The biogeographical history of major groups of bees with worldwide distributions have often been explained through hypotheses based on Gondwanan vicar

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.

Calcrete aquifers of the Yilgarn area of Western Australia and the Ngalia Basin, Northern Territory, Australia are known to contain a rich invertebrate stygofauna, including the world’s most diverse assemblage of subterranean diving beetles. Here we determine the generic relationships of these subterranean diving beetle species in the tribe Hydroporini and assess their evolutionary origins. Phylogenetic analyses of 1642 base pairs of mitochondrial DNA (mtDNA), comprising segments of CO1, 16S rRNA, tRNAleu and ND1 genes, revealed that the subterranean species from the arid zone, previously classified under the genus Nirripirti Watts & Humphreys (Hydroporini), are all closely related to the genus Paroster Sharp. We synonymise the stygobitic genus Nirripirti with the genus Paroster. Factors that may have been important for the transitions to stygobitic life such as historical and contemporary species distributions, reproductive ecology and body size are discussed. We show that pre-adaptations such as preference for temporary, but seasonally reliable, water and preference to live among gravel and sand along running water would have favoured transitions from surface to stygobitic life, but that large body size may have restricted the likelihood of successful transitions.

Regressive evolution, the reduction or total loss of non-functional characters, is a fairly common evolutionary phenomenon in subterranean taxa. However, the genetic basis of regressive evolution is not well understood. Here we investigate the molecular evolution of the eye pigment genecinnabarin several independently evolved lineages of subterranean water beetles using maximum likelihood analyses. We found that in eyeless lineagescinnabarhas an increased rate of sequence evolution, as well as mutations leading to frame shifts and stop codons, indicative of pseudogenes. These results are consistent with the hypothesis that regressive evolution of eyes proceeds by random mutations, in the absence of selection, that ultimately lead to the loss of gene function in protein-coding genes specific to the eye pathway.