Life histories and ecotype conservation in an adaptive vertebrate: Genetic constitution of piscivorous brown trout covaries with habitat stability

Abstract

Ecotype variation in species exhibiting different life history strategies may reflect heritable adaptations to optimize reproductive success, and potential for speciation. Traditionally, ecotypes have, however, been defined by morphometrics and life history characteristics, which may be confounded with individual plasticity. Here, we use the widely distributed and polytypic freshwater fish species brown trout (Salmo trutta) as a model to study piscivorous life history and its genetic characteristics in environmentally contrasting habitats; a large lake ecosystem with one major large and stable tributary, and several small tributaries. Data from 550 fish and 13 polymorphic microsatellites (H e = 0.67) indicated ecotype‐specific genetic differentiation (θ = 0.0170, p < .0001) among Bayesian assigned small riverine resident and large, lake migrating brown trout (>35 cm), but only in the large tributary. In contrast, large trout did not constitute a distinct genetic group in small tributaries, or across riverine sites. Whereas life history data suggest a small, river resident and a large migratory piscivorous ecotype in all studied tributaries, genetic data indicated that a genetically distinct piscivorous ecotype is more likely to evolve in the large and relatively more stable river habitat. In the smaller tributaries, ecotypes apparently resulted from individual plasticity. Whether different life histories and ecotypes result from individual plasticity or define different genetic types, have important consequence for conservation strategies.

Anadromy, potamodromy and residency in brown trout Salmo trutta: the role of genes and the environment

“…Based on size at maturity, lake and sea feeding is superior to remaining within the river, albeit the relative importance of lake and sea feeding varies among catchments. If lacustrine S. trutta become piscivorous (Campbell, ; Wollebaek et al ., ), they can reach a larger size than anadromous conspecifics. Thus, in both Britain and Ireland, the largest rod‐caught piscivorous lacustrine S. trutta to date have had a greater mass than the largest anadromous S. trutta (Ferguson et al ., ), although the abundance of prey fish is such that only a small proportion of individuals can adopt piscivory (Campbell, ; Hughes et al ., ), compared with the greater abundance of prey fish at sea.…”

Alternative routes to piscivory: Contrasting growth trajectories in brown trout (Salmo trutta) ecotypes exhibiting contrasting life history strategies

“…It appears that in some cases both of these can occur in the same system. Wollebaek et al, (2018) for example, found genetic differentiation between piscivores and invertebrate feeders only in large tributaries and not in smaller ones of same catchment. These authors suggest that a genetically distinct piscivorous ecotype might be more likely to evolve in the relatively more stable large river habitat.…”

Unique sympatric quartet of limnetic, benthic, profundal and piscivorous brown trout populations resolved by 3D sampling and focused molecular marker selection

“…Given that ferox forms have also been found elsewhere to be genetically distinct from other co-occurring trout (Duguid et al, 2006;Ferguson & Taggart, 1991), the evidence for a distinct ferox population in Loch Laidon is compelling. However, a recent paper suggests that feroxlike forms can also arise within genetic populations in some situations (Wollebaek, Heggenes, & Roed, 2018).…”