Divergence along a steep ecological gradient in lake whitefish (Coregonussp.)

Abstract

To understand mechanisms structuring diversity in young adaptive radiations, quantitative and unbiased information about genetic and phenotypic diversity is much needed. Here, we present the first in‐depth investigation of whitefish diversity in a Swiss lake, with continuous spawning habitat sampling in both time and space. Our results show a clear cline like pattern in genetics and morphology of populations sampled along an ecological depth gradient in Lake Neuchâtel. Divergent natural selection appears to be involved in shaping this cline given that trait specific PST‐values are significantly higher than FST‐values when comparing populations caught at different depths. These differences also tend to increase with increasing differences in depth, indicating adaptive divergence along a depth gradient, which persists despite considerable gene flow between adjacent demes. It however remains unclear, whether the observed pattern is a result of currently stable selection‐gene flow balance, incipient speciation, or reverse speciation due to anthropogenic habitat alteration causing two formerly divergent species to collapse into a single gene pool.

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

“…“pelagic intermediate” (“ Pelagic intermediate ”). For the species found spawning along the depth gradient, we find a strong association of individual genetic variation with growth rate and gill‐raker counts, traits suggested to be evolving under divergent selection in whitefish (Østbye et al., 2006; Præbel et al., 2013; Rogers & Bernatchez, 2007; Vonlanthen et al., 2009). These findings are consistent with predictions of isolation‐by‐adaptation and ecological speciation along clines in our studied depth gradient (Funk, Nosil, & Etges, 2006; Nosil, 2012; Rundle & Nosil, 2005).…”

“…Alpine whitefish with lower gill‐raker densities, on the other hand, have been shown to be more efficient at foraging for large benthic prey items (Lundsgaard‐Hansen, Matthews, Vonlanthen, Taverna, & Seehausen, 2013). These predictable differences in feeding efficiency are suggestive of fitness trade‐offs in gill‐raker number between the respective niches of coexisting Alpine whitefish species, corroborated by genetic evidence that within‐lake patterns of gill‐raker count variation are driven by divergent natural selection regimes in the Alpine and other whitefish radiations (Hudson et al., 2013; Præbel et al., 2013; Rogers & Bernatchez, 2007; Vonlanthen et al., 2009). Whitefish growth rate is a complex physiological trait impinging on many other aspects of the overall phenotype such as body shape.…”

“…Additional roles for growth rate in whitefish adaptive divergence and speciation may include escaping size‐related predation windows differing among niches (Kahilainen & Lehtonen, 2002) and size assortative mate choice (Foote & Larkin, 1988). Again, genetic evidence supports the role of divergent natural selection in driving patterns of interspecific variation in growth rate in different whitefish radiations (Rogers & Bernatchez, 2007; Vonlanthen et al., 2009). While both gill‐raker number and growth rate are clearly ecologically important traits involved in adaptive divergence and potentially speciation, the frequency distributions of adult body size, indicative of growth rate, better reflected individual genetic differences among sampled depth gradient whitefish than gill‐raker counts.…”

“…All fish were genotyped at 10 microsatellite loci: Cocl‐Lav49, Cocl‐Lav61, Cocl‐Lav6, Cocl‐Lav68, Cocl‐Lav10, Cisco‐157, Cocl‐Lav4, Cocl‐Lav45, Cocl‐Lav18 and BWF‐2 following Vonlanthen et al. (2009). …”

On the origin of species: insights from the ecological genomics of lake whitefish

“…Moreover, the life history and ecology of sympatric whitefish populations have been well documented (e.g. Amundsen et al 2004;Harrod & Kahilainen 2006;Hudson et al 2007;Kahilainen et al 2007) such that the genomics of phenotypic divergence and reproductive isolation can be interpreted in a natural, ecological context (reviewed in Bernatchez 2004;Østbye et al 2005b;Landry et al 2007a;Vonlanthen et al 2009). …”