Split sex ratios in the social Hymenoptera: a meta-analysis (original) (raw)
Related papers
On the Robustness of Split Sex Ratio Predictions In Social Hymenoptera
Journal of Theoretical Biology, 1997
Using inclusive fitness models, this study determines the optimal patterns of split-sex-ratio allocation for hymenopteran workers when colonies have a single queen, and queens mate with either one or two males. This particular colony kin-structure is common in social Hymenoptera. Importantly, the basic split-sex-ratio pattern of allocation, with some colonies producing exclusively or largely males and the others producing exclusively or largely queens, is shown to be robust with respect to the parameters investigated: errors in the assessment of queen mating frequency by workers, male-production by workers, unequal male contributions to paternity in double-mated queens, and partial queen control. Conditions under which split sex ratios are not expected, or may be non-extreme, are discussed.
Testing kin selection with sex allocation data in eusocial Hymenoptera
Heredity, 1999
Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the eectiveness of kin selection, because queens and workers dier in their relatedness to females and males. The ®rst studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne ( with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also aect sex allocation. Secondly, the relative cost of females and males is dicult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspe-ci®c studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always eective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes aecting sex allocation in eusocial Hymenoptera.
Queens versus workers: sex-ratio conflict in eusocial Hymenoptera
Trends in Ecology & Evolution, 2003
Studies of sex-ratio conflict in the eusocial Hymenoptera (ants, bees and wasps) have provided the most rigorous tests of kin selection theory. The hymenopteran haplodiploid system of sex determination generally renders workers more closely related to their sisters than to their brothers, whereas queens are equally related to their sons and daughters. Kin selection theory therefore predicts that resource allocation
Journal of Genetics, 1985
A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the 'points of view' of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen's optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy (ESS) does not exist but the 'best' strategy is merely immune from extinction. A true ESS exists under worker control in colonies with singly mated queens but there is an asymmetry between the dominant and recessive alleles so that for some values of sex ratio a recessive allele goes to fixation but a dominant allele with the same properties fails to do so. Under multiple mating, again, a true ESS does not exist but a frequency dependent region emerges. The best strategy here is one that is guaranteed fixation against any competing allele with a lower relative frequency. Our results emphasize the need to determine levels of local mate competition and multiple mating before drawing any conclusions regarding the outcome of queen-worker conflict in social hymenoptera. Multiple mating followed by sperm mixing, both of which are known to occur in social hymenoptera, lower average genetic relatedness between workers and their reproductive sisters. This not only shifts the optimum sex ratio from the workers' 'point of view' in favour of males but also poses problems for the kin selection theory. We show that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.
Entomologia Experimentalis et Applicata, 2012
Complementary sex determination is the ancestral sex-determination mechanism in the Hymenoptera. Under this system, diploid individuals develop into females if they are heterozygous at an autosomal sex-determining locus or loci, whereas haploid individuals develop into males because they are hemizygous at the sex-determining locus or loci. However, diploid males can still arise from fertilized eggs if such individuals are homozygous at the sex-determining locus or loci. Diploid males are often viable but sire few daughters, thereby representing a substantial genetic load in hymenopteran populations. Here, we review the effects of complementary sex determination and diploid male production from the perspective of female hymenopterans. Because female hymenopterans need not mate to produce haploid sons, complementary sex determination can cause special forms of mating failures by preventing some females from controlling the sex ratio of their brood and producing the desired number of daughters. Under some circumstances, complementary sex determination can cause complete mating failure by preventing females from producing daughters altogether. Although we outline serious gaps of knowledge in the field, the data at hand suggest that diploid male production can substantially increase mating failures in small populations of economically and ecologically important hymenopterans.
2005
Because workers in the eusocial Hymenoptera are more closely related to sisters than to brothers, theory predicts that natural selection should act on them to bias (change) sex allocation to favor reproductive females over males. However, selection should also act on queens to prevent worker bias. We use a simulation approach to analyze the coevolution of this conflict in colonies with single, once-mated queens. We assume that queens bias the primary (egg) sex ratio and workers bias the secondary (adult) sex ratio, both at some cost to colony productivity. Workers can bias either by eliminating males or by directly increasing female caste determination. Although variation among colonies in kin structure is absent, simulations often result in bimodal (split) colony sex ratios. This occurs because of the evolution of two alternative queen or two alternative worker biasing strategies, one that biases strongly and another that does not bias at all. Alternative strategies evolve because the mechanisms of biasing result in accelerating benefits per unit cost with increasing bias, resulting in greater fitness for strategies that bias more and bias less than the population equilibrium. Strategies biasing more gain from increased biasing efficiency whereas strategies biasing less gain from decreased biasing cost. Our study predicts that whether queens or workers evolve alternative strategies depends upon the mechanisms that workers use to bias the sex ratio, the relative cost of queen and worker biasing, and the rates at which queen and worker strategies evolve. Our study also predicts that population and colony level sex allocation, as well as colony productivity, will differ diagnostically according to whether queens or workers evolve alternative biasing strategies and according to what mechanism workers use to bias sex allocation.
Biological Journal of the Linnean Society, 2014
Males are under different selective pressures than females, which results in differences in the physiology of the two sexes to maximize their fitness. In terms of immunity, males are typically considered as the 'sicker sex', where immunocompetence is reduced to favour increased reproductive output. However, male social Hymenoptera are also haploid and therefore lack allelic variation at the individual level, which can also lead to reduced immunocompetence. Over the last decade, several studies have provided evidence for a higher susceptibility to disease in males of social Hymenoptera, without clarifying whether this susceptibility was a direct consequence of their haploid condition or the result of a 'live hard, die young' overall evolutionary strategy. In the present study, we used an experimental approach of bacterial challenge to test the immune response of males and females in two species of social Hymenoptera (honey bees, Apis mellifera; paper wasps, Polistes dominula), where males show very different life-history traits. Drones benefit from colony protection for most of their life, whereas P. dominula males leave their colonies and have to survive for weeks at leks. If the haploid condition is responsible for a higher susceptibility in males, we should expect a lower immune response in males of both species compared to females. Conversely, if the immunocompetence depends on the life-history traits of males, an opposite trend is expected in males of the two species. Our results do not support the 'haploid susceptibility hypothesis' but are in accordance with the different life history of males from the two species.
Colony-level sex ratio selection in the eusocial Hymenoptera
Journal of Evolutionary Biology, 1991
We present an inclusive fitness model on worker-controlled sex investments in eusocial Hymenoptera which expands the existing theory for random mating populations as formulated by Trivers and Hare (1976) and Benford (1978). We