Rapid Evolution of a Geographic Cline in Size in an Introduced Fly

Abstract

The introduction and rapid spread of Drosophila subobscura in the New World two decades ago provide an opportunity to determine the predictability and rate of evolution of a geographic cline. In ancestral Old World populations, wing length increases clinally with latitude. In North American populations, no wing length cline was detected one decade after the introduction. After two decades, however, a cline has evolved and largely converged on the ancestral cline. The rate of morphological evolution on a continental scale is very fast, relative even to rates measured within local populations. Nevertheless, different wing sections dominate the New versus Old World clines. Thus, the evolution of geographic variation in wing length has been predictable, but the means by which the cline is achieved is contingent.

Adaptation and colonization history affect the evolution of clines in two introduced species

“…The establishment of clines is a feature of many species invasions and has been interpreted as a hallmark example of adaptive evolution in action (Johnston & Selander, 1964;Lacey, 1988;Weber & Schmid, 1998;Huey et al, 2000;Kollmann & Banuelos, 2004;Maron et al, 2004Maron et al, , 2007Leger & Rice, 2007;Etterson et al, 2008;Montague et al, 2008). In our study, divergence was often observed in excess of the neutral expectation generated by ancestry, offering particularly strong evidence that the clines are adaptive.…”

“…Any effect of hitchhiking would tend to make our test for adaptation more conservative, as some of the putatively neutral variance controlled for may be linked to regions under selection. Our approach should be complementary to other methods of inferring robust evidence for clinal evolution, such as the observation of coincident parallel clines reported for several species invasions (Huey et al, 2000;Leger & Rice, 2007;Maron et al, 2007). Our method could be especially useful in this context, by controlling for colonization history that might otherwise obscure a parallel cline.…”

“…Because founding events can generate genetic structure and deviations from the equilibrium balance between gene flow, drift and selection (Whitlock & McCauley, 1990, 1999McCauley et al, 1995), multiple introductions can quickly generate patterns that resemble isolation by distance or clinal variation when sources establish at different points of introduction (for example, Roman, 2006;Keller & Taylor, 2008). Numerous studies of species invasions have reported latitudinal clines for traits such as body size and mass, height, number of stems, flowering time, fecundity and physiology (Johnston & Selander, 1964;Weber & Schmid, 1998;Huey et al, 2000;Kollmann & Banuelos, 2004;Maron et al, 2004Maron et al, , 2007Leger & Rice, 2007;Montague et al, 2008). Although colonization history is expected to have a major influence on the population and quantitative genetics of introduced species, few studies have attempted to control for colonization history when analysing clines (but see Maron et al, 2004).…”

Flies evolved small bodies and cells at high or fluctuating temperatures

“…Comparative analyses of phenotypic plasticity in laboratory experiments (Atkinson, 1994) and genetic variation along latitudinal clines (Huey et al., 2000) established that most ectotherms mature at larger sizes in colder environments. This phenotypic plasticity has been considered a product of physical constraints as well as natural selection (Angilletta et al., 2004; Atkinson & Sibly, 1997).…”

Gloger's rule in North American Barn Owls

“…At a large geographic scale, such as across a continent, ecological and climatic factors vary greatly among regions, promoting the evolution of specific phenotypes adapted to these specific local conditions (Huey et al 2000). Local adaptation requires populations to differ genetically (Blanquart et al 2013), potentially leading to speciation even in the presence of gene flow (Barton 2010).…”