Morphological and trophic divergence of lake and stream minnows (Phoxinus phoxinus)

Abstract

Phenotypic divergence in response to divergent natural selection between environments is a common phenomenon in species of freshwater fishes. Intraspecific differentiation is often pronounced between individuals inhabiting lakes versus stream habitats. The different hydrodynamic regimes in the contrasting habitats may promote a variation of body shape, but this could be intertwined with morphological adaptations to a specific foraging mode. Herein, I studied the divergence pattern of the European minnow ( Phoxinus phoxinus ), a common freshwater fish that has received little attention despite its large distribution. In many Scandinavian mountain lakes, European minnows are considered as being invasive and were found to pose threats to the native fish populations due to resource competition. Minnows were recently found to show phenotypic adaptations in lake versus stream habitats, but the question remained if this divergence pattern is related to differences in resource use. I therefore studied the patterns of minnow divergence in morphology (i.e., using geometric morphometrics) and trophic niches (i.e., using stomach content analyses) in the lake Ånnsjön and its tributaries to link the changes in body morphology to the feeding on specific resources. Lake minnows showed a strong reliance on benthic Cladocera and a more streamlined body shape with a more upward facing snout, whereas stream minnows fed on macroinvertebrates (larvae and adults) to a higher degree and had a deeper body with a snout that was pointed down. Correlations showed a significant relationship of the proportion of macroinvertebrates in the gut and morphological features present in the stream minnows. The results of this study highlight the habitat‐specific divergence pattern in morphology and resource use in this ubiquitous freshwater fish. Consequently, interspecific interactions of invasive minnows and the native fish population could differ in the respective food webs and resource competition could target different native fish species in the contrasting habitats.

Comparative Phylogeography of Phoxinus, Delminichthys, Phoxinellus and Telestes in Dinaric Karst: Which Factors Have Influenced Their Current Distributions?

“…Thus, Phoxinus is resilient to predation and plastic with regard to dietary preferences. When introduced to non-native rivers and lakes, Phoxinus species quickly spread and are considered invasive in Scandinavia and Spain [52,79,97], attesting again to the adaptability of the genus to new environments [92]. It is clear that Phoxinus species are generalists with a high migratory potential, confirmed also in previous studies [37,39,98], which detected several occasions of the crossing of the Adriatic-Black Sea divide in Dinaric Karst.…”

“…However, as summarized above, Phoxinus species have wider distribution ranges than the species of Delminichthys, Phoxinellus and Dinaric Telestes, suggesting a factor that is influencing their potential to migrate. Phoxinus can endure cold climatic conditions, as well as severe winters under ice [52,89]. At the same time, some species can tolerate high water temperatures, providing that the concentration of the oxygen is high [90,91].…”

Phenotypic plasticity of a generalist fish species resident to lotic environments: Insights from the Great Lakes region

“…We regressed Procrustes coordinates against centroid size, which is the square root of the sum of squared distances of all landmarks from an object's centroid, to remove allometric effects and used the regression residuals in subsequent analyses (Klingenberg, 2011; Scharnweber, 2020). A canonical variate analysis (CVA) was conducted to determine the significance of shape variation between sites followed by a discriminant function analysis (DFA) to visualize the shape change between pairs of sites (Scharnweber, 2020). These preliminary statistical analyses were completed using Morpho J v1.07a (Klingenberg, 2011).…”

“…Fish resident to streams and rivers face selective pressures from flow, predators, habitat modification, and food availability and all play a role in triggering morphologic changes (Langerhans et al., 2004; Lostrom et al., 2015; Scharnweber, 2020). Research to date has generally focused on comparing a single fish species between lotic and lentic habitats (Franssen, 2011; Haas et al., 2010; Lang et al., 2018; Ramler et al., 2016) showing that lake or reservoir populations are deeper bodied while stream populations are streamlined (Franssen, 2011; Haas et al., 2010).…”

The Complete Mitochondrial Genome of Eurasian Minnow (Phoxinus cf. Phoxinus) from the Heilongjiang River, and Its Phylogenetic Implications

“…High phenotypic plasticity makes species delimitation of Phoxinus difficult and the wide distribution range makes comparisons between different types of minnows inconvenient [ 5 , 7 , 10 , 11 , 12 , 13 , 14 ]. Based on molecular data, a multispecies complex of Phoxinus in the Western Balkan Peninsula was reported and dispersion through subterranean water in karst formations was suggested [ 5 ].…”