Polyandry in a marine turtle: females make the best of a bad job

Abstract

The female perspective on reproductive strategies remains one of the most active areas of debate in biology. Even though a single mating is often sufficient to satisfy the fertilization needs of most females and the act of further mating incurs costs, multiple paternity within broods or clutches is a common observation in nature. Direct or indirect advantage to females is the most popular explanation. However, the ubiquity of this explanation is being challenged by an increasing number of cases for which benefits are not evident. For the first time, we test possible fitness correlates of multiple paternity in a marine turtle, an organism that has long attracted attention in this area of research. Contrary to the wide-spread assumption that multiple mating by female marine turtles confers fitness benefits, none were apparent. In this study, the environment played a far stronger role in determining the success of clutches than whether paternity had been single or multiple. A more likely explanation for observations of multiply sired clutches in marine turtles is that these are successful outcomes of male coercion, where females have conceded to superfluous matings as a compromise. Thus, multiple matings by female marine turtles may be a form of damage control as females attempt to make the best of a bad job in response to male harassment.

Fig. 1.

Contribution of different fathers to multiply sired clutches. TT4, TP48, TP53, TT9, TT11, and TT13 are clutches in which the primary father has contributed significantly >50% of the clutch (see text).

Fig. 2.

The proportion of fertilized eggs that had survived plotted against the proportion sired by the father with the highest paternity in the clutch (primary father). No association occurred between these variables. In contrast, more clutches laid in the cooler beaches had higher proportion of the clutch surviving than those in the warmer beach.