The relative role of relatives in conspecific brood parasitism

Conspecific brood parasites lay their eggs in the nests of other females in the same population, leading to a fascinating array of possible games among parasites and their hosts (Davies 2000; Lyon & Eadie 2008). Almost 30 years ago, Andersson & Eriksson (1982) first suggested that perhaps this form of parasitism was not what it seemed-indeed, perhaps it was not parasitism at all! Andersson & Eriksson (1982) observed that conspecific brood parasitism (CBP) was disproportionally common in waterfowl (Anatidae), a group of birds for which natal philopatry is female-biased rather than the more usual avian pattern of male-biased natal philopatry. Accordingly, Andersson (1984) reasoned (and demonstrated in an elegantly simple model) that relatedness among females might facilitate the evolution of CBP-prodding us to reconsider it as a kin-selected and possibly cooperative breeding system rather than a parasitic interaction. The idea was much cited but rarely tested empirically until recently-a number of new studies, empowered with a battery of molecular techniques, have now put Anderssons hypothesis to the test (Table 1). The results are tantalizing, but also somewhat conflicting. Several studies, focusing on waterfowl, have found clear evidence that hosts and parasites are often related (Andersson & Ahlund 2000; Roy Nielsen 2006; Andersson & Waldeck 2007; Waldeck 2008; Jaatinen 2009; Tiedemann . 2011). However, this is not always the case (Semel & Sherman 2001; Anderholm 2009; and see Poysa 2004). In a new study reported in this issue of Molecular Ecology, Jaatinen (2011a) provide yet another twist to this story that might explain not only why such variable results have been obtained, but also suggests that the games between parasites and their hosts-and the role of kinship in these games-may be even more complex than Andersson (1984) imagined. Indeed, the role of kinship in CBP may be very much one of relative degree!