Evidence for alternative male morphs in a Tanganyikan cichlid fish

Teleost fishes show tremendous variation in breeding systems. In particular, indeterminate growth and external fertilization create great disparities in reproductive success among males, which drive the evolution of male reproductive polymorphisms. Here, we present evidence for alternative male reproductive tactics in Neolamprologus modestus, a substrate- spawning African cichlid fish. We observed two types of males in our study site: 1) males that guarded large territories comprised of smaller sub-territories of several females; and 2) males that did not hold territories and were vigorously attacked by the guarding males upon intrusion into the guarding male’s territory. We hypothesized that these intruder males constitute an alternative male phenotype. To test this prediction, we collected both territorial males and these  intruder males to determine if there were differences in overall body size, gonad size, age, orhormone profiles between the two male phenotypes that would be consistent with alternative eproductive tactics in this species. We also collected guarded offspring from territorial male and female pairs to determine if there was any extra-pair paternity in N. modestus that could indicate  the possibility of alternative reproductive tactics. We found that intruder males were significantly smaller in body size and had significantly larger testes in absolute and relative mass compared with territorial paired males. While we assigned no paternity to any collected intruder males, we found that extra-pair paternity occurred in 8/12 collected broods and accounted fo approximately 27% of all offspring across all broods. Finally, the two sets of males did not differ significantly in age or in circulating androgen levels, suggesting that individuals may not changemorphs within their lifetime, but instead may adopt distinct life history strategies. Collectivelywe provide strong evidence that intruder N. modestus males represent an alternative small-bodiedmale morph that may practice alternative reproductive tactics