Displaying in the dark: light-dependent alternative mating tactics in the Alpine newt

Environment plays a major role for determining the kind of courtship behaviours or alternative mating tactics employed, but the effect of physical variables on fitness has received little attention. The Alpine newt courts during both day and night times and exhibits a complex suite of behaviours involving olfactory, visual and tactile cues. Displaying in both dark and light conditions may increase the number of mating opportunities and alleviate predation risk, but the frequency and efficacy of the various tactics deployed may vary across light conditions, leading males to vary their use of these tactics across different light regimes. To test this hypothesis, we video-recorded sexual encounters at two light intensities in a controlled experimental design. When courting in the dark, males used comparatively more olfactory rather than visual displays. They also relied more on positive feedback from the female before releasing a spermatophore for her to pick up. The particular mix of tactics used under each light condition is likely to be adaptive because in the dark (1) visual communication is hampered, making olfactory displays possibly more effective and (2) males depositing spermatophores are more likely to lose fertilizations to competitors. Mating in light and dark conditions has similar reproductive payoffs, which shows that displaying in the dark is not detrimental and may even be advantageous if predation risk is reduced at night. These results confirm the importance of taking into account physical variables to understand the evolution of sexual communication in animals.