Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

Abstract

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder ( Platichthys stellatus ) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole‐body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown. Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast‐start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast‐start performance. Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast‐start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate. Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species

“…It is possible that, perch metabolism and morphology evolve in parallel in response to differences in habitat use, since our analyses showed no relationship between these two traits. Our results agree with the finding of studies on Atlantic cod ( Gadus morhua ), yellow perch (Perca flavescens ), and starry flounder ( Platichthys stellatus ), but not brook trout (Salvelinus fontinalis) (Bergstrom et al, 2019 ; Boily & Magnan, 2002 ; Reidy et al, 2000 ; Rouleau et al, 2010 ). This pattern may indicate that differences in ecological lifestyle, such as locomotor performance, associated with the comparatively high metabolic rates in salmonids also affect the relationship between morphology and metabolism (Killen et al, 2016 ).…”

“…Studies on polymorphic species often focus on intraspecific variation in diet, morphology, and behavior and how these traits can provide the competitive advantage that allows an individual or a group of individuals to exploit a specific niche or habitat (Hayden et al, 2014 ; Skúlason et al, 2019 ; Skúlason & Smith, 1995 ). Including metabolic rates as part of this larger suite of traits is comparatively rare, even though differences in metabolic rates could impact individual fitness as much as other aspects of the phenotype (but see Rouleau et al ( 2010 ) and Bergstrom et al ( 2019 )). Like morphological traits, specific metabolic phenotypes can be related to genetic differences, but also display a degree of plasticity that helps individuals persist under variable conditions (Norin & Metcalfe, 2019 ; Svanbäck & Eklöv, 2006 ).…”

Sex-specific covariance between metabolic rate, behaviour and morphology in the ground beetle Carabus hortensis

“…, Biro et al, 2020 ; Cornwell, McCarthy & Biro, 2020 ), and between metabolic rate and morphology ( e.g. , Baktoft et al, 2016 ; Bergstrom et al, 2019 ), have been studied in different taxa, but rarely in insects (but see: Royauté et al, 2015 ; Krams et al, 2017 ), or on a sex-specific basis ( Hämäläinen et al, 2018 ), despite: (a) differences in physiology between insects and more commonly studied vertebrates ( Schmidt-Nielsen, 2007 ); and (b) differences between males and females that might influence trait covariances ( Hämäläinen et al, 2018 ). Consequently, our study is among the first to investigate sex-specific metabolic trait covariances with both a personality trait and morphology, in insects.…”

Insights into the Mitochondrial Genetic Makeup and Miocene Colonization of Primitive Flatfishes (Pleuronectiformes: Psettodidae) in the East Atlantic and Indo-West Pacific Ocean

“…Furthermore, the extraordinary transformation from bilateral pelagic larval symmetry to adult flattened symmetry limits flatfishes to demersal zones on the sea bottom, owing to their unusual temperature-mediated spawning behavior [10]. While most flatfish species have either a right-sided (dextral) or a left-sided (sinistral) mouth, several species, including Psettodes, display varying degrees of dextral to sinistral polymorphism [11]. This sexual dimorphism in external morphology often poses challenges in species identification.…”