Plastic response to a novel environment by exotic anadromous rainbow trout (Oncorhynchus mykiss)

LIBEROFF, ANA LAURA; RIVA ROSSI, CARLA; CIANCIO, JAVIER; PASCUAL, MIGUEL

Mar del Plata

Congreso; 2nd World Conference on Biological Invasions and Ecosystem Functioning; 2011

Salmonid species have successfully established exotic populations around the globe. Their  high level of diversity and phenotypic plasticity might have played a key role on establishment in suitable new environments and adaptation in response to new selective pressures. However, anadromous forms (e.g. ocean migratory) have been less successful in novel environments reflecting the problems of organisms with more complex life cycles to adapt. Rainbow trout (Oncorhynchus mykiss) introduced in the Santa Cruz river is the first known case of development of a self sustained partial anadromous population where anadromous and freshwater resident forms coexist. These fish differ from their native parental populations in several life history traits, most notably in their high level of iteroparity (the ability to repeat spawning). In general, iteroparity occurs at the expense of female gonadal investment, itself closely related to juvenile survivorship and early growth. However, this study shows that in Santa Cruz fish maternal investment remains high and maternal effects (non-genetic heritance of characters) on anadromous progeny is significant, reflecting in better early condition and growth of anadromous descendents as compared to resident offspring. Whether these distinctive traits are pure phenotypic plasticity or the result of genetic adaptation is still unknown. Regardless, Santa Cruz river and surrounding marine areas appear to provide matching conditions for requirements of the anadromous life cycle. Because migration to the ocean in Santa Cruz river fish appears to be triggered by high juvenile growth, maternal effects might have played a key role during initial colonization stages, speeding up the development of anadromy.