Alternative developmental pathways and the propensity to migrate: a case study in the Atlantic salmon (original) (raw)
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Divergent compensatory growth responses within species: linked to contrasting migrations in salmon
Oecologia, 2007
Animals often exhibit accelerated or ''compensatory'' growth (CG) after periods of environmentally induced growth depression, raising important questions about how they cope with environmental variability. We tested an underexplored hypothesis regarding the evolutionary consequences of CG; namely, that natural populations differ in CG responses. Common-garden experiments were used to compare subadult growth following food restriction between groups (control, treatment) of two Atlantic salmon (Salmo salar) populations and their firstgeneration (F 1 ) hybrids. The populations are found at similar latitudes but characterized by differences in migration distance. We predicted that long-distance migrants would better maintain growth trajectories following food restriction than short-distance migrants because they:
Canadian Journal of Fisheries and Aquatic Sciences, 2015
Although studies addressing natural selection have primarily focused on additive genetic effects because of their direct relationship with responses to selection, nonadditive genetic and maternal effects can also significantly influence phenotypes. We partitioned the phenotypic variance of survival and fitness-related traits in juvenile Atlantic salmon (Salmo salar) from three allopatric populations (LaHave, Sebago, and Saint-Jean) into additive genetic, nonadditive genetic, and maternal environmental effects using a full-factorial breeding design. We also modelled the potential increase in offspring performance if nonrandom mating (e.g., mate choice) is considered instead of random mating. The three populations exhibited significant differences in trait values as well as the genetic architecture of the traits. Nevertheless, nonadditive genetic and maternal environmental effects tended to be larger than the additive genetic effects. There was also a shift from maternal environmental to genetic effects during development in two of the populations. That is, maternal environmental effects were larger at early (egg and alevin) life stages, whereas nonadditive effects were larger at the later (fry) life stage. The amount of additive genetic effects was small, suggesting the traits will respond slowly to selection. We discuss how different maternal environmental effects across years may influence the genetic architecture of offspring traits.
A critical review of adaptive genetic variation in Atlantic salmon: implications for conservation
Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect on fitness. Thus, body size in Atlantic salmon tends to be positively correlated with freshwater and marine survival, as well as with fecundity, egg size, reproductive success, and offspring survival. By contrast, the fitness implications of variation in behavioural traits such as aggression, sheltering behaviour, or timing of migration are largely unknown. The adaptive significance of molecular variation in salmonids is also scant and largely circumstantial, despite extensive molecular screening on these species. Adaptive variation can result in local adaptations (LA) when, among other necessary conditions, populations live in patchy environments, exchange few or no migrants, and are subjected to differential selective pressures. Evidence for LA in Atlantic salmon is indirect and comes mostly from ecological correlates in fitness-related traits, the failure of many translocations, the poor performance of domesticated stocks, results of a few common-garden experiments (where different populations were raised in a common environment in an attempt to dissociate heritable from environmentally induced phenotypic variation), and the pattern of inherited resistance to some parasites and diseases. Genotype x environment interactions occur for many fitness traits, suggesting that LA might be important. However, the scale and extent of adaptive variation remains poorly understood and probably varies, depending onhabitat heterogeneity, environmental stability and the relative roles of selection and drift. As maladaptation often results from phenotype-environment mismatch, weargue that acting as if populations are not locally adapted carries a much greater risk of mismanagement than acting under the assumption for local adaptations when there are none. As such, an evolutionary approach to salmon conservation is required, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered. This may require minimising alterations to native genotypes and habitats to which populations have likely become adapted, but also allowing for population size to reach or extend beyond carrying capacity to encourage competition and other sources of natural mortality.Key words: adaptive variation, local adaptation, heritabilities, phenotypic plasticity, genotype-by-environment interaction, fitness, conservation, Atlantic salmon,salmonids.
Though genetic diversity is necessary for population persistence in rapidly changing environments, little is known about how climate-warming influences patterns of intra-population genetic variation. For a pink salmon population experiencing increasing temperatures, we used temporal genetic data (microsatellite = 1993, 2001, 2009; allozyme = 1979, 1981, 1983) to quantify the genetic effective population size (N e ) and genetic divergence due to differences in migration timing and to estimate whether these quantities have changed over time. We predicted that temporal trends toward earlier migration timing and a corresponding loss of phenotypic variation would decrease genetic divergence based on migration timing and N e . We observed significant genetic divergence based on migration timing and genetic heterogeneity between early-and late-migrating fish. There was also some evidence for divergent selection between early-and late-migrating fish at circadian rhythm genes, but results varied over time. Estimates of N e from multiple methods were large (>1200) and N e /N c generally exceeded 0.2. Despite shifts in migration timing and loss of phenotypic variation, there was no evidence for changes in within-population genetic divergence or N e over the course of this study. These results suggest that in instances of population stability, genetic diversity may be resistant to climate-induced changes in migration timing.
Genetic architecture of survival and fitness-related traits in two populations of Atlantic salmon
Heredity, 2013
The additive genetic effects of traits can be used to predict evolutionary trajectories, such as responses to selection. Non-additive genetic and maternal environmental effects can also change evolutionary trajectories and influence phenotypes, but these effects have received less attention by researchers. We partitioned the phenotypic variance of survival and fitnessrelated traits into additive genetic, non-additive genetic and maternal environmental effects using a full-factorial breeding design within two allopatric populations of Atlantic salmon (Salmo salar). Maternal environmental effects were large at early life stages, but decreased during development, with non-additive genetic effects being most significant at later juvenile stages (alevin and fry). Non-additive genetic effects were also, on average, larger than additive genetic effects. The populations, generally, did not differ in the trait values or inferred genetic architecture of the traits. Any differences between the populations for trait values could be explained by maternal environmental effects. We discuss whether the similarities in architectures of these populations is the result of natural selection across a common juvenile environment.
Environmental and genetic influences on fitness-related traits in a hatchery coho salmon population
Canadian Journal of Fisheries and Aquatic Sciences, 2021
Many natural and managed organisms will require substantial functional genetic variation to respond to selection in the face of rapid environmental change. Pacific salmon have experienced strong fluctuations in critical fitness traits over the past five decades. We examined genetic and phenotypic variability over three generations in a pedigreed hatchery population of coho salmon (Oncorhynchus kisutch) by monitoring seven fitness-related traits. Three-year-old adult return numbers varied more than fivefold, and jack (2-year-old males) numbers varied 13-fold. Body sizes of Inch Creek coho salmon decreased consistently such that fish were only 40.7% as heavy in 2015 as in 2006, and female reproductive traits also decreased. During the study period, the majority of families produced returning adult progeny, and effective population size was relatively constant. Heritability estimates for phenotypic traits were significantly greater than zero except for condition factor, and the estimat...
Marine Ecology Progress Series, 2010
Chinook salmon is an anadromous species that varies in size at freshwater emigration, which is hypothesized to increase population resiliency under variable environmental regimes. In California's Central Valley (USA), the majority of naturally spawned juveniles emigrate in 2 pulses: small juveniles (referred to as fry), typically ≤55 mm fork length (FL), emigrate from natal streams in February-March, whereas larger juveniles (smolts), typically > 75 mm FL, emigrate in mid-April-May. In some river systems, there is a smaller pulse of emigrants of intermediate size (parr), typically 56 to 75 mm FL. Although the relative contribution of these migratory phenotypes to the adult population is unknown, management activities focus on survival of larger emigrants and most artificially produced fish (98%) are released from hatcheries at parr and smolt sizes. We reconstructed individual length at freshwater emigration for a sample of adult Central Valley Chinook salmon from 2 emigration years using chemical (Sr:Ca and Ba:Ca) and structural otolith analyses. The adult sample was comprised of individuals that emigrated as parr (mean = 48%), followed by smolts (32%) and fry (20%). Fry-sized emigrants likely represent natural production because fish ≤55 mm FL comprise < 2% of the hatchery production. The distribution of migratory phenotypes represented in the adult sample was similar in both years despite apparent interannual variation in juvenile production, providing evidence for the contribution of diverse migratory phenotypes to the adult population. The contribution of all 3 migratory phenotypes to the adult population indicates that management and recovery efforts should focus on maintenance of life-history variation rather than the promotion of a particular phenotype.
Evolutionary Applications, 2015
Understanding the extent, scale and genetic basis of local adaptation is important for conservation and management. Its relevance in salmonids at microgeographic scales, where dispersal (and hence potential gene flow) can be substantial, has however been questioned. Here we compare the fitness of communally-reared offspring of local and foreign Atlantic salmon Salmo salar from adjacent Irish rivers and reciprocal F 1 hybrid crosses between them, in the wild 'home' environment of the local population. Experimental groups did not differ in wild smolt output but a catastrophic flood event may have limited our ability to detect freshwater performance differences, which were evident in a previous study. Foreign parr exhibited higher, and hybrids intermediate, emigration rates from the natal stream relative to local parr, consistent with genetically-based behavioural differences. Adult return rates were lower for the foreign compared to the local group. Overall lifetime success of foreigners and hybrids relative to locals was estimated at 31% and 40% (mean of both hybrid groups), respectively. The results imply a genetic basis to fitness differences among populations separated by only 50km, driven largely by variation in smolt to adult return rates. Hence even if supplementary stocking programs obtain broodstock from neighbouring rivers, the risk of extrinsic outbreeding depression may be high.
Environmental Biology of Fishes, 2017
Environmental heterogeneity may strongly influence the amount of heritable variation in phenotypic traits and thus affect evolutionary responses to natural selection. However, the question of whether heritabilities change across environmental gradients has received little empirical attention, particularly for wild vertebrates. We tested whether levels of heritable variation in body size, morphology and survival of juvenile Atlantic salmon (Salmo salar) differed between water flow regimes. We exposed individuals of known genetic relationships to rearing habitats characterized by slow and rapid water flows in a field experiment. We found that the additive genetic variation in body size tended to be higher for individuals reared under rapid water flows. By contrast, the heritabilities of other morphological traits were not consistently higher in either water flow. We also Electronic supplementary material The online version of this article (