Sexual selection on population-level mating opportunities drives morph ratios in a fig wasp with extreme male dimorphism

Background Alternative mating tactics are widespread in animals and associated with extreme morphological polymorphism in some insects. Some fig wasps have both highly modified wingless males and dispersing winged males. Wingless males mate inside figs before females disperse, while winged males mate elsewhere after dispersal. Hamilton proposed a model for this system with morphs determined by alternative alleles. This has an equilibrium where the proportion of winged males equals the proportion of females dispersing unmated; i.e. the proportion of matings that they obtain. Previously, we have shown qualitative support for this prediction across nine wing-dimorphic fig wasp species. Here I test the quantitative prediction in the fig wasp Pseudidarnes minerva. In addition, some fig wasp species that lack winged males, but have two wingless morphs, show a conditional strategy with morph determination influenced by the number of wasps developing in a patch. I also test for this alternative pattern in the wing-dimorphic P. minerva. Results I sampled 114 figs that contained a mean of 2.1 P. minerva wasps from 44 trees across four sites in Sydney, Australia. At the whole population level, the proportion of winged males (0.84 or 0.79 corrected for sampling bias) did not differ significantly from the proportion of unmated females (0.84), providing strong quantitative support for the prediction of Hamilton’s model. In addition, there was no evidence for other factors, such as local mate competition or fighting between wingless males, that could violate simplifying assumptions of the model. Meanwhile, the proportion of winged males was not correlated with the number of wasps per fig, providing no evidence for a conditional strategy. Conclusion The morph ratio in P. minerva is consistent with Hamilton’s simple Mendelian strategy model, where morph ratios are set by average mating opportunities at the population level. This contrasts with some fig wasps from another subfamily that show conditional morph determination, allowing finer scale adaptation to fig-level mating opportunities. However, these conditional cases do not involve wing polymorphism. Male polymorphism is common and variable in fig wasps and has evolved independently in multiple lineages with apparently different underlying mechanisms.

Sexual Selection on Population-level Mating Opportunities Drives Morph Ratios in a Fig Wasp with Extreme Male Dimorphism

Background Alternative mating tactics are widespread in animals and associated with extreme morphological polymorphism in some insects. Some fig wasps have both highly modified wingless males and dispersing winged males. Wingless males mate inside figs before females disperse, while winged males mate elsewhere after dispersal. Hamilton proposed a model for this system with morphs determined by alternative alleles. This has an equilibrium where the proportion of winged males equals the proportion of females dispersing unmated; i.e. the proportion of matings they obtain. Previously, we have shown qualitative support for this prediction across nine fig wasp species. Here I test the quantitative prediction in a population of the fig wasp Pseudidarnes minerva. In addition, while Hamilton envisaged simple Mendelian strategies, some fig wasp species with two wingless male morphs (but no winged males) show a conditional strategy with morph determination influenced by the number of wasps developing in a patch - I also test for this pattern in P. minerva. Results I sampled 114 figs that contained a mean of 2.1 P. minerva wasps from 44 trees across four sites in Sydney, Australia. At the whole population level, the proportion of winged males (0.84 or 0.79 corrected for sampling bias) did not differ significantly from the proportion of unmated females (0.84), providing strong quantitative support for the prediction of Hamilton’s model. In addition, there was no evidence for other factors, such as local mate competition or fighting between wingless males, that could violate simplifying assumptions of the model. Meanwhile, the proportion of winged males was not correlated with the number of wasps per fig, providing no evidence for a conditional strategy. Conclusions Morph ratios in P. minerva are consistent with Hamilton’s simple Mendelian strategy model, where morph ratios are set by average mating opportunities at the population level. This contrasts with some fig wasps from another subfamily that show conditional morph determination, allowing finer scale adaptation to fig-level mating opportunities. However, these conditional cases do not involve wing polymorphism. Male polymorphism is common and variable in fig wasps and has evolved independently in multiple lineages with apparently different underlying mechanisms.

Superorganismal anisogamy: queen–male dimorphism in eusocial insects

Colonies of insects such as ants and honeybees are commonly viewed as ‘superorganisms’, with division of labour between reproductive ‘germline-like’ queens and males and ‘somatic’ workers. On this view, properties of the superorganismal colony are comparable with those of solitary organisms to such an extent that the colony itself can be viewed as a unit analogous to an organism. Thus, the concept of a superorganism can be useful as a guide to thinking about life history and allocation traits of colonies as a whole. A pattern that seems to reoccur in insects with superorganismal societies is size dimorphism between queens and males, where queens tend to be larger than males. It has been proposed that this is analogous to the phenomenon of anisogamy at the level of gametes in organisms with separate sexes; more specifically, it is suggested that this caste dimorphism may have evolved via similar selection pressures as gamete dimorphism arises in the ‘gamete competition’ theory for the evolution of anisogamy. In this analogy, queens are analogous to female gametes, males are analogous to male gametes, and colony survival is analogous to zygote survival in gamete competition theory. Here, we explore if this question can be taken beyond an analogy, and whether a mathematical model at the superorganism level, analogous to gamete competition at the organism level, may explain the caste dimorphism seen in superorganismal insects. We find that the central theoretical idea holds, but that there are also significant differences between the way this generalized ‘propagule competition’ theory operates at the levels of solitary organisms and superorganisms. In particular, we find that the theory can explain superorganismal caste dimorphism, but compared with anisogamy evolution, a central coevolutionary link is broken, making the requirements for the theory to work less stringent than those found for the evolution of anisogamy.

Is male dimorphism under sexual selection in humans? A meta-analysis

Humans are sexually dimorphic: men and women differ in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone. Sexual selection hypotheses posit that, ancestrally, more ‘masculine’ men may have acquired more mates and/or sired more viable offspring. Thus far, however, evidence for either association is unclear. Here, we meta-analyze the relationship between six masculine traits and mating/reproductive outcomes (96 studies, 474 effects, N = 177,044). Voice pitch, height, digit ratios, and testosterone all predicted mating; however, strength/muscularity was the strongest and only consistent predictor of both mating and reproduction. Facial masculinity did not significantly predict either. There was insufficient evidence for any effects of masculinity on offspring viability. Our findings support arguments that strength/muscularity can be considered sexually selected in humans, but raise concerns over other forms of masculinity and highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.

Two new species of Manahunca, redescription of its type species, current conservation status of the genus and a survey of male glands in Stenostygninae (Opiliones: Laniatores: Biantidae)

Manahunca bielawskii Šilhavý, 1973, the type species of the genus Manahunca Šilhavý, 1973, is redescribed based on abundant material from the type locality, including new data on its morphological variability and penis morphology. A neotype for M. bielawskii is herein designated due to the unknown whereabouts of the original holotype. Manahunca silhavyi Avram, 1977, is regarded as a new junior subjective synonym of M. bielawskii. In addition, two new species of Manahunca are described, M. turquino Alegre, Gainett & Giribet, n. sp. and M. matazon Alegre, Gainett & Giribet, n. sp. based on additional specimens from eastern Cuba, for which we provide new data on their geographical distribution, intraspecific variability and habitat. A new diagnosis and emended geographic distribution of the known species of Manahunca are provided, with hints on the current conservation status. The sexually dimorphic glandular structures found on the metatarsus III of males are explored for taxonomic significance in ten species of Stenostygninae. The existence of male dimorphism, most evident in the robustness of the chelicerae, is reported for two of the studied Manahunca species.

Alternative reproductive strategies in black-winged territorial males of Paraphlebia zoe (Odonata, Thaumatoneuridae)

Alternative reproductive strategies are commonly associated with male dimorphism. In Paraphlebia zoe, a species of damselfly whose males are dimorphic in wing coloration, black-and-white-winged (BW) males defend territories, while hyaline-winged (HW) males usually play the role of satellites. We found that several BW males can sometimes share a territory, and we hypothesized that within this morph there are two alternative tactics: submissive and dominant. We conducted an experiment to test whether dominant and submissive roles are plastic or stable and fixed on each individual. To this end, we manipulated black and white spots of BW males in four treatments: (i) painting over white and black spots without changing their size, (ii) erasing the white spot using black painting, (iii) increasing the black spot and moving the white spot maintaining its size and (iv) control males. Additionally, we investigated the correlation between some phenotypic variables (wing asymmetry, survival and recapture probabilities) and male behaviour (in terms of quality of the territory). We found that the two behavioural roles (submissive and dominant) were not affected by the manipulative experiments, therefore suggesting that they are stable and fixed. Additionally, we found a positive correlation between body size and survival in both sexes, and a positive effect of territory quality and lifespan on mating success. Moreover, the largest and youngest BW males were the most symmetrical. We conclude that Paraphlebia zoe holds high behavioural diversity, with two types of strategies in BW males, dominant and submissive. The occurrence of this intra-morph behavioural diversity might depend on demographic factors such as population density and/or the relative frequency of the different morphs.

Notes on Phalangiidae (Arachnida: Opiliones) of southern Africa with description of new species and comments on within-species variation

Notes are provided on a collection of Afrotropical harvestmen (Opiliones: Palpatores: Phalangiidae) from the California Academy of Sciences. A new species of Rhampsinitus, R. conjunctidens n. sp., is described from Limpopo province of South Africa. Rhampsinitus flavobrunneus Staręga 2009 and R. silvaticus Lawrence 1931 are recognised as junior synonyms of R. nubicolus Lawrence 1963 and R. vittatus Lawrence 1931, respectively. Both R. conjunctidens and R. nubicolus are recognised as exhibiting strong male dimorphism with major males exhibiting larger body size and greatly enlarged chelicerae relative to minor males; minor males cannot be readily identified to species without examination of genitalia. A discussion is also provided on generic boundaries within Afrotropical Phalangiidae, and a generic key to males of the region is presented.