Hybridization in the Recent Past

Abstract

The question we address in this article is how hybridization in the recent past can be detected in recently evolved species. Such species may not have evolved genetic incompatibilities and may hybridize with little or no fitness loss. Hybridization can be recognized by relatively small genetic differences between sympatric populations because sympatric populations have the opportunity to interbreed whereas allopatric populations do not. Using microsatellite DNA data from Darwin's finches in the Galapagos archipelago, we compare sympatric and allopatric genetic distances in pairs of Geospiza and Camarhynchus species. In agreement with the hybridization hypothesis, we found a statistically strong tendency for a species to be more similar genetically to a sympatric relative than to allopatric populations of that relative. Hybridization has been studied directly on two islands, but it is evidently more widespread in the archipelago. We argue that introgressive hybridization may have been a persistent feature of the adaptive radiation through most of its history, facilitating evolutionary diversification and occasionally affecting both the speed and direction of evolution.

Possible human impacts on adaptive radiation: beak size bimodality in Darwin's finches

“…Species integrity in a young adaptive radiation is usually attributed to some combination of low hybridization rates (formation of hybrids) and low hybrid fitness (survival and reproductive success; Schluter 2000). For ground finches, natural hybridization does occur and intrinsic genetic incompatibilities are lacking (Grant 1986;Grant & Grant 1996;Grant et al 2004Grant et al , 2005. Species integrity in this radiation thus depends at least in part on natural selection against hybrids that fall between ecological niches (Grant & Grant 1996).…”

“…Of particular relevance to our study, the small ground finch (Geospiza fuliginosa) has a small beak and preferentially consumes small/soft seeds, the large ground finch (Geospiza magnirostris) has a large beak and preferentially consumes large/hard seeds and the medium ground finch (Geospiza fortis) has an intermediate-sized beak and preferentially consumes intermediate-sized seeds. All of the ground finch species lack intrinsic genetic incompatibilities (Grant 1986;Grant & Grant 1996;Grant et al 2004Grant et al , 2005, and so may be susceptible to human impacts that promote species fusion.…”

Legal implications of range expansions in a terrestrial carnivore: the case of the golden jackal (Canis aureus) in Europe

“…It has been demonstrated that the probability of hybridization among canids is affected by the stability of social groups. [On wolf culling and hybridization with jackals (and also dogs) see Moura et al (2014); for effects of social group disruption on hybridization among canids see Grant et al (2005), Rutledge et al (2010Rutledge et al ( , 2012 and Bohling and Waits (2015)]. Survival of breeding individuals is the main factor affecting pack stability, and is under strong influence of anthropogenic mortality.…”

Origin of year-long bean (Phaseolus dumosusMacfady, Fabaceae) from reticulated hybridization events between multiplePhaseolusspecies

“…A further suggestive finding of the DArT analysis was the presence of admixture and genetic similarity between the representatives of P. dumosus and P. coccineus from Guatemala, including from the area of Quetzaltenango associated with the Santa Maria de Jesus volcano (Figs 1-3; Table 1). Between closely related species, a higher genetic similarity and higher admixture in regions of sympatry is considered good evidence of hybridization events occurring during speciation (Seehausen, 2004;Grant et al, 2005;McKinnon, 2005). The evidence for such a hybridization event can be summarized as follows: (1) intermediate morphology between P. coccineus and P. vulgaris; (2) ancient forms of P. dumosus are found only in Guatemala and are in sympatry with ancient forms of its putative parental, P. coccineus (Schmit and Debouck, 1991); (3) artificial crosses can produce fertile offspring (Freytag and Debouck, 2002); and (4) molecular evidence indicates an incongruence between relationships observed from nuclear and chloroplast genome analyses, now reconfirmed in this study across all available accessions of wild P. dumosus.…”