No terminal investment in pipefish males: only young males exhibit risk-prone courtship behavior

Abstract

Animals are expected to trade-off current and future reproduction in order to maximize lifetime reproductive success. Old individuals may accept higher risks during courtship and mate choice as their residual reproductive value (RRV) diminishes (the terminal investment hypothesis). Alternatively, young individuals may be forced to take higher risks during courtship to compensate for their lower competitiveness and/or attractiveness (the compensation hypothesis). In this study, we used the sex-role reversed pipefish Syngnathus typhle to test how mate choice and courtship behavior of males with different RRV were affected by an increase in predation risk. Males of different ages were given the opportunity to court and choose between 2 partners. In half of the trials, a predator was present in a separate aquarium. We found no support for the terminal investment hypothesis: no difference in response to the increased predation risk by males of different ages was evident. In agreement with the compensation hypothesis, young males invested more in courtship behavior compared with older males. In addition, in the absence of a predator, we found that a high female activity was important for male mate choice decisions. During increased predation risk, this relationship was, however, reversed and males preferred less active, and thus less conspicuous, partners. This suggests that both female activity and size are important factors for male mating decisions in this species and that these decisions mainly are affected by predation risk and advantages in mate acquisition.