Ecosystem size matters: the dimensionality of intralacustrine diversification in Icelandic stickleback is predicted by lake size

Abstract

Cases of evolutionary diversification can be characterized along a continuum from weak to strong genetic and phenotypic differentiation. Several factors may facilitate or constrain the differentiation process. Comparative analyses of replicates of the same taxon at different stages of differentiation can be useful to identify these factors. We estimated the number of distinct phenotypic groups in three‐spine stickleback populations from nine lakes in Iceland and in one marine population. Using the inferred number of phenotypic groups in each lake, genetic divergence from the marine population, and physical lake and landscape variables, we tested whether ecosystem size, approximated by lake size and depth, or isolation from the ancestral marine gene pool predicts the occurrence and the extent of phenotypic and genetic diversification within lakes. We find intralacustrine phenotypic diversification to be the rule rather than the exception, occurring in all but the youngest lake population and being manifest in ecologically important phenotypic traits. Neutral genetic data further indicate nonrandom mating in four of nine studied lakes, and restricted gene flow between sympatric phenotypic groups in two. Although neither the phenotypic variation nor the number of intralacustrine phenotypic groups was associated with any of our environmental variables, the number of phenotypic traits that were differentiated was significantly positively related to lake size, and evidence for restricted gene flow between sympatric phenotypic groups was only found in the largest lakes where trait specific phenotypic differentiation was highest.

Distribution of Eurasian minnows (Phoxinus: Cypriniformes) in the Western Balkans

“…Since the habitatinduced body shape changes (e.g. head length, eye diameter, gape and body width) may blur morphological differences between species or genetic clades (Walker, 1997;Langerhans et al, 2007;Langerhans and Reznick, 2010;Lucek et al, 2016), they should be regarded in all future morphological species delimitations in the genus Phoxinus .…”

Morphological divergence of lake and stream Phoxinus of Northern Italy and the Danube basin based on geometric morphometric analysis

“…Furthermore, the shape changes we found between ITA L and ITA S closely resemble the ones between DAN L and DAN S, although considerable genetic distance separates DAN L from DAN S. Thus, despite the genetic distance of 9% based on cyt b and 5% based on COI (Table ), the morphological differences detected between DAN L and DAN S appear to be a consequence of habitat. It is conceivable that, in extreme cases, habitat‐induced body shape changes (e.g., head length, eye diameter, gape and body width) may mask morphological differences between species/genetic groups (Langerhans & Reznick, ; Langerhans et al., ; Lucek, Kristjánsson, Skúlason, & Seehausen, ; Walker, ). This should be accounted for in future approaches on morphological species delimitations in this genus.…”

Managing cryptic biodiversity: Fine‐scale intralacustrine speciation along a benthic gradient in Alpine whitefish (Coregonusspp.)

“…The number of SL classes, potentially representing distinct taxon groupings differing in growth rate, was further determined using a dynamic hybrid tree cut (Langfelder, Zhang, & Horvath, 2008), following Lucek, Kristjánsson, Skúlason, and Seehausen (2016). In short, this method is based on a bottom-up algorithm that first identifies preliminary clusters within a data set, depending on a given minimal cluster size, the distance and distinctiveness of its neighbouring objects and the connectivity of branches within a cluster.…”