Patterns and repeatability of multi‐ecotype assemblages of sympatric salmonids

Abstract

AimHigh repeatability among assemblages of closely related but ecologically distinct ecotypes implies predictability in evolution and assembly of communities. The conditions under which ecotype assemblages form predictably, and the reasons, have been little investigated. Here, we test whether repeatability declines as the number of ecotypes builds.LocationPostglacial lakes with a circumboreal distribution.Time PeriodData were extracted from studies published between 1982 and 2019.Major Taxa StudiedEcotype assemblages from two Salmonid genera – Salvelinus and Coregonus. Fish in postglacial lakes commonly occur as pairs of ecotypes, typically with a pelagic and a littoral/benthic form, but in Salvelinus and Coregonus, assemblages commonly contain multiple sympatric ecotypes.MethodsWe used a meta‐analysis of Salvelinus and Coregonus to empirically assess how repeatability varies across assemblages of two to seven ecotypes. We examined repeatability of use of broad niche categories as well as underlying phenotypic traits.ResultsWithin Coregonus, repeatability across multi‐ecotype assemblages did not break down with the addition of a third or fourth ecotype. However, in Salvelinus, repeatability was largely absent and independent of the number of ecotypes. Repeatability of trait frequency distributions was absent in both genera, yet associations between trait means and niche categories were evident, especially in Coregonus.Main ConclusionsThese results show that repeatability can vary greatly between lineages; that repeatability need not break down as the number of ecotypes builds; and that high repeatability of broad niche categories may result despite marked differences in the underlying frequency distribution of trait means. These findings not only affirm the presence of repeatable ecotype assembly and early stages of divergence in postglacial fishes at a global scale, but also highlight variability among taxa and underlying phenotypic traits.

Environmental correlates of adaptive diversification in postglacial freshwater fishes

“…The focus for studies of speciation in postglacial fishes has often been the morphological and genetic features of the ecomorphs themselves, rather than the ecological conditions under which these ecomorphs persist or reasons for divergence (Blain et al, 2023;Østbye et al, 2006;Scharnweber et al, 2016;Verspoor et al, 2010). A large number of lakes therefore remain unstudied or understudied, with presence of multimodal ecomorphs frequently not being linked to ecological data.…”

“…The positive associations between degree of phenotypic divergence and lake size in Icelandic, Scandinavian, Fennoscandian, and Siberian lakes (Gordeeva et al, 2015;Lucek et al, 2016;Öhlund et al, 2020;Siwertsson et al, 2010) support the idea that increasing lake size increases ecological opportunity for divergence, particularly in terms of feeding ecology, and may therefore be key in allowing multiple ecomorphs to coexist. However, the lack of a relationship found in British Columbian lakes (Vamosi, 2003), the non-linear relationship identified in western Canadian lakes (Bolnick & Lau, 2008), and the negative correlation by Landry et al (2007) show that the relationship between divergence and lake size is complex and may depend on other characteristics of the lake and the species (Blain et al, 2023). Importantly, although lake size is relatively frequently studied and reported, the studies we evaluated used different statistical and descriptive approaches of bathymetric and biological diversity.…”

“…Nutrients such as phosphorus and nitrogen, as well as water qualities such as pH, may alter prey availability and level of vegetated habitat (Klug, 2002;Persson et al, 2008;Straskrabova et al, 2009), as well as water clarity and color. Opportunity for divergence and specialization to different diets, habitats, and light regimes depends on these factors to varying extents (Blain et al, 2023). Selection on traits such as sexual signaling depend on light regime at different depths or levels of vegetation, and thus visibility of signals such as red coloring in G. aculeatus, leading to sexual isolation (Boughman, 2001;Boughman et al, 2005).…”

“…It has been widely established that postglacial fish populations show high levels of genetic, heritable plastic/epigenetic, and developmental diversity (reviewed in, e.g., Elmer, 2016;Skúlason et al, 2019). This diversity corresponds to niche-related characteristics such as feeding morphology (Ahi et al, 2014;Blain et al, 2023;Guðbrandsson et al, 2018;Lundsgaard-Hansen et al, 2013), body shape and swimming physiology (Laporte et al, 2016;Recknagel et al, 2017), colouration (Boughman, 2001;Boughman et al, 2005), and anti-predator morphology (Smith et al, 2015). It is also widely accepted that selection acting on this variation is likely to be linked to differences in environmental conditions among lakes (Harrod, Mallela & Kahilainen, 2010;Öhlund et al, 2020;Siwertsson et al, 2010;Skúlason et al, 2019).…”

“…It is also widely accepted that selection acting on this variation is likely to be linked to differences in environmental conditions among lakes (Harrod, Mallela & Kahilainen, 2010;Öhlund et al, 2020;Siwertsson et al, 2010;Skúlason et al, 2019). It is not well understood precisely which conditions are relevant and whether they are consistent drivers of divergence across postglacial fish species and geographical areas, though evidence exists that repeatability of trait divergence may vary among species (Blain et al, 2023). Research to date has investigated biotic and abiotic factors to varying extents and in local or regional contexts and particular species.…”