Academic literature on the topic 'Sexual dimorphism (Plants); Plant ecology; Plants'

Abstract Dioecious plants exhibit sexual dimorphism in both sexual features (reproductive organs) and secondary sex characteristics (vegetative traits). Sexual differences in secondary traits, including morphological, physiological and ecological characters, have been commonly associated with trade-offs between the cost of reproduction and other plant functions. Such trade-offs may be modified by environmental stressors, although there is evidence that sexually dimorphic responses to stress do not always exist in all plant species. When sexual dimorphism exists, sexually different responses appear to depend on the species and stress types. Yet, further studies on dioecious plant species are needed to allow the generalization of stress effects on males and females. Additionally, sexual dimorphism may influence the frequency and distribution of the sexes along environmental gradients, likely causing niche differentiation and spatial segregation of sexes. At the present, the causes and mechanisms governing sex ratio biases are poorly understood. This review aims to discuss sex-specific responses and sex ratio biases occurring under adverse conditions, which will advance our knowledge of sexually dimorphic responses to environmental stressors.

Angiosperms possess diverse sexual systems, often with different combinations of hermaphroditic, pistillate and staminate flowers. Despite this sexual diversity, most populations are either monomorphic or dimorphic with respect to gender strategy, where gender refers to the relative contribution that individuals make to fitness through female and male function. An important problem in evolutionary biology is to determine how and why variation in gender strategies originates and is maintained. Wurmbea (Colchicaceae), a genus of insect-pollinated geophytes, has recently become the focus of ecological and evolutionary studies aimed at understanding these issues. Phylogenetic reconstructions suggest dispersal from Africa to Australia, then New Zealand, and multiple transitions between monomorphic and dimorphic sexual systems within Australia. Microevolutionary studies of W. dioica and W. biglandulosa, two wide-ranging taxa with monomorphic and dimorphic populations, provide insights into the selective mechanisms governing transitions between sexual systems. Dimorphic populations of these taxa likely comprise independent origins of dimorphism via the gynodioecious pathway by invasion of females into monomorphic populations. Shifts in pollination biology and flower size, and their consequent effects on mating patterns, may have contributed to the evolution of gender dimorphism. Pollinator-mediated selfing and inbreeding depression provide a sufficient fertility advantage for females to be maintained in dimorphic populations. Once dimorphism establishes, increasing gender specialisation is associated with invasion of more arid environments. Inbreeding avoidance, particularly under stressful ecological conditions, is the most likely selective mechanism maintaining gender dimorphism in Wurmbea. We conclude our review by suggesting avenues for future research that might provide a more comprehensive picture of the evolution of gender strategies in Wurmbea.

The term facilitation generally describes positive interactions between plants, and a common approach in these studies is to identify a dominant plant to structure sampling. Unfortunately, whilst this field has rapidly expanded community ecology, it rarely includes other trophic levels such as insects and pollinators. Here, we combine facilitation, pollination, and reciprocity measures to explore the general hypothesis that sexual dimorphism in a benefactor plant species mediates its impact. The following three predictions were tested and supported using the gynodioecious alpine cushion plant Silene acaulis (L.) Jacq.: (i) that the trait set of a gynodioecious benefactor plant varies between genders; (ii) that dimorphism changes the facilitation of other plants, arthropods, and pollinators; and (iii) that insect selectivity, particularly pollinators, reciprocally impacts the reproductive output of the two genders. Female S. acaulis cushion plants produced significantly more flowers but they were smaller than those of hermaphrodites. Hermaphrodite cushions facilitated other plant species and pollinators more effectively than females, whilst females strongly facilitated more arthropods. Finally, female plants have significantly higher reproductive output as estimated by fruit and seed production, and this was directly related to visitation rate by pollinators. Hence, this study clearly establishes the value of combining some of the common themes of pollination biology such as sexual dimorphism, floral morphology, and measuring reproduction with the study of positive plant–plant interactions.

The New Zealand karaka tree, Corynocarpus laevigatus J.R. & G.Forst., is shown to be gynodioecious. Flowers on female plants have large but empty anthers and many set fruit. Flowers on male plants produce pollen and each has a fully developed ovule. On most male plants, a low proportion of flowers set fruit. Inflorescences and flowers on male and female trees are similar in overall appearance, except that the flower parts on males are larger and flowers open more widely. Even the gynoecia on male plants are larger in most respects. We also report that although trees retain their gender, their intensity of fruiting varies from year to year. Some observations indicate that other species of Corynocarpus in Australia and the south-western Pacific might also be gender dimorphic.

The sexual dimorphism of reproductive investment (measured as dry mass of reproductive tissues) at stem and whole plant (i.e., genet) levels in a dioecious clonal shrub, Ilex leucoclada (Maxim.) Makino., was examined over 2 consecutive years. Five patches in which different genets had already been distinguished using molecular markers in a previous study were selected, and the stem length, numbers of flowers and fruits, and sex of each stem were recorded. Fresh inflorescences and fruits were randomly sampled to estimate the reproductive investment of each stem. The male plants invested more resources in flowering at both the stem and genet levels than female plants, but females invested more resources than males when fruit masses were considered in addition to flower masses. The degrees of sexual dimorphism in reproductive investment at the stem and genet levels were similar, for both flowering alone and flowering plus fruiting. However, the reproductive investment was more restricted to large stems in female genets than in males. Inter-year fluctuations in reproductive investment were greater for females than males at both levels. These results suggest that patterns of reproductive investment should be examined simultaneously at multiple modular levels to obtain a thorough understanding of gender-associated variations in clonal plants.

The reproductive ecology of the dioecious herb Aciphylla simplicifolia (F.Muell.) Benth. (Apiaceae, Mountain Aciphylla) was examined in Kosciuszko National Park. Differences in floral display and flowering phenology between male and female plants were consistent with predictions based on theories concerning sexual dimorphism in dioecious plants. For example, male plants had larger floral displays than females at the alpine sites sampled. Male inflorescences had four times as many flowers as females and more than three times the area of floral display. In addition to differences in floral display, there was a sex-specific pattern in flowering phenology at six alpine sites. At these sites, there were more male inflorescences with buds and flowers and more female inflorescences finished flowering than would be expected if gender did not affect flowering phenology. To determine whether increasingly severe conditions associated with higher-altitude sites were associated with male-biased sex ratios, the number of male and female plants were compared for 20 sites over a 600-m altitudinal range from montane to alpine (total 4274 plants). As altitude increased and as the vegetation zone changed from subalpine to alpine, the sex ratio became increasingly male-biased, with sites in the alpine ranging from 1.45 males per female to 8.53 males per female. Sexual dimorphism in floral display, flowering phenology and sex ratios was consistent with what would be predicted for plants with sex-specific differences in resource allocation.

Sexual dimorphism in dioecious plant species is widely attributed to the differential impacts of reproduction on male v. female plants. We investigated sexual dimorphism in reproductive, morphological and physiological traits of Maireana pyramidata (Benth.) Paul G.Wilson (Chenopodiaceae), a dioecious, semi-arid shrub endemic to Australia. We estimated reproductive allocation for each sex by calculating the relative biomass allocated to flowers and fruits per gram of leaf tissue, based on one branch per sample plant. Morphological measurements included leaf mass, stem mass, specific leaf area, plant height and plant leaf area index. We also measured leaf nitrogen and chlorophyll, gas exchange and Δ13C. Reproductive allocation was nine times greater in females than in males. No significant difference between the sexes in photosynthetic rate or transpiration could be detected but instantaneous water use efficiency (photosynthesis/transpiration) was significantly lower in females than in males during the fruiting period. Δ13C did not differ between the sexes. The results indicate that greater reproductive allocation in females has an immediate impact on their capacity for conservative water use but does not lead to long-term differences in water use efficiency.

In this study we explore morphological and ecological variation in sympatric populations of Pagamea coriacea s.l. - a species complex from white-sand vegetation in the Amazon. A total of 147 trees were sampled and monitored at three nearby sites in Central Amazon, Brazil. Multivariate analyses of morphology indicated two distinct groups (A and B), which also differed in bark type, each containing subgroups associated with sexual dimorphism. However, a single hermaphroditic individual was observed within group B. As expected, all pistillate plants produced fruits, but 23% of the staminate plants of group B, and 5% of group A also produced fruits. This variation suggests that the sexual systems of both groups are between dioecy and gynodioecy. There was an overlap in flowering phases between the two groups, but the pattern of floral maturation differed. Ecologically, plants of group B were found in more shaded habitats and over sandstone bedrocks, while group A was prevalent in deeper sandy soils as canopy plants. The significances of morphological and environmental differences were tested by a multivariate analysis of variance, and a canonical discriminant analysis assessed the importance of variables. The coexistence in sympatry of two discrete morphological groups in the P. coriacea s.l., with different habitat preferences and reproductive behaviors, indicates they represent distinct species.

Sexual dimorphism in reproductive costs between females and males in dioecious plants is associated with divergent morphologies, life histories, and physiologies between the sexes. In Sagittaria latifolia Willd. (Alismataceae), a previous experiment has shown that sexual reproduction imposes asymmetric costs for females vs. males, with greater biomass costs for females and greater nitrogen costs for males. Here we investigate whether sexual dimorphism in nitrogen expenditure for reproduction influences the nitrogen content of leaves under natural conditions and, if so, whether it is associated with differences in photosynthetic rates between the sexes. As expected, we found significantly lower leaf nitrogen content among males compared with females and a positive association between leaf nitrogen content and photosynthetic rates. However, this difference in nitrogen content between the sexes was not associated with different photosynthetic rates for females vs. males. Our study demonstrates that an underlying difference in nitrogen content between the sexes is maintained during flower and fruit production in a natural population, but, at least at the site used for this study, this difference was not associated with divergent photosynthetic rates.

Neste trabalho objetivou-se estudar o comportamento de acasalamento de Cyrtomon luridus Boheman (Coleoptera: Curculionidae), bem como a presença de semioquímicos mediando o acasalamento e a interação com a planta hospedeira Duboisia sp. (Solanaceae). Machos e fêmeas adultos recém-emergidos foram coletados no campo e levados para o laboratório. Incialmente foi determinado o melhor parâmetro morfológico para diferenciação de machos e fêmeas. Verificou-se que machos deste curculionídeo possuem a abertura genital oclusa pelo último tergito. O comportamento de acasalamento foi observado em casais virgens durante nove dias. Verificou-se que machos e fêmeas de C. luridus atingiram a maturidade sexual dois dias após a emergência. Machos e fêmeas realizaram acasalamentos repetidos com o mesmo parceiro em qualquer horário do dia. O comportamento de acasalamento deste curculionídeo foi dividido nas fases pré-copulatória, copulatória e pós-copulatória. Além disso, estudos de olfatometria revelaram que machos e fêmeas de C. luridus foram fortemente atraídos por voláteis de machos se alimentando sobre a planta hospedeira. A coleta e análise destes voláteis revelaram a presença dos compostos (Z)-3-hexenal, hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, fenilacetaldeido, linalol e geraniol, como eletrofisiologicamente ativos. O presente trabalho traz importantes informações sobre o comportamento de acasalamento e ecologia química de Entiminae e servirão de base para estudos com outras espécies desta importante subfamília de Curculionidae.
This work aimed to study the mating behavior of Cyrtomon luridus Boheman (Coleoptera: Curculionidae), as well as the presence of semiochemicals mediating the mating and the interaction of the insects with the host plant, Duboisia sp. (Solanaceae). Newly emerged males and females adults were collected in the field and taken to the laboratory. Initially it determined the best morphological parameter to differentiate males and females. It was found that males possess the genital opening occluded by the last tergite. The mating behavior was observed in virgin couples for nine days. It was found that males and females C. luridus reached sexual maturity two days after emergence. Males and females made repeated matings with the same partner at any time of day. The mating behavior was clearly divided into the pre-copulatory, copulatory, and post-copulatory phases. In addition, olfatometrics studies revealed that males and females C. luridus were strongly attracted to volatile males feeding on the host plant. The collection and analysis of these volatiles revealed the compounds (Z)-3-hexenal, hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, phenylacetaldehyde, linalool and geraniol as being eletrophysiologically. The present work brings important information about the mating behavior and chemical ecology of Entiminae, which will serve as support for studies with other species of this important subfamily of Curculionidae.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第21176号
人博第848号
新制||人||203(附属図書館)
29||人博||848(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 加藤 眞, 教授 市岡 孝朗, 教授 瀬戸口 浩彰
学位規則第4条第1項該当

In dioecious plants, selection due to sex function differences has produced sex-specific life histories, morphologies, and physiologies. In many dioecious seed plants, dimorphisms and population sex ratios have been plausibly linked, but similar links are not yet apparent in dioecious bryophytes. Population sex ratio bias is often expected to favor the sex with lower investment in sexual reproduction, especially in resource-poor environments. Unlike in seed plants, bryophyte males may have higher average reproductive investment than females, which typically have low offspring production rates due to sperm limitation. However, traits aside from reproductive investment such as shoot and leaf arrangement may be differentially selected and could influence life history and sex ratio, but these are rarely tested. My questions concentrated on the dimorphic traits responsible for sex ratio bias and their links to sex function. My studies, using the moss Bryum argenteum, included field and greenhouse experiments investigating sex ratio bias and morphological plasticity along a light/canopy openness (exposure) gradient, a greenhouse comparison of clump morphology and water-holding capacity, and a field and growth chamber study on sex-specific responses to stress (high temperature and desiccation). The sex ratio of urban Lexington, KY was highly female-biased, did not correlate with exposure, and was not linked with pre-zygotic reproductive investment. Leaf characteristics of B. argenteum plastically responded to exposure but were not sex-specific. However, juvenile females produced shoots at a faster rate and grew taller in high light. Juvenile male shoots held more external water than female shoots, but this did not predict mature clump water-holding capacity. Male clumps were shorter, denser, and held less water than females likely to shed sperm-laden water for sexual reproduction. Clump height did not trade off with reproductive investment, adding evidence that sex-specific size is linked with other aspects of sex function. Although chlorophyll fluorescence data (a measure of the status of photosystem II) from both field and growth chamber experiments indicated subtle sex-specific stress recovery responses among sexually immature and mature plants, differences were weaker than predicted and sexually mature shoots did not fare worse than vegetative shoots. The sex differences in size, clump morphology, and clump water-holding capacity very likely affect survival, growth, competitive ability, and ultimately adult sex ratio bias.

Els processos metabòlics en plantes, com ara la fotosíntesi, la fotorespiració i la respiració, comporten l’inevitable producció d’espècies reactives de l’oxigen (ROS) en cloroplasts, peroxisomes i mitocondris. En determinades concentracions les ROS poden actuar com a molècules implicades en la senyalització cel•lular, però degut a la seva elevada reactivitat, un augment de les ROS provoca l’oxidació de components cel•lulars alterant-ne la seva funció biològica i provocant dany oxidatiu a la planta. En condicions d’estrès, tant biòtic com abiòtic, les plantes experimenten un increment dels nivells de ROS. Per tal de mantenir l’homeòstasi redox, aquestes han desenvolupat un seguit de mecanismes antioxidants capaços de reduir els nivells de ROS evitant un possible dany oxidatiu. La recerca per desxifrar les respostes de les plantes a l’estrès ha anat en augment en els últims anys, però encara avui en dia és poc el coneixement que tenim sobre els mecanismes implicats en el cas de les plantes perennes, tot i que constitueixen una part molt important del regne vegetal. Per altra banda, tot i l’evident importància de l’estrès oxidatiu, són escassos els estudis que s’han plantejat com aquest es pot veure afectat per factors intrínsecs de la planta, com l’edat o el sexe. L’objectiu principal d’aquesta tesi ha estat determinar com l’edat de la planta, tant la cronològica com la fisiològica, i el sexe poden influir en l’estrès oxidatiu en plantes perennes. L’anàlisi del nivells d’estrès oxidatiu es va dur a terme mitjançant les mesures de diferents mecanismes antioxidants com els carotenoides, l’alfa-tocoferol i els antocians, però centrant-nos sobretot en el paper de l’àcid malondialdehid, un subproducte de la peroxidació lipídica. Els estudis es van realitzar en fulles i plantes juvenils de Pistacia lentiscus L., una espècie dioica i perenne típica del clima mediterrani, i en arbres moribunds de Fagus sylvatica L., proporcionant un bon model a causa de la seva avançada edat, tant cronològica com fisiològica. Els resultats obtinguts revelen que l’augment dels nivells de peroxidació lipídica com a indicador d’estrès oxidatiu pot significar un dany o un possible mecanisme de senyalització interna; per això, la consideració conjunta de l’edat cronològica i els nivells d’estrès oxidatiu és un bon indicador de l’edat fisiològica, tant a nivell de fulla com de planta sencera. L’esforç reproductiu en plantes dioiques ocasiona canvis en els mecanismes fotoprotectors en les femelles respecte als mascles en condicions ambientals adverses. Tot i que les femelles presenten uns nivells d’estrès oxidatiu superiors als dels mascles, no es veuen afectades negativament, el que suggereix un possible rol en senyalització. Així mateix, l’estudi a nivell modular mitjançant la comparació entre brots reproductius i no reproductius en femelles va revelar una major fotoprotecció en els brots reproductius, com indicaven els nivells d’antioxidants i la major dissipació d’excés d’energia en forma de calor, emfatitzant la importància de la diferenciació entre mòduls en l’estudi de les diferències entre sexes en plantes dioiques.
Metabolic processes in plants such as photosynthesis, photorespiration and respiration, produce reactive oxygen species (ROS). ROS are highly toxic molecules but besides of its damaging nature they are implicated in cell signaling in different cellular processes. However, under stress conditions plants can suffer an increase of ROS levels. When ROS concentration becomes high enough to overwhelm antioxidant systems, plant suffer oxidative stress as a consequence of the unbalanced cellular redox status. Despite the importance to unravel plant stress responses, little is known about the mechanisms implicated in perennial plants. Furthermore, the possible effect of plant intrinsic factors, as plant age or reproductive effort, in oxidative stress levels is still poorly understood. The main objective of this thesis was to determine how plant age, both chronological and physiological, as well as reproductive effort may influence oxidative stress levels in perennial plants. With this purpose levels of antioxidants as carotenoids, anthocyanins and alpha-tocopherol together with endogenous contents of stress hormones were measured, but with special emphasis in malondialdehyde acid levels, a byproduct of lipid peroxidation. To better understand the plant age effect we used leaves and juvenile plants of Pistacia lentiscus as well as moribund beech trees. Increases in lipid peroxidation not only could mean an oxidative damage but play a signaling role. Therefore, chronolorgical age concomitantly with the measure of oxidative stress levels is a good indicator of plant physiological age. Sex-related changes in photoprotection mechanisms between female and male plants of Pistacia lentiscus, a dioecious plant, where observed under climatological adverse conditions. Although females phowed higher oxidative stress levels compared to males, females were not affected negatively, suggesting a role in signaling. In addition, photoprotection capacity was higher in reproductive shoots relative to non-reproductive shoots in females, thus suggesting that females prioritized protection to fruit-bearing shoots.

Thesis (Ph.D.)--York University, 2003. Graduate Programme in Biology.
Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ99195

This chapter examines pollination, mating, and reproduction in plants. Plant reproduction can be either sexual or asexual, but the generation of new variants (which is the underlying necessity for adaptation to new or changing conditions and for evolutionary change) requires that at some point in the life cycle sexual reproduction occurs. In the case of angiosperms, the pollen grain is the male gamete, the equivalent of a spore in simpler plants. The ovule (egg) contains the female gamete. The chapter first provides an overview of plant fertilization before discussing plant sex and plant mating systems. It then considers the benefits of cross-fertilization and self-fertilization in plants, along with methods for avoiding selfing within a flower. It also describes methods for avoiding selfing between flowers within a plant and concludes with an analysis of methods for ensuring selfing.

The study of mating is one of the most active areas in evolutionary ecology. What fuels this research is curiosity about a stunning diversity of ways in which zygotes are formed. Many plants and some animals can reproduce without combining gametes. Many other plants combine gametes but do so within the same individual (selfing). Still other plants and animals require a gamete from another individual to stimulate reproduction but do not incorporate the genetic material contained in that gamete in the offspring. Finally, many organisms combine gametes produced from different individuals in sexual reproduction, but the ways in which these individuals get together to reproduce are also amazingly diverse and have major implications for how selection acts in these populations. Why are there so many different ways to reproduce? Answering this question is a major challenge for evolutionary ecologists. Our approach begins with how a variety of ecological factors affect selection on reproductive traits. Because many reproductive traits show genetic variation, diversity in selective pressures can lead to a diversity of evolutionary changes. Thus, understanding the evolutionary ecology of mating systems can help to interpret the significance of this variation and can provide new insight into related phenomena. For example, costs of female reproduction associated with development of offspring greatly impact other aspects of the life history, and males are often limited by mates (Savalli, this volume). Factors such as levels of selfing, inbreeding depression, and allocation of resources play a part in mating systems of both plants and animals (Waser and Williams, this volume), and sex allocation theory has been used in both plants and animals to explore the evolution of hermaphroditism and unisexuality (Campbell 2000; Orzack, this volume). This chapter explores some of the major forces affecting mating systems. Our treatments of plants and animals differ in emphasis, but our goal is to use the perspective of evolutionary ecology to define more fully the similarities, differences, and diversity in plant and animal mating systems, and to highlight potentially interesting yet currently unanswered questions. Diversity in patterns of zygote production arises in part from ecological factors influencing two issues: selection on the evolution of sexual reproduction itself and differentiation of the sexes.

The diversity of known strategies for parasitic lifestyles is truly astonishing. Many species of parasitic worms, for example, utilize only one host species, while others cycle between two or more (as many as four) different species of hosts. Some parasites are highly virulent, seriously debilitating or even killing their hosts, while others cause only minor damage. Some parasites (such as viruses) are very small relative to their hosts and have the capacity for explosive reproduction. Others are almost as large as their hosts, and have relatively slow generation times. Therefore, parasites are difficult to categorize. Here, I use parasite to refer to organisms that have an obligate association with, and a negative effect on, another organism (the host). Host strategies for dealing with parasites are equally complex. Vertebrates have highly specialized immune systems that can rapidly respond to infection and then store information that can be used to mount future responses to the same type of infection. Invertebrates lack the memory cells of true immune systems, but they do have complex self-nonself recognition systems for recognizing and killing foreign tissues. Plants also have highly specialized defenses against pathogens, and the genetic basis of these defenses is especially well known due to the work of plant pathologists on crop plants. The myriad of details involved in the interactions between hosts and their parasites is overwhelming, but there are some shared, general aspects of these interactions that are of particular interest to evolutionary ecologists. First, parasites may attack in a frequency-dependent way. In other words, the probability of infection for a particular host genotype is expected to be, at least in part, a function of the frequency of that host genotype. This expectation has implications for sexual selection and the evolutionary maintenance of cross-fertilization (Sakai, this volume; Savalli, this volume). Second, parasites may affect the population density of their hosts, and host density may feed back to affect the numerical dynamics of the parasite. Host density may also affect natural selection on the reproductive rates of parasites, which in turn is likely to affect host fitness and host dynamics.

This chapter describes nine case studies that illustrate how meta-analysis has contributed to theoretical developments in basic research in ecology and evolution. The main research topics cover are maintenance of biodiversity (Case 1); sexual selection (mate choice/fighting behavior) (cases 2, 8, 9); sex ratio theory (Case 3); allometric scaling (Case 4); the invasiveness of exotic plants (Case 5); seed size and plant abundance (Case 6); and the role of competition and predation in structuring communities (Case 7). It is hoped that these case studies will resonate with the reader and provide “templates” for ways to conduct comparable tests on analogous controversies in their own fields of research.