Reproductive concessions between related and unrelated members promote eusociality in bees

Abstract

Animal societies exhibit remarkable variation in their breeding strategies. Individuals can maximize their fitness by either reproducing or by helping relatives. Social hymenopterans have been key taxa for the study of Hamilton’s inclusive fitness theory because the haplodiploid sex-determination system results in asymmetric relatedness among breeders producing conflict over the partitioning of reproduction. In small cooperative groups of insects, totipotent individuals may maximize their inclusive fitness by controlling reproduction despotically rather than helping their relatives. Here, we demonstrate that the dominant females of the primitively eusocial bee Euglossa melanotricha (Apidae: Euglossini) control reproduction, but concede part of the reproductive output with their related and unrelated subordinates. As expected, a dominant female capitalizes on the direct reproduction of related subordinates, according to her interests. We found that reproductive skew was positively correlated with relatedness. The concessions were highly reduced in mother-daughter and sibling nests (relatedness r ± s.d. = 0.54 ± 0.02 and 0.79 ± 0.02, respectively) but much more egalitarian in unrelated associations (r = −0.10 ± 0.01). We concluded that reproductive skew in these primitively eusocial bees is strongly related to the genetic structure of associations, and also that females are able to assess pairwise relatedness, either directly or indirectly, and use this information to mediate social contracts.

Multiple Aggressions Among Nestmates Lead to Weak Dominance Hampering Primitively Eusocial Behaviour in an Orchid Bee

“…The studies of species showing advanced levels of eusociality like the honeybee A. mellifera have contributed to knowledge about caste differentiation, division of labour and several conflicts involving workers and queens. The studies on primitively eusocial species have contributed to understand not only the transition from solitary to social but the adaptations, costs and benefits for sociality (Schwarz et al, 1998;Schwarz et al, 2007;Kocher & Paxton, 2014;Prager, 2014;Rehan et al, 2014;Andrade et al, 2016). This study shows that E. annectans has a unique social structure that exhibits aspects of communal and primitively eusocial societies where multiple females are prone to attack each other and multiple female are performing oophagy.…”

“…This common behaviour trait developed by young bees seems to maximize resin use inside the nest. In contrast to primitively eusocial orchid bees there was no evidence for the presence of a single dominant female as seen for Euglossa atroveneta Dressler, 1978(Ramirez-Arriaga et al, 1996, E. fimbriata and Euglossa cordata Linnaeus, 1758 (Augusto & Garófalo, 2009;2010, respectively) and E. melanotricha (Andrade-Silva & Nascimento, 2012;Andrade et al, 2016) neither for the presence of a subordinated female specialized in guarding the nest entrance as reported for Euglossa viridissima Friese, 1899 (Boff et al, 2015).…”

“…In parallel to eusocial species in which only the queen lays most of the eggs, worker policing behaviour, oophagy and social contracts helps to reduce potential reproductive conflicts (Ratnieks, 1988;Ratnieks et al, 2006;Andrade et al, 2016). However, in the course of evolution some species may have selected traits in order to mitigate direct conflicts.…”

“…Thus, aggression arises because of, or is highly correlated with, genetic relatedness, or is highly correlated with selfishness. If on one hand higher degree of altruism is found in genetically related individuals on the other hand when resources at stake is important/rare genetically unrelated societies may display equal, if not more, degree of altruism and cooperation (Andrade et al, 2016).…”

“…Thus, studies on species whose individuals exhibit more alternative or facultative social behaviour (compared to species with predetermined caste differentiation) may help to provide more clear evidences of how advanced forms of sociality may have evolved (Dunn & Richards, 2003;Peso & Richards, 2010;Prager, 2014;May-Itzá et al, 2014;Rehan et al, 2014;Andrade et al, 2016).…”