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 Andersson’s 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 et al. 2006; Andersson & Waldeck 2007; Waldeck et al. 2008; Jaatinen et al. 2009; Tiedemann et al. 2011). However, this is not always the case (Semel & Sherman 2001; Anderholm et al. 2009; and see Poysa 2004). In a new study reported in this issue of Molecular Ecology, Jaatinen et al. (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! Table 1. A summary of recent studies that have tested for evidence of relatedness between hosts and parasites in avian conspecific brood parasites Species Evidence of host–parasite relatedness? Evidence of local kin structure? Relatedness > expected spatially r Host–Parasite r Population Costs or benefits measured? Method Source CBP, conspecific brood parasitism. Common moorhen (Gallinula chloropus) Mixed Some parasitism between relatives Yes Limited dispersal of both sexes No Not greater than expected — — No (but discussed) DNA minisatellite fingerprints McRae & Burke (1996) Common goldeneye (Bucephala clangula) Yes Number of parasitic eggs also increased with relatedness Not tested; high female philopatry Yes 0.132 — No Protein fingerprints 50 bands Andersson & Ahlund (2000) Wood duck (Aix sponsa) No (parasites avoid relatives) Not tested; high female philopatry No Significantly less likely to parasitize local kin — — No Behavioural observation Semel & Sherman (2001) Common goldeneye (B. clangula) No Relatedness unlikely to explain CBP Not tested Not measured — — Yes Field measures Poysa (2004) Wood duck (A. sponsa) Yes (for primary parasites) No Yes (for primary parasites) 0.04 (all) 0.11 (primary parasites) 0.01–0.02 No 5 microsatellites Roy Nielsen et al. (2006) Common eider (Mollissima somateria) Yes No Yes 0.122 (all) 0.126, 0.162 (two colonies) −0.065 (neighbours 1–10 m) No Protein fingerprints 30 bands Andersson & Waldeck (2007) Common eider (M. somateria) Yes Number of parasitic eggs also increased with relatedness Yes Relatedness declined with distance Possibly Host–parasite relatedness > close neighbours in 1 of 2 analyses 0.18–0.21 0.09 (neighbours) No Protein fingerprints 51 bands Waldeck et al. (2008) Barnacle goose (Branta llucopsis) No Weak Females within 40 m more closely related No 0.04 −0.0008 No Protein fingerprints 28 bands Anderholm et al. (2009) Barrow’s goldeneye (Bucephala islandica) Yes Number of parasitic eggs increased with relatedness Weak Slight decline in relatedness with distance No Host–parasite relatedness similar to neighbours 0.08 −0.015 0.11 (neighbours) No 19 microsatellites Jaatinen et al. 2009 Common eider (M. somateria) Yes Interaction with parasite status No Yes 0.39 (mean) 0.48, 0.28 (different sites) 0.0 No 7 microsatellites Tiedemann et al. (2011)