Sexual selection and the evolution of exclusive paternal care in arthropods

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.

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.

How the sperm lost its tail: the evolution of aflagellate sperm

The typical sperm is comprised of a head, midpiece and flagellum. Around this theme there is an enormous diversity of form--giant sperm, multi-flagellate sperm and also sperm that lack flagella entirely. Explaining this diversity in sperm morphology is a challenging question that evolutionary biologists have only recently engaged in. Nonetheless, one of the selective forces identified as being an important factor in the evolution of sperm form is sperm competition, which occurs when the sperm of two or more males compete to fertilize a female's ova. In species with a truly monandrous mating system, the absence of sperm competition means that the selection pressure on males to produce motile sperm may be relaxed. Potentially aflagellate sperm are less costly to produce, both in terms of energy and time. Thus, selection may therefore favour the loss of the sperm flagellum and any other motile mechanisms in monandrous taxa. A review of the literature revealed that 36 taxonomic groups, from red algae to fish, were found independently to have evolved aflagellate sperm. I review what is known about the mating systems of each of these taxa and their nearest sister taxa. A sister-group analysis using this information provided weak evidence suggesting that the evolution of aflagellate sperm could be linked to the removal of selective pressures generated by sperm competition.

The Evolution of Paternal Care with Overlapping Broods

Most attempts to model the evolution of parental care assume that caring and mating are mutually exclusive activities (i.e., individuals acquire and guard broods "sequentially"). However, in most fish and certain insects, males can keep mating and collecting additional eggs while continuing to guard broods obtained earlier (i.e., males guard "overlapping" broods). We present a model of parental care with overlapping broods in which males can mate and guard simultaneously, even though there is a trade-off between these two activities. Within this framework, we show that male care is favored by short female processing times and high population densities, which minimize the mating cost of care. Relatively low mortality while guarding is also important for the stability of male care. Female care, on the other hand, is favored by long female processing times and low populations densities, which lead to longer intermating intervals. Biparental care is stable only when the cost to benefit ratio of care was not biased toward either sex. We derive quantitative estimates of fitness for different strategies for two species of assassin bugs with male and female uniparental care and show that the model predicts the correct form of care for both species. We believe our model might help explain the prevalence of male uniparental care in certain taxa, such as fish.

Evolutionary transitions in parental care and live bearing in vertebrates

We provide the first review of phylogenetic transitions in parental care and live bearing for a wide variety of vertebrates. This includes new analyses of both numbers of transitions and transition probabilities. These reveal numerous transitions by shorebirds and anurans toward uniparental care by either sex. Whereas most or all of the shorebird transitions were from biparental care, nearly all of the anuran transitions have been from no care, reflecting the prevalence of each form of care in basal lineages in each group. Teleost (bony) fishes are similar to anurans in displaying numerous transitions toward uniparental contributions by each sex. Whereas cichlid fishes have often evolved from biparental care to female care, other teleosts have usually switched from no care to male care. Taxa that have evolved exclusive male care without courtship-role reversal are characterized by male territoriality and low costs of care per brood. Males may therefore benefit from care through female preference of parental ability in these species. Primates show a high frequency of transitions from female care to biparental care, reflecting the prevalence of female care in basal lineages. In the numerous taxa that display live bearing by females, including teleosts, elasmobranchs, squamate reptiles and invertebrates, we find that live bearing has always evolved from a lack of care. Although the transition counts and probabilities will undoubtedly be refined as phylogenetic information and methodologies improve, the overall biases in these taxa should help to place adaptive hypotheses for the evolution of care into a stronger setting for understanding directions of change.

Evolution of exclusive paternal care in arthopods

Exclusive male care of offspring is the rarest form of postzygotic parental care among animals and has arisen independently in only 13 arthropod taxa. To distinguish the effects of sexual selection from those of natural selection on the evolution of arthropod paternal care, predictions concerning several life-history and behavioral traits resulting from both forms of selection are made and tested across all known taxa with exclusive paternal care. Comparisons suggest parallels between prezygotic nuptial gifts and exclusive postzygotic male care and support the hypothesis that, in arthropods, male behaviors that enhance female reproductive success either directly, by releasing females from the fecundity constraints of maternal care (enhanced fecundity hypothesis), or indirectly, by identifying mates with superior genes (handicap principle), are traits on which sexual selection has acted. Under such conditions, males that are willing to guard young become preferred mates for gravid females and enjoy greater promiscuity than males that are unable or unwilling to guard. Females use nest construction or the act of guarding another female's eggs as honest signals of paternal intent and quality.