Abstract
It is now accepted that changes in the Earth’s climate are having a profound effect on the distributions of a wide variety of species. One aspect of these changes that has only recently received any attention, however, is their potential effect on levels of within-species genetic diversity. Theoretical, empirical and modelling studies suggest that the impact of trailing-edge population extirpation on range-wide intraspecific diversity will be most pronounced in species that harbour the majority of their genetic variation at low latitudes as a result of changes during the Quaternary glaciations. In the present review, I describe the historical factors that have determined current patterns of genetic variation across the ranges of Northern North Atlantic species, highlight the fact that the majority of these species do indeed harbour a disproportionate level of genetic diversity in rear-edge populations, and outline how combined species distribution modelling and genetic analyses can provide insights into the potential effects of climate change on their overall genetic diversity.
Highlights
Shifts in species’ ranges in response to recent cli‐ mate change have been observed across a wide range of taxa, including marine species (Parmesan and Yohe 2003, Perry et al 2005, Hickling et al 2006, Lima et al 2007, Kelly and Goulden 2008)
Climate‐mediated changes in the distributions of organisms are not a new phenomenon, : the ice ages of the Quaternary period resulted in periodic episodes of retreat into climatically suitable refugia for many species, followed by expansion during subsequent warm‐ ing phases (Hewitt 1999, Provan and Bennett 2008). One consequence of these fluctuations is that genetic variation is often not distributed evenly across species’ ranges, with former refugial areas instead harbouring a large proportion of the total diversity (Hampe and Petit 2005)
Loss of genetic diversity is considered extremely detrimental from a conser‐ vation point of view, since low levels of diversity are generally correlated with reduced adaptive potential (Allendorf and Luikart 2007)
Summary
Shifts in species’ ranges in response to recent cli‐ mate change have been observed across a wide range of taxa, including marine species (Parmesan and Yohe 2003, Perry et al 2005, Hickling et al 2006, Lima et al 2007, Kelly and Goulden 2008). 2.6 MA– present) resulted in periodic episodes of retreat into climatically suitable refugia for many species, followed by expansion during subsequent warm‐ ing phases (Hewitt 1999, Provan and Bennett 2008) One consequence of these fluctuations is that genetic variation is often not distributed evenly across species’ ranges, with former refugial areas instead harbouring a large proportion of the total diversity (Hampe and Petit 2005). Given that such rear edge populations are those most imme‐ diately under threat from climatic change, many researchers are considering the possible ef‐ fects of extirpation of rear‐edge populations on the overall genetic diversity within a species The aim of the current review is to describe the processes that have shaped the distribution of genetic varia‐ tion across northern North Atlantic marine species ranges, and to highlight the potentially dispropor‐ tionate impact of rear‐edge population extirpation on intraspecific genetic diversity
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