Caste differentiation and division of labor are the hallmarks of social insect colonies [1, 2]. The current dogma for female caste differentiation is that female eggs are totipotent, with morphological and physiological differences between queens and workers stemming from a developmental switch during the larval stage controlled by nutritional and other environmental factors (e.g., [3-8]). In this study, we tested whether maternal effects influence caste differentiation in Pogonomyrmex harvester ants. By conducting crossfostering experiments we identified two key factors in the process of caste determination. New queens were produced only from eggs laid by queens exposed to cold. Moreover, there was a strong age effect, with development into queens occurring only in eggs laid by queens that were at least two years old. Biochemical analyses further revealed that the level of ecdysteroids was significantly lower in eggs developing into queens than workers. By contrast, we found no significant effect of colony size or worker exposure to cold, suggesting that the trigger for caste differentiation may be independent of the quantity and quality of resources provided to larvae. Altogether these data demonstrate that the developmental fate of female brood is strongly influenced by maternal effects in ants of the genus Pogonomyrmex.
Male dominance hierarchies are usually linked to relative body size and to weapon size, i.e. to determinants of fighting ability. Secondary sexual characters that are not directly used as weapons could still be linked to dominance if they reveal determination or overall health and vigour and hence, indirectly, fighting ability. We studied the mating behaviour of the minnow (Phoxinus phoxinus), a cyprinid fish in which males develop breeding tubercles during the spawning season. The function of these breeding tubercles is still not clear. Using microsatellites markers we determined the male reproductive success under controlled conditions. We found that the minnows were territorial and that they quickly established a dominance hierarchy at the beginning of the spawning season. Dominance was strongly and positively linked to fertilisation success. Although body size and number of breeding tubercles were not significantly correlated in our sample, both large males and males with a higher number of breeding tubercles were more dominant and achieved a higher fertilization success than small males or males with few tubercles. We found multi-male fertilization in most clutches, suggesting that sperm competition is important in this species. Females showed behaviour that may be linked to spawning decision, i.e. male dominance might not be the only determinant of male reproductive success in minnows.
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