Steroid 5α-reductases in the brain: From neurosteroidogenesis to therapeutic implications.

In their book Major Transitions in Evolution, Smith and Szathmáry () highlighted that eusociality is one of the major transitions in evolution where individuals forgo their own ability to reproduce to cooperate as a group to form a more complex being, analogous to genes integrating to form genomes. The defining characteristics–cooperative brood care, reproductive division of labor, and overlapping generations–have been observed in a wide variety of taxa, including mammals, shrimps, and insects, such as bees, ants, wasps and beetles (Crozier and Pamilo ; Revely et al. ; Legendre and Grandcolas ; Jennifer et al. ; Solomon et al. ). Blattodea (cockroaches and termites) and other groups exhibit a spectrum of sociality, including subsociality which involves parental care and gregarious behaviour (Hölldobler and Wilson ; Crozier and Pamilo ; Legendre and Fabien L Condamine ). While Hymenoptera (bees, ants and wasps) have historically dominated eusocial research (Sandra et al. ), possibly due to historical and geographic research bias as well as having multiple origins of eusociality (Peters et al. ). Blattodea offers a unique comparative model where eusociality arose only once in the termites. Blattodea spans a full continuum of social complexity, from solitary and gregarious to subsocial, primitively eusocial and highly eusocial lifestyle. (Roth and Nalepa ; Legendre and Grandcolas ; Bornberg et al. ; Fouks et al. ). Blattodea possesses distinct biological features that contrast sharply with Hymenoptera. Unlike the holometabolous Hymenoptera, termites are hemimetabolous. Furthermore, termite colonies also consist of both diploid males and females, including long lived reproductives of both sexes (Tasaki et al. ) with XY sex chromosomes (Lacy ) while hymenopteran colonies are typically founded on a haplodiploid system with female workers. These fundamental differences make Blattodea an essential group for disentagling universal molecular signatures of social evolution from those that are clade-specific. Exploring the molecular details underlying the evolution of Blattodea has only become feasible recently, with five termite and three cockroach genomes having been published to date of this analysis (Mark et al. ; Bornberg et al. ; Terrapon et al. ; Fouks et al. ; Meng et al. ; Li et al. ; Shigenobu et al. ), which we consider as key species for this study. All of these have shown that the genome size of termites are smaller then cockroaches both in size and gene content, in keeping with the trends found in hymenoptera social evolution. In Blattodea, other remarkable insights have identified mechanisms of viviparity (live bearing) and genomic changes related to social evolution, including the regulation of chemical perception, a hallmark of insect societies used to recognise nestmates, caste status or sense food sources. Interestingly, termites exhibit significant expansions in ionotropic receptors (Mark et al. ), in contrast to the expansion of odorant receptors found in Hymenoptera (Zhou et al. ), although the later may be rather flight loss in in hymenopteran females (Gautam et al. ). The divergent expansion of two chemoreceptor families indicates that while social transitions required conserved functional shift in chemical perception the specific underlying molecular mechanisms driving those shifts vary between orders. Another convergent pattern includes alterations in methylation patterns associated with caste-specific gene regulation (Mark et al. ; Lyko et al. ; Glastad et al. ), although this relationship is not necessarily consistent (Glastad et al. ). Specific regulatory pathways, such as the juvenile hormone pathway, involved in caste determination, also convergently changed in both Blattodea and Hymenoptera (Mark et al. ; Robinson and Vargo ). However, a more general understanding of regulatory changes related to social evolution in Blattodea has not been conducted. It remains unclear whether similar convergent patterns exist in termites. To this end, Harrison et al. (2018) identified expansions in zinc fingers in termites (Mark et al. ) but changes in regulatory regions were not studied.