A Mid-Cretaceous Origin of Sociality in Xylocopine Bees with Only Two Origins of True Worker Castes Indicates Severe Barriers to Eusociality

School of Biological Sciences, Flinders University of South Australia, Adelaide, South Australia, Australia.
PLoS ONE (Impact Factor: 3.23). 04/2012; 7(4):e34690. DOI: 10.1371/journal.pone.0034690
Source: PubMed


The origin of sterile worker castes, resulting in eusociality, represents one of the major evolutionary transitions in the history of life. Understanding how eusociality has evolved is therefore an important issue for understanding life on earth. Here we show that in the large bee subfamily Xylocopinae, a simple form of sociality was present in the ancestral lineage and there have been at least four reversions to purely solitary nesting. The ancestral form of sociality did not involve morphological worker castes and maximum colony sizes were very small. True worker castes, entailing a life-time commitment to non-reproductive roles, have evolved only twice, and only one of these resulted in discrete queen-worker morphologies. Our results indicate extremely high barriers to the evolution of eusociality. Its origins are likely to have required very unusual life-history and ecological circumstances, rather than the amount of time that selection can operate on more simple forms of sociality.

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    • "Presocial taxa are fundamental to understanding the origins of sociality and can give insights into the evolutionary steps from solitary to social life. The Xylocopinae are a monophyletic grouping of xylophilous bees consisting of four tribes: Xylocopini, Manueliini, Allodapini and Ceratinini (Rehan et al. 2012). Xylocopini have shown that species display parasociality but never exhibit eusociality (Michener 1990). "
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    • "However, transitions from socially hierarchical to more or less egalitarian societies have also been inferred in multiple lineages (e.g. Danforth and Ji 2001; Rehan et al. 2012; Gibbs et al. 2012). Gibbs et al. (2012) proposed that communal nesting in Australian halictines is derived from an ancestral eusocial state and that communal behaviour in a Patellapis species (Timmermann and Kuhlmann 2008) and in Lasioglossum (Dialictus) figueresi (Wcislo et al. 1993) may also be derived from eusocial ancestors. "
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    • "Facultatively social bees have been rarely studied by neuroecologists but offer great insights into the relative roles of phylogenetic history and social experience on brain investment and development pathways. Ceratina are an emerging model system for understanding the evolutionary development of neuroanatomy and social complexity as species of this genus range the full solitary to eusocial spectrum [Michener, 1985; Rehan et al., 2012]. "
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