Skew in ovarian activation depends on domicile size in a facultatively social thrips

Costs and benefits of group living are a fundamental topic in behavioural ecology. Resource availability affects individuals breeding prospects alone and in groups, as well as how reproduction is distributed within groups (\"reproductive skew\"). Here, we provide correlational evidence in facultatively social thrips that breeding resources are associated with (1) whether solitary or social living is favoured, and (2) the degree of ovarian skew.\n\nDunatothrips aneurae (Thysanoptera, Phlaeothripidae) cooperatively build silk \"domiciles\" on Australian Acacias, feeding exclusively from internal phyllode surfaces. Per capita productivity scaled differently with group size depending on domicile volume - females in small domiciles did better alone than in groups, whereas in large domiciles single and group-nesting females did equally well. Ovarian dissections revealed that in small domiciles some females were nonreproductive, indicating ovarian (i.e. reproductive) skew. Skew increased as domicile size decreased and group size increased. Breeders had smaller oocyte volume in smaller domiciles, especially those containing nonreproductives.\n\nThese findings suggest group formation and reproductive skew in D. aneurae may be influenced by reproductive competition for breeding resources. Nonreproductive females in small domiciles may be reproductively suppressed, subfertile, or waiting to reproduce. We speculate they may avoid eviction by contributing as \"helpers\" to domicile maintenance.