Meeting Abstract
In animals with bi-parental care, maintaining a pair-bond is of adaptive value because it increases reproductive success and reduces costs, such as energy and time, for finding a new mate. Hormones are important mediators of social behaviors as well as parental care, and endocrine mechanisms therefore are likely to be involved in the decision whether to stay with the same mate or separate after a breeding season. Because behavioral compatibility has been shown to increase fitness and hormones regulate behavioral traits, the implications from documenting the degree of endocrine similarity have broad applications for reproductive success and pair-bond longevity. We used a three-year study on free-living great tits (Parus major) to test if mates had similar hormone levels during the parental phase. We tested specifically if the metabolic hormone corticosterone was related to pair-bond longevity and reproductive success. Baseline, but not stress-induced, corticosterone concentrations were highly correlated between members of a pair and became more similar between members of a stable pair over multiple years. Pairs that increased their hormonal similarity within a season (from the pre-breeding to the breeding) had the highest reproductive success. Pairs with more similar baseline corticosterone levels and higher reproductive success were more likely to remain together after the breeding season. The results of this study suggest that pair-bond longevity is related to endocrine similarity and reproductive success, and raises the possibility that hormonal mechanisms may be under sexual selection.
