A solitary bee transformed into a social insect

Bees, like ants and termites, are known for their complex organization. Their population is divided into castes of fertile individuals and sterile individuals: in most cases there is a reproductive female, queen and workers, who do not reproduce but participate in the care of the young (larva, pupa and eggs ). This is called a eusocial organization. But not all bees live like this: some have a solitary lifestyle. This suggests that during evolution solitary insects came together to form these complex societies. However, the conditions of this important evolutionary transition are poorly understood. To find out, Lucas Hearn of Flinders University in Australia and his colleagues turned to the native Australian bee. Amphilius MorosA species that has recently been in colonies and which offers a unique insight into the early stages of social evolution.

bee Amphilius Moros It thrives in the high montane forests of the Great Dividing Range, where it nests among the foliage of trees. The particularity of this species is that it is the only one of its family (Colletidae) to have evolved recently towards eusociality, from individual breeding to altruistic colonies. There are two reasons to think that this transition is recent: “On the one hand, since it is the only known social species of the family Colletidae, the common ancestor to all may not have developed social traits; We have an independent social background here,” says Hearn. This is not the primary strategy of the species, although it may be. Together, these two aspects indicate that, in an evolutionary context, species have recently evolved social traits.

study socialism a. moroseIn this study, the researchers looked at the characteristics of social nests. During his fieldwork, he observed that there were rarely more than two females in the nests. and unlike other species of eusocial bees, such as honey bees, the females of a. morose They do not show typical morphological differences between queens and workers. Therefore, analysis of genomic data was necessary to determine how females contribute to reproduction within a colony.

This analysis showed that, in one of the nests, one of the two females was laying eggs, while the other, which was closely related to her, did not reproduce. On the other hand, the latter participate in the defense of the nest, an equally important function for the species because of the strong parasitic pressure under which it is responsible for the high risk of mortality at the different stages of reproduction. The reproductive sacrifice of one of the females will be compensated by a strong bond with the laying female, hence the interest in protecting her offspring. According to the researchers, the differences in fecundity reveal an unexpected bias in this species hitherto considered as egalitarian and composed only of unrelated individuals. But how is this transition to social life to be explained?

The current consensus is that there are several evolutionary steps that lead to sociality. At the start, the individuals are grouped together and all have the capacity to reproduce: there is therefore no reproductive bias. It appears later, when some individuals become sterile and are morphologically different from progenitors due to natural selection. Evolutionary biologist William Hamilton called this “kinship selection” in a theory developed in the 1960s. In this theory, the development of sociability relies on some females breeding to help their mates reproduce, for example guarding the nest and helping to care for the young.

Hearn and his colleagues found that the organization of the Australian bee, which is in the early stages of sociality, is consistent with this theory. study of a. morose This suggests that development towards a ‘caring’ community is likely to occur more rapidly than previously thought, during the initial transition from solitary to social life. Indeed, in this specific case, there is no visible morphological difference between the individuals, with a very early sterility of certain females with the transition to social life.

Alyssa Dore

Article translated and adapted by Research and Science with permission from Por la Science.

Background: “Extreme reproductive bias at the dawn of sociality is consistent with inclusive fitness theory but is problematic for pathways of eusociality”; Lucas R. Hearn, Olivia K. Davis and Michael P. Schwarz en Proceedings of the Royal Society B, volume. 289, Item No. 20220652, June