Evolutionary transitions towards eusociality in snapping shrimps

Abstract

Animal social organization varies from complex societies where reproduction is dominated by a single individual (eusociality) to those where reproduction is more evenly distributed among group members (communal breeding). Yet, how simple groups transition evolutionarily to more complex societies remains unclear. Competing hypotheses suggest that eusociality and communal breeding are alternative evolutionary endpoints, or that communal breeding is an intermediate stage in the transition towards eusociality. We tested these alternative hypotheses in sponge-dwelling shrimps, Synalpheus spp. Although species varied continuously in reproductive skew, they clustered into pair-forming, communal and eusocial categories based on several demographic traits. Evolutionary transition models suggested that eusocial and communal species are discrete evolutionary endpoints that evolved independently from pair-forming ancestors along alternative paths. This 'family-centred' origin of eusociality parallels observations in insects and vertebrates, reinforcing the role of kin selection in the evolution of eusociality and suggesting a general model of animal social evolution.

Ecological generalism facilitates the evolution of sociality in snapping shrimps

“…We categorised each species' social organisation as either being eusocial, communal breeding or pair‐living based upon a previous quantitative classification of Synalpheus that used a variety of demographic measures (Chak et al . ; Hultgren et al . ) and is directly correlated with measures of the eusociality index in this group (Duffy & Macdonald ).…”

“…multiple mated pairs per sponge), to eusocial colonies with one or multiple queens and a variable number of non‐breeding workers (Chak et al . ; Hultgren et al . ).…”

“…; Duffy & Macdonald ), and eusociality and communal breeding represent distinct social systems that arose independently from pair‐living ancestors along alternative evolutionary paths (Chak et al . ). Moreover, these independently evolved social systems in snapping shrimps – communal breeding and eusociality – are likely to have been selected for by different ecological factors (Chak et al .…”

“…Moreover, these independently evolved social systems in snapping shrimps – communal breeding and eusociality – are likely to have been selected for by different ecological factors (Chak et al . ). We used phylogenetic comparative analyses to test the alternative hypotheses that (1) sociality promotes niche expansion and ecological generalism (social conquest hypothesis) vs. (2) ecological generalism facilitates the transition to sociality (social transition hypothesis).…”

Evolutionary diversity as a catalyst for biological discovery

“…The capacity for empathy-like consoling behavior has evolved in corvids (Corvidae), rodents (Rodentia), elephants (Elephantidae), dogs ( Canis familiaris ), and primates (Burkett et al, 2016; Clay & de Waal, 2013; de Waal & Preston, 2017; Fraser et al, 2008). And eusocial systems have evolved in termites (Isoptera); ants, bees, and wasps (Hymenoptera); Synalpheus shrimp; and African mole rats (Bathyergidae) (Chak et al, 2017; Duffy & Macdonald, 2010; Nowak et al, 2010; Thorne, 1997; Toth & Rehan, 2017). …”