Temperature‐related physiological adaptations promote ecological divergence in a sympatric species pair of temperate freshwater fish,Coregonusspp.

Abstract

Summary 1.Understanding the ecological forces that are responsible for the evolution and coexistence of closely related sympatric species is a major interest in evolutionary ecology. In a freshwater system context, flocks or pairs of sympatrically occurring fishes are commonly studied to identify causes and mechanisms of ecological divergence and speciation. 2. Whereas habitat and diet segregation along the pelagic-benthic axis is frequent in many species pairs in temperate freshwaters, two pelagic planktivores coexist in the post-glacial Lake Stechlin, Germany (common vendace, Coregonus albula and the endemic Fontane cisco, C. fontanae ). Accordingly, disruptive selection on traits not related to feeding may have contributed to divergence. Since both species differ slightly in their vertical distribution, species-specific physiological adaptations related to temperature are likely. 3. We investigated standard and active metabolic rates (AMR) over the range of environmental temperature, which both species experience naturally (4-15 ° C). Eighty-four specimens of 7-22 cm length were exposed to five relative flow velocities between 0·5 and 2·0 body lengths per second (BL s -1 ) in swim tunnel respirometers. 4. Fontane cisco showed a reduced standard metabolic rate (SMR) compared to vendace over the entire temperature range. Further, activity metabolism was associated with lower energetic costs in Fontane cisco at 4 ° C, but higher costs than in vendace at 8 ° C and 15 ° C. Total metabolic costs when swimming at 2 BL s -1 were higher for vendace at < 8 ° C, but higher for Fontane cisco if temperature exceeds 8 ° C. 5.The results indicate that species-specific physiological adaptations contribute to ecological divergence, thus preventing competitive exclusion between the pelagic coregonids of Lake Stechlin. The existence of a vertical gradient in water temperature was probably a crucial factor for the evolution of both competing temperature-related physiological strategies.

Adaptive Phenotypic Diversification along a Temperature-Depth Gradient

“…This model outcome matches the experimentally determined species-specific thermal preferences and corresponding temperatures of lowest swimming costs (4.2Њ and 9.0ЊC; Ohlberger et al 2008bOhlberger et al , 2008c and is in good accordance with the experienced water temperatures of the coregonids in Lake Stechlin (4.0Њ-6.0Њ and 6.5Њ-9.0ЊC; Mehner et al 2010a). These comparisons show that the two populations that evolve in our model represent well the natural populations in terms of their distributions and trait values.…”

“…This might have facilitated a differentiation in lightdependent feeding efficiencies along the depth gradient. However, there is good evidence that the two species do not differ in their foraging efficiency at light intensities experienced in the lake (Ohlberger et al 2008a). Other factors that might have facilitated the evolutionary divergence of an ancestral population include a species-poor environment and a high level of intraspecific competition at the time of colonization, conditions that are often found in newly colonized postglacial lakes and are believed to promote ecologically based adaptive diversification in fishes (Vamosi 2003;Bolnick 2004).…”

“…ciation drive the ecological differentiation that enables the coexistence of closely related species in sympatry (Schluter 2000;Coyne and Orr 2004). Previous empirical studies on the species pair in Lake Stechlin had revealed that the two coexisting coregonids have diverged with respect to their vertical distribution in the lake (Helland et al 2007(Helland et al , 2009), the temperature dependence of their metabolisms (Ohlberger et al 2008b), and their associated thermal preferences (Ohlberger et al 2008c). The concordance in the ecological, physiological, and behavioral differentiation of the species with respect to temperature suggests thermal specialization as the main driver of their eco-evolutionary divergence.…”

“…Hence, mechanisms reducing competition and thus potentially driving divergence between the species are not significantly related to diet. Instead, an important factor promoting ecological divergence between the species is a difference in temperature-dependent metabolic costs of swimming (Ohlberger et al 2008b). This directly influences the competitive abilities of the two populations via their efficiency of foraging at a specific temperature, and thus depth.…”

Morphology and life history of the Great Slave Lake ciscoes (Salmoniformes: Coregonidae)

“…Although the evolutionary history of the North American ciscoes has been studied (Bernatchez et al 1991;Turgeon et al 1999;Turgeon & Bernatchez 2001a,b, 2003Turgeon 2002), the phenotypic and life-history divergence of sympatric ciscoes in of North American lakes is less well known. Similar challenges with resolving coregonine taxonomy and evolutionary history occur in Europe (Kahilainen et al 2005(Kahilainen et al , 2007Ohlberger et al 2008;Helland et al 2009) and Asia (Politov et al 2004;Sukhanova et al 2012).…”