Genetic architecture of gene transcription in two Atlantic salmon (Salmo salar) populations.

Gene expression regulation has an important role in short-term acclimation and long-term adaptation to changing environments. However, the genetic architecture of gene expression has received much less attention than that of traditional phenotypic traits. In this study, we used a 5 × 5 full-factorial breeding design within each of two Atlantic salmon (Salmo salar) populations to characterize the genetic architecture of gene transcription. The two populations (LaHave and Sebago) are being used for reintroduction efforts into Lake Ontario, Canada. We used high-throughput quantitative real-time PCR to measure gene transcription levels for 22 genes in muscle tissue of Atlantic salmon fry. We tested for population differences in gene transcription and partitioned the transcription variance into additive genetic, non-additive genetic and maternal effects within each population. Interestingly, average additive genetic effects for gene transcription were smaller than those reported for traditional phenotypic traits in salmonids, suggesting that the evolutionary potential of gene transcription is lower than that of traditional traits. Contrary to expectations for early life stage traits, maternal effects were small. In general, the LaHave population had higher additive genetic effects for gene transcription than the Sebago population had, indicating that the LaHave fish have a higher adaptive potential to respond to the novel selection pressures associated with reintroduction into a novel environment. This study highlights not only the profound variation in gene transcription possible among salmonid populations but also the among-population variation in the underlying genetic architecture of such traits.

Effects of competition on fitness-related traits.

While interspecific competition is prevalent in natural systems, we do not yet understand how it can influence an individual's phenotype within its lifetime and how this might affect performance. Morphology and swimming performance are two important fitness-related traits in fishes. Both traits are essential in acquiring and defending resources as well as avoiding predation. Here, we examined if interspecific competition could induce changes in morphology and affect the swimming performance of two strains of juvenile Atlantic salmon (Salmo salar). We imposed competitive scenarios on the fish using artificial streams containing different combinations of four interspecific competitors. Exposure to interspecific competitors induced morphological changes over time, through the development of deeper bodies, whereas controls free of interspecific competitors developed more fusiform body shapes. Furthermore, swimming performance was correlated to fusiform morphologies and was weaker for Atlantic salmon in competitive scenarios vs. CONTROLS: This implies that interspecific competition has direct effects on these fitness-related traits in Atlantic salmon. To the best of our knowledge, this is the first time that morphology, an important fitness-related trait linked to swimming performance, has been shown to be negatively impacted through interactions with an interspecific competitor.

Genetic architecture and maternal contributions of early-life survival in lake trout Salvelinus namaycush.

The influences of additive, non-additive and maternal effects on early survival (uneyed embryo survival, eyed embryo survival, alevin survival and overall survival to first feeding) were quantified in lake trout Salvelinus namaycush using a 7 × 7 full-factorial breeding design. Maternal effects followed by non-additive genetic effects explained around one third of the phenotypic variance of the survival traits. Although the amount of additive genetic effects were low (<1%), suggesting a limited potential of the traits to respond to new selection pressures, how maternal and non-additive genetic effects may respond to selection under certain circumstances are discussed.

Predictability of multispecies competitive interactions in three populations of Atlantic salmon Salmo salar.

Juvenile Atlantic salmon Salmo salar from three allopatric populations (LaHave, Sebago and Saint-Jean) were placed into artificial streams with combinations of four non-native salmonids: brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss, Chinook salmon Oncorhynchus tshawytscha and coho salmon Oncorhynchus kisutch. Non-additive effects, as evidenced by lower performance than predicted from weighted summed two-species competition trials, were detected for S. salar fork length (LF ) and mass, but not for survival, condition factor or riffle use. These data support emerging theory on niche overlap and species richness as factors that can lead to non-additive competition effects.