Abstract
As a conservation measure to protect European whitefish in Scotland, a translocated population was established in Loch Sloy from Loch Lomond stock between 1988 and 1990. Previous study has assumed that current morphological differences between adults from the donor and refuge lakes have arisen through phenotypic plasticity. The present study compared the morphologies of whitefish at three life stages: alevins and fry raised in a common garden, and wild-caught adults. Alevins were clearly distinguishable by their lake of origin. Loch Sloy alevins were distinguishable also by family, although this was not the case for Loch Lomond. Differential allometric trajectories facilitated the persistence of morphological differences associated with lake of origin through the fry stage into adulthood. Overall, the whitefish from Loch Lomond displayed morphologies associated with pelagic feeders, while the more robust heads and ventrally positioned snouts of the Loch Sloy whitefish conformed to expectations for more benthic feeding habits. That differences between populations were present not only in wild adults, but also in alevins and fry from a common garden setup, strongly suggests that the divergence between populations is due to inheritance mechanisms, rather than differential plastic responses, and questions the effectiveness of translocation as a conservation measure.
Highlights
Intraspecific phenotypic variation is a common feature of fishes of the fragmented, heterogeneous environments of lakes in regions that were recently glaciated (Carvalho 1993; Klemetsen 2013), where, generally, species diversity is low, resulting in opportunities to exploit alternative foraging resources (Gíslason et al 1999)
The significant differences in morphology seen between adult whitefish from the donor and refuge populations (Loch Lomond and Loch Sloy, respectively) in the present study accord with those found by Etheridge et al (2010)
Heritability of morphological traits was not tested directly, and other explanations are possible and examined below, this study suggests that the differences in adult morphology between populations are, at least in part, inherited
Summary
Intraspecific phenotypic variation is a common feature of fishes of the fragmented, heterogeneous environments of lakes in regions that were recently glaciated (Carvalho 1993; Klemetsen 2013), where, generally, species diversity is low, resulting in opportunities to exploit alternative foraging resources (Gíslason et al 1999) Such lakes are young and often geologically isolated, with attendant low dispersal of freshwater fishes. Disruptive selection may promote and maintain intraspecific phenotypic structuring expressed as specialists in alternative foraging strategies, growth rates, or spawning times or habitats, with different morphological features (Adams et al 2016; Brown and Scott 1994; Vonlanthen et al 2009) This may occur in heterogeneous environments, when alternative morphologies confer greater fitness advantages upon trophic specialists than an intermediate might do (Draghi and Whitlock 2012; Fusco and Minelli 2010). When such specialisms result in reproductive isolation, intraspecific divergence may become firmly established (Schluter 2009)
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