The influence of swimming demand on phenotypic plasticity and morphological integration: a comparison of two polymorphic charr species

Abstract

In northern freshwater lakes, several fish species have populations composed of discrete morphs, usually involving a divergence between benthic and limnetic morphs. Although it has been suggested that swimming demand plays an important role in morphological differentiation, thus influencing habitat selection, it is unclear how it affects reaction norms, patterns in character correlation, and levels of morphological integration. We examined whether swimming demand could induce morphological plasticity in the directions expected under divergent habitat selection, and evaluated its influence on the morphological integration in Arctic charr ( Salvelinus alpinus) and brook charr ( S. fontinalis), two congeneric species exhibiting conspicuous and subtle resource polymorphism, respectively. We found that changes in morphology were induced by differential swimming demands in both species. The length of the pectoral fin was the character that responded most strongly according to the predicted morphological expectations under divergent habitat selection. High levels of morphological plasticity, relatively low levels of integration, and differences found in the morphological correlation structure among water velocity treatments suggest that constraints on morphological change are unlikely in either species, thus allowing great potential for phenotypic flexibility in both species. The magnitude of character integration, however, was larger for Arctic charr than for brook charr. This latter result is discussed in the light of the differences in the level of polymorphism between the two species in the wild. The results of the present study indicate that swimming demand alone may not be sufficient to generate the polymorphism encountered in nature. Given that both diet and swimming demands can induce morphological changes, it would be important to conduct experiments targeting the interaction between the morphological modules related to trophic and swimming demands.

Old wine in new bottles: reaction norms in salmonid fishes

“…Including papers that fulfilled the keyword search criteria for salmonid reaction norms through 2009 (n ¼ 62) and the eight 'reaction-norm' papers published by Beacham and Murray, fewer than 25 provide experimental evidence of genetic variability in reaction norms among members of the same species (Table 1; Peres-Neto and Magnan (2004) constructed reaction norms at the species level). Most of these are for univariate continuous reaction norms, that is, those for which the phenotypic value of a single trait changes continuously with changes to the environment, as opposed to univariate traits that vary with the environment in a discontinuous manner.…”

Replicated Evolution of Integrated Plastic Responses During Early Adaptive Divergence

“…We then tested for differences in the level of integration between each lake pair of ecomorphs, using the software MorphInt (P. R. Peres-Neto, 2005, http://uregina.ca/ ϳperesnep/). This program estimates a standardized value of integration varying between zero (no integration) and one (maximum integration) for two population matrices and then determines the level of significance using 10,000 bootstrap randomizations following Peres-Neto and Magnan (2004). For each bootstrap replicate, the variances of the eigenvalues e1 for matrix 1 and e2 for matrix 2 and their difference (Di ϭ e1 Ϫ e2) are estimated.…”

Dynamic skeletogenesis in fishes: Insight of exercise training on developmental plasticity

“…However, developmental plasticity has been tested experimentally on a variety of species, phenotypes, and environmental factors. Phenotypic plasticity has been primarily studied in teleosts [e.g., adrianichthyid (Kawajiri et al, 2011), anarhichadids (Pavlov and Moksness, 1994), cichlids (Crispo and Chapman, 2010), clupeids (Fuiman et al, 1998), cyprinids (Mabee et al, 2000), gasterosteids (Garduno-Paz et al, 2010), moronids (Georgakopoulou et al, 2007), salmonids (Pakkasmaa and Piironen, 2001;Peres-Neto and Magnan, 2004;Grü nbaum et al, 2007Grü nbaum et al, , 2008Fischer-Rousseau et al, 2009;Cloutier et al, 2010;Totland et al, 2011)] most likely owing to the facility of rearing experiences; however, there is no a priori reason to think that it is limited to teleosts.…”

“…A wide range of plastic responses has been reported in the literature. Focusing on anatomical plasticity, the following traits exemplify the types of responses: size [e.g., gills (Crispo and Chapman, 2010), brain (Crispo and Chapman, 2010), head (Meyer, 1987), body (Pakkasmaa and Piironen, 2001;Peres-Neto and Magnan, 2004;Georgakopoulou et al, 2007;Grü nbaum et al, 2008;Schmidt and Starck, 2010;Frommen et al, 2011;Kawajiri et al, 2011), fins (Fischer-Rousseau et al, 2009)] and shape changes [e.g., head (Meyer, 1987), pharyngeal (Muschnick et al, 2011) and oral jaws (Meyer, 1987), body (Pakkasmaa and Piironen, 2001;Peres-Neto and Magnan, 2004;Georgakopoulou et al, 2007;Grü nbaum et al, 2007;Fischer-Rousseau et al, 2009;Garduno-Paz et al, 2010;Frommen et al, 2011)], bone matrix (Totland et al, 2011), number of serially repeated elements [e.g., pharyngeal teeth, vertebrae, fin rays, spines (Arratia and Schultze, 1992;Mabee et al, 2000;Georgakopoulou et al, 2007;Shkil et al, 2010;Kawajiri et al, 2011)], and timing of ossification Moksness, 1994, 1997;Fuiman et al, 1998;Mabee et al, 2000;Cloutier et al, 2010, Fiaz et al, 2012. It is also known that fin positioning is plastic with respect to changes in hydrodynamic conditions …”