The timing and interval of mate encounter affects investment during mating

Abstract

The benefits obtained from mating are usually condition-dependent, favouring the evolution of flexible investment during copulation; for example, in terms of invested time, energy or sperm. Flexible investment strategies are predicted to depend on the likelihood of acquiring alternative mates and therefore they should depend on the timing of mate encounter. However, scarce experimental evidence for this hypothesis exists. In the present study, we manipulated the time delay until first mating and the interval between first and second mating in the polygynandrous common lizard Zootoca vivipara. We determined treatment effects on fertilization success and copulation duration, with the latter being a proxy for investment in mating and for the quantity of transferred sperm. The duration of the second copulation decreased with increasing inter-mating interval and depended on the fertilization success of first mates. The former provides evidence for time-dependent investment strategies, most likely resulting from the progression of the female's reproductive cycle. The fertilization success of first mates increased with increasing inter-mating interval and was higher when females were closer to ovulation, showing that flexible investment strategies significantly affected male reproductive success. This indicates fertilization assurance, which may mitigate the negative effects of low population density on reproductive success (e.g. Allee effects).