Conditional monogyny: female quality predicts male faithfulness

We found that all categories were continuously present with relatively stable frequencies despite changes in the operational sex ratio. Males were more likely monogynous when copulating with relatively heavy and old females and otherwise bigynous.Our results imply that males make conditional mating decisions based on the quality of the first female they encounter but do not adjust their mating tactic to the local selection regime.In males the variety of mating tactics is high and often different tactics are associated with an intra-sexual morphological polymorphism [1,2]. In many species small males use a ‘sneaker’ or ‘parasitic’ tactic to get access to females that are guarded by larger, ‘bourgeois’ males [3,4]. Furthermore, male mating tactics may differ in their optimal mating rate. In species with traditional sex roles, males are known to maximize their fitness by increasing their mating rate whereas multiply mating in females does not necessarily elevate fitness [5,6]. However, in many cases males mate at a lower than maximum rate, for example when they provide parental care [7]. These deviations from traditional sex roles are of particular interest for the understanding of mating system evolution and the expression of alternative tactics. While sex role reversal and bi-parental care is well explained by the general theory [8,9], low male mating rates with low or even no paternal care (here called monogyny) are less well understood. By theory, monogynous mating systems are suggested to evolve if they are associated with a highly efficient paternity protection such that the fertilization success of monogynous males is higher than the average of a polygynous strategy [10]. The evolution of paternity protection, however, only makes sense under a male biased effective sex ratio (ratio between males and females that mate at least once) and a high degree of sperm competition within a species.Monogyny can be found within several taxa such as insects [11,12] and fishes