Do forced extrapair copulations and interspecific brood amalgamation facilitate natural hybridisation in wildfowl?

Abstract

Wildfowl species (Anseriformes; subfamily Anatinae; Aves) differ in some behavioural aspects from other avian orders. They show relatively high rates of (i) forced extrapair copulations (FEPC), (ii) interspecific brood amalgamation (IRBA) or nest parasitism, and (iii) hybridisation. Some authors, therefore, tried to link the first two behavioural aspects with hybridisation. I collected data about FEPC, IRBA and hybridisation from different studies to test for causes and effects. I used a binary logistic regression since causes (FEPC/IRBA) and an effect (hybridisation) were assumed. The stepwise binary regression showed a significant influence of IRBA on hybridisation, but not of FEPC (Table 1). Further, tribe was also included in the stepwise model, suggesting a strong phylogenetic effect. However, the influence of IRBA remained after including tribe and genus as categorically coded variables in order to control for phylogenetic effects. FEPC was also a significant factor when used in a univariate analysis. Using matched pairs of closely related species it was determined that IRBA had a significant influence on hybridisation (measured as the number of other species with which hybrids were produced). FEPC was also a significant factor (Table 2). It is concluded that interspecific brood amalgamation has a stronger impact on natural hybridisation in wildfowl than forced extrapair copulations.