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Full-Text Articles in Life Sciences
Field Evidence Challenges The Often-Presumed Relationship Between Early Male Maturation And Female-Biased Sexual Size Dimorphism, Marie Claire Chelini, Eileen Hebets
Field Evidence Challenges The Often-Presumed Relationship Between Early Male Maturation And Female-Biased Sexual Size Dimorphism, Marie Claire Chelini, Eileen Hebets
Eileen Hebets Publications
Female-biased sexual size dimorphism (SSD) is often considered an epiphenomenon of selection for the increased mating opportunities provided by early male maturation (i.e., protandry). Empirical evidence of the adaptive significance of protandry remains nonetheless fairly scarce. We use field data collected throughout the reproductive season of an SSD crab spider, Mecaphesa celer, to test two hypotheses: Protandry provides fitness benefits to males, leading to female-biased SSD, or protandry is an indirect consequence of selection for small male size/large female size. Using field-collected data, we modeled the probability of mating success for females and males according to their timing of …
Polyandry In The Absence Of Fitness Benefits In A Species With Female-Biased Sexual Size Dimorphism, Marie Claire Chelini, Eileen A. Hebets
Polyandry In The Absence Of Fitness Benefits In A Species With Female-Biased Sexual Size Dimorphism, Marie Claire Chelini, Eileen A. Hebets
Eileen Hebets Publications
Most studies exploring the evolution of female mating systems focus on species in which females are either monandric (mate with a single male) or highly polyandric (mate with multiple males), but less is understood about variation in mating decisions within a species. How and why do females of a single species decide whether or not to copulate with additional mates? In this study we attempt to answer this question in the highly dimorphic crab spider, Mecaphesa celer, whose females may be either monandric or polyandric. We tested three hypotheses: (1) a female’s decision to remate is based on sequential mate …
Proximate And Evolutionary Causes Of Sexual Size Dimorphism In The Crab Spider Mecaphesa Celer, Marie Claire Chelini
Proximate And Evolutionary Causes Of Sexual Size Dimorphism In The Crab Spider Mecaphesa Celer, Marie Claire Chelini
School of Biological Sciences: Dissertations, Theses, and Student Research
Animal species’ body sizes result from the balance between selection for survival and selection for reproduction. In species with sexual size dimorphism (SSD), this balance differs between females and males, resulting in distinct sizes despite similar constraints. I used an integrative approach to understand how sexual section, and differences in developmental trajectories and metabolic physiology, resulted in the female biased SSD of the crab spider Mecaphesa celer (Thomisidae). SSD in spiders is often assumed to be a consequence of selection for early male maturation, which should provide males with additional mating opportunities. My results allow us to discard mate …
Testosterone, Migration Distance, And Migratory Timing In Song Sparrows Melospiza Melodia, Alannah H. Lymburner, Tosha R. Kelly, Keith A. Hobson, Elizabeth A. Macdougall-Shackleton, Scott A. Macdougall-Shackleton
Testosterone, Migration Distance, And Migratory Timing In Song Sparrows Melospiza Melodia, Alannah H. Lymburner, Tosha R. Kelly, Keith A. Hobson, Elizabeth A. Macdougall-Shackleton, Scott A. Macdougall-Shackleton
Biology Publications
In seasonally migratory animals, migration distance often varies substantially within populations such that individuals breeding at the same site may overwinter different distances from the breeding grounds. Shorter migration may allow earlier return to the breeding grounds, which may be particularly advantageous to males competing to acquire a breeding territory. However, little is known about potential mechanisms that may mediate migration distance. We investigated naturally-occurring variation in androgen levels at the time of arrival to the breeding site and its relationship to overwintering latitude in male and female song sparrows (Melospiza melodia). We used stable isotope analysis of hydrogen …
A Dimensionless Invariant For Relative Size At Sex Change In Animals: Explanation And Implications, Andy Gardner, David Allsop, Eric Charnov, Stuart West
A Dimensionless Invariant For Relative Size At Sex Change In Animals: Explanation And Implications, Andy Gardner, David Allsop, Eric Charnov, Stuart West
Biology Faculty & Staff Publications
Recent comparative studies across sex-changing animals have found that the relative size and age at sex change are strikingly invariant. In particular, 91%-97% of the variation in size at sex change across species can be explained by the simple rule that individuals change sex when they reach 72% of their maximum body size. However, this degree of invariance is surprising and has proved controversial. In particular, it is not clear why this result should hold, given that there is considerable biological variation across species in factors that can influence the evolutionarily stable timing of sex change. Our overall aim here …
Shrimp Adjust Their Sex Ratio To Fluctuating Age Distributions, Eric Charnov, Robert Hannah
Shrimp Adjust Their Sex Ratio To Fluctuating Age Distributions, Eric Charnov, Robert Hannah
Biology Faculty & Staff Publications
Long-term data sets that quantitatively confirm basic ecological theory are rare for field populations. Highly variable recruitment often causes wide temporal variation in population age distribution and basic theory for adaptive sex ratio often predicts sex ratio tracking' to match the fluctuating age distribution. Using sex-changing shrimp as a model system, we test this in a new data set of 20 years duration. The new data support the theory, despite intense fishery exploitation that itself has greatly altered the age distribution in recent years.
Natural Selection And Sex Change In Pandalid Shrimp: Test Of A Life History Theory, Eric Charnov
Natural Selection And Sex Change In Pandalid Shrimp: Test Of A Life History Theory, Eric Charnov
Biology Faculty & Staff Publications
This article presents a graphical approach to the genetical theory of sex change (similar to one recently applied to the evolution of simultaneous hermaphroditism). The graphs will help clarify a set of predictions to be tested against data from Pandalid shrimp. These shrimp are protandrous hermaphrodites (reproduce first as males). The goal is to use the genetical theory to predict the age of sex change. Since these shrimp show much geographic variation in this age, they provide a good opportunity to test the evolutionary model.
Sex Ratio: Adaptive Response To Population Fluctuation In Pandalid Shrimp, Eric Charnov, Daniel Gotshall, Jack Robinson
Sex Ratio: Adaptive Response To Population Fluctuation In Pandalid Shrimp, Eric Charnov, Daniel Gotshall, Jack Robinson
Biology Faculty & Staff Publications
Pandalus jordani is a protandrus (sequential) hermaphrodite. Populations show large year-to-year variation in age composition. In response to this variation, individuals alter the age at which they change sex. This response is predicted by a genetic model that assumes an individual shrimp maximizes its genetic contribution to the next generation.