A Dimensionless Invariant for Relative Size at Sex Change in Animals: Explanation and Implications (original) (raw)
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Divergent sex-specific plasticity and the evolution of sexual dimorphism in long-lived vertebrates
Journal of Evolutionary Biology
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On the role of body size for life-history evolution
Ecological Entomology, 1997
1. Body size is a central element in current theories of life-history evolution. Models for optimal age at maturity are based on the assumptions that there is a trade-off between development time and adult size and that larger size provides a reproductive advantage.
Constant relative age and size at sex change for sequentially hermaphroditic fish
Journal of Evolutionary Biology, 2003
A general problem in evolutionary biology is that quantitative tests of theory usually require a detailed knowledge of the underlying trade-offs, which can be very hard to measure. Consequently, tests of theory are often constrained to be qualitative and not quantitative. A solution to this problem can arise when life histories are viewed in a dimensionless way. Recently, dimensionless theory has been developed to predict the size and age at which individuals should change sex. This theory predicts that the size at sex change/maximum size (L 50 /L max ), and the age at sex change/age at first breeding (s/a) should both be invariant. We found support for these two predictions across 52 species of fish. Fish change sex when they are 80% of their maximum body size, and 2.5 times their age at maturity. This invariant result holds despite a 60 and 25 fold difference across species in maximum size and age at sex change. These results suggest that, despite ignoring many biological complexities, relatively simple evolutionary theory is able to explain quantitatively at what point sex change occurs across fish species. Furthermore, our results suggest some very broad generalities in how male fitness varies with size and age across fish species with different mating systems.
Potential causes and life-history consequences of sexual size dimorphism in mammals
Mammal Review, 2005
1. Male-biased sexual size dimorphism (SSD) in mammals has been explained by sexual selection favouring large, competitive males. However, new research has identified other potential factors leading to SSD. The aim of this review is to evaluate current research on the causes of SSD in mammals and to investigate some consequences of SSD, including costs to the larger sex and sexual segregation. 2. While larger males appear to gain reproductive benefits from their size, studies have also identified alternative mating strategies, unexpected variance in mating success and found no clear relationship between degree of polygyny and dimorphism. This implies that sexual selection is unlikely to be the single selective force directing SSD. 3. Latitude seems to influence SSD primarily through variation in overall body size and seasonal food availability, which affect potential for polygyny. Likewise, population density influences resource availability and evidence suggests that food scarcity differentially constrains the growth of the sexes. Diverging growth patterns between the sexes appear to be the primary physiological mechanism leading to SSD. 4. Female-biased dimorphism is most adequately explained by reduced male-male competition resulting in a decrease in male size. Female-female competition for dominance and resources, including mates, may also select for increased female size. 5. Most studies found that sexual segregation arises through asynchrony of activity budgets between the sexes. The larger sex can suffer sex-biased mortality through increased parasite load, selective predation and the difficulty associated with sustaining a larger body size under conditions of resource scarcity. 6. None of the variables considered here appears to contribute a disproportionate amount to SSD in mammals. Several promising avenues of research are currently overlooked and long-term studies, which have previously been biased toward ungulates, should be carried out on a variety of taxa.
Evolutionary Ecology, 2011
Invariant life-history theory has been used to identify parallels in life histories across diverse taxa. One important invariant life-history model predicts that, given simple assumptions and conditions, size-at-sex-change relative to maximum attainable body size (relative size-at-sex-change, RSSC) will be invariant across populations and species in sequential hermaphrodites. Even if there are broad species-wide limits to RSSC, populations could fine-tune RSSC to local conditions and, consequently, exhibit subtle but important differences in timing of sex change. Previous analyses of the invariant sexchange model have not explicitly considered the potential for meaningful differences in RSSC within the confines of a broader 'invariance'. Furthermore, these tests differ in their geographical and taxonomic scope, which could account for their conflicting conclusions. We test the model using several populations of three female-first sex-changing Caribbean parrotfish species. We first test for species-wide invariance using traditional log-log regressions and randomisation analyses of population-specific point estimates of RSSC.
Divergent Sex-Specific Plasticity in Long-Lived Vertebrates with Contrasting Sexual Dimorphism
2013
Sex-specific plasticity can profoundly affect sexual size dimorphism (SSD), but its influence in femalelarger-SSD vertebrates remains obscure. Theory predicts that sex-specific plasticity may drive SSD evolution if the larger sex benefits from optimal-growth conditions when available (condition-dependent hypothesis), or if attaining a suboptimal size is penalized by selection (adaptive canalization hypothesis). Sex-specific plasticity enhances the size of the larger sex in male-larger-SSD turtles but whether the same occurs in female-larger species is unknown. Sexual shape dimorphism (SShD) is also widespread in nature but is understudied, and whether SShD derives from sex-specific responses to identical selective pressures or from sex-specific selection remains unclear.
SEX-RATIO EVOLUTION IN SEX CHANGING ANIMALS
Evolution, 2004
Sex allocation theory is often able to make clear predictions about when individuals should facultatively adjust their offspring sex ratio (proportion male) in response to local conditions, but not the consequences for the overall population sex ratio. A notable exception to this is in sex changing organisms, where theory predicts that: (1) organisms should have a sex ratio biased toward the ''first'' sex;
Ontogeny of sexual size dimorphism revisited: Females grow for a longer time and also faster
PLOS ONE
Sex-specific mechanisms of the determination of insect body sizes are insufficiently understood. Here we use the common heath moth, Ematurga atomaria (Lepidoptera: Geometridae) to examine how larval growth trajectories differ between males and females. We monitored the development of 1379 larvae in controlled laboratory conditions. Sexually dimorphic development times during the first four instars were associated with sexual size dimorphism (SSD) in the beginning of the fifth (last) instar, when females were on average 15% heavier than males. Similarly, the duration of the last instar was about 13% longer in females. Further, we specifically focussed on the estimates of differential (instantaneous) growth rates of the larvae based on 24h mass increments of the 2 nd , 3 rd , 4 th and 5 th day in the beginning of the last instar. We calculated 'allometric' differential growth rates as the per-day increase in cube-root-transformed mass of the larvae. We found that allometric growth rates were slightly but significantly larger in females than in males. As this measure of growth rate (in contrast to the relative growth rate, based on the ratio of masses recorded at consecutive measurements) did not depend on body size, it allows an unambiguous separation of the effects of sex and size. We conclude that in accordance with an emerging general pattern, larger female body size in E. atomaria is achieved primarily by means of a longer growth period. Furthermore, our study shows that the differential growth rate can also be sexually dimorphic and contribute to SSD. This contribution, however, is lower than that of the development time by an order of magnitude. In addition to development periods and growth rates, other parameters of the non-linear growth curves of insect larvae also need to be considered in the context of SSD determination. In particular, weight loss prior to pupation was shown to be considerably larger in females than in males.
The evolution of sexual dimorphism in animals: Hypotheses and tests
Trends in Ecology & Evolution, 1989
LandelO. When he modelled this case, Slatkin found that each sex would evolve to its own separate optimum unless the genetic con'+ lation between the sexes was I .O. Thus, the dimorphic niche hypothesis is plausible, and does not require a low genetic correlation between the sexes.
Sex-specific plasticity can profoundly affect sexual size dimorphism (SSD), but its influence in femalelarger-SSD vertebrates remains obscure. Theory predicts that sex-specific plasticity may drive SSD evolution if the larger sex benefits from optimal-growth conditions when available (condition-dependent hypothesis), or if attaining a suboptimal size is penalized by selection (adaptive canalization hypothesis). Sex-specific plasticity enhances the size of the larger sex in male-larger-SSD turtles but whether the same occurs in female-larger species is unknown. Sexual shape dimorphism (SShD) is also widespread in nature but is understudied, and whether SShD derives from sex-specific responses to identical selective pressures or from sex-specific selection remains unclear.