The relative influence of natural selection and geography on gene flow in guppies

Abstract

Two general processes may influence gene flow among populations. One involves divergent selection, wherein the maladaptation of immigrants and hybrids impedes gene flow between ecological environments (i.e. ecological speciation). The other involves geographic features that limit dispersal. We determined the relative influence of these two processes in natural populations of Trinidadian guppies (Poecilia reticulata). If selection is important, gene flow should be reduced between different selective environments. If geography is important, gene flow should be impeded by geographic distance and physical barriers. We examined how genetic divergence, long-term gene flow, and contemporary dispersal within a watershed were influenced by waterfalls, geographic distance, predation, and habitat features. We found that waterfalls and geographic distance increased genetic divergence and reduced dispersal and long-term gene flow. Differences in predation or habitat features did not influence genetic divergence or gene flow. In contrast, differences in predation did appear to reduce contemporary dispersal. We suggest that the standard predictions of ecological speciation may be heavily nuanced by the mating behaviour and life history strategies of guppies.

Upstream guppies (Poecilia reticulata, Peters, 1859) go against the flow

“…Fish that are displaced from the UN during seasonal flood events may be prevented from returning upstream by barriers to gene flow such as waterfalls (Crispo et al 2006, van Oosterhout et al 2007a. Compensatory upstream migration in the lowlands may allow the return of displaced fish that have not been swept over such barriers (see Barson et al 2009, Willing et al 2010).…”

Environmental correlates of geographic divergence in a phenotypic trait: A case study using bat echolocation

“…Gene flow can be restricted in such situations either by selection against dispersers moving between populations in different habitats or by individual preference for remaining in a particular habitat (Nosil, 2004; Nosil, Vines, & Funk, 2005). This is usually manifested by an association between phenotypic differences and environmental differences (IbE, Crispo, Bentzen, Reznick, Kinnison, & Hendry, 2006; Nosil, 2012; Rundle & Nosil, 2005; Shafer & Wolf, 2013). …”

Microsatellite genetic differentiation among populations of the Trinidadian guppy

“…Conversely, the Oropouche drainage likely had confluences with a different drainage system on mainland South America and would have been exposed to different colonizing events. Second, a study has provided a detailed analysis of populations from within a single river system, the Marianne (Crispo et al, 2006). This study revealed considerable differentiation among sites within the river and attributed the differentiation to waterfall barriers and isolation by distance.…”

“…The second involves adaptive divergence under variable selection pressures whereby dispersers or hybrids tend to have lower fitness than residents and gene flow between ecological environments can thus be impeded (Lu and Bernatchez, 1999;Ogden and Thorpe, 2002;Rundle, 2002;reviewed by Schluter, 2000;Hendry, 2004). Yet, assessing the contribution of these various processes to intraspecific genetic structure remains a major challenge in population biology (Rundle and Nosil, 2005;Crispo et al, 2006;Nosil and Crespi, 2006).…”

“…The first involves topographical features including water connectivity and barriers that can affect contemporary dispersal (Castric et al, 2001;Crispo et al, 2006;Caldera and Bolnick, 2008). The second involves adaptive divergence under variable selection pressures whereby dispersers or hybrids tend to have lower fitness than residents and gene flow between ecological environments can thus be impeded (Lu and Bernatchez, 1999;Ogden and Thorpe, 2002;Rundle, 2002;reviewed by Schluter, 2000;Hendry, 2004).…”