Hybridization and hybrid speciation under global change

Abstract

Contents Summary1170I.Introduction1170II.Hybrid formation1172III.Hybrid establishment: overcoming intrinsic and extrinsic post‐zygotic barriers1175IV.Outcomes of hybridization1180V.Outlook1183Acknowledgements1184References1184 Summary An unintended consequence of global change is an increase in opportunities for hybridization among previously isolated lineages. Here we illustrate how global change can facilitate the breakdown of reproductive barriers and the formation of hybrids, drawing on the flora of the British Isles for insight. Although global change may ameliorate some of the barriers preventing hybrid establishment, for example by providing new ecological niches for hybrids, it will have limited effects on environment‐independent post‐zygotic barriers. For example, genic incompatibilities and differences in chromosome numbers and structure within hybrid genomes are unlikely to be affected by global change. We thus speculate that global change will have a larger effect on eroding pre‐zygotic barriers (eco‐geographical isolation and phenology) than post‐zygotic barriers, shifting the relative importance of these two classes of reproductive barriers from what is usually seen in naturally produced hybrids where pre‐zygotic barriers are the largest contributors to reproductive isolation. Although the long‐term fate of neo‐hybrids is still to be determined, the massive impact of global change on the dynamics and distribution of biodiversity generates an unprecedented opportunity to study large numbers of unpredicted, and often replicated, hybridization ‘experiments’, allowing us to peer into the birth and death of evolutionary lineages.

Hybridization in Plants: Old Ideas, New Techniques

“…One reason for this trend is that genomic data are particularly well suited to address the problem of detecting gene flow. Another is the growing recognition that hybridization is widespread and may have significant evolutionary consequences, a long-held belief about plants that is increasingly extended to animals (Mallet, 2005;Arnold, 2006;Abbott et al, 2013;Vallejo-Marín and Hiscock, 2016).…”

Partial interfertility between independently originated populations of the neo-allopolyploid Mimulus peregrinus

“…Despite the widespread occurrence of WGD, polyploids need to surmount considerable challenges arising at their origin, including genetic and meiotic instability, minority cytotype disadvantage, and ecological competition with parental taxa (Levin 1975;Ramsey and Schemske 2002;Comai 2005;Arrigo and Barker 2012;Soltis et al 2014b;Vallejo-Marín and Hiscock 2016). One of the challenges that polyploids need to overcome is the expected reduction in genetic diversity associated with the birth of a polyploid species.…”

Interspecies gene flow is a key evolutionary process for the adaptation of long-lived species to new environmental conditions

“…In long lived animals, a single case of homoploid speciation has been documented in a dolphin genus (Amaral et al, 2014). Homoploid hybrid speciation is considered to be rare both in plants and animals, likely because it requires several restrictive conditions, i.e., the arising of a stable, fertile and reproductively isolated hybrid lineage without change in chromosome number (Vallejo-Marin & Hiscock, 2016). Reproductive isolation between parental and hybrid taxa may be achieved by diverse evolutionary processes.…”

“…Theory predicts that, besides species intrinsic properties regarding pre-zygotic barriers and postzygotic isolation forces (see Vallejo-Marin & Hiscock, 2016, for a review), interspecies hybridization depends on environmental factors, more specifically the habitat and climate conditions, determining the relative abundance of species and the relative frequency of gametes involved in intra-and interspecific reproduction (Cannon & Lerdau, 2015;Klein et al,2017). In long-lived species predominantly consisting of large primarily outcrossing organisms with slow replacement rate (see above), under unfavourable environmental conditions, individual's survival is generally favoured over their reproductive investment (Bromham, 2011).…”