Local adaptation along an environmental cline in a species with an inversion polymorphism

Abstract

Polymorphic inversions are ubiquitous across the animal kingdom and are frequently associated with clines in inversion frequencies across environmental gradients. Such clines are thought to result from selection favouring local adaptation; however, empirical tests are scarce. The seaweed fly Coelopa frigida has an α/β inversion polymorphism, and previous work demonstrated that the α inversion frequency declines from the North Sea to the Baltic Sea and is correlated with changes in tidal range, salinity, algal composition and wrackbed stability. Here, we explicitly test the hypothesis that populations of C. frigida along this cline are locally adapted by conducting a reciprocal transplant experiment of four populations along this cline to quantify survival. We found that survival varied significantly across treatments and detected a significant Location x Substrate interaction, indicating local adaptation. Survival models showed that flies from locations at both extremes had highest survival on their native substrates, demonstrating that local adaptation is present at the extremes of the cline. Survival at the two intermediate locations was, however, not elevated at the native substrates, suggesting that gene flow in intermediate habitats may override selection. Together, our results support the notion that population extremes of species with polymorphic inversions are often locally adapted, even when spatially close, consistent with the growing view that inversions can have direct and strong effects on the fitness of species.

Genetic divergence and phenotypic plasticity contribute to variation in cuticular hydrocarbons in the seaweed fly Coelopa frigida

“…We also detected plasticity in CHC composition due to the environment; the wrackbed itself had a strong influence on the CHC composition (Figure c). Wrackbed composition and microbiome (i.e., the food source for C. frigida larvae) vary across C. frigida populations in Europe (E. L. Berdan, M. Wellenreuther, & K. Johannesson, unpublished data, Butlin & Day, ; Day et al, ; Wellenreuther et al, ). Consequently, the CHC composition of C. frigida is likely to differ between natural populations in accordance with other research showing that larval diet impacts CHC composition (Etges & de Oliveira, ; Liang & Silverman, ; Rundle, Chenoweth, Doughty, & Blows, ; Stojkovic et al, ).…”

“…Coelopa frigida lives in "wrackbeds," accumulations of decomposing seaweed on shorelines that act as both habitat and food source for larvae and adults. Local adaptation in response to wrackbed composition has been demonstrated in Swedish C. frigida (Wellenreuther, Rosenquist, Jaksons, & Larson, 2017). Furthermore, CHCs may be under sexual selection as it is possible that CHCs are used as a mating signal in this system.…”

Comparative analysis of adaptive and neutral markers ofDrosophila mediopunctatapopulations dispersed among forest fragments

“…Variations in genetic polymorphisms concomitant with environmental gradients can be considered signs of local adaptation which may lead to population divergence (Wellenreuther et al, ). We could not find a consistent pattern of geographical variation for any microsatellite locus.…”

“…They allow insights on the action of natural selection in both natural and laboratory populations by monitoring inversion frequency shifts (Dobzhansky, ; Dobzhansky & Levene, ). These shifts in natural populations are often associated with seasonal (Wellenreuther, Rosenquist, Jaksons, & Larson, ) and long‐term variation (Batista, Ananina, & Klaczko, ; Etges, Arbckle, & Levitan, ; Orengo, Puerma, & Aguadé, ). Similarly, assessing geographical variation one can unveil patterns, which might be interpreted as prima facie evidence of natural selection (Ayala et al, ; Simões, Calabria, Picão‐Osório, Balanyà, & Pascual, ).…”

“…They allow insights on the action of natural selection in both natural and laboratory populations by monitoring inversion frequency shifts (Dobzhansky, 1947;Dobzhansky & Levene, 1948). These shifts in natural populations are often associated with seasonal (Wellenreuther, Rosenquist, Jaksons, & Larson, 2017) and long-term variation (Batista, Ananina, & Klaczko, 2012;Etges, Arbckle, & Levitan, 2006;Orengo, Puerma, & Aguadé, 2016).…”