Breeding strategy of the male brooding water bug,Diplonychus major esaki (Heteroptera: Belostomatidae): Is male back space limiting?

The 150th anniversary of The Descent of Man: Darwin and the impact of sex-role reversal on sexual selection research

The year 2021 marks the 150th anniversary of the publication of Charles Darwin’s extraordinary book The Descent of Man and Selection in Relation to Sex. Here, we review the history and impact of a single profound insight from The Descent of Man: that, in some few species, females rather than males compete for access to mates. In other words, these species are ‘sex-role reversed’ with respect to mating competition and sexual selection compared to the majority of species in which sexual selection acts most strongly on males. Over the subsequent 150 years, sex-role-reversed species have motivated multiple key conceptual breakthroughs in sexual selection. The surprising mating dynamics of such species challenged scientists’ preconceptions, forcing them to examine implicit assumptions and stereotypes. This wider worldview has led to a richer and more nuanced understanding of animal mating systems and, in particular, to a proper appreciation for the fundamental role that females play in shaping these systems. Sex-role-reversed species have considerable untapped potential and will continue to contribute to sexual selection research in the decades to come.

Sexual dimorphism in Belostoma angustum Lauck (Insecta: Heteroptera: Belostomatidae) may be related to paternal care

The structures involved in parental care are often dimorphic. Female Belostoma angustum water bugs lay eggs on the hemelytra of their mates, where the eggs are brooded until hatching. Males use their hind legs to carry, aerate and protect the eggs. After controlling for covariance between variables, we fitted a series of structural equation models (SEMs) and evaluated the existence of sexual dimorphism in the size of the body and hind legs, in the shape and centroid size of the hemelytrum, and among the static allometry slopes of the size-related differences. Landmarks were used to capture phenotypic variation, by eliminating all non-shape variations with a Procrustes superimposition. Neither the shape of the hemelytrum nor its centroid size was related significantly to the aforementioned linear body measurements. Instead, the differences in the size of the hind legs were mediated by body dimensions only in males. We also found that males were wider and had longer heads than females, according to the SEM intercept values. Our findings suggest that sexual dimorphism in B. angustum may be related to a balance between sexual role reversal and viability costs.

Sexual selection of male parental care in giant water bugs

Paternal care can be maintained under sexual selection, if it helps in attracting more mates. We tested the hypothesis in two giant water bug species, Appasus major and Appasus japonicus, that male parental care is sexually selected through female preference for caring males. Females were given an opportunity to choose between two males. In the first test of female mate choice, one male carried eggs on its back, while the other did not. The egg status was switched between these two males in the second test. The experiment revealed that females of both species preferred caring males (i.e. egg-bearing) to non-caring males. Nonetheless, the female mate preference for egg-bearing males was stronger in A. major than in A. japonicus. Our results suggest that sexual selection plays an important role in maintaining elaborate paternal care in giant water bugs, but the importance of egg-bearing by males in female mate choice varies among species.

Sexual competition among females: What causes courtship-role reversal?

In most animals, males are the competitive sex whereas females are typically non-competitive and choosy of mates. In a variety of taxa, certain species (or populations within species) show a reversal in these typical courtship roles. Recent research with these organisms supports a central tenet of sexual selection theory: that it is the relative investment of the sexes in offspring that controls the number of males and females available for mating, and thus is the main determinant of the degree of sexual competition in each sex.

Is it risky to be a father? Survival assessment depending on sex and parental status in the water bug Abedus breviceps using multistate modelling

We carried out a capture–recapture multistate modelling approach to estimate survival and recapture probabilities and transition rates between parental and nonparental status in an adult wild population of the water bug Abedus breviceps Stål, 1862 (Hemiptera: Belostomatidae). The global model included the following parameters: sex, male parental status (brooding or not), and transience (individual’s permanent movement from the site after first capture). Models were selected by means of the information-theory paradigm. The best supported model shows no difference in survival between males and females regardless of male parental status. Thus, the frequently assumed cost of parental care in terms of survival is not supported by our data. Furthermore, during the study, male expected adult life span in the wild was lower than the time needed to brood a batch of eggs from oviposition to hatching. We discuss potential consequences of such a short male expected adult life span in terms of parental behaviour decision rules related to fitness maximization.