scholarly journals Individual variation in parental care drives divergence of sex roles

2020 ◽  
Author(s):  
Xiaoyan Long ◽  
Franz J. Weissing
Keyword(s):  
Sexual Selection ◽  
Parental Care ◽  
Individual Variation ◽  
Sex Roles ◽  
Sex Role ◽  
Random Mating ◽  
Analytical Models ◽  
Parental Roles ◽  
Care Pattern ◽  
Individual Based Simulation

AbstractIn many animal species, parents provide care for their offspring, but the parental roles of the two sexes differ considerably between and within species. Here, we use an individual-based simulation approach to investigate the evolutionary emergence and stability of parental roles. Our conclusions are in striking contrast to the results of analytical models. In the absence of initial differences between the sexes, our simulations do not predict the evolution of egalitarian care, but either female-biased or male-biased care. When the sexes differ in their pre-mating investment, the sex with the highest investment tends to evolve a higher level of parental care; this outcome does not depend on non-random mating or uncertainty of paternity. If parental investment evolves jointly with sexual selection strategies, evolution results in either the combination of female-biased care and female choosiness or in male-biased care and the absence of female preferences. The simulations suggest that the parental care pattern drives sexual selection, and not vice versa. Finally, our model reveals that a population can rapidly switch from one type of equilibrium to another one, suggesting that parental sex roles are evolutionarily labile. By combining simulation results with fitness calculations, we argue that all these results are caused by the emergence of individual variation in parental care strategies, a factor that was hitherto largely neglected in sex-role evolution theory.

scholarly journals Sex roles, parental care and offspring growth in two contrasting coucal species

2016 ◽  
Vol 3 (10) ◽  
pp. 160463 ◽  
Author(s):  
Wolfgang Goymann ◽  
Ignas Safari ◽  
Christina Muck ◽  
Ingrid Schwabl
Keyword(s):  
Sexual Selection ◽  
Parental Care ◽  
Sex Roles ◽  
Evolutionary Ecology ◽  
Recent Theory ◽  
Uniparental Care ◽  
Trade Offs ◽  
Offspring Growth ◽  
Adult Sex Ratio

The decision to provide parental care is often associated with trade-offs, because resources allocated to parental care typically cannot be invested in self-maintenance or mating. In most animals, females provide more parental care than males, but the reason for this pattern is still debated in evolutionary ecology. To better understand sex differences in parental care and its consequences, we need to study closely related species where the sexes differ in offspring care. We investigated parental care in relation to offspring growth in two closely related coucal species that fundamentally differ in sex roles and parental care, but live in the same food-rich habitat with a benign climate and have a similar breeding phenology. Incubation patterns differed and uniparental male black coucals fed their offspring two times more often than female and male white-browed coucals combined. Also, white-browed coucals had more ‘off-times’ than male black coucals, during which they perched and preened. However, these differences in parental care were not reflected in offspring growth, probably because white-browed coucals fed their nestlings a larger proportion of frogs than insects. A food-rich habitat with a benign climate may be a necessary, but—perhaps unsurprisingly—is not a sufficient factor for the evolution of uniparental care. In combination with previous results (Goymann et al . 2015 J. Evol. Biol . 28 , 1335–1353 ( doi:10.1111/jeb.12657 )), these data suggest that white-browed coucals may cooperate in parental care, because they lack opportunities to become polygamous rather than because both parents were needed to successfully raise all offspring. Our case study supports recent theory suggesting that permissive environmental conditions in combination with a particular life history may induce sexual selection in females. A positive feedback loop among sexual selection, body size and adult sex-ratio may then stabilize reversed sex roles in competition and parental care.

Sex-Role Reversal in the Black-Chinned Tilapia, Sarotherodon Melanotheron (RÜPpel) (Cichlidae)

Behaviour ◽  
1995 ◽  
Vol 132 (11-12) ◽  
pp. 861-874 ◽  
Author(s):  
Sigal Balshine-Earn ◽  
Brendan J. Mcandrew
Keyword(s):  
Sexual Selection ◽  
Mate Choice ◽  
Sex Roles ◽  
Sex Role ◽  
Role Reversal ◽  
Recent Theory ◽  
Animal Kingdom ◽  
Sex Role Reversal ◽  
Reproductive Rates ◽  
Sarotherodon Melanotheron

AbstractIn the animal kingdom most species follow standard sex roles: males compete more intensely for mates and females exert greater mate choice. Recent theory suggests that the direction of sexual selection is the outcome of sexual differences in potential reproductive rates (PRRs): the sex with the higher PRR will compete for mates and the sex with the lower PRR will be most selective. This study tests the theory experimentally by examining competition for mates and mate choice in the black-chinned tilapia, Sarotherodon melanotheron, a paternal mouth brooding cichlid. In this species, the PRR of males is lower than that of females. In laboratory competition trials, females were more aggressive: they bit, chased and initiated mouth fights more often than males. Dominant females were also much better at monopolising potential mates compared to dominant males. A second experiment confirmed that males were choosy for size, preferring large partners over small ones, while females did not discriminate for size. Therefore, the prediction of sex role reversal (competitive females and discriminating males) is confirmed.

scholarly journals Lonely hearts or sex in the city? Density-dependent effects in mating systems

2006 ◽  
Vol 361 (1466) ◽  
pp. 319-334 ◽  
Author(s):  
Hanna Kokko ◽  
Daniel J Rankin
Keyword(s):  
Sexual Selection ◽  
Mate Choice ◽  
Parental Care ◽  
Mating Systems ◽  
Sex Role ◽  
Mate Guarding ◽  
Mating Strategies ◽  
Male Mating ◽  
Density Dependent ◽  
Basic Ideas

Two very basic ideas in sexual selection are heavily influenced by numbers of potential mates: the evolution of anisogamy, leading to sex role differentiation, and the frequency dependence of reproductive success that tends to equalize primary sex ratios. However, being explicit about the numbers of potential mates is not typical to most evolutionary theory of sexual selection. Here, we argue that this may prevent us from finding the appropriate ecological equilibria that determine the evolutionary endpoints of selection. We review both theoretical and empirical advances on how population density may influence aspects of mating systems such as intrasexual competition, female choice or resistance, and parental care. Density can have strong effects on selective pressures, whether or not there is phenotypic plasticity in individual strategies with respect to density. Mating skew may either increase or decrease with density, which may be aided or counteracted by changes in female behaviour. Switchpoints between alternative mating strategies can be density dependent, and mate encounter rates may influence mate choice (including mutual mate choice), multiple mating, female resistance to male mating attempts, mate searching, mate guarding, parental care, and the probability of divorce. Considering density-dependent selection may be essential for understanding how populations can persist at all despite sexual conflict, but simple models seem to fail to predict the diversity of observed responses in nature. This highlights the importance of considering the interaction between mating systems and population dynamics, and we strongly encourage further work in this area.

scholarly journals Darwinian sex roles confirmed across the animal kingdom

2016 ◽  
Vol 2 (2) ◽  
pp. e1500983 ◽  
Author(s):  
Tim Janicke ◽  
Ines K. Häderer ◽  
Marc J. Lajeunesse ◽  
Nils Anthes
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Parental Care ◽  
Sex Roles ◽  
Recent Criticism ◽  
Animal Kingdom ◽  
Female Behavior ◽  
Selection Theory ◽  
Evolutionary Forces ◽  
Sexual Selection Theory

Since Darwin’s conception of sexual selection theory, scientists have struggled to identify the evolutionary forces underlying the pervasive differences between male and female behavior, morphology, and physiology. The Darwin-Bateman paradigm predicts that anisogamy imposes stronger sexual selection on males, which, in turn, drives the evolution of conventional sex roles in terms of female-biased parental care and male-biased sexual dimorphism. Although this paradigm forms the cornerstone of modern sexual selection theory, it still remains untested across the animal tree of life. This lack of evidence has promoted the rise of alternative hypotheses arguing that sex differences are entirely driven by environmental factors or chance. We demonstrate that, across the animal kingdom, sexual selection, as captured by standard Bateman metrics, is indeed stronger in males than in females and that it is evolutionarily tied to sex biases in parental care and sexual dimorphism. Our findings provide the first comprehensive evidence that Darwin’s concept of conventional sex roles is accurate and refute recent criticism of sexual selection theory.

scholarly journals Sex roles and the evolution of parental care specialization

2019 ◽  
Vol 286 (1909) ◽  
pp. 20191312 ◽  
Author(s):  
Jonathan M. Henshaw ◽  
Lutz Fromhage ◽  
Adam G. Jones
Keyword(s):  
Parental Care ◽  
Parental Investment ◽  
Sex Roles ◽  
Sex Role ◽  
Relative Size ◽  
Female Competition ◽  
Male Mating ◽  
Recent Theory ◽  
Mating Competition ◽  
Uniparental Care

Males and females are defined by the relative size of their gametes (anisogamy), but secondary sexual dimorphism in fertilization, parental investment and mating competition is widespread and often remarkably stable over evolutionary timescales. Recent theory has clarified the causal connections between anisogamy and the most prevalent differences between the sexes, but deviations from these patterns remain poorly understood. Here, we study how sex differences in parental investment and mating competition coevolve with parental care specialization. Parental investment often consists of two or more distinct activities (e.g. provisioning and defence) and parents may care more efficiently by specializing in a subset of these activities. Our model predicts that efficient care specialization broadens the conditions under which biparental investment can evolve in lineages that historically had uniparental care. Major transitions in sex roles (e.g. from female-biased care with strong male mating competition to male-biased care with strong female competition) can arise following ecologically induced changes in the costs or benefits of different care types, or in the sex ratio at maturation. Our model provides a clear evolutionary mechanism for sex-role transitions, but also predicts that such transitions should be rare. It consequently contributes towards explaining widespread phylogenetic inertia in parenting and mating systems.

scholarly journals Size Dimorphism, Intrasexual Competition, and Sexual Selection in Wattled Jacana (Jacana Jacana), A Sex-Role-Reversed Shorebird in Panama

The Auk ◽  
2004 ◽  
Vol 121 (2) ◽  
pp. 391-403 ◽  
Author(s):  
Stephen T. Emlen ◽  
Peter H. Wrege
Keyword(s):  
Sexual Selection ◽  
Parental Care ◽  
Sex Role ◽  
Intrasexual Competition ◽  
Operational Sex Ratio ◽  
Same Sex ◽  
Size Dimorphism ◽  
Future Reproduction ◽  
The Republic ◽  
Reproductive Rates

AbstractWe studied sexual size dimorphism, intrasexual competition, and sexual selection in an individually marked population of Wattled Jacanas (Jacana jacana) in the Republic of Panama. Males are the sole incubators of eggs (28-day incubation) and primary providers of chick care (50–60 days). Females were 48% heavier than, and behaviorally dominant over, males. Females also showed greater development of secondary sexual characters (fleshy facial ornamentation and wing spurs) than males. Both sexes defended territories throughout the year against same-sex conspecifics. Competition for territorial space was intense, and many individuals of both sexes did not become breeders. Resident females further competed with one another to accumulate multiple mates, resulting in a mating system of simultaneous polyandry. Female and male residents (territory holders) were larger, heavier, and more ornamented than adult floaters of the same sex. Larger and heavier females also had more mates than smaller females. Body size was thus a critical predictor of success in intrasexual competition for territories (both sexes) and for mates (females). Three measures of sexual selection—(1) sex difference in the opportunity for sexual selection, (2) female-to-male ratio of potential reproductive rates, and (3) operational sex ratio—each indicated that sexual selection is currently operating more strongly on females than on males (female-to-male ratios ranged from 1.43:1 to 2.22:1). Values of 1.61:1 and 1.43:1 represent the first published quantitative estimates of the opportunity for sexual selection for any sex-role-reversed bird. Our study supports the theory that when increased parental care entails reduced opportunities for future reproduction, asymmetries in parental care behaviors of the sexes can influence the intensity of competition for mates and the direction and strength of sexual selection.

scholarly journals How do ecological and social environments reflect parental roles in birds? A comparative analysis

2020 ◽  
Author(s):  
Xiaoyan Long ◽  
Yang Liu ◽  
András Liker ◽  
Franz J. Weissing ◽  
Jan Komdeur ◽  
...  
Keyword(s):  
Parental Care ◽  
Social Environment ◽  
Evolutionary Biology ◽  
Sex Roles ◽  
Ecological Factors ◽  
Food Type ◽  
Social Environments ◽  
Colonial Species ◽  
Parental Roles ◽  
Care Patterns

AbstractParental roles are highly diverse in animal taxa. Since caring is an important determinant of fitness, understanding the origin and maintenance of various parental care strategies is a key question in evolutionary biology. Here we investigate parental care patterns in birds, which exhibit a remarkable diversity of parental sex roles. By means of phylogenetically informed comparative analyses we investigate whether and how care provisioning is predicted by ecology and social environment. Making use of the most comprehensive dataset including 1101 species that represent 126 avian families, we show that sex differences in parental care are neither related to food type nor to nest type, two key ecological factors. However, we found an effect of the social environment, as males tend to care relatively more in in colonial species than in non-colonial species. Taken together, these results highlight the importance of social effects for evolution of diverse parental sex roles.

scholarly journals Degree of anisogamy is unrelated to the intensity of sexual selection

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Judit Mokos ◽  
István Scheuring ◽  
András Liker ◽  
Robert P. Freckleton ◽  
Tamás Székely
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Life History ◽  
Parental Care ◽  
Sex Roles ◽  
Sexual Size Dimorphism ◽  
Ecological Factors ◽  
Size Dimorphism ◽  
Wide Range ◽  
Males And Females

AbstractMales and females often display different behaviours and, in the context of reproduction, these behaviours are labelled sex roles. The Darwin–Bateman paradigm argues that the root of these differences is anisogamy (i.e., differences in size and/or function of gametes between the sexes) that leads to biased sexual selection, and sex differences in parental care and body size. This evolutionary cascade, however, is contentious since some of the underpinning assumptions have been questioned. Here we investigate the relationships between anisogamy, sexual size dimorphism, sex difference in parental care and intensity of sexual selection using phylogenetic comparative analyses of 64 species from a wide range of animal taxa. The results question the first step of the Darwin–Bateman paradigm, as the extent of anisogamy does not appear to predict the intensity of sexual selection. The only significant predictor of sexual selection is the relative inputs of males and females into the care of offspring. We propose that ecological factors, life-history and demography have more substantial impacts on contemporary sex roles than the differences of gametic investments between the sexes.

scholarly journals Not all sex ratios are equal: the Fisher condition, parental care and sexual selection

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160312 ◽  
Author(s):  
Michael D. Jennions ◽  
Lutz Fromhage
Keyword(s):  
Sex Differences ◽  
Sex Ratio ◽  
Parental Care ◽  
Sex Roles ◽  
Sex Role ◽  
Sex Ratios ◽  
Theoretical Models ◽  
Evolution Of Sex ◽  
Offspring Production ◽  
Adult Sex Ratio

The term ‘sex roles’ encapsulates male–female differences in mate searching, competitive traits that increase mating/fertilization opportunities, choosiness about mates and parental care. Theoretical models suggest that biased sex ratios drive the evolution of sex roles. To model sex role evolution, it is essential to note that in most sexually reproducing species (haplodiploid insects are an exception), each offspring has one father and one mother. Consequently, the total number of offspring produced by each sex is identical, so the mean number of offspring produced by individuals of each sex depends on the sex ratio (Fisher condition). Similarly, the total number of heterosexual matings is identical for each sex. On average, neither sex can mate nor breed more often when the sex ratio is even. But equally common in which sex ratio? The Fisher condition only applies to some reproductive measures (e.g. lifetime offspring production or matings) for certain sex ratios (e.g. operational or adult sex ratio; OSR, ASR). Here, we review recent models that clarify whether a biased OSR, ASR or sex ratio at maturation (MSR) have a causal or correlational relationship with the evolution of sex differences in parental care and competitive traits—two key components of sex roles. We suggest that it is more fruitful to understand the combined effect of the MSR and mortality rates while caring and competing than that of the ASR itself. In short, we argue that the ASR does not have a causal role in the evolution of parental care. We point out, however, that the ASR can be a cue for adaptive phenotypic plasticity in how each sex invests in parental care. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

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