Intraspecific variation in diet, growth, and morphology of landlocked Galaxias maculatus during its larval period: the role of food availability and predation risk

Abstract

Food availability and predation risk have been shown to affect phenotypes during early life history of fishes. Galaxias maculatus, a small fish widely distributed around the southern hemisphere, clearly exhibits a complex trade-off between feeding and predation avoidance during growth over the larval period. We studied the effect of different environmental variables on diet, growth, mortality, and morphology through field surveys and data revision in the literature for limnetic G. maculatus larvae in five oligotrophic lakes of Patagonia. Both number of food categories and prey ingested by larvae were directly related to zooplankton density. Larval growth rate was related with zooplankton density and temperature. Lakes with high zooplankton densities and low predation risk had larvae with deeper bodies and shorter caudal peduncles, while in lakes with less food and high predation risk larvae were slender with shallower bodies and longer peduncles. Food availability and predation risk seem to operate on the swimming performance of G. maculatus larvae through the slenderness of the body and the length of the caudal peduncle. The observed phenotypic variation in growth and morphology could be a key feature that has allowed this species to successfully colonize a wide variety of environments in the southern hemisphere.

Stable isotope analysis of trophic structure, energy flow and spatial variability in a large ultraoligotrophic lake in Northwest Patagonia

“…These items were chosen because they are directly or indirectly part of the consumer's diet and because they were sampled in the three sites. Salmonids and creole perch prey on crayfish (Juncos et al, 2013(Juncos et al, , 2015; and, although they do not feed directly on zooplankton, they prey over the main planktivorous fish in the lake, the small puyen (Cervellini et al, 1993;Reissig et al, 2003;Barriga et al, 2012;Juncos et al, 2015). The SIAR model also requires incorporation of a Trophic Enrichment Factor (TEF) for the food web as well as C and N elemental concentrations for dietary sources (obtained along with the δ 13 C and δ 15 N values from the laboratory).…”

“…Small puyen is the main planktivorous species of the lake, with the juveniles consuming mainly zooplankton and adults combining pelagic and littoral prey such as chironomid larvae (Cervellini et al, 1993;Reissig et al, 2003;Barriga et al, 2012;Milano et al, 2013). These differences in diet are reflected in the enriched 15 N observed in the juveniles of small puyen.…”

“…Due to their high mobility, fish function as a strong link between bentho-littoral and pelagic habitats by feeding on prey from both habitats (Schindler and Scheuerell, 2002;Vander Zanden and Vadeboncoeur, 2002;Barriga et al, 2012;Reissig et al, 2015). In Patagonian lakes, exotic salmonids, particularly rainbow trout, play a major role in habitat coupling through predation in both bentho-littoral and pelagic habitats (Juncos et al, 2013).…”

“…However, there has been little research on whole food-web structure and the role of fish in connecting habitats within this oligotrophic lake. In particular, two native fish, the galaxiids Galaxias platei and Galaxias maculatus, are also an important link between bentho-littoral and pelagic habitats (Barriga et al, 2012;Reissig et al, 2015). This occurs in two ways: Galaxias spp.…”

Niche segregation facilitates coexistence between native and introduced fishes in a deep Patagonian lake

“…In this context, we can consider G. maculatus as a keystone species, without which the ecosystem could have been severely impacted after salmonid introduction. The pre-adaptation of this fish to predation , combined with its plasticgeneralist life cycle (Barriga et al, 2012) and its high annual production (Vigliano et al, 2009), could enable it to act as a buffer, thus alleviating the impact of introductions, despite the high predation pressures involved. Galaxias maculatus seems to represent a permanent food supply for both native and salmonid fish predators, limiting the negative interactions generated by fish introductions, and thus promoting the coexistence of native fish with exotic salmonids.…”