Dissertations / Theses on the topic 'Frogs – Breeding'

Normal male dwarf African clawed frogs, Hymenochirus sp., possess bilateral, sexually dimorphic, subcutaneous breeding glands just posterior to the forelimbs. Previous studies have shown these glands release pheromones that attract conspecific females. This thesis shows the pheromones also stimulate the reproductive system of conspecific females. Females exposed to normal males prior to mating then allowed to mate with the normal males released a higher number of eggs than females who were not exposed to normal males prior to mating. Microscopic examination of ovarian tissue revealed that females exposed to normal males also produced more highly-developed oocytes than did females not exposed to normal males. These results suggest male Hymenochirus use pheromones not only to attract potential mates, but to increase female receptivity and readiness to mate. Evolutionarily, these pheromonal effects would likely benefit males by increasing their chances of breeding, increasing the number of eggs released by their mates, and thus the number of offspring in the next generation.

Anurans rely mainly on vocalizations for mate attraction while urodeles rely mainly on pheromones. However, the presence of breeding glands suggests that anurans may also communicate with pheromones during reproduction. Previous studies have shown that male Hymenochirus sp. are able to attract females in a Y-maze, most likely through chemical means, but the source of the attractant has not been identified. By exposing female Hymenochirus sp. to choice tests in a Y -maze it was demonstrated that the breeding glands of male Hymenochirus sp. are the source of a mate-attractant pheromone. This study represents the first experimental evidence for a pheromonal function of breeding glands and further supports the idea that anurans utilize pheromones in reproduction. Evidence is also presented suggesting that the mate attraction is temperature sensitive with an upper limit around 30°C.

Anurans rely mainly on vocalizations for mate attraction while urodeles rely mainly on pheromones. However, the presence of breeding glands suggests that anurans may also communicate with pheromones during reproduction. Previous studies have shown that male Hymenochirus sp. are able to attract females in a Y-maze, most likely through chemical means, but the source of the attractant has not been identified. By exposing female Hymenochirus sp. to choice tests in a Y -maze it was demonstrated that the breeding glands of male Hymenochirus sp. are the source of a mate-attractant pheromone. This study represents the first experimental evidence for a pheromonal function of breeding glands and further supports the idea that anurans utilize pheromones in reproduction. Evidence is also presented suggesting that the mate attraction is temperature sensitive with an upper limit around 30°C.

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 26, 2007) Includes bibliographical references.

Batrachochytrium dendrobatidis (Bd) has contributed to population declines and extinction of amphibians worldwide. Disease-caused extinction is rare, but may occur where reservoirs exist or where transmission is independent of host density. Because some species persist after Bd epizootic events, they may act as potential reservoirs of the infection. I studied seasonal and elevational patterns of prevalence and intensity of Bd infection in eight pond-breeding species that persisted after an epizootic event at three low- and three mid-elevation ponds in Central America. I visited each pond three times over the rainy season to sample for Bd and to quantify frog density. I recorded air and water temperature at each pond. I analyzed 1,288 samples and detected Bd in all six ponds and in six of the eight species. Elevation and time affected Bd prevalence (F2,7 = 8.90, p = 0.01) and Bd intensity (F2,8 = 9.09, p = 0.008). Frog density was not correlated with Bd prevalence (F1,7= 4.75, p= 0.06), and temperature did not affect prevalence or intensity of the infection. Bd is enzootic at all 6 sites and six pond-breeding species are reservoirs. The presence of abundant reservoirs at enzootic conditions explains the persistence of Bd in areas where other species declined without showing evidence of recovery. Low intensities of infection explain the survivorship of these reservoir species. I suggest that temperature might not be the principal factor molding Bd dynamics in the humid Neotropical forests, and present evidence that ponds are ecosystems where frogs might clean or reduce their infections

This study developed a heirarchical approach to improve the efficiency and reliability of surveys for stream-breeding frogs in the montane forests of south-eastern Australia. Areas with suitable climate for some of these species were first determined by bioclimatic modelling. Landscape and habitat preferences were then determined for the four species commonly found in far East Gippsland, along with an assessment of survey techniques from which effective survey protocols were developed. The climate of localities at which five stream-breeding species had been previously found was modelled using BIOCLIM, and maps of the predicted potential distributions having similar climate were developed. Litoria phyllochroa was found to occur in coastal to alpine areas from Melbourne to Nowra, and potentially further inland, in areas with relatively low temperatures and low summer rainfall. Litoria lesueuri had a slightly larger known and predicted distribution, covering a wide range of values for the temperature and precipitation parameters. Both species had predicted areas inland from Melbourne and the Blue Mountains where they had never been recorded, probably largely due to land clearing. The rare Heleioporus australiacus had a slightly more northerly distribution, closer to the coast and adjacent ranges from Central Gippsland to just north of Sydney, with a generally warmer climate and large range of average annual precipitation values. Litoria citropa occupies an even narrower area along the coast, extending slightly further north again, with a climatic profile of few extremes but with relatively high rainfall particularly in summer. The rare Mixophyes balbus had a more northerly known and predicted narrow range along the NSW coast, just extending into Victoria and Queensland, characterised by the subtropical influence of higher summer rainfall. The southern extension into far East Gippsland appears to have an extreme sub-climate, and is hence considered highly susceptible to climate change. Future monitoring sites for these species can now be systematically chosen to include their full climatic range, so that any negative effects of climate change on amphibian populations may have a greater chance of detection. Four species were found commonly enough in the far East Gippsland study area for more detailed study - the three stream-breeding specialist species, L. phyllochroa, L citropa, and L. lesueuri, along with Crinia signifera which was not restricted to streams but commonly found along them. Three species, L. phyllochroa, L citropa and L. lesueuri, were not found at the few higher altitudes sites on the Errinundra Plateau, however they may have been restricted by habitat requirements other than altitude. Litoria phyllochroa was otherwise widespread, but preferred larger in-stream pools and backwaters for breeding with overhanging vegetation for perch and call sites. The other three species preferred stream reaches characterised by wide bedrock outcrops and associated wide break in the tree canopy, which may allow their preferred perch sites on rocky substrates to retain heat after sunset. Litoria lesueuri tadpoles were found in both unconnected and connected pools, and the common association of this species with bedrock outcrops may explain its range being largely restricted to granitic substratum where these outcrops mostly occurred. Litoria citropa preferred reaches with bedrock and boulder outcrops, although frogs used both rocky and vegetative substrates as perch sites, with tadpoles caught in both unconnected pools and backwaters. Crinia signifera tadpoles were mostly restricted to unconnected pools, with frogs generally only detected within or very close beside these. Habitat models varied in their predictive ability, from 67.5% for L. phyllochroa frogs to 92.7% for L. lesueuri tadpoles. Models developed from normally-distributed habitat variables by discriminant function analysis were generally more predictive than those from logistic regression analysis. The occurrence of frogs and tadpoles of L. phyllochroa, L. citropa and L. lesueuri can be predicted by the measurement of five habitat variables along a 50m reach: average width between the banks, average channel width, an average of the maximum depth of channel cross-sections along the reach, channel slope, and proportion of the stream length as pools. The occurrence of C. signifera along reaches can be predicted with the additional measurement of the proportion of the banks covered in ferns, the maximum cross-sectional channel depth along the reach, and the number of unconnected pools. Several different techniques for surveying frogs were compared for the four species commonly found along the streams. Probability of detection models were derived for each species for each technique, which allowed calculation of the statistical confidence of detecting a species that actually occurred at a site for any given number of surveys. For transect-based techniques, models were also developed which allowed determination of the minimum number of surveys required without detecting a species to be 95 percent statistically confident that the species did not occur there, for various transect lengths. This level of confidence can be obtained for the four common species by four surveys using the reliable night encounter technique along 500m stream transects, during the period from Ocotber to March, with air temperatures above 10°C. The application of habitat models to select favourable 50m reaches for survey also generally improved the detectability of each species. Timer-activated tape recorders, which automatically recorded the calls of frogs for many consecutive nights at a site, were very efficient at detecting all species except the quietcalling L. lesueuri. Night encounter surveys along stream transects detected all species from a reasonable effort, and dip-netting for tadpoles was also effective for most species. Active visual encounter surveys were less reliable, and day encounter surveys detected few frogs but provided some additional data when other activities were being performed along the streams. The findings of this study have important implications for future amphibian surveys and monitoring undertaken in East Gippsland and the south coast of New South Wales. If the standardised survey techniques recommended by this study are used in Environmental Impact Assessments, their results can be objectively assessed and defended. The use of habitat modelling and improvement in survey reliability can also be used more efficiently to find sites with populations suitable for monitoring. The likely amount of effort required by a long-term monitoring program can also be determined so as to largely overcome daily variations in the detection of each species.

Amphibians globally are declining with roughly a third facing extinction due primarily to threats linked to human impacts. One way in which this is being combated is by captive breeding programs. Nordens Ark in Sweden, in collaboration with other organizations, is attempting to breed one of the most threatened frogs for future reintroduction to the wild. The mountain chicken (Leptodactylus fallax) has unique characteristics related to its reproduction which make it challenging to breed successful offspring. Using Nordens Ark’s data on environmental conditions within breeding enclosures, this study attempts to determine which extrinsic factors are having the most influence on reproduction, in order to increase the success of the captive breeding program. Multiple linear regression analysis and model simplification using Stepwise regression and Akaike information criterion (AIC) were performed in order to determine which explanatory variables had the most influence in relation to foam nests. A reduced model with significant values for explanatory variables was deemed the best model based on the dataset. Of the 14 environmental variables tested, minimum temperature after nest construction had the most influence on foam nest length. When compared to wild habitats, temperatures within enclosures may be too high or lack seasonal cyclical patterns. Barometric pressure and humidity also had influence on foam nests, but the relationships between these environmental conditions is difficult to parse. Food supplements were also a significant factor and suggest that lack of vitamins or nutrients can have a negative effect on reproductive success. Ensuring the optimal conditions can be difficult for captive breeding programs, especially as amphibians are under-represented and face biases in conservation and research.

Amphibian populations worldwide are currently in decline. One approach to preventing extinction of some of the affected species is to create assurance colonies. These sustainable captive populations might some day be used to reestablish wild populations. One issue with creating assurance colonies is successful breeding; often difficulties arise when attempting to breed exotic animals in captivity. Sexual conditioning, a form of Pavlovian conditioning, has been shown to improve breeding behavior. In this project the efficacy of sexual conditioning to improve breeding behavior in the dyeing dart frog (Dendrobates tinctorius) was tested. The frogs were trained with a stimulus that was either predictive of or independent of exposure to a member of the opposite sex. The group trained with the predictive stimulus showed shorter latencies to a variety of breeding behaviors and produced more eggs than the control groups. The sexual conditioning procedure also increased expression of various breeding behaviors allowing for careful examination of calls and visual signaling within this species.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on September 25, 2007) Vita. Includes bibliographical references.

The recent decline and disappearance of many amphibians around the world is thought to be the sign of an impending sixth mass extinction that is driven by disease, habitat loss and pollution. Reproductive technologies are now required to establish captive colonies followed by reintroduction into suitable habitats. The AMPHIPLEX method is a hormone mixture that has successfully stimulated spawning in several amphibians. However, its extensive application requires further experimentation and knowledge regarding the basic neuroendocrine control of reproduction in amphibians. The role of the catecholamine neurotransmitter dopamine in the regulation of spawning and gonadotropin synthesis was investigated using multiple time- and dose-related approaches in the field and laboratory. These end points were explored in two distantly-related frog species: the Northern leopard frog (Lithobates pipiens) and the Western clawed frog (Silurana tropicalis). Northern leopard frogs were injected during the natural breeding season with three doses of a gonadotropin-releasing hormone agonist (GnRH-A) (0.1 μg/g , 0.2 μg/g and 0.4 μg/g) alone and in combination with two doses of the selective dopamine receptor D2 antagonist metoclopramide (MET) (5 μg/g and 10 μg/g). Injected animals were allowed to breed in mesocosms in an outdoor field. Time to amplexus and oviposition were assessed, and egg mass release, incidences of amplexus, egg mass weight, total egg numbers and fertilization rates were measured. The results revealed no statistically significant interaction between GnRH-A and MET on amplexus and oviposition. A series of GnRH-A dose-response spawning studies were conducted in the Western clawed frog. The current findings indicate that partial ovulation, male sexual behavior and fertilization can be induced by 4 μg/g of GnRH-A alone and in combination with 10 μg/g of MET. This represents a first step towards understanding basic neuroendocrine reproductive mechanisms in this species. These spawning results were paired with a second end point which explored the molecular mechanisms of gonadotropin synthesis in response to GnRH-A and MET alone and in combination. Pituitary gene expression results in the Northern leopard frog indicate a potentiating action of MET when combined with GnRH-A on the mRNA levels of gonadotropin subunits 36 hours following injection. The postulated mechanisms of action are through the upregulation of gonadotropin-releasing hormone receptor 1 and the downregulation of dopamine receptor D2. Such gene expression pathways were similarly explored in the Western clawed frog, however no significant changes in pituitary gonadotropin and receptor gene expression were present at 12 hours post-injection. The hypothesized inhibitory action of dopamine was supported by pituitary gene expression analysis, but not by spawning outcome. The results from this study provide a fundamental framework for future time- and dose-response investigations to improve current spawning methods in amphibians.

There is limited research regarding amphibian distribution and status in rural upland habitats in Britain. Previous studies suggest potential influences on distribution and abundance arising from habitat modification and acidification. However, the extent to which these factors influence distribution at the landscape level is unclear. This study aimed to evaluate whether particular features of the aquatic and terrestrial habitat influence distribution and breeding ecology of common frogs (Rana temporaria L.) in rural upland areas. In particular, the extent to which aquatic and early terrestrial life-stages might be impacted upon by the quality of their respective habitats was investigated. Common frogs were found to be widespread and ubiquitous throughout the study area. No evidence was found to suggest that any specific biotic or abiotic feature of either the aquatic or terrestrial habitat significantly influenced distribution and relative abundance of breeding adults. However, reproductive success was found to be significantly impacted upon by acidity in coniferous and hilltop habitats. It is probable that juvenile recruitment at some ponds is chronically reduced and populations are maintained through immigration. Recruitment in improved habitats was highly variable between ponds and between years, although it was not possible to elucidate precise controls on larval populations in the natural habitats studied. Significant differences in physical condition at metamorphosis among wild populations were demonstrated. This may signify possible differences in future growth, life-fitness and dispersal ability between populations, or at least between natal ponds. Dispersal by new juveniles is potentially affected by the vegetation structure surrounding breeding ponds. Intra- and interspecific differences in behaviour regarding microhabitat use were demonstrated. Rural upland habitats can be valuable habitats for amphibians and the common frog in particular. However, further research is required to better understand rates of recruitment and immigration and how terrestrial habitats mediate juvenile survival and dispersal.

Research Doctorate - Doctor of Philosophy (PhD)
Environmental sustainability through the successful management of the impacts of forestry related activities on native wildlife in New South Wales (NSW) is a core requirement for Forests NSW, the government authority overseeing timber harvesting in the state. Populations of all native species must be protected adequately to allow their survival into the foreseeable future. A major proportion of the timber harvesting in NSW occurs along the coast and adjacent ranges of central and northern NSW. Timber is extracted using selective logging (not clearfelling) and the impacts of this activity on wildlife ameliorated through the use of strategies such as the placement of buffers around riparian sites, and the retention of hollow bearing trees, downed woody debris and undisturbed corridors of vegetation. This region, encompassing Latitudes 30o to 34o South, is dominated by native temperate wet and dry sclerophyll forests distributed along a gradient from coastal lowlands to montane areas over 1000 m. There are two families of anurans present in this region, the hylidae (approximately 25 species) and myobatrachidae (approximately 20 species), and are considered to have evolved in the region over at least 60 million years. Understanding of the effectiveness of protective measures requires a confident understanding of the habitat requirements of the frogs present in the forests so that they are used in appropriate locations. Presenting scientifically based information on the response of frogs to disturbances with these measures in place is also of primary interest to provide indications as to the effectiveness of these measures. Studies of pond breeding frogs in this region were undertaken to provide information on their habitat requirements and so direct the appropriate placement of the required protective measures. Tests were also undertaken to assess if there is an evident negative relationship between forestry disturbances and the use of ponds by frogs, indicating if current protective measures are effective. Current monitoring data was also investigated to provide insights into successful monitoring strategies for frogs which will provide the opportunity to more effectively demonstrate ecologically sustainable management of frogs into the future. Finally, records available on the distributions of frogs were used to study relationships between frog records and the current protected area system to assess its value as a means of protecting the frog species in the study region and throughout Australia. The majority of the research work undertaken was based on surveys of anurans at 93 semi-permanent and permanent ponds found in four areas: The Watagan Mountains, Bulahdelah, Wauchope and Dorrigo. Each site was surveyed on multiple occasions between 2001 and 2008, using aural and visual nocturnal searches conducted over different seasons to provide long-term information on the species using the sites. The presence and abundance of each species at each pond on each occasion was recorded as was micrometeorological data during the surveys. Each site was also visited in the day-time to collect data on variables associated with both the breeding pond and with the habitat within an 80 m radius of the site. A basic understanding of the extent and types of habitats individual frogs use is an important first step in understanding the extent of area requiring management for ongoing conservation. Published studies of frog movements were collated and reviewed to provide data on the likely habitat requirements and patterns of habitat use of frogs. The data, obtained from a 68 studies covering 50 species world-wide, indicating that in most cases (39 of 57 studies) adults have both specific breeding and non-breeding habitats. Mean distances moved from breeding to non-breeding habitats ranged from 38-1810 m and means for different anuran families falling around 300 m. Individuals in non-breeding habitat tended to restrict their activity to core areas (means from 6.3 m2 to 5099m2). This review indicated the strong need to consider both the breeding ponds and the surrounding habitat in the management of frogs. The calling seasons assigned by field guides to anuran species present within the study region are both highly variable and often vague. Therefore an objective assessment of the calling seasons of the frogs in eastern mesic NSW was developed to more accurately determine the months during which each species is most likely to call – the core calling period – and so be best surveyed. This was defined for each species as the months that covered > 90% of calling records. The 17,461 records covering 67 species provided enough information to reasonably determine the core calling periods for 46 species. Of these, 43 had clearly definable core calling seasons centred on the spring-summer months, two called year-round and one had an uncertain calling season, but probably calls year-round. Increasing latitude usually, but not always, led to a small reduction in the core calling period. This information confirmed the appropriate timing of surveys used in this study and should improve the outcomes of future research, management, and conservation. Micrometeorlogical variables such as temperature and rainfall are well recognised for their potentially significant influence on the calling activity of anurans, but this effect has been little tested in Australia. The calling records of frogs obtained through the study were compared with the micrometeorological variables temperature, humidity and (previous) 24 and 72 hour rainfall to assess how these related to calling activity. Models obtained for nine species all found calling activity to relate to at least two of these four variables. Calling showed a positive relationship with 72 hour rainfall in eight species, but no relationship for one species. Calling showed a positive relationship with 24 hour rainfall for six species, a negative relationship for two species and no relationship for one species. Temperature and humidity were found to have a mixture of positive, negative or no relationships with calling being evident. Rainfall over the previous 72 hours appears to be the best predictor consider when planning surveys. Other factors such as social environment and circannual rhythms are likely to be interacting with micrometeorology; hence the complex results. Further work is required to understand them fully. The results do indicate that surveys undertaken for this study were suitably timed to provide good results. Understanding if there are specific features of available habitats that correlate strongly with the presence/absence of frogs is important for managing frogs. This information may identify which breeding sites specific frogs are likely to use (or use in greater numbers) and habitat elements that may be critical for their survival. It may also provide indications of how human induced modifications may be affecting the frogs in an area. The presence/absence and abundance of anurans was recorded at 45 ponds in the Watagan Mountains, 100 km north of Sydney, and compared with 24 habitat variables. Only nine species occupied > 33% of the ponds. Canonical Correspondence Analysis (CCA) indicated there was no strong community structure. Species richness at a site was related significantly to depth and % emergent vegetation, but neither provided great explanatory power, based on their parameter estimates. Total anuran abundance related significantly to 12 variables that accounted for substantial variation in the data, but all contributed small amounts. Models for the four commonest species found many variables with statistically significant relationships to the frog counts, but neither pond attributes nor surrounding habitat attributes explained large amounts of variance in the data. There was little commonality in the habitat variables significant for the four species. This study indicated that no single variable could be said to influence general anuran presence and abundance and that habitat may not play a large role in determining the presence or abundance of anurans in this system. The initial study was confined to a relatively small geographic area to minimise differences resulting from variations in altitude, climate and geology. This was followed with a generalised linear model analysis that covered the 93 sites in the four forest blocks. The comparison with the recorded anurans and habitat also considered variation in altitude, geology and habitat types and included GIS derived variables covering more landscape habitat features around the ponds (eg, moisture indices and solar radiation indices). Species richness increased significantly with increasing emergent vegetation and the presence of sandstone, and decreased as the Prescott Index (a measure of ground moisture), elevation and latitude increased. Total frog abundance increased with increasing emergent vegetation and pond area and decreased with elevation, pond density and the Prescott Index. No consistent patterns were evident between the anuran counts and the significant habitat variables. Pond shading was the variable most commonly related to the presence/abundance of individual species (appearing in models for eight species), followed by tree height (six species). Models explained up to 64% of the deviance for presence-absence and 48% for abundance, but usually explained < 35% deviance. Local scale variables account for 8/17 significantly related variables in presence models and 26/42 in abundance models. There was no pattern evident based on phylogeny and human disturbances showed little relationship with anuran counts, suggesting their influence was minimal. Managing forest frogs requires consideration of multiple scales and multiple features of the environment. No one pond fits all frogs. Not all breeding species that occur in the study area are considered common and widespread. Conservation of rare and threatened species is usually considered to be of most importance and relies on identifying their specific habitat requirements or specialisations. The heath frog, Litoria littlejohni, is a rarely observed threatened species confined to a limited area of the Watagan Mountains. It is protected by placing broad buffer zones around known breeding sites with little knowledge of how this might protect individuals. The distribution pattern of this anuran in the Watagan Mountains was assessed by comparing 12 habitat variables associated with 10 presence and 36 absence sites from the region. Logistic Regression Modelling indicated only that the species was more prevalent at ponds in forests with little grass cover (P = 0.0479, Beta = -0.1759). A logistic regression comparing GIS derived habitat features within 500 m of 61 presence and 20,000 randomly allocated absence sites located within the Sydney region indicated that the presence of the heath frog was positively associated with an increasing Prescott (Moisture) Index (Z = 4.22; P < 0.001) and negatively associated with increasing roughness of the surrounding terrain (Z = -3.62; P < 0.001). Using a regression tree to predict the presence of this species within an area, I classified presence sites (94%) based on a combination of the Prescott Index and Solar Radiation. However, these features provide only a very general ability to identify potential sites. The continued presence of the species at sites logged and burnt multiple times provides confidence that this species is able to cope with some degree of disturbance. The capacity to effectively monitor populations of anurans to detect early population changes is paramount in their ongoing management. A central requirement is to regularly assess the data being obtained to determine if the program has the statistical power to detect significant changes in population size. The power of the current monitoring program for the threatened northern corroboree frog (Pseudophryne pengilleyi) was assessed to determine its sensitivity to detect both increases and declines in the numbers of calling males being recorded at 14 sites. Based on the data collected over nine years, the power analysis indicated that only an annual decline of 7% or greater would be statistically detectable after 10 years (cumulative > 52% decline). Being able to successfully detect a 3% annual decline over ten years (25% total decline) in this population will require sixty sites to be monitored. This increase in sites could be achieved by combining data from other monitoring programs being undertaken in the region. The northern corroboree frog has consistent and easily monitored calling behaviour, yet detecting changes in numbers of calling males is difficult due to inter-year variance in counts at sites. Developing standard effective monitoring programs for “typical” species with inconsistent calling spread over long seasons will be difficult and likely require considerable resources. In addition to the application of wildlife management practices to maintain populations of amphibians in production forests, there is a need to ensure that species are adequately represented in protected areas (PAs) that can provide populations of animals that migrate into production forests to maintain metapopulations and/or genetic flows. The relative reservation status of anuran species in Australia was determined using the Australian Natural Heritage Tool Database (ANHAT), a very large database with multiple sources of anuran site records. The number of records for each species inside and outside protected areas was noted, as well the number of reserves from which each species was recorded. Given approximately 10.5% of Australia is covered by PAs, a random allocation of records would result in species having a mean 10% of records falling in PAs. The proportion of records coming from reserves was greater than expected with a mean 30% of sites per species occurring within PAs. Thirty six species had > 45% of record sites in PAs and 18 species < 10% within PAs. The majority of the latter group of species are found in < 10 reserves. Relatively poorly “reserved” species occur within northern Australia or highly productive and poorly protected agricultural belts in eastern and western Australia. All forest dwelling species from eastern NSW are relatively well recorded from the PAs. Species dependent on native vegetation prevalent in agricultural areas are the most pressing conservation issue. Forestry management practices include the use of controlled burns to reduce the incidence of high intensity and uncontrolled wildfires that threaten forest assets. The effect of these controlled burns on wildlife is widely debated. The impact of a controlled burn on anurans in the Dorrigo area was examined by comparing the trends in counts of anurans obtained at four burnt “experimental” ponds with those obtained at four unburnt “control” ponds. The analysis indicated that the trends in counts at burnt ponds and unburnt ponds did not differ. The fauna and flora of this region has evolved in an environment subjected to regular fires and the anurans present may have developed strategies to cope with low intensity fires. Current protection of anurans in forests in NSW are based around the retention of areas of undisturbed habitat, with an emphasis on protecting ponds and the adjacent 20-30 m band of vegetation. Linkage corridors of undisturbed vegetation are also required for migration. For threatened species, larger protection zones are usually set in place, often specifying the exclusion of fire as an important element in conserving species. Hydrology research indicates that 20-30 m buffer zones around breeding sites will protect water quality and such buffers will also protect individuals engaged in reproductive activities. Such a band will not provide significant protection to the surrounding forest that is used as non-breeding habitat and, where there is genuine cause for concern in regard to negative impacts of forestry activities on a species, this buffer should be expanded to a minimum 300 m. However, the studies on habitat relationships indicate that anurans in the region do not have specialised habitat requirements that may become unusable through disturbance and there were no obvious negative relationships between logging, fire or grazing and the presence/absence or abundance of anurans. In general, anurans appear to be relatively robust to the types of forest habitat modification resulting from selective logging and buffer zones greater than 20 m are not likely to be required to maintain populations in such an environment. Species with narrow habitat requirements, such as rainforest/wet forest specialists, may be the exception to this and require consideration in management plans.

Thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Master of Science.
Breeding was observed in the foam nest frog, Chiromantis xerampelina, over three breeding seasons The mating pattern was characterized by an extended breeding season with a male-biased operational sex ratio and asynchronous and unpredictable female arrival. At more than 90% of nests, from one to seven unpaired males ('peripheral males') gathered around the amplexing pair during nest construction. Those peripheral males closest to the pair competed 'With each other, and with the amplexing male, to position their cloacae against the female's cloaca during oviposition bouts. In a detailed study of a single population, over 80% of males were observed as peripheral males, and 57% of males were observed both in amplexus and as peripheral males. Male mating success and participation at nests was unrelated to size or weight. Chorus participation was the best predictor of male, mating success and participation at nests. The most plausible explanation for the presence of peripheral males was a sperm competition hypothesis; namely that peripheral males compete with the amplexing male for fertilizations by shedding sperm into the nest. I collected data on body mass and testis mass for 13 African anurans. Using additional published data on 19 Japanese anurans, an allometric relationship between body mass and testis mass was calculated. using 16 genera as independent data points. This revealed that C. xerampelina have testes fourteen times heavier than predicted on the basis of body mass. This is consistent with a trend seen in several taxa where testis size is related to the intensity of sperm competition. An additional experiment, in which the arnplexing male was prevented from shedding sperm into the nest, showed that peripheral males are capable of fertilizing eggs. I conclude that peripheral males are engaged in an opportunistic alternative mating tactic involving sperm cosnpetition. More than half the observed females bred polyandrously, some mating with up to three males, This was the result of amplexing males dismounting between nesting sessions, and males displacing one another from amplexus.
Andrew Chakane 2018

In dense mating aggregations, such as insect and anuran choruses, signals produced at the same time can overlap and interfere with one another, reducing the ability of receivers to discriminate between individual signals. Thus, evolution by sexual selection is expected to result in mating signal timing strategies that avoid overlap. Patterns of signal alternation between competing males are commonly observed in leks and choruses across taxa. In some species, however, signalers instead deliberately overlap, or ‘synchronize’, their mating signals with neighboring conspecifics. Given the assumed high cost of reduced mate attraction when signals overlap, mating signal synchronization has remained an evolutionary puzzle. Synchronization may be beneficial, however, if overlapping signals reduce the attraction of nontarget receivers (predator avoidance hypothesis). Synchronized signals could also constructively interfere, increasing female attraction to the mating aggregation (the beacon effect hypothesis). I investigate these functions of synchronized signaling in two species of tree frogs that synchronize their mating calls: the pug-nosed tree frog (Smilisca sila) and the Ryukyu Kajika frog (Buergeria japonica). To examine the trade-offs imposed by call synchronization in each species, I conduct a series of field and laboratory playback experiments on target (female frogs) and nontarget (eavesdropping predators) receivers of frog calls. Results from these experiments support both hypotheses, suggesting that synchronized frog calls can reduce the attraction of predators and attract mates to the chorus. In addition, I found reduced preferences for fine-scale call timings in female S. sila and B. japonica, deviating from the expected preferences observed in many other anuran and non-anuran species. Thus, while males may enjoy multiple benefits from synchronized mating signals, relaxed sexual selection for non-synchronous signals may be key to the evolution and maintenance of mating signal synchrony.

Amphibian populations are declining globally due to a litany of factors including pollution, disease, climate change, and most importantly, habitat destruction. As most amphibian life histories involve their populations being recruitment limited, focusing on the mechanism behind breeding habitat selection will reveal useful cues that managers may use to increase abundance and breeding success. Though there are many theoretical models that describe the distribution of animals in response to a resource, the ideal free distribution (IFD) theory has not yet been applied to amphibian settling decisions. Through this application of the IFD, I have found that a population of wood frogs (Lithobates sylvaticus) in Patuxent National Wildlife Refuge select vernal pools that are large, deep, and hold water into the summer months to breed from 2010-2015. This information will provide managers with the ability to predict sites where wood frogs will breed in the future, as well as describe the cues that wood frogs are cueing in on so we can protect, alter, or create ideal breeding habitat.

The conservation of aquatic-breeding amphibian populations and their habitats is increasingly challenged by urban and rural development, which is occurring more intensively and more rapidly than ever before. Some species are now impacted by development throughout their range. This has forced a re-evaluation of the potential of developed landscapes for providing habitat and contributing to regional conservation strategies. For many amphibians, little is known about the criteria necessary for persistence in a developed landscape. Considerable variation in the physiology, habitat requirements, and movement behaviour of amphibians suggests that responses to habitat loss, alteration, and fragmentation are species-specific. In this thesis, I investigate species-habitat relationships for the northern red-legged frog (Rana aurora) and the Pacific chorus frog (Pseudacris regilla) in a mixed urban-rural landscape in southwestern British Columbia to evaluate the potential for species persistence despite urban and rural development throughout their range. I used repeat auditory surveys of the species’ breeding chorus to determine presence or absence at potential breeding wetlands. I then related species occurrence and abundance to characteristics of the aquatic and terrestrial environment measured at multiple spatial scales. Both species were found to use rural and urban wetlands, though R. aurora were rarely detected while P. regilla were common. Occurrence was best explained by characteristics of the terrestrial environment, rather than within-wetland characteristics, though influential terrestrial characteristics and their scale of impact differed between species. Within the context of the developed landscape, I identify species-specific positive and negative habitat associations and suggest the spatial scales at which management of these habitat characteristics will be most effective. These criteria may help to explain the species’ current distribution, prioritize management strategies, predict the effectiveness of habitat conservation and restoration projects, and inform development in municipalities seeking to maintain or enhance amphibian diversity.
Graduate
2019-09-11

Acoustic communication in anurans plays a critical role in species recognition, defending territories and resources, and finding a mate. Anurans use a number of different call note types to communicate, from which the most notable are advertisement- and aggression calls. Optimum weather conditions are a precursor to the commencement of the breeding season for all frog species and their calling behaviour is therefore readily influenced by atmospheric conditions. Male frogs within a chorus also tend to call from territories within a specific range of distances from one another. The objectives of this study were to 1) determine a possible context in which call note types are produced, 2) to determine the effect of atmospheric conditions on calling behaviour and 3) to determine the spacing distances between males and females in a chorus of Queckett’s River Frog (Amietia quecketti). Pre-recorded note types were used in a playback experiment to determine a context for elicited responses. A context was derived for six of the responses. Advertisement (clicks and whines), aggression (creaks), encounter (tonal notes), territorial (whine-tonal notes), and release calls (squeaks) were described. Calls and atmospheric conditions were recorded and correlated for an entire breeding season. Water temperature, wind speed, humidity and barometric pressure had a significant effect on calling intensity. As water temperature decreased calling intensity increased, while increased wind temperature led to increased calling intensity. Amietia quecketti calls from the water, explaining the effect while increased wind speed decreases water temperature and can carry sound further. Both humidity and barometric pressure showed increased calling intensity only at specific levels. Humidity and barometric pressure have a direct effect on one another, which most likely causes the correlation between calling intensity and both these variables. In this study A. quecketti was shown to have breeding ponds for males and resting ponds and positions for non-gravid females. This prevents unwanted or unnecessary amplexus. Males showed much smaller and less variable territory sizes than females. This is most likely because males have a small range of optimal spacing distance while females move towards and away from males. The presence of vegetation resulted in smaller territories. This is possibly because smaller males act as satellite males and cannot be seen by larger males in vegetation. The size of males did not affect territory size. Males have a specific inter-male spacing distance regardless of size.
MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015