Temperature-related Physiological Adaptations Promote Ecological Divergence in a Sympatric Species Pair of Temperate Freshwater Fish, Coregonus spp.

1. The question which ecological forces are responsible for the evolution and coexistence of closely relates sympatric species is of major interest for evolutionary ecologists. In a freshwater system context, flocks or pairs of closely related fishes occurring sympatrically 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 temperate freshwaters, in few lakes two or more pelagic planktivores coexist. Accordingly, disruptive selection on traits not related to feeding may have contributed to divergence. 3. In the postglacial Lake Stechlin (Germany), the common vendace (Coregonus albula) and the endemic dwarf-sized Fontane cisco (C. fontanae) coexist. Both species are pelagic planktivores, but differ slightly in their vertical distribution, such that species-specific temperature-related physiological adaptations are likely. 4. We investigated standard and active metabolic rates over the range of environmental temperature both species experience naturally (4 to 15°C). 84 specimens of 7 to 22 cm length were exposed to five relative flow velocities between 0.5 and 2.0 body lengths per second in swim tunnel respirometers. 5. Fontane cisco showed a reduced standard metabolic rate compared to vendace over the whole 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 and 15°C. Total metabolic costs when swimming at 2 body lengths per second were higher for vendace at less than 8°C, but higher for Fontane cisco if temperature exceeds 8°C. 6. The results indicate that species-specific physiological adaptations contribute to ecological divergence, thus preventing competitive exclusion within the pelagic coregonids of Lake Stechlin. The existence of a vertical gradient in water temperature was probably one crucial factor for the evolution of both competing temperature-related physiological strategies.

OHLBERGER Jan;  MEHNER Thomas;  STAAKS Georg;  HOELKER Franz; 

2008-06-17

BLACKWELL PUBLISHING

JRC42781

0269-8463,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC42781,   

10.1111/j.1365-2435.2008.01391.x,