Unequal subfamily proportions among honey bee queen and worker brood

122

Social groups are vulnerable to cheating because the reproductive interests of group members are rarely identical. All cooperative systems are therefore predicted to involve a mix of cooperative and cheating genotypes, with the frequency of the latter being constrained by the suppressive abilities of the former. The most significant potential conflict in social insect colonies is over which individuals become reproductive queens rather than sterile workers. This reproductive division of labor is a defining characteristic of eusocial societies, but individual larvae will maximize their fitness by becoming queens whereas their nestmates will generally maximize fitness by forcing larvae to become workers. However, evolutionary constraints are thought to prevent cheating by removing genetic variation in caste propensity. Here, we show that one-fifth of leaf-cutting ant patrilines cheat their nestmates by biasing their larval development toward becoming queens rather than workers. Two distinct mechanisms appear to be involved, one most probably involving a general tendency to become a larger adult and the other relating specifically to the queen-worker developmental switch. Just as evolutionary theory predicts, these ''royal'' genotypes are rare both in the population and within individual colonies. The rarity of royal cheats is best explained as an evolutionary strategy to avoid suppression by cooperative genotypes, the efficiency of which is frequency-dependent. The results demonstrate that cheating can be widespread in even the most cooperative of societies and illustrate that identical principles govern social evolution in highly diverse systems.caste ͉ polymorphism ͉ social evolution ͉ polyandry ͉ social insect

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Genetic royal cheats in leaf-cutting ant societies

Hughes

Boomsma

2008

122

“…Mutant cheaters can undermine the reproductive division of labor by reproducing without helping. Indeed, such selfish behaviors have been reported in some workers of honey bees (Apis mellifera) that produce their own sons (25) or even queendestined asexual daughters (26) in queen-right colonies, and in immature females sired by particular males of several polyandrous (queen multiple mating) species that show higher potential to develop into new queens than other patrilines (27)(28)(29). However, direct comparison of fitness between cooperators and cheaters is lacking in these cases.…”

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confidence: 99%

Public goods dilemma in asexual ant societies

Dobata

Tsuji

2013

Cooperation in biological, social, and economic groups is underpinned by public goods that are generated by group members at some personal cost. Theory predicts that public goods will be exploited by cheaters who benefit from the goods by not paying for them, thereby leading to the collapse of cooperation. This situation, described as the "public goods dilemma" in game theory, makes the ubiquity of cooperation a major evolutionary puzzle. Despite this generalization, the demonstration of genetic background and fitness effects of the public goods dilemma has been limited to interactions between viruses and between cells, and thus its relevance at higher levels of organismal complexity is still largely unexplored. Here we provide experimental evidence for the public goods dilemma in a social insect, the ant Pristomyrmex punctatus. In this species, all workers are involved in both asexual reproduction and cooperative tasks. Genetic cheaters infiltrate field colonies, reproducing more than the workers but shunning cooperative tasks. In laboratory experiments, cheaters outcompeted coexisting workers in both survival and reproduction, although a group composed only of cheaters failed to produce offspring. The operations of the public goods dilemma in P. punctatus showed a remarkable convergence with those in microbial societies, not only in fitness consequences but also in behavioral mechanisms. Our study reinforces the evolutionary impact of cheaters on diverse cooperative systems in the laboratory and in the field. social evolution | public goods game | social parasitism | self-organization | phenotypic plasticity

“…Genetic analysis has shown that different ejaculates become progressively more mixed over the course of several months (38,39), leading to a homogeneous distribution in mature colonies (40,41). If different ejaculates remain clumped in the spermatheca, the colony phenotype may vary over time, both in which patrilines are present and their frequency.…”

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confidence: 99%

Patriline shifting leads to apparent genetic caste determination in harvester ants

Wiernasz

Cole

2010

The harvester ant, Pogonomyrmex occidentalis, is characterized by high levels of intracolonial genetic diversity resulting from multiple mating by the queen. Within reproductively mature colonies, the relative frequency of different male genotypes (patrilines) is not stable. The difference between samples increases with time, nearing an asymptote after a year. Patriline distributions in gynes and workers display similar patterns of change. A consequence of changing patriline distributions is that workers and gynes appear to have different fathers. However, apparent genetic differences between castes are caused by changing paternity among all females. Temporal variation in the relative frequency of patrilines may be a consequence of processes that reflect sexual conflict, such as sperm clumping. Recent work documenting genotype differences between physical castes (workers and gynes; major and minor workers) in several species of ants has been interpreted as evidence of genetic caste determination. Reanalysis of these studies found little support for this hypothesis. Apparent caste determination may result from temporal variation in sperm use, rather than from fertilization bias among male ejaculates. M orphological traits frequently display phenotypic plasticity (reviewed in refs. 1, 2); such variation is especially common in insects (3). Phenotypic plasticity generally is assumed to be responsible for physical castes in the social insects, including differences between gynes (virgin queens) and workers (nonreproductive caste) and differences between workers (major and minor worker castes). The proximal cause of the plasticity is thought to be largely nutritional (4, 5), and in some species, such as the honey bee, the underlying nutritional mechanisms are well understood (6, 7). As with any phenotype, physical caste is unlikely to be completely environmentally determined, and genotypes may differ in their propensity to develop into gynes or workers under a given set of environmental conditions (4, 8). Historically, genetic variation among individuals has not been thought to contribute to caste determination, although a number of scattered publications have suggested a role for genetic differences, especially in the ants (9-13).However, several recent studies have reported genetic determination of caste in ants. Reproductive females in some species of ants are produced clonally, whereas workers are produced sexually [e.g., Cataglyphis cursor (14); Wasmannia auropunctata (15)]. Some populations of harvester ants (Pogonomyrmex) comprise two independent but interacting genetic lineages. The genome of reproductive females in such populations is composed of a single lineage, whereas females that contain genes from both lineages become workers (16)(17)(18). A similar phenomenon occurs in hybridizing populations of fire ant species (19). In these species, there is a clear genetic effect.A second set of studies involves species with polyandrous queens that find differences in the distribution of male genotypes between gyn...