COS 137-3 - CANCELLED - Body shape, growth rate, and off-plane phenotypes induced in mosquitofish by the functionally distinct predators bluegill sunfish and dragonfly naiads

Background/Question/Methods

Repeated presentation of divergent selection can drive replicated diversification among populations, often similarly for multiple species. A commonly replicated pattern in fishes is predator-associated burst speed (PABS) ecophenotypy involving a reduced head and trunk and enlarged caudal region. PABS morphology increases burst speed and ability to escape pursuit predators. In the absence of pursuit predators, non-PABS morphology can improve endurance swimming and attractiveness to mates. PABS morphology is under at least partial genetic control and has evolved multiple times. It is unknown whether additional selective agents such as alternative predators exert a cost relevant to the evolutionary maintenance of PABS ecophenotypy. It is also unclear whether phenotypic plasticity plays a role in determining PABS phenotypy.

We reared mosquitofish (Gambusia affinis) in a factorial combination of the presence or absence of bluegill sunfish (Lepomis macrochirus) and dragonfly naiads. After 63 days of rearing, mosquitofish size and shape were assessed with geometric morphometrics.

We addressed whether either predator induced morphological differentiation in mosquitofish and whether simultaneous exposure to the predators induced additive or nonadditive phenotypic intermediacy or entirely novel aspects of morphology. We considered whether naiad-induced morphology would be likely to exert a defensive cost with respect to bluegill sunfish.

Results/Conclusions

Bluegill sunfish induced in mosquitofish relative to controls 36 % smaller size, PABS ecophenotypy, posterior displacement of the dorsal fin on the peduncle, and shortened anal fin bases. Naiads induced upturned heads and broadened anal fin bases. Presence of both predators produced in part intermediacy between the pure predator effects but also unique elements off the plane of expectations for intermediacy. Bluegill-induced morphology would be adaptive plasticity in the PABS functional paradigm. There was no functional paradigm to predict value of naiad-induced phenotypy. However, presence of naiads with bluegill sunfish interfered with production of PABS morphology and would reduce defense with respect to attack by bluegill. Predators in combination induced both intermediate and unique shape effects. Unique effects suggested dissonance between developmental pathways or phenotypy uniquely fit to simultaneous predator exposure.