Sperm phenotypic plasticity in a cichlid: a territorial male's counterstrategy to spawning takeover

Studies of sperm competition in species with alternative reproductive tactics (ARTs) often pay attention to the differences in investments in sperm between sneakers facing a higher sperm competition risk and bourgeois males facing a lower risk. Here, we examined within-tactic as well as among-tactic variations in sperm investments in the Lake Tanganyika shell-brooding cichlid Telmatochromis vittatus, a species with 2 types of parasitic tactics. Territorial male T. vittatus suffer reproductive parasitism by both smaller sneaker males and larger pirate males ("pirates" take over the spawning event during which territorial males perform sneaking as a counterstrategy). We hypothesized that both territorial males living under the risk of pirates and sneakers face increased risk of sperm competition and therefore should produce high-quality sperm compared with both territorial males that experienced no piracy risk and pirates. As expected, field studies showed that the former 2 males produced longer lived sperm than the other males. Aquarium experiments demonstrated that a visual stimulus of a pirate was enough to induce an increase in sperm longevity in territorial males compared with when no such stimulus was given. These results indicate that territorial male T. vittatus can plastically adjust at least one sperm quality trait in response to piracy risk. Moreover, long-term monitoring of males in the field showed that small territorial males grow into large territorial males and finally into pirates, so ARTs are not fixed over life. Accordingly, male T. vittatus appear to ontogenetically change their sperm longevity in response to size-dependent sperm competition risks. Copyright 2010, Oxford University Press.