The Evolution of Infidelity in Socially Monogamous Passerines Revisited: A Reply to Griffith

摘要

We were pleased to see that Simon Griffith (2007, in this issue) welcomes the more stringent and quantitative approach to the study of extrapair copulations (EPC) in birds that we recently introduced (Arnqvist and Kirkpatrick 2005). Griffith argues that our main conclusion may have been premature for, it seems, the following four reasons. First, Griffith suggests that we did not include all the relevant data. We noted that our estimate of indirect selection was based on all studies reporting direct measures of "growth, survival, recruitment ... and/or reproductive success" (Arnqvist and Kirkpatrick 2005, p. S27) as proxies for offspring fitness. We explicitly stated that "a few studies reporting other forms of potential but less direct fitness correlates were also not included" (p. S27). The study mentioned by Griffith (Johnsen et al. 2000) focused on measures of wing swelling and was not included for this reason. On closer examination, however, we see that John-sen et al. (2000) also reported measures of offspring growth, and it should thus have been included in our estimate of indirect selection. However, the indirect effects on growth reported by Johnsen et al. (2000) were extremely small (0.0% and 0.2% of total variance in offspring growth) and statistically insignificant, and so its inclusionwould only have added force to our conclusion regarding indirect selection.