Search

Migration in animals and associated adaptations to contrasting environments are underpinned by complex genetic architecture. Here, we explore the genomic basis of facultative anadromy in brown trout (Salmo trutta), wherein some individuals migrate to sea while others remain resident in natal rivers, to better understand how alternative migratory tactics (AMTs) are maintained evolutionarily. To identify genomic variants associated with AMTs, we sequenced whole genomes for 194 individual trout from five anadromous–resident population pairs, situated above and below waterfalls, in five different Irish rivers. These waterfalls act as natural barriers to upstream migration and hence we predicted that loci underpinning AMTs should be under similar divergent selection across these replicate pairs. A sliding windows based analysis revealed a highly polygenic adaptive divergence between anadromous and resident populations, encompassing 329 differentiated genomic regions. These regions were associated with 292 genes involved in various processes crucial for AMTs, including energy homeostasis, reproduction, osmoregulation, immunity, circadian rhythm and neural function. Furthermore, examining patterns of diversity we were able to link specific genes and biological processes to putative AMT trait classes: migratory‐propensity, migratory‐lifestyle and residency. Importantly, AMT outlier regions possessed higher genetic diversity than the background genome, particularly in the anadromous group, suggesting balancing selection may play a role in maintaining genetic variation. Overall, the results from this study provide important insights into the genetic architecture of migration and the evolutionary mechanisms shaping genomic diversity within and across populations. [ABSTRACT FROM AUTHOR]

Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focussing on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. Application of a theoretical model indicates that the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.

Although historical records of introductions that trigger successful biological invasions are common, subsequent patterns of dispersal and colonisation routes are unclear. We use microsatellites to examine genetic population structuring of established invasive brown trout (Salmo trutta) populations in Newfoundland, Canada, for evidence of 'natural' dispersal, humanmediated introductions, and colonisation routes. We also explored ancestry of contemporary populations relative to presumed progenitors. Results analysed using STRUCTURE, DAPC, a NJ tree and [F.sub.ST] comparisons support records of historical introductions; current Newfoundland populations are largely descended from Scottish stock, with St. John's the primary introduction site. Subsequent dispersal of these trout was facilitated principally by anadromy, largely consistent with a classic stepping-stone model, with significant isolation-by-distance. With one exception, dispersal along the north and south coasts of the Avalon peninsula appears to be natural and independent, involving stochastic processes resulting in unique outcomes for population composition. This study is a good example of dispersal patterns during a contemporary invasion underscoring the potential for non- anadromous founders to re-express anadromy, facilitating colonization of distant sites. Bien que les cas documentes d'introductions qui declenchent des envahissements biologiques durables soient repandus, les motifs de dispersion et les voies de colonisation subsequents ne sont pas bien etablis. Nous utilisons les microsatellites pour examiner la structure genetique de populations de truites brunes (Salmo trutta) envahissantes etablies a Terre-Neuve (Canada) afin de chercher des indices de dispersion << naturelle >> et d'introductions mediees par l'humain et de l'information sur d'eventuelles voies de colonisation. Nous explorons egalement l'ascendance de populations actuelles par rapport a des progeniteurs presumes. Les resultats analyses avec STRUCTURE, DAPC, un arbre phylogenetique et la comparaison de [F.sub.ST] appuient les cas documentes passes d'introductions; les populations actuelles a Terre-Neuve descendent en bonne partie du stock ecossais, St. John's en constituant le principal lieu d'introduction. La dispersion subsequente de ces truites a principalement ete facilitee par l'anadromie, ce qui concorde assez bien avec un modele classique d'etapes intermediates, l'isolement par la distance etant aussi importante. A une exception pres, les dispersions le long des cotes nord et sud de la peninsule d'Avalon semblent etre naturelles et independantes, mues par des processus stochastiques qui ont produit des resultats uniques sur le plan de la composition des populations. L'etude fournit un bon exemple de motifs de dispersion durant un envahissement moderne, soulignant la possibilite pour des fondateurs non anadromes de reexprimer une anadromie, facilitant ainsi la colonisation de sites distaux. [Traduit par la Redaction], Introduction The distribution of species through time and space is the result of the complex interplay between evolutionary history and everchanging ecological factors. Identifying the colonisation pathways and mechanisms involved [...]

Explaining the evolution of sex differences in cooperation remains a major challenge. Comparative studies highlight that offspring of the more philopatric sex tend to be more cooperative within their family groups than those of the more dispersive sex but we do not understand why. The leading "Philopatry hypothesis" proposes that the more philopatric sex cooperates more because their higher likelihood of natal breeding increases the direct fitness benefits of natal cooperation. However, the "Dispersal trade-off hypothesis" proposes that the more dispersive sex cooperates less because preparations for dispersal, such as extra-territorial prospecting, trade-off against natal cooperation. Here, we test both hypotheses in cooperatively breeding white-browed sparrow weavers (Plocepasser mahali), using a novel high-resolution automated radio-tracking method. First, we show that males are the more dispersive sex (a rare reversal of the typical avian sex difference in dispersal) and that, consistent with the predictions of both hypotheses, females contribute substantially more than males to cooperative care while within the natal group. However, the Philopatry hypothesis cannot readily explain this female-biased cooperation, as females are not more likely than males to breed within their natal group. Instead, our radio-tracking findings support the Dispersal trade-off hypothesis: males conduct pre-dispersal extra-territorial prospecting forays at higher rates than females and prospecting appears to trade-off against natal cooperation. Our findings thus highlight that the evolution of sex differences in cooperation could be widely attributable to trade-offs between cooperation and dispersal; a potentially general explanation that does not demand that cooperation yields direct fitness benefits. Why do the more philopatric sex tend to be more cooperative within family groups than the more dispersive sex? This study uses radio tracking of white-browed sparrow weavers to reveal that sex differences in cooperation can be attributable to sex differences in the direct costs of cooperation, arising from a trade-off between cooperation and dispersal. [ABSTRACT FROM AUTHOR]

The deliberate release of captive‐bred individuals, the accidental escape of domesticated strains, or the invasion of closely related conspecifics into wild populations can all lead to introgressive hybridization, which poses a challenge for conservation and wildlife management. Rates of introgression and the magnitude of associated demographic impacts vary widely across ecological contexts. However, the reasons for this variation remain poorly understood. One rarely considered phenomenon in this context is soft selection, wherein relative trait values determine success in intraspecific competition for a limiting resource. Here we develop an eco‐genetic model explicitly focussed on understanding the influence of such competitive interactions on the eco‐evolutionary dynamics of wild populations experiencing an influx of foreign/domesticated individuals. The model is applicable to any taxon that experiences natural or human‐mediated inputs of locally maladapted genotypes ('intrusion'), in addition to phenotype‐dependent competition for a limiting resource (e.g. breeding sites, feeding territories). The effects of both acute and chronic intrusion depended strongly on the relative competitiveness of intruders versus locals. When intruders were competitively inferior, density‐dependent regulation limited their reproductive success (ability to compete for limited spawning sites), which prevented strong introgression or population declines from occurring. In contrast, when intruders were competitively superior, this amplified introgression and led to increased maladaptation of the admixed population. This had negative consequences for population size and population viability. The results were sensitive to the intrusion level, the magnitude of reproductive excess, trait heritability and the extent to which intruders were maladapted relative to locals. Our findings draw attention to under‐appreciated interactions between phenotype‐dependent competitive interactions and maladaptive hybridization, which may be critical to determining the impact captive breeding programmes and domesticated escapees can have on otherwise self‐sustaining wild populations. [ABSTRACT FROM AUTHOR]

While evolutionary responses require heritable variation, estimates of heritability ([h.sup.2]) from wild fish populations remain rare. A 20-year molecular pedigree for a wild Scottish population of Atlantic salmon (Salmo salar) was used to investigate genetic contributions to (co)variation in two important, correlated, phenotypic traits: 'sea age' (number of winters spent at sea prior to spawning) and size-at-maturity (body length just prior to spawning). Sea age was strongly heritable ([h.sup.2] = 0.51) and size exhibited moderate heritability ([h.sup.2] = 0.27). A very strong genetic correlation ([r.sub.G] = 0.96) between these traits implied the same functional loci must underpin variation in each. Indeed, body size within sea ages had much lower heritability that did not differ significantly from zero. Thus, within wild S. salar populations, temporal changes in sea age composition could reflect evolutionary responses, whereas rapid changes of body size within sea ages are more likely due to phenotypic plasticity. These inheritance patterns will influence the scope of evolutionary responses to factors such as harvest or climate change and, hence, have management implications for salmonid populations comprising a mix of sea ages. Si une variation heritable est necessaire pour permettre des reactions evolutives, les estimations de l'heritabilite ([h.sup.2]) obtenues pour des populations sauvages demeurent rares. Un pedigree moleculaire de 20 ans pour une population sauvage ecossaise de saumons atlantiques (Salmo salar) a ete utilise pour etudier les contributions genetiques a la (co)variation de deux caracteres phenotypiques correles importants, a savoir <> (le nombre d'hivers passes en mer avant le frai) et la taille a la maturite (la longueur du corps juste avant le frai). L'age marin est fortement heritable ([h.sup.2] = 0,51) et la taille presente une heritabilite moderee ([h.sup.2] = 0,27). Une correlation genetique tres forte ([r.sub.G] = 0,96) entre ces caracteres indique que les memes sites fonctionnels doivent sous-tendre la variation des deux caracteres. En effet, la taille du corps pour des ages marins donnes presente une heritabilite beaucoup plus faible qui n'est pas significativement differente de zero. Ainsi, dans les populations sauvages de S. salar, les changements dans le temps de la composition des ages marins pourraient refleter des reactions evolutives, alors que des changements rapides de la taille du corps au sein de classes d'age marin sont plus probablement le fait d'une plasticite phenotypique. Ces motifs d'heredite influenceront la portee des reactions evolutives a des facteurs comme l'exploitation ou les changements climatiques, ce qui a des consequences pour la gestion de populations de salmonides composees d'un melange d'ages marins. [Traduit par la Redaction], Introduction Life-history traits such as age and size at first reproduction are typically expected to be under strong selection, given their close links with Darwinian fitness (Stearns 1992; Roff 2002). [...]

Global warming has been implicated in widespread demographic changes in Atlantic salmon Salmo salar populations, but projections of life‐history responses to future climate change are lacking. Here, we first exploit multiple decades of climate and biological data from the Burrishoole catchment in the west of Ireland to model statistical relationships between atmospheric variables, water temperature, and freshwater growth of juvenile Atlantic salmon. We then use this information to project potential changes in juvenile growth and life‐history scheduling under three shared socioeconomic pathway and representative concentration pathway scenarios from 1961 to 2100, based on an ensemble of five climate models. Historical water temperatures were well predicted with a recurrent neural network, using observation‐based atmospheric forcing data. Length‐at‐age was in turn also well predicted by cumulative growing degree days calculated from these water temperatures. Most juveniles in the Burrishoole population migrated to sea as 2‐year‐old smolts, but our future projections indicate that the system should start producing a greater proportion of 1‐year‐old smolts, as increasingly more juveniles cross a size‐based threshold in their first summer for smoltification the following spring. Those failing to cross the size‐based threshold will instead become 2‐year‐old smolts, but at a larger length relative to 2‐year‐old smolts observed currently, owing to greater overall freshwater growth opportunity. These changes in age‐ and size‐at‐seaward migration could have cascading effects on age‐ and size‐at‐maturity and reproductive output. Consequently, the seemingly small changes that our results demonstrate have the potential to cause significant shifts in population dynamics over the full life cycle. This workflow is highly applicable across the range of the Atlantic salmon, as well as to other anadromous species, as it uses openly accessible climate data and a length‐at‐age model with minimal input requirements, fostering improved general understanding of phenotypic and demographic responses to climate change and management implications. [ABSTRACT FROM AUTHOR]