Extended mother-offspring relationships in invasive crayfish.

Crayfish shows a relatively complex parental behaviour if compared to other invertebrates, but the literature provides only anecdotal accounts of this phenomenon. In Procambarus clarkii, we described the “return” behaviour of third-stage juveniles when offered four types of adults: biological mothers, foster mothers, non-brooding females, and males. Then, we analysed the posture and behaviour of the adults to understand the role played by the putative mother in attracting the juveniles. Contrary to non-brooding individuals, both biological and foster mothers displayed a relatively scarce locomotion, executed few cleaning and feeding acts, and never attempted to prey on juveniles. They often assumed a “spoon-like telson posture” that seemed to facilitate offspring’s approaches. Juveniles increased the frequency of tail-flips away in the presence of non-brooding adults; conversely, they accepted foster mothers, along with biological mothers, but not as fast as the latter. Taken together, these results suggest that mother-offspring relationship in P. clarkii is more refined than previously thought, being possibly a key factor enabling this species to thrive in harsh environmental conditions.