Intraspecific variation among Chinook Salmon populations indicates physiological adaptation to local environmental conditions

Abstract

Understanding interpopulation variation is important to predicting species responses to climate change. Recent research has revealed interpopulation variation among several species of Pacific salmonids; however, the environmental drivers of population differences remain elusive. We tested for local adaptation and countergradient variation by assessing interpopulation variation among six populations of fall-run Chinook Salmon from the western United States. Juvenile fish were reared at three temperatures (11, 16 and 20°C), and five physiological metrics were measured (routine and maximum metabolic rate, aerobic scope, growth rate and critical thermal maximum). We then tested associations between these physiological metrics and 15 environmental characteristics (e.g. rearing temperature, latitude, migration distance, etc.). Statistical associations between the five physiological metrics and 15 environmental characteristics supported our hypotheses of local adaptation. Notably, latitude was a poor predictor of population physiology. Instead, our results demonstrate that populations from warmer habitats exhibit higher thermal tolerance (i.e. critical thermal maxima), faster growth when warm acclimated and greater aerobic capacity at high temperatures. Additionally, populations with longer migrations exhibit higher metabolic capacity. However, overall metabolic capacity declined with warm acclimation, indicating that future climate change may reduce metabolic capacity, negatively affecting long-migrating populations. Linking physiological traits to environmental characteristics enables flexible, population-specific management of disparate populations in response to local conditions.

Local Thermal Adaptation occurs via Modulation of Mitochondrial Activity in Chinook Salmon

“…Notably, the thermal optima (Topt) for AAS varied from 17.9°C in AK fish to as high as 24.6°C in the WA fish (Figure 1a). The WA population was particularly notable as the predicted Topt of 24.5°C is well above the Topt usually observed in this species Zillig, Lusardi, et al, 2023), which may reflect adaption to the thermally challenging stream in which this population spawns, where summer temperatures commonly exceed 26°C (Small et al, 2011) similar to the summer temperatures seen at the extreme southern end of this species range (Zillig, FitzGerald, et al, 2023).…”

“…These iconic fish are essential to the culture, food security and economy of the North Pacific, and are threatened across their range, with rising stream temperatures highlighted as a major contributor to this decline (Crozier et al, 2021). The vulnerability of Pacific salmon to high temperature stems from their anadromous life history, which promotes local adaption of reproductively isolated populations to historical streams conditions as a result of their return to natal streams to spawn (Eliason et al, 2011;Farrell et al, 2008;Zillig, FitzGerald, et al, 2023). As cold-water species, even modest increases in temperature can have severe consequences on population viability by reducing cardio-respiratory performance, which has been widely suggested to constrain thermal tolerance in salmonids (Clark et al, 2008) (Eliason et al, 2013), however the mechanistic basis of this vulnerability is an open question.…”

Fish Blood Response to Ash-Induced Environmental Alkalinization, and their Implications to Wildfire-Scarred Watersheds

“…To rapidly address the acute acid-base challenge, salmon appeared to have released glucose from glycogen stores and upregulated anaerobic respiration. However, the strategy appears to be temperature specific: salmon in the 20°C treatment have a lower aerobic scope than their 15°C counterparts (Zillig et al, 2023), so they may have 1) hastened their release of glucose from glycogen stores and 2) upregulated metabolic proton production (as evident by plasma lactate build-up (Robergs et al, 2004) to aid in rapid recovery of pH e . In contrast, salmon in the 15°C treatment did not significantly upregulate their glucose until 24 hours of exposure, and lactate levels were consistently about half those in fish at the warmer temperature.…”

The impacts of diel thermal variability on growth, development and performance of wild Atlantic salmon (Salmo salar) from two thermally distinct rivers

“…Different habitats are expected to exert different selection pressures leading to different genotypic adaptations in salmonids ( Dionne et al, 2009 ; Weitemier et al, 2021 ; Zillig et al, 2021 ). The extent of local adaptation for salmon populations has been extensively discussed (in Garcia de Leaniz et al, 2007 ; Fraser et al, 2011 ; Primmer, 2011 ), and evidence for its occurrence has surfaced based on comparisons of physiology or genomics of adult ( Taylor, 1991 ; Lee et al, 2003 ; Unwin et al, 2003 ) and juvenile ( Zillig et al, 2023 ) salmon from different locations. For example, Sockeye salmon ( Oncorhynchus nerka ) from warmer environments tend to have better swim performance at warmer temperatures ( Eliason et al, 2011 ).…”