Kin recognition and cannibalism in a subsocial spider

Evolution of cooperation and group living in spiders from subsocial family groups may be constrained by their cannibalistic nature. A tendency to avoid cannibalizing kin may facilitate tolerance among spiders and implies the ability to identify relatives. We investigated whether the subsocial spider Stegodyphus lineatus discriminates kin by recording cannibalism among juveniles in experiments during which amount of food and size difference among spiders in groups were varied. We hypothesized that family groups should be less cannibalistic than groups of mixed‐parental origin. Further, we tested whether food‐stress would influence cannibalism rates differently in kin and nonkin groups and the effect of relatedness on cannibalism within groups of spiders of variable size compared with those of homogenous size. In groups of six spiders, more spiders were cannibalized in nonsib groups than in sib groups under low food conditions. A tendency for nonkin biased cannibalism in starved spider pairs supported that kin recognition in S. lineatus is expressed when food is limited. Size variance of individuals within well‐fed groups of siblings and unrelated spiders had no influence on cannibalism rates. Apparently, both hunger and high density are important promoters of cannibalism. In addition to inclusive fitness benefits, we suggest that an ability to avoid cannibalizing kin will favour the evolution of cooperation and group living in phylogenetically pre‐adapted solitary species.     

New species of the genus Salganea (Blattaria, Blaberidae, Panesthiinae) from Myanmar, with molecular phylogenetic analyses and notes on social structure

A new species of the genus Salganea is described from Mount Victoria, Chin State, Myanmar under the name of Salganea matsumotoi sp. nov. Morphological investigation suggests that this species belongs to the S. nigrita species group. The inferred molecular phylogenetic tree indicates that S. matsumotoi is most closely related to the taxa S. incerta, S. taiwanensis, S. gressiti and S. esakii, distributed in Thailand, Taiwan and Japan, all of which belong to the S. nigrita species group. Social structural data suggest that this species is subsocial, and in contrast to other studied species in the genus, potentially has more than one reproductive episode.     

Description of the basic features of parent‐offspring stomodeal trophallaxis in the subsocial wood‐feeding cockroach Salganea esakii (Dictyoptera,Blaberidae, Panesthiinae)

In subsocial xylophagous cockroaches it is thought that parental feeding is important for the survival and growth of the altricial offspring, but the details of parental feeding in these groups are poorly known. We observed stomodeal (oral) trophallaxis between parents and the 2nd or 3rd instars of the wood‐feeding cockroach Salganea esakii Roth, and here report basic features of trophallaxis in young families. Both the female and male parents fed young nymphs with stomodeal food, and there was no difference in the frequency of the behavior between parental sexes. Up to three nymphs could be fed simultaneously during a single trophallactic event. Adults occasionally rejected contact with nymphs by blocking them with their forelegs. Nymphs utilized trophallactic food from parents more frequently than feeding independently on wood pieces or fecal pellets. Trophallaxis between sibling nymphs was never observed. These results suggest that the 2nd and 3rd instar nymphs rely on the stomodeal substances provided by their parents, and that provisioning is an essential component of subsocial behavior in biparental wood‐feeding cockroaches.