primary sexdetermining gene, in contrast to previous models for heterogametic transitions. A more immediate implication of these findings is that many reptile species believed to have strict TSD (in particular, lizards and crocodilians), may in fact have a sex-determining system of GSD-TSD interaction, where there is an equilibrium between GSD and TSD individuals within the population.

Adult green anoles, Anolis carolinensis, exhibit numerous sex differences resulting from divergent strategies for maximizing reproductive success. I focused on the ontogeny of sex differences in behavior in juveniles, in relation to adult sex differences, by documenting the behavior of free-ranging juveniles, examining the structure and use of headbobbing displays, and determining the role of the androgen testosterone (T) in producing behavioral sex differences. Field observations indicated that juvenile males eat and forage actively more often than juvenile females. This divergent feeding behavior may result from sexual selection, given that body size is a major factor in determining the reproductive success of males. Analyses of headbobbing displays, used by adults in aggressive and sexual interactions, revealed that juvenile males and females each give the same three A, B, and C display types described for adults. However, there may be a maturational component to display structure, as juvenile displays differ from those of adults in within-display temporal structure, and are not as stereotyped. Concerning display use, social context affects neither the types of display interactions observed nor the rates of displays and related behaviors. However, size affects nearly every aspect of display behavior. Both juvenile males and females show increased display rates and probabilities of expressing display-related behaviors with increasing body size, although in the largest juveniles, male display rates become higher than those of females. These results, like those from analyses of display structure, suggest a maturational component to display use, perhaps mediated by changes in the underlying motivational states of juveniles. Consistent with the divergence in display rates in large juveniles, males of approximately 30 d of age and older have higher plasma T concentrations than females. Furthermore, juvenile males and females that have been given T implants each respond with increased behavior levels, approaching those of breeding adult males. These analyses indicate that sexual dimorphisms in behavior in adults likely arise through underlying physiological differences between males and females that mediate the expression of behavior, rather than through fundamental sex differences in the ability to perform these behaviors.
Ph. D.

Gravity Fails is a collection of four short stories and two memoirs that explore the ways in which characters adjust and fit into to a world that is destructive, fragmented and sometimes alien. Many of these pieces deal not with the moment of crisis, but with the aftermath. In "Gravity Fails," the young Danielle struggles to feel safe after the violent murder of her mother. Eliza Morrison negotiates the disappearance of her husband in "More Colors." "Following Rebecca" chronicles a woman's return to normalcy after her alcoholic husband divorces her. These characters are not happy; they are not healthy. Their lives have, in some way, been fragmented. But they find ways to move on by whatever possible means, and at their core, they are searching not just for a way to survive, but for a way to put themselves back together and find wholeness.
M.A.
Department of English
Arts and Sciences
English

Host-parasite relationships are one of the most common symbiotic relationships present in a diverse array of ecosystems. There are numerous factors that impact the dynamics of these relationships. Major factors that can influence the degree of parasitism include host sex, hormonal state, reproductive condition, and behavior. It has been observed in several vertebrate taxa that males have higher ectoparasite intensities than females and males with increased testosterone have increased ectoparasite intensities. One potential reason for these observations is that testosterone concentrations are elevated in males, particularly during the breeding season, and when circulating concentrations increase males become more vulnerable to ectoparasitism. Here I first tested the hypothesis that higher circulating testosterone concentrations in male western fence lizards (Sceloporus occidentalis) induce higher tick intensities. To examine this hypothesis I implanted male lizards with either testosterone or blank implants in the field. The testosterone-implanted males had significantly higher tick intensities compared to the control males. However, in contrast, control males had significantly higher mite intensities compared to testosterone-implanted males. These results are consistent with other studies suggesting that testosterone impacts certain aspects of host-parasite relationships. However, the exact mechanism for how testosterone influences parasite intensities remains unclear. There are two major current hypotheses for how testosterone influences ectoparasite intensities on males, the first involving immunosuppression and the second involving behavioral patterns and movement. However, another potential reason for why male lizards, particularly those with high circulating testosterone, have higher ectoparasite intensities than female and low testosterone male lizards is that the parasites preferentially choose their host. Furthermore, it has been demonstrated that vitellogenic female lizards have diminished immune function and this could potentially lead to increased ectoparasitism in much the same way that testosterone does in male lizards. Therefore, it is possible that a host preference is also present with vitellogenic versus non-vitellogenic female lizards. Although there have been a few interspecific studies done on this topic there have been no such studies on parasite host preference in reptiles to date. Here I tested three hypotheses: 1. Ticks prefer male lizards to female lizards. 2. Ticks prefer male lizards with high testosterone concentrations to male lizards with normal testosterone concentrations. 3. Ticks prefer vitellogenic female lizards to non-vitellogenic female lizards. All three experiments demonstrated no preference of host by ticks, which suggests they will attach to any suitable host they come across. However, during the male versus female host choice experiment ticks fed faster on vitellogenic female lizards than male lizards and non-vitellogenic female lizards. These results, taken together with previous studies showing higher tick intensities on male lizards, lizards with experimentally elevated testosterone, and reproductive female lizards, provide evidence that ticks do not preferentially choose their host, but instead are found in higher numbers on certain hosts due to some other reason. Other potential explanations include differences in immune function, microhabitat use, and behavioral patterns. One of the major hypotheses as to why male lizards, particularly those with high testosterone concentrations, have higher ectoparasite intensities than female lizards and male lizards with low testosterone concentrations is that these lizards perform more territorial behaviors, have increased movements, and larger home range sizes, thus exposing them to more parasites. Several studies have shown testosterone to increase the frequency of behaviors, movement, and home range size in lizards, but few, if any, have related it to ectoparasite intensities. Here I tested two hypotheses: 1. High testosterone male lizards have larger home ranges than male lizards with lower testosterone concentrations and female lizards. 2. High testosterone male lizards perform a higher frequency of territorial behaviors than male lizards with lower testosterone concentrations and female lizards. To test these hypotheses I implanted male lizards with either testosterone or blank-control implants, left female lizards unaltered, and performed behavioral observations in the field for 25 days. At the end of this time period, home range sizes were calculated as minimum convex polygons and ectoparasite intensities were quantified. Results of this study revealed no significant difference in ectoparasite intensities between high and low testosterone male lizards, but male lizards did have significantly higher ectoparasite intensities than female lizards. Furthermore, home range size and frequencies of territorial behaviors were not significantly different between high and low testosterone male lizards. However, male lizards did have larger home ranges and performed more territorial behaviors and movements than female lizards. These results suggest that home range, movement, and territorial behavior frequency contribute to higher ectoparasite intensities on male lizards, particularly those on males with high circulating testosterone. However, future studies need to address the behavioral and physiological mechanisms responsible for the observed effects of testosterone on parasitism, including parasite intensity, immunosuppression, and parasitic effects on host fitness.

An introduction is given to the Caspian Sea, grey mullet species, and the grey mullet fishing method in the southern Caspian Sea, together with an introduction to the quantitative assessment in the fishery. 11,614 specimens of the grey mullets Liza aurata and L. saliens were collected from the catches being obtained at 91 sample sites along the Iranian side of the Caspian Sea in the fishing seasons 1993-94 and 1994-95. The specimens were identified by a rapid identification method. Basic biometrical measurements were recorded from the whole sample and a further set of measurements from a subsample of 1301. Scales and otoliths for age determination were collected. The age of all specimens was determined by scales, and an improved method for removing the otoliths was developed. The growth and morality of L. aurata and L. saliens were estimated by several methods. Biomass and maximum sustainable yield for both species were estimated by using different methods. Removed stomach contents were examined and food items identified and counted. Frequency of occurrence (F%) and numerical percentage (N%) methods for quantifying food items in the stomachs were employed. Ovary maturation and fecundity of L. aurata and L. saliens were investigated and compared with the results of other studies. Finally recommendations have been made to help the Iranian fishing managers exploit the grey mullet species in the Caspian Sea whilst conserving the present biomass.

Vertebrate genomes exhibit global methylation of cytosine residues where they occur in a cytosine-guanine dinucleotide (CpG) context and this epigenetic mark is generally thought to be repressive to transcription. Punctuating this pervasive DNA methylation landscape are short, contiguous regions of non-methylated DNA which are found at two thirds of mammalian gene promoters. These non-methylated regions exhibit CpG content close to expected levels as they escape the depletion of CpGs observed across the methylated fraction of the genome. The unique nucleotide properties of these CpG island (CGI) regions enable their identification by computational prediction in mammalian genomes. Owing to a lack of high-resolution genome-wide DNA methylation profiles in non-mammalian species, these CGI predictions have often been used as a proxy for non-methylated DNA in these organisms. In contrast to mammals, CGI predictions in cold-blooded vertebrates rarely coincide with gene promoters, leading to the belief that CGls are significantly divergent between vertebrate species, and that unique promoter-associated features may have been acquired during warmblooded vertebrate evolution. This thesis is primarily concerned with the location, establishment and biological function of non-methylated islands of DNA in vertebrate genomes. To experimentally determine genome-wide profiles of non-methylated DNA, a novel biochemical technique was established called biotinylated ZF-CxxC affinity purification (Bio-CAP), and development of this method is discussed in Chapter 3. Experimental analysis of non-methylated DNA profiles in this thesis initially addresses two main questions: (1) 'How does the non-methylated DNA landscape compare genome-wide for seven vertebrates considering distinct tissue types and developmental stages?' (2) 'How are vertebrate non-methylated regions of DNA defined and interpreted in the nuclear environment?' To address the first question, non-methylated DNA was profiled by Bio-CAP sequencing across the genomes of seven diverse vertebrate species, representing all major branch points of vertebrate evolution, and the results are discussed in Chapters 4 and S. Contrary to previously held dogma, experimentally determined nonmethylated islands of DNA (NMls) constitute an ancient epigenetic feature of vertebrate gene regulatory elements. However, despite having numerous high-resolution maps of vertebrate non-methylated DNA, the means by which NMls are identified and maintained in the nuclear environment remains poorly understood. To address the second question and identify features which determine the methylation state of DNA, exogenous DNA sequences were introduced into mouse embryonic stem (ES) c~.II~. Non-methylated DNA was profiled by Bio-CAP sequencing to investigate how different features, such as sequence-specific binding motifs, chromatin architecture and nucleotide composition of a given DNA sequence impact local DNA methylation patterns. Interestingly, the majority of exogenous promoters were appropriately non-methylated in mouse ES cells, germline and somatic cells suggesting that gene promoters have retained strong signals for the nonmethylated state across millions of years of evolution (discussed in Chapter 6). During mouse embryogenesis, genome-scale DNA demethylation and remethylation events occur to remodel the epigenetic landscape and loss of DNA methylation during this time leads to embryonic lethality. To investigate the biological function of non-methylated DNA, the third question addressed in this thesis is (3) 'What is the developmental importance of non-methylated islands of DNA during vertebrate embryogenesis?' To investigate this, members of the ZF-CxxC domain-containing family of chromatin modifiers were ablated in zebrafish embryos to perturb the chromatin landscape at NMls, and therefore interfere with their function during early development (Chapter 7). Early embryonic development and patterning was disrupted in knockdown embryos, suggesting that interpretation of non-methylated DNA and placement of chromatin modifications at NMls is essential for normal zebrafish embryogenesis. Together this work sheds light on the evolutionary origins of NMls, the mechanisms involved in the recognition and establishment of nonmethylated loci and provides an insight into the function of non-methylated DNA during early embryonic development.

The leopard gecko (Eublepharis macularius) is a reptile species in which embryonic temperature contributes both to sex determination and within- sex polymorphisms. Its life history makes the leopard gecko a model system for seeking ontogenic and proximate explanations for within-sex variation in sexually dimorphic behavior and neurophysiology, necessary attributes for reproductive success. For my dissertation I have incorporated the role of androgens that potentially modulate incubation temperature effects on behavioral and brain variation, which I approached using embryo and adult leopard geckos. First, I found that that the bias of same-sex clutch siblings is primarily incubation temperature- dependent and any maternal or genetic effects on same-sex clutch siblings are secondary. Second, I found that testosterone concentrations in the yolk-albumen were higher in eggs of late development than early development at 26 °C, a female-producing incubation temperature, but did not differ from eggs incubated at another female-biased temperature. This increase in testosterone concentrations during the temperature sensitive period in putative females is a finding opposite of reported trends in most other reptiles studied to date. Further, I found that the embryonic environment influences male sociosexual investigation in the absence of gonadal hormones. Lastly, in adult males of 32.5 °C, a male-biased incubation temperature, I found that the phosphoprotein DARPP-32 that is activated by the D1 dopamine receptor in limbic brain regions is correlated to this sociosexual investigatory behavior. Neurons immunopositive for phosphorylated DARPP-32 were not only less dense in the nucleus accumbens of males who spent more time with other males, but also more dense in the preoptic area of males who spent more time with females. The use of phosphorylated DARPP-32 as marker for sociosexual exposure is novel in a lizard species. Taken together, in support of previous studies, these results show that differences in embryonic environment stem primarily from incubation temperature, can explain behavioral differences in adulthood in the absence of hormones, and, in concert with hormonal manipulation, can influence neuronal marker sensitivity to sociosexual exposure.
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Lacertid lizards have long been a fruitful field of scientific enquiry with many people working on them over the past couple of hundred years. The scope of the field has steadily increased, beginning with taxonomy and anatomy and gradually spreading so that it includes such topics as phylogenetics, behaviour, ecology, and conservation. Since 1992, a series of symposia on lacertid lizards of the Mediterranean basin have taken place every three years. The present volume stems from the 2004 meeting in the Aeolian Islands. In the volume a wide range of island topics are considered, including the systematics of the species concerned, from both morphological and molecular viewpoints, interaction with other taxa, and conservation. The last topic is especially important, as island lizards across the world have often been vulnerable to extinction, after they came into contact with people and the animals they introduced. The volume also has papers on the more positive aspects of human influence, specifically the benign effects of traditional agriculture on at least some reptile species. Olive trees, cork oaks and the banks and walls of loose rocks that crisscross the Mediterranean scene all often contribute to elevated lizard populations. Nor is more basic biology neglected and there are articles on morphology, reproduction, development and thermoregulation. Finally, it is good to see one paper on non-Mediterranean species is included. For, to fully understand the lacertids of this region, it is necessary to appreciate their close relatives in Africa, Asia and the archipelagos of the northeastern Atlantic Ocean. (From Preface by E. Nicholas Arnold & Wolfgang Böhme)

When I was a child, I lived near Kennedy Space Center in Florida. To me, science was all about rocket science: big rockets that flew where no one has gone before, powered by fiery oxidative chemistry and guided by precise measurements. I could watch the space shuttle go up, and trust it would come down, connecting Earth’s orbit to the ground at my feet. That we could send hollow metal capsules on such immense journeys was a wonder I never quite got over, not even when two of the shuttles failed to return home. I had a different view of evolution. It seemed messy, haphazard, cruel, and wasteful, nothing like the sleek engineered rockets at the Space Center. Most of all, I think it just seemed boring. Why study the unpredictable? To be sure about something, you need to see it work multiple times, right? I missed the chance to see evolution work multiple times, right in my home county. In the next lagoon over from where I once dredged up sulfurous muck for my science projects, on six small islands, the tape of life was being replayed six separate times. All six times, it gained the same result. Evolution might be messy, haphazard, cruel, and wasteful, but it is also predictable. In 1995, scientists brought Cuban brown anole lizards to six small islands in Mosquito Lagoon, which only had green anole lizards at the time. Each time, scientists watched what happened and compared the results to five nearby islands that remained green-lizard-only zones. After three years of competition, the green lizards changed their behavior and perched twice as high in the trees. In 2010, the scientists returned and examined the lizards’ feet. On the invaded islands, the green lizards had larger toepads with more wrinkly lamellae than on the non-invaded islands. This difference in feet was mirrored by differences in the lizards’ genes. In a 15-year span, the lizards evolved. (During the same time span, my opinion of evolution also evolved, as I learned about a chemical order behind the biological messiness.)

‘History of reptiles’ describes the origin and early evolution of reptiles, from the early ancestor-like Hylonomus and Petrolacosaurus 320 million years ago (mya) in the Carboniferous period. The end-Permian mass extinction, 250 mya, removed over 90 per cent of the world’s species of animals and plants, but one group—the archosaurs—began to expand and diversify. The archosaurs included the dinosaurs, made up of the Theropoda, the Sauropodomorphs, the Ornithischia, the pterosaurs, and the crocodiles. In the Mesozoic Era, several new kinds of reptiles evolved adaptations for life in the sea—plesiosaurs, ichthyosaurs, and others. The end-Cretaceous mass extinction, 66 mya, ended the dinosaurs, but many lizards, snakes, chelonians, and crocodiles survived.

I have a Hardin cartoon on my office door. It shows a series of animals thinking about the meaning of life. In sequence, we see a lobe-finned fish, a salamander, a lizard, and a monkey, all thinking, “Eat, survive, reproduce; eat, survive, reproduce.” Then comes man: “What's it all about?” he wonders. Organisms live to reproduce. The ultimate selective pressure on any organism is to survive long enough and well enough to pass genetic material to a next generation that will also be successful in reproducing. In this sense, then, every morphological, physiological, biochemical, or behavioral adaptation contributes to reproductive success, making the field of life cycle evolution a very broad one indeed. Key components include mode of sexuality, age and size at first reproduction (Roff, this volume), number of reproductive episodes in a lifetime, offspring size (Messina and Fox, this volume), fecundity, the extent to which parents protect their offspring and how that protection is achieved, source of nutrition during development, survival to maturity, the consequences of shifts in any of these components, and the underlying mechanisms responsible for such shifts. Many of these issues are dealt with in other chapters. Here I focus exclusively on animals, and on a particularly widespread sort of life cycle that includes at least two ecologically distinct free-living stages. Such “complex life cycles” (Istock 1967) are especially common among amphibians and fishes (Hall and Wake 1999), and within most invertebrate groups, including insects (Gilbert and Frieden 1981), crustaceans, bivalves, gastropods, polychaete worms, echinoderms, bryozoans, and corals and other cnidarians (Thorson 1950). In such life cycles, the juvenile or adult stage is reached by metamorphosing from a preceding, free-living larval stage. In many species, metamorphosis involves a veritable revolution in morphology, ecology, behavior, and physiology, sometimes taking place in as little as a few minutes or a few hours. In addition to the issues already mentioned, key components of such complex life cycles include the timing of metamorphosis (i.e., when it occurs), the size at which larvae metamorphose, and the consequences of metamorphosing at particular times or at particular sizes. The potential advantages of including larval stages in the life history have been much discussed.

There are large biological differences between the mammals and the primitive living amniotes as represented by turtles, lizards, and crocodiles ● Differentiated dentition with occluding post-canine teeth, and radical reorganisation of jaw musculature to operate them ● Differentiation of vertebral column and limb musculature, and repositioning of limbs to bring feet under the body, increasing agility of locomotion ● Relatively huge brain and highly sensitive sense organs ● Endothermic temperature physiology, with very high metabolic rates, insulation, and high respiratory rates ● Precise osmoregulatory and chemoregulatory abilities using loops of Henle in the kidney and an array of endocrine mechanisms Incomplete as it is, the fossil record of the mammal-like reptiles, or ‘non-mammalian synapsids’ permits the reconstruction of a series of hypothetical intermediate stages that offers considerable insight into how, when, and where this remarkable transition occurred. Deriving these stages starts with a cladogram of the relevant fossils that is then read as an evolutionary tree, with hypothetical ancestors represented by the nodes. The characters that define a node, plus the characters of the previous nodes, constitute the reconstruction. The differences in characters between adjacent nodes represent the evolutionary transitions that by inference occurred, and the whole set of successive nodes generates all that can be inferred about the sequence of acquisition of characters. If a hypothetical ancestral synapsid is placed at the base of the cladogram, and a hypothetical ancestral mammal as the final node, then the set of nodes in between represents everything the fossil record is capable of revealing about the pattern by which mammalian characters evolved: the sequence of their acquisition, the correlations between characters, and possibly the rates of their evolution. Of course, the inferred pattern of evolution of characters is only as reliable as the cladogram which generated it, and that in turn is only as realistic as the model of evolution used in its construction from the character data. And of course, there must have been many intermediate stages in the transition than cannot be reconstructed for want of appropriate fossil representation of those particular grades. Nevertheless, limited as it may be, this is what can be known from the fossil record.

Abstract An attempt was made to independently verify the proposed performance of the Liza 1 field using only data available in the public domain. The data used in modelling was sourced from news reports, company disclosures and the analogue Jubilee field in Ghana. Reservoir rock and fluid data from Jubilee Field was deemed an appropriate fit because of the corroboration provided by the Atlantic Drift Theory. A major challenge in creating the model, was determining the aerial extent of the field. According to Yang and Escalona (2011), the subsurface can be reasonably approximated using the surface topography which is possible via the use of GIS software. Google Earth Pro software was used to estimate the coordinates and areal extent of the Liza 1 reservoir. A scaled image of the field location showing the Guyana coastline was re-sized to fit the coastline in Google Pro and then the coordinates for the Liza field and wildcat well locations were estimated. This was used to create the isopach map and set reservoir boundaries to create the static and dynamic models in Schlumberger's Petrel E & P Software Platform (2017) and Computer Modelling Group IMEX Black Oil and Unconventional Simulator CMG IMEX (2016). The initialized model investigated the reservoir performance with and without pressure maintenance over a twenty (20) year period. The original oil in place (OOIP) estimated by the model was 7% larger than the OOIP estimated by ExxonMobil for Liza field. The model produced 35% of the OOIP compared to 50% of OOIP as forecasted by the operators. (See Table 1). The factors that strongly influenced this outcome were, the well positioning and the water injection rates. A significant percentage of the oil remained unproduced in the lower layers of the model after the 20-year period. Time did not permit further modelling to improve the performance of the model. Table 1 Comparison of The Created Model and ExxonMobil's Proposal for Liza. Property ExxonMobil's statement on Liza field Modelled field Result Original Oil in Place (MMbbl) 896 967 Oil Recovery Factor (%) 50 35 Gas production from the model would be used as gas injection from three injector wells and as fuel for the proposed 200 MW power plant for Guyana. Even so, significant volumes of natural gas remained unallocated and subsequently a valuable resource may have to be flared.

Abstract The Liza Phase 1 development project, offshore Guyana, is an unique example of what the offshore oil and gas industry is capable of when working together to deliver a common objective. ExxonMobil and the Stabroek Block co-venturers, Hess Guyana Exploration Limited and CNOOC Petroleum Guyana Limited, commenced oil production from the Liza Destiny floating production, storage, and offloading (FPSO) vessel in December of 2019, less than 5 years from the initial discovery of hydrocarbons in the Staebroek block. With the production and export of its first barrels of oil, the project completed the establishment of a nascent oil and gas industry in Guyana that is poised for tremendous growth in the coming years. The Liza Phase 1 development consists of a 120 kbd conversion FPSO (The Liza Destiny) and a network of subsea infrastructure to produce from and inject in two drill centers. It is expected to develop a resource of about 450 MBO gross estimated ultimate recovery. The water depth ranges from 1,690–1,860 m throughout the development which is located approximately 200 km offshore Guyana. This paper highlights the scope and pace of the project and discusses three specific challenges overcome: the uncertainty of the metocean conditions, extending the application of the selected riser technology, and executing in a challenging and frontier offshore location. A key to the success of the project was the unified approach between stakeholders and the commitment to act as One Team. The Liza Phase 1 project rapidly developed a newly discovered deep water resource in a frontier location while overcoming numerous challenges. By delivering Guyana's first ever oil production among industry leading cycle times, the Liza Phase 1 project has set the foundation for the future of deep water developments in Guyana.