Malin Ah-King

Genital Evolution: Why Are Females Still Understudied?

In many animal groups genital structures appear to have evolved extremely rapidly, prompting enduring interest in why this is so. Throughout this literature there remains a bias towards studying male genitalia; here we examine the extent of that bias and its possible causes.

The influence of territoriality and mating system on the evolution of male care: a phylogenetic study on fish

Evolution of male care is still poorly understood. Using phylogenetically matched‐pairs comparisons we tested for effects of territoriality and mating system on male care evolution in fish. All origins of male care were found in pair‐spawning species (with or without additional males such as sneakers) and none were found in group‐spawning species. However, excluding group spawners, male care originated equally often in pair‐spawning species with additional males as in strict pair‐spawning species. Evolution of male care was also significantly related to territoriality. Yet, most pair‐spawning taxa with male care are also territorial, making their relative influence difficult to separate. Furthermore, territoriality also occurs in group‐spawning species. Hence, territoriality is not sufficient for male care to evolve. Rather, we argue that it is the combination of territoriality and pair spawning with sequential polygyny that favours the evolution of male care, and we discuss our results in relation to paternity assurance and sexual selection.

On anisogamy and the evolution of ‘sex roles’

In a recent Opinion piece, Scharer et al. [1] claim that the ‘sex roles’ we observe in nature, with predominant male–male competition (i), female choosiness (ii), and conventional care patterns (iii), cannot be due to chance, but must be due to sex-specific selection ultimately caused by anisogamy. Here I discuss several problems with their Opinion including that: (1) a correlation between anisogamy and ‘sex roles’ is not equal to causation, (2) their problematic use of the term ‘sex roles’, and (3) their misinterpretation of chance or stochastic effects in the models to which they object.

Sex in an Evolutionary Perspective : Just Another Reaction Norm

It is common to refer to all sorts of clear-cut differences between the sexes as something that is biologically almost inevitable. Although this does not reflect the status of evolutionary theory on sex determination and sexual dimorphism, it is probably a common view among evolutionary biologists as well, because of the impact of sexual selection theory. To get away from thinking about biological sex and traits associated with a particular sex as something static, it should be recognized that in an evolutionary perspective sex can be viewed as a reaction norm, with sex attributes being phenotypically plastic. Sex determination itself is fundamentally plastic, even when it is termed “genetic”. The phenotypic expression of traits that are statistically associated with a particular sex always has a plastic component. This plasticity allows for much more variation in the expression of traits according to sex and more overlap between the sexes than is typically acknowledged. Here we review the variation and frequency of evolutionary changes in sex, sex determination and sex roles and conclude that sex in an evolutionary time-frame is extremely variable. We draw on recent findings in sex determination mechanisms, empirical findings of morphology and behaviour as well as genetic and developmental models to explore the concept of sex as a reaction norm. From this point of view, sexual differences are not expected to generally fall into neat, discrete, pre-determined classes. It is important to acknowledge this variability in order to increase objectivity in evolutionary research.

Phylogenetic analysis of twinning in Callitrichinae

The callitrichines are known for twinning and for a communal rearing system in which all or most group members help care for the offspring. The origin of twinning has been the subject of much speculation. In this study predictions from earlier hypotheses are tested on the basis of two alternative phylogenetic trees. From this analysis we infer that helping behavior and male care preceded the origin of twinning, and that these traits did not coevolve with, but might have been important prerequisites for twinning in callitrichines. Small body size does not necessarily result in twinning, although it might still have been a prerequisite for its evolution. Gum feeding was an ecological change which evolved along with twinning. If nutrition was a limiting factor in the number of offspring produced, then the use of a new feeding resource could have been crucial for the origin of twinning in callitrichines. According to one of the two alternative solutions inferred by the total evidence tree, and in accordance with the morphological tree, semi‐annual breeding appears in the marmosets together with specialization in gum feeding. The fact that gums are available for these monkeys all year may have facilitated semi‐annual breeding. We suggest that the exploitation of gums as a feeding resource could have been the decisive factor in the increase of the reproductive rate by twinning and by semi‐annual breeding. Am. J. Primatol. 51:135–146, 2000.

The “Sex Role” Concept: An Overview and Evaluation

Abstract“Sex roles” are intuitively associated to stereotypic female and male sexual strategies and in biology, the term “sex role” often relates to mating competition, mate choice or parental care. “Sex role reversals” imply that the usual typological pattern for a population or species is deviates from a norm, and the meaning of “sex role reversal” thus varies depending upon whatever is the usual pattern of sex-typical behavior in a given taxon. We identify several problems with the current use of the “sex role” concept. (1) It is typological and reflects stereotypic expectations of the sexes. (2) The term “sex role” parses continuous variation into only two categories, often obscuring overlap, between the sexes in behavior and morphology, and variability in relation to ecological circumstances. (3) Common generalizations such as “sex role as seen in nature” mask variation upon which selection may act. (4) The general meaning of “sex roles” in society (i.e. “socially and culturally defined prescriptions and beliefs about the behavior and emotions of men and women”) is contrary to biological “sex role” concepts, so that confusing the two obscure science communication in society. We end by questioning the validity of the “sex role” concept in evolutionary biology and recommend replacing the term “sex role” with operational descriptions.

Sexual Selection Revisited — Towards a Gender-Neutral Theory and Practice A Response to Vandermassen's `Sexual Selection: A Tale of Male Bias and Feminist Denial'

In a recent issue of this journal, Vandermassen suggested that feminists should include sexual selection theory and evolutionary psychology in a unifying theory of human nature. In response, this article aims to offer some insight into the development of sexual selection theory, to caution against Vandermassens unreserved assimilation and to promote the opposite ongoing integration — an inclusion of gender perspectives into evolutionary biology. In society today, opinions about maintaining traditional sex roles are often put forward on the basis of what is natural and how animals behave. However, the natural sciences have proved to be pervaded by gendered values and interests; Darwins theory of sexual selection has been criticized for being male biased, and partly due to the unwillingness of Darwins scientific contemporaries to accept female choice, research has been overwhelmingly focused on males. More recently, theory has become less gender biased and research has come to include a large variety of issues not present in the first version of the theory. However, there is a need to increase the awareness of gender bias in order to develop a gender-neutral evolutionary biology.

Reaction Norms of Sex and Adaptive Individual Flexibility in Reproductive Decisions

Biology at large is in the midst of a revolution in our understanding of the determination of phenotypes. Epigenetics has shifted our focus from genetic determinism to ecological origins of gene expression. We argue that this shift should be incorporated into sexual selection, changing the conceptualization of sex from a discrete trait to a developmental reaction norm. “Sex is a reaction norm” implies that the variation within and between the sexes is a result of genetic, epigenetic and environmental influences on developmental plasticity of phenotypes. “Choosy females” and “indiscriminate males” constitute one of the best examples of assumed strict sex differences that are in fact phenotypically plastic in response to environmental, social and internal factors. Here we summarize the empirical evidence, which empiricists have explained with trade-off hypotheses: individuals trade-off energy of reproductive decision-making with diverse, usually unitary factors: predation risk or density or OSR, etc. Gowaty and Hubbell’s (2009) Switch-Point Theorem simplifies and unifies these trade-offs into a single hypothesis and works as an integrative framework, both for reinterpreting earlier findings and as a pointer to new directions for sexual selection research. We conclude that it is time to pay more attention to morphological, physiological, and behavioural phenotypes as developmentally plastic and/or individually flexible.

Plenty of sex, but no sexuality in biology undergraduate curricula

Researchoverthelastdecadeshasstimu-lated a paradigm shift in biology fromassuming fixed and dichotomous maleand female sexual strategies to anappreciation of significant variation insex and sexual behaviour both withinand between species. This has resultedin the development of a broader bio-logical understanding of sexual strat-egies, sexuality and variation in sexualbehaviour. However, current introduc-tory biological textbooks have not yetincorporated these new research find-ings. Our analysis of the content of cur-rent biology texts suggests that inundergraduate biology curricula vari-ation in sexual behaviour, sexual strat-egies and sexuality barely feature, eventhough sex is discussed in a range ofcontexts. Inthisaspect, biological teach-ing is lagging behind current research.Here, we draw attention to new findingsin the biology of sex, and suggest howthese might be incorporated in under-graduateteachingtoprovideamorecon-temporary and inclusive education forbiology students.