Multimodal signaling in fiddler crab: waving to attract mates is condition-dependent but other sexual signals are not

Abstract

Many animals utilize multimodal signals for mate attraction and courtship. Each one of these signals could possibly provide information to receivers about aspects of the sender’s quality. Demonstrating condition-dependence of each of the multiple signals may shed light on which are related to the sender’s quality. This is because condition-dependence can reliably convey the sender’s quality due to the costs associated with signal production; only males in good condition are able to pay the costs of producing the signal. Male fiddler crabs use multimodal signals to attract females from a distance (they build semidomes and produce attraction waves) and for courting the females once they have approached (they produce courtship waves and substrate vibrations). Here, we investigate condition-dependence of the multimodal signals produced by the fiddler crab Austruca lactea. We manipulated the food levels of focal crabs (added food, control, removed food) for approximately 2 weeks in the field. We then compared the intensity of the male’s signals and the male’s blood lactate level. We found that the number of attraction waves significantly differed among treatments; the number of the waves increased with food availability. Blood lactate concentration also increased in the food-addition treatment. However, other signal traits were not significantly affected by the level of food available. These results suggest that adding food facilitated an increase in the male’s ability to produce attraction waves, and this would impose higher energy costs. In this species, only attraction waving reflects male nutritional condition and so could potentially be used by females to distinguish between low- and high-quality males. Animals often employ multimodal signals for mating. Here, we examine whether each of the multimodal signals is dependent on male condition in Austruca lactea. We compared the intensity of their multimodal signals, i.e., semidome, attraction waving, courtship waving, and vibration, among three nutritional treatments (food-addition, control, food-removal). Energy costs were additionally estimated by measuring blood lactate level. The number of attraction waves and the blood lactate level increased in food-adding treatment, while the frequency of semidome construction, rate of courtship waving, and pulse interval in vibrations were not influenced by nutritional condition. This suggests that additional food improved male condition and increased the number of attraction waving. Only attraction waving potentially conveys information about the male nutritional quality. Attraction waves could potentially be used by females to distinguish between low- and high-quality males.