Differential gene expression associated with behavioral variation in ecotypes of Lake Superior brook trout (Salvelinus fontinalis)

Associations between behaviors and the development of different life history tactics have been documented in several species of salmon, trout, and charr. While it is well known that such behaviors are heritable the genes and molecular pathways connected to these behaviors remain unknown. We used an RNA-seq approach to identify genes and molecular pathways differentially regulated in brain tissue between "shy" and "bold" brook trout (Salvelinus fontinalis). A small number of genes were differentially expressed between the behavioral types at several months after hatching and two years of age. Pathway analysis revealed that EIF2 signaling differed consistently between shy and bold individuals suggesting large-scale differences in protein synthesis between behavioral types in the brain. Additionally, the RNA-seq data were used to find polymorphisms within the brook trout genome and a GWAS approach was used to test for statistical associations between genetic variants and behavior type. One allele located in a transcription factor (TSHZ3) contained a protein-coding non-synonymous SNP suggesting that functional variation within TSHZ3 is connected to the development of different behaviors. These results suggest that the molecular basis of behavioral development is complex and due to the differential expression of many genes involved in a wide-range of different molecular pathways.

Natural selection for body shape in resource polymorphic Icelandic Arctic charr

Resource polymorphisms exhibit remarkable intraspecific diversity and in many cases are expected to be maintained by diversifying selection. Phenotypic trade-offs can constrain morphologically intermediate individuals from effectively exploiting both alternate resources, resulting in ecological barriers to gene flow. Determining if and how phenotypic trade-offs cause fitness variation in the wild is challenging because of phenotypic and environmental correlations associated with alternative resource strategies. We investigated multiple pathways through which morphology could affect organismal performance, as measured by growth rate, and whether these effects generate diversifying selection in polymorphic Icelandic Arctic charr (Salvelinus alpinus) populations. We considered direct effects of morphology on growth and indirect effects via trophic resource use, estimated by stable isotopic signatures, and via parasitism associated with trophic resources. We sampled over 3 years in (lakes) Thingvallavatn and Vatnshlíðarvatn using the extended selection gradient path analytical approach and estimating size-dependent mortality. We found evidence for diversifying selection only in Thingvallavatn: more streamlined and terminally mouthed planktivore charr experienced greater growth, with the opposite pattern in small benthic charr. However, this effect was mediated by parasitism and nontrophic pathways, rather than trophic performance as often expected. Detection of between-morph differences in the presence (Vatnshlíðarvatn) and direction (Thingvallavatn) of size-dependent mortality, together with nontrophic effects of shape, suggests that a morphological trophic performance explanation for polymorphism is insufficient. This rare insight into selection during early diversification suggests that a complex of interacting local factors must be considered to understand how phenotype influences fitness, despite morphological variation reflecting intuitive trade-off explanations.

Rainbow trout personality: individual behavioural variation in juvenile Oncorhynchus mykiss

We evaluated the variation in dispersal, exploration, and aggression across time in juvenile progeny produced from wild caught rainbow trout (Oncorhynchus mykiss) at a critical developmental shift associated with the highest mortality in fish. By testing multiple ecologically relevant behaviours repeatedly in the same individuals, we simultaneously tested multiple hypotheses regarding personality, plasticity, and behavioural syndromes to better understand the innate behavioural variation in a population containing both migratory and resident life histories. There were consistent behavioural differences, or personality, between individuals across time, for dispersal, aggression, and exploration, unrelated to size or sex. The significant repeatabilities (0.10–0.46) indicate that these traits are potentially heritable. Also, we found both habituation in all behaviours and significant differences between individuals in the rate of that habituation, despite no evidence of a behavioural syndrome. The identification of this individual level variation is a step towards understanding which heritable traits selection could influence.