Genomics of hybridization and its evolutionary consequences

Abstract

Hybridization and its consequences have been of longstanding interest to evolutionary biologists. Darwin (1859) included a chapter on hybrids and the expression and causes of hybrid sterility in The Origin of Species, while the main proponents of the neoDarwinian synthesis discussed the topic at varying length in the mid-1900s (Haldane 1932;Dobzhansky 1937;Stebbins 1950;Mayr 1963). Subsequently, Grant (1981) underlined the importance of hybridization to plant evolution, devoting six chapters of Plant Speciation to the topic, while Arnold (1997;2006;2015) has written three books on hybridization and its evolutionary consequences over the last 20 years. Building upon this enduring foundation, there has been an enormous expansion in the study of hybridization over the past decade. This exciting resurgence has been fuelled by advances in DNA sequencing that now enable the rapid collection of genomic data across the tree of life and the ongoing development of population genetic theory and analytical tools that facilitate the analysis and interpretation of these powerful data.

Patterns of genetic, phenotypic, and acoustic variation across a chiffchaff (Phylloscopus collybita abietinus/tristis) hybrid zone

“…Distinguishing between these scenarios makes it possible to understand the mechanisms underlying variation in observed patterns of biodiversity across regions. Hybrid zones, geographic regions where there is an overlap between distribution ranges and gene flow occurs between taxonomic units, can serve as “natural laboratories” allowing for close observation of microevolutionary processes that may lead to population differentiation and, ultimately, speciation (Abbott, Barton, & Good, 2016; Barton & Hewitt, 1989; Payseur & Rieseberg, 2016). In the Palearctic and Nearctic regions, such hybrid zones are naturally most often secondary contact zones, the results of distribution range expansions following the latest glaciation period (Hewitt, 2004, 2011).…”

“…By studying the secondary contact hybrid zones closely, we may investigate if there are any barriers to gene flow between the taxa involved and combine that with information about potential forces behind divergence, that is if taxa have diverged because of random acquisition of incompatibility alleles (observed trait differences not related to ecology) or if adaptation has played a major role in the divergence process (potential trait differences clearly associated with ecology) (Toews & Irwin, 2008). In addition, studying secondary contact zones can give information about the designation of lineages with unclear taxonomic status by allowing for quantification of genetic differentiation and potential introgression between involved taxa (Abbott et al., 2016; Delmore et al., 2015; Payseur & Rieseberg, 2016). …”

Persistence of an endangered native duck, feral mallards, and multiple hybrid swarms across the main Hawaiian Islands

“…However, given the lack of large, pure populations of koloa into which hybrids can backcross, hybrid swarms will likely persist on these islands. Continued interbreeding or backcrossing with feral mallards risks the complete loss of koloa genetics on these islands (Abbott, Barton, & Good, ; Allendorf et al, ).…”

Similar Morphologies but Different Origins: Hybrid Status of Two More Semi-creeping Taxa of Melastoma

“…Therefore, it is probable that rapid concerted evolution resulted in the homogenization of the M. normale nrITS copy in the individual. Even at a low level of introgression, adaptive alleles and corresponding adaptive traits may be transferred from one species to another, likely contributing to adaptation to various environments (Abbott et al, 2016; e.g., Lamichhaney et al, 2016). The extent of introgression and loci of adaptive introgression in Melastoma can be further explored with genomic scanning in the future.…”