Asymmetric isolating barriers between different microclimatic environments caused by low immigrant survival

Abstract

Spatially variable selection has the potential to result in local adaptation unless counteracted by gene flow. Therefore, barriers to gene flow will help facilitate divergence between populations that differ in local selection pressures. We performed spatially and temporally replicated reciprocal field transplant experiments between inland and coastal habitats using males of the common blue damselfly (Enallagma cyathigerum) as our study organism. Males from coastal populations had lower local survival rates than resident males at inland sites, whereas we detected no differences between immigrant and resident males at coastal sites, suggesting asymmetric local adaptation in a source-sink system. There were no intrinsic differences in longevity between males from the different environments suggesting that the observed differences in male survival are environment-dependent and probably caused by local adaptation. Furthermore, the coastal environment was found to be warmer and drier than the inland environment, further suggesting local adaptation to microclimatic factors has lead to differential survival of resident and immigrant males. Our results suggest that low survival of immigrant males mediates isolation between closely located populations inhabiting different microclimatic environments.

Immigrant inviability produces a strong barrier to gene flow between parapatric ecotypes of Senecio lautus

“…Postzygotic barriers prevent backcrossing and movement of genes from one population into another. They are frequently asymmetrical, in that they may prevent gene flow in one direction but not the other (Tiffin et al 2001;Moyle et al 2004;Turelli and Moyle 2007;Gosden et al 2015), and also increase in strength as populations diverge (Coyne and Orr 1989).…”

“…Intrinsic postzygotic barriers are important as they can complete the speciation process, but when speciation is driven by divergent selection these reproductive barriers may evolve after RI is complete (Martin and Willis 2007;Sobel et al 2010;see Seehausen et al 2014, Box 2). The continuous nature of divergence means that determining the barriers present between closely related populations gives the most accurate insight into the mechanisms of speciation (Sobel et al 2010;Gosden et al 2015).…”

Changing the habitat: the evolution of intercorrelated traits to escape from predators

“…Additional common garden experiments are needed to understand the cause of any intraspecific differences in this genus. Local adaptations via genetic differentiation have been reported in damselflies (Shama et al ., ; Gosden et al ., ). However, we hypothesize intraspecific differences in all Leucorrhinia species to stem from phenotypic plasticity rather than genetic differentiation, because dragonflies (Corbet, ), including Leucorrhinia species (Pajunen, ; McCauley, ), disperse widely.…”

Spatial variation in climate mediates gene flow across an island archipelago

“…; Cox and Rabosky ; Gosden et al. ), and species with higher levels of phenotypic and genetic diversity are predicted to be more resilient in the face of rapid environmental change (Angilletta ; Hoffmann and Sgro ).…”

“…In cases where genetic adaptation and plasticity both generate fixed differences in phenotypes, they can give rise to large‐scale patterns of gene flow whereby immigrants have reduced fitness in novel climates (Gosden et al. ).…”