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Stephen C Weeks - One of the best experts on this subject based on the ideXlab platform.
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a field test of a model for the stability of Androdioecy in the freshwater shrimp eulimnadia texana
Journal of Evolutionary Biology, 2014Co-Authors: Stephen C Weeks, Sadie K Reed, Chiara Benvenuto, Robert J Duff, Zhong Hui Duan, Patrice DavidAbstract:The evolution of hermaphroditism from dioecy is a poorly studied transition. Androdioecy (the coexistence of males and hermaphrodites) has been suggested as an intermediate step in this evolutionary transition or could be a stable reproductive mode. Freshwater crustaceans in the genus Eulimnadia have reproduced via Androdioecy for 24+ million years and thus are excellent organisms to test models of the stability of Androdioecy. Two related models that allow for the stable maintenance of males and hermaphrodites rely on the counterbalancing of three life history parameters. We tested these models in the field over three field seasons and compared the results to previous laboratory estimates of these three parameters. Male and hermaphroditic ratios within years were not well predicted using either the simpler original model or a version of this model updated to account for differences between hermaphroditic types (‘monogenic’ and ‘amphigenic’ hermaphrodites). Using parameter estimates of the previous year to predict the next year's sex ratios revealed a much better fit to the original relative to the updated version of the model. Therefore, counter to expectations, accounting for differences between the two hermaphroditic types did not improve the fit of these models. At the moment, we lack strong evidence that the long-term maintenance of Androdioecy in these crustaceans is the result of a balancing of life history parameters; other factors, such as metapopulation dynamics or evolutionary constraints, may better explain the 24+ million year maintenance of Androdioecy in clam shrimp.
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Integrative and Comparative Biology Advance Access published May 5, 2006 When males and hermaphrodites coexist: a review of Androdioecy in animals
2013Co-Authors: Stephen C Weeks, Chiara Benvenuto, Sadie K ReedAbstract:Synopsis Androdioecy (populations consisting of males and hermaphrodites) is a rare mating system in plants and animals: up to 50 plants and only 36 animals have been described as being androdioecious, with most of the latter being crustaceans. To date, a thorough comparative analysis of Androdioecy in animals has not been undertaken. Herein we present such an analysis. Androdioecy has only been extensively surveyed in 2 animal taxa: the nematode Caenorhabditis and the clam shrimp Eulimnadia. The other major taxon having androdioecious species is the Cirripedia (barnacles), but there are only limited studies on Androdioecy in this group. In animals, Androdioecy is found either in species that have morphologically and ecologically distinct sexes (that is, hermaphrodites and small, “complemental ” males) that are derived from hermaphroditic ancestors (that is, the barnacles) or in species that have similarly-sized males and hermaphrodites that have been derived from dioecious ancestors (the remaining androdioecious species). We suggest that the barnacles have evolved a sexual specialization in the form of these complemental males that can more efficiently use the constrained habitats that these barnacles often experience. For the remaining species, we suggest that Androdioecy has evolved as a response to reproductive assurance in species that experience episodic low densities. Additionally, we hypothesize that the development of mechanisms allowing reproductive assurance in species with a number of sexually differentiated traits is most likely to result in Androdioecy rather than gynodioecy (mixtures of females and hermaphrodites), and that these species may be developmentally constrained to stay androdioecious rather than being capable of evolving into populations solely consisting of efficient, self-compatible hermaphrodites. We conclude by suggesting several areas in need of further study to understand more completely the evolution and distribution of this interesting mating system in animals
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The role of Androdioecy and gynodioecy in mediating evolutionary transitions between dioecy and hermaphroditism in the animalia.
Evolution; international journal of organic evolution, 2012Co-Authors: Stephen C WeeksAbstract:Dioecy (gonochorism) is dominant within the Animalia, although a recent review suggests hermaphroditism is also common. Evolutionary transitions from dioecy to hermaphroditism (or vice versa) have occurred frequently in animals, but few studies suggest the advantage of such transitions. In particular, few studies assess how hermaphroditism evolves from dioecy or whether Androdioecy or gynodioecy should be an "intermediate" stage, as noted in plants. Herein, these transitions are assessed by documenting the numbers of androdioecious and gynodioecious animals and inferring their ancestral reproductive mode. Both systems are rare, but Androdioecy was an order of magnitude more common than gynodioecy. Transitions from dioecious ancestors were commonly to Androdioecy rather than gynodioecy. Hermaphrodites evolving from sexually dimorphic dioecious ancestors appear to be constrained to those with female-biased sex allocation; such hermaphrodites replace females to coexist with males. Hermaphrodites evolving from sexually monomorphic dioecious ancestors were not similarly constrained. Species transitioning from hermaphroditic ancestors were more commonly androdioecious than gynodioecious, contrasting with similar transitions in plants. In animals, such transitions were associated with size specialization between the sexes, whereas in plants these transitions were to avoid inbreeding depression. Further research should frame these reproductive transitions in a theoretical context, similar to botanical studies.
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evolutionary transitions among dioecy Androdioecy and hermaphroditism in limnadiid clam shrimp branchiopoda spinicaudata
Journal of Evolutionary Biology, 2009Co-Authors: Stephen C Weeks, Eric G Chapman, D C Rogers, Diana M Senyo, Walter R HoehAbstract:Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: dioecy to hermaphroditism. A fruitful approach to studying this latter transition can be sought by studying clades in which transitions between dioecy and hermaphroditism have occurred multiple times. Freshwater crustaceans in the family Limnadiidae comprise dioecious, hermaphroditic and androdioecious (males + hermaphrodites) species, and thus this family represents an excellent model system for the assessment of the evolutionary transitions between these related breeding systems. Herein we report a phylogenetic assessment of breeding system transitions within the family using a total evidence comparative approach. We find that dioecy is the ancestral breeding system for the Limnadiidae and that a minimum of two independent transitions from dioecy to hermaphroditism occurred within this family, leading to (1) a Holarctic, all-hermaphrodite species, Limnadia lenticularis and (2) mixtures of hermaphrodites and males in the genus Eulimnadia. Both hermaphroditic derivatives are essentially females with only a small amount of energy allocated to male function. Within Eulimnadia, we find several all-hermaphrodite populations ⁄ species that have been independently derived at least twice from androdioecious progenitors within this genus. We discuss two adaptive (based on the notion of ‘reproductive assurance’) and one nonadaptive explanations for the derivation of all-hermaphroditism from Androdioecy. We propose that L. lenticularis likely represents an all-hermaphrodite species that was derived from an androdioecious ancestor, much like the all-hermaphrodite populations derived from Androdioecy currently observed within the Eulimnadia. Finally, we note that the proposed hypotheses for the dioecy to hermaphroditism transition are unable to explain the derivation of a fully functional, outcrossing hermaphroditic species from a dioecious progenitor.
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Can males successfully invade hermaphroditic populations of clam shrimp (Eulimnadia texana)
Current Science, 2009Co-Authors: Stephen C WeeksAbstract:Androdioecy (mixtures of males and hermaphrodites) is distinguished by its rarity, being found in only -40 animal species. Many of these species are clam shrimp in the genus Eulimnadia. A metapopulation model for the maintenance of Androdioecy is tested herein by examining male success in aquaria with a single male-producing hermaphrodite introduced into an otherwise all-hermaphrodite population. This migration experiment did allow males to persist in these populations for seven generations, although at levels below those found in other populations of these shrimp. These results suggest that the maintenance of Androdioecy via 'reproductive assurance' is unlikely by way of migration of male-producing hermaphrodites.
Naida Zucker - One of the best experts on this subject based on the ideXlab platform.
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maintenance of Androdioecy in the freshwater shrimp eulimnadia texana sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of out-crossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329-337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Copyright 2002.
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Maintenance of Androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of outcrossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329–337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Key words: Androdioecy, branchiopod crustaceans, evolution of breeding systems, inbreeding, mating success, mating tactics, mixed mating system, selffertilization. [Behav Ecol 13:561–570 (2002)]
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maintenance of Androdioecy in the freshwater clam shrimp eulimnadia texana longevity of males relative to hermaphrodites
Canadian Journal of Zoology, 2001Co-Authors: Naida Zucker, Brian Stafki, Stephen C WeeksAbstract:The clam shrimp Eulimnadia texana exhibits a rare mixed mating system known as Androdioecy. In this ephemeral-pond branchiopod crustacean, males coexist with hermaphrodites, which can outcross with males or self-fertilize. We provide an estimate of the longevity of males relative to hermaphrodites (1 σ), an important parameter of a model that was developed to explain the conditions under which this system would be stable. Under both optimal rearing conditions and various sex-ratio treatments, hermaphrodites from two study populations lived significantly longer than males. Since various aspects of mating have been found to be costly to males and females/hermaphrodites in other taxa, we explored this possibility as well. Hermaphrodites showed no differences in longevity when kept in groups provided with different mating opportunities. Males, however, lived significantly longer when mating opportunities were increased, a result contrary to what we had expected. Behavioral observations, however, suggested t...
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implications for the maintenance of Androdioecy in the freshwater shrimp eulimnadia texana packard encounters between males and hermaphrodites are not random
Ethology, 2000Co-Authors: Vicki L Medland, Naida Zucker, Stephen C WeeksAbstract:Androdioecy is a mixed-mating system in which there are males and hermaphrodites but no pure females. Few species exhibit such a mating system. Eulimnadia texana is a branchiopod crustacean that has recently been identified as an androdioecious species. This system is ideal for testing questions related to the evolution of sexual reproduction. We are testing a model that predicts Androdioecy to be a stable mixed-mating system under certain conditions. Specifically, we investigated whether encounters between males and hermaphrodites are random or if either sex seeks out the other for mating. Focal male or hermaphrodite clam shrimp were presented with stimulus shrimp of the other sex or kept alone. Swimming speed and time spent within different areas of a test chamber were recorded. Males did not alter mean swimming speed or spend more time than expected by chance near partitioned hermaphrodites. Hermaphrodites, however, decreased mean swimming speed in the presence of males and also spent more time than expected by chance near partitioned males, suggesting that hermaphrodites respond to male chemical and/or visual stimuli. Modified swimming behaviour probably facilitates inter-sexual contact, thereby increasing opportunities for out-crossing above that expected by random encounters.
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maintenance of Androdioecy in the freshwater shrimp eulimnadia texana estimates of inbreeding depression in two populations
Evolution, 2000Co-Authors: Stephen C Weeks, Bobbi R Crosser, Robert J Bennett, Melissa M Gray, Naida ZuckerAbstract:Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Andro- dioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of ''late'' inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial ( d5 0.68) in the more diverse population and somewhat lower ( d5 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of Androdioecy in this system is likely only if hermaphrodites are unable to self-fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted.
John R Pannell - One of the best experts on this subject based on the ideXlab platform.
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Female sterility associated with increased clonal propagation suggests a unique combination of Androdioecy and asexual reproduction in populations of Cardamine amara (Brassicaceae)
Annals of botany, 2015Co-Authors: Andrew Tedder, John R Pannell, Matthias Helling, Rie Shimizu-inatsugi, Tetsuhiro Kawagoe, Julia Van Campen, Jun Sese, Kentaro ShimizuAbstract:Background and Aims The coexistence of hermaphrodites and female-sterile individuals, or Androdioecy, has been documented in only a handful of plants and animals. This study reports its existence in the plant species Cardamine amara (Brassicaceae), in which female-sterile individuals have shorter pistils than seed-producing hermaphrodites. Methods Morphological analysis, in situ manual pollination, microsatellite genotyping and differential gene expression analysis using Arabidopsis microarrays were used to delimit variation between female-sterile individuals and hermaphrodites. Key Results Female sterility in C. amara appears to be caused by disrupted ovule development. It was associated with a 2.4- to 2.9-fold increase in clonal propagation. This made the pollen number of female-sterile genets more than double that of hermaphrodite genets, which fulfils a condition of co-existence predicted by simple Androdioecy theories. When female-sterile individuals were observed in wild androdioecious populations, their ramet frequencies ranged from 5 to 54 %; however, their genet frequencies ranged from 11 to 29 %, which is consistent with the theoretically predicted upper limit of 50 %. Conclusions The results suggest that a combination of sexual reproduction and increased asexual proliferation by female-sterile individuals probably explains the invasion and maintenance of female sterility in otherwise hermaphroditic populations. To our knowledge, this is the first report of the coexistence of female sterility and hermaphrodites in the Brassicaceae.
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gender variation and transitions between sexual systems in mercurialis annua euphorbiaceae
International Journal of Plant Sciences, 2008Co-Authors: John R Pannell, Marcel E Dorken, Benoit Pujol, Regina BerjanoAbstract:Evolutionary transitions between hermaphroditism and dioecy have occurred numerous times in the land plants. We briefly review the factors thought to be responsible for these transitions, and we provide a synthesis of what has been learned from recent studies of the annual herb Mercurialis annua, in which dioecy (males and females), monoecy (functional hermaphrodites), and Androdioecy (males and hermaphrodites) occur in different parts of its geographic range. Previous research on M. annua has revealed the importance of genome duplication and hybridization in the origin of much of the observed variation. Here we show, however, that spatial transitions in the sexual system also occur within the same ploidy level. In particular, we present an analysis, using flow cytometry data, of ploidy variation across a previously unstudied transition between hermaphroditism and Androdioecy, in which we find that the sexual‐system transition is uncoupled from the shift in ploidy levels. We review recent research that sh...
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gender variation and transitions between sexual systems in mercurialis annua euphorbiaceae
International Journal of Plant Sciences, 2008Co-Authors: John R Pannell, Marcel E Dorken, Benoit Pujol, Regina BerjanoAbstract:Evolutionary transitions between hermaphroditism and dioecy have occurred numerous times in the land plants. We briefly review the factors thought to be responsible for these transitions, and we provide a synthesis of what has been learned from recent studies of the annual herb Mercurialis annua, in which dioecy (males and females), monoecy (functional hermaphrodites), and Androdioecy (males and hermaphrodites) occur in different parts of its geographic range. Previous research on M. annua has revealed the importance of genome duplication and hybridization in the origin of much of the observed variation. Here we show, however, that spatial transitions in the sexual system also occur within the same ploidy level. In particular, we present an analysis, using flow cytometry data, of ploidy variation across a previously unstudied transition between hermaphroditism and Androdioecy, in which we find that the sexual‐system transition is uncoupled from the shift in ploidy levels. We review recent research that sh...
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hybridization polyploidy and the evolution of sexual systems in mercurialis euphorbiaceae
Evolution, 2006Co-Authors: Darren J Obbard, Richard J A Buggs, Stephen A Harris, John R PannellAbstract:Hybridization and polyploidy are widely believed to be important sources of evolutionary novelty in plant evolution. Both can lead to novel gene combinations and/or novel patterns of gene expression, which in turn provide the variation on which natural selection can act. Here, we use nuclear and plastid gene trees, in conjunction with morphological data and genome size measurements, to show that both processes have been important in shaping the evolution of the angiosperm genus Mercurialis, particularly a clade of annual lineages that shows exceptional variation in the sexual system. Our results indicate that hexaploid populations of M. annua, in which the rare sexual system Androdioecy is common (the occurrence of males and hermaphrodites) is of allopolyploid origin involving hybridization between an autotetraploid lineage of M. annua and the related diploid species M. huetii. We discuss the possibility that Androdioecy may have evolved as a result of hybridization between dioecious M. huetii and monoecious tetraploid M. annua, an event that brought together the genes for specialist males with those for hermaphrodites.
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the evolution of gender specialization from dimorphic hermaphroditism paths from heterodichogamy to gynodioecy and Androdioecy
Evolution, 2006Co-Authors: John R Pannell, Miguel VerdúAbstract:Several different pathways for the evolution of dioecy from hermaphroditism have been invoked and analyzed. These have largely considered either the spread of male- or female-sterility mutations in a monomorphic hermaphroditic population (i.e., the evolution of gynodioecy or Androdioecy, respectively) or the gradual divergence in sex allocation of two classes of individuals, one that becomes increasingly male and the other that becomes increasingly female in functional gender (the paradioecy pathway). Here we assess the conditions under which male- or female-sterility mutations may invade and spread in a heterodichogamous population, that is, a dimorphic population composed of protandrous and protogynous individuals. Our model is formally applied to heterodichogamous populations, but the ideas we explore may also apply to the evolution of separate sexes in distylous species, where plants are either long- or short-styled. The model predicts that, under many circumstances, conditions for the evolution of gynodioecy and Androdioecy in a heterodichogamous population are the same as those for their evolution from monomorphic populations. However, if one or the other of the two morphs are already somewhat specialized in their functional gender, as might occur if the quality or quantity of seed set is time dependent, the conditions for the invasion of males or females are relaxed. In particular, Androdioecy can evolve more easily under such circumstances in heterodichogamous populations than in monomorphic hermaphroditic populations.
Vicky G Hollenbeck - One of the best experts on this subject based on the ideXlab platform.
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maintenance of Androdioecy in the freshwater shrimp eulimnadia texana sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of out-crossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329-337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Copyright 2002.
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Maintenance of Androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of outcrossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329–337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Key words: Androdioecy, branchiopod crustaceans, evolution of breeding systems, inbreeding, mating success, mating tactics, mixed mating system, selffertilization. [Behav Ecol 13:561–570 (2002)]
William R. Gould - One of the best experts on this subject based on the ideXlab platform.
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maintenance of Androdioecy in the freshwater shrimp eulimnadia texana sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of out-crossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329-337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Copyright 2002.
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Maintenance of Androdioecy in the freshwater shrimp Eulimnadia texana: sexual encounter rates and outcrossing success
Behavioral Ecology, 2002Co-Authors: Vicky G Hollenbeck, Stephen C Weeks, William R. Gould, Naida ZuckerAbstract:The clam shrimp Eulimnadia texana has a rare mating system known as Androdioecy, in which males and hermaphrodites cooccur but there are no pure females. In this species, reproduction takes place by outcrossing between males and hermaphrodites, or by selfing within a hermaphrodite; this system provides a unique opportunity to examine the adaptive significance of outcrossing and selfing in animals. Our study examined mating behavior in hermaphrodites and males from two populations to understand the propensity of these shrimp to mate and to estimate a parameter of a model developed by Otto et al. (American Naturalist 141:329–337), which predicts the conditions for stability of the mixed mating system in E. texana. Here we present evidence that mating frequency is environmentally sensitive, with greater numbers of encounters and matings per male when males are rare and in younger males. However, the effects of shrimp density, relative male frequency, and shrimp age interact in a complex way to determine male mating success. Overall, mating frequency was determined by a combination of encounter rates between the sexes and the proportion of encounters resulting in mating. The mating rates were then used to estimate one of four parameters of the Otto et al. model, and these estimates were combined with previous estimates of the other three parameters to examine the fit of the predicted to the observed sex ratios in the two populations. Key words: Androdioecy, branchiopod crustaceans, evolution of breeding systems, inbreeding, mating success, mating tactics, mixed mating system, selffertilization. [Behav Ecol 13:561–570 (2002)]