Male terrestrial salamanders demonstrate sequential mate choice based on female gravidity and size

In many vertebrate mating systems, mate choice evolves when signalling via visual, chemical or auditory traits is an energetically costly process. Selection may favour individuals that can discriminate among potential mates and invest in signalling to mates with particular characteristics. Most commonly, females with costly gametes are thought to be the more selective sex; however, runaway sexual selection can produce elaborate male ornaments and behaviours that are similarly costly to produce, which can lead to male mate choice. In this study, we used behavioural trials to experimentally test male mate choice in a terrestrial salamander, Plethodon shermani. We investigated whether males altered the proportion of time they spent performing a potentially costly courtship display, 'foot dancing', in the presence of females. Specifically, we explored male mate choice in two experiments: (1) measuring how males modified the time they invested in courtship based solely on female reproductive value, and (2) determining whether males varied the amount of time they invested in courting females of varying sizes but similar reproductive value. In the first experiment, we quantified the duration of male courtship displays when males were paired with females of differing levels of fecundity (nongravid, weakly gravid and strongly gravid). Males displayed longest for females of high reproductive value (strongly gravid females) and less for weakly gravid and nongravid females. In the second experiment, we showed that males paired sequentially with different-sized females of similar reproductive values displayed significantly more often to larger females (i.e. male effort positively correlated with female size). In conclusion, male P. shermani are one of the few vertebrates known to modify their display behaviour based on female mate quality, and visual signs, such as size, may provide honest indicators of fitness.