Abstract:Hybridisation and gene flow can have both deleterious and adaptive consequences for natural populations and species. To better understand the extent of hybridisation in nature and the balance between its beneficial and deleterious outcomes in a changing environment, information on naturally hybridising nonmodel organisms is needed. This requires the characterisation of the structure and extent of natural hybrid zones. Here, we study natural populations of five keystone mound‐building wood ant species in the Fo… Show more
Hybridization between invasive pest species may lead to signi cant genetic and economic impacts that require close monitoring. The two most invasive and destructive termite species worldwide, Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann), have the potential for hybridization in the eld. A three-year eld survey conducted during the dispersal ight season of Coptotermes in Taiwan identi ed alates with atypical morphology, which were con rmed as hybrids of the two Coptotermes species using microsatellite and mitochondrial analyses. Out of 27,601 alates collected over three years, 4.4% were con rmed as hybrid alates, and some advanced hybrids (>F1 generations) were identi ed. The hybrid alates had a dispersal ight season that overlapped with the two parental species 13 out of 15 times.Most of the hybrid alates were female imply that backcross mating opportunities beyond F1 may primarily be possible through female hybrids. However, the incipient colony growth results from all potential mating combinations suggest that only backcross colonies with hybrid males could sometimes lead to brood development. The observed asymmetrical viability and fertility of hybrid alates may critically reduce the probability of advanced-hybrid colonies being established in the eld.
Hybridization between invasive pest species may lead to signi cant genetic and economic impacts that require close monitoring. The two most invasive and destructive termite species worldwide, Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann), have the potential for hybridization in the eld. A three-year eld survey conducted during the dispersal ight season of Coptotermes in Taiwan identi ed alates with atypical morphology, which were con rmed as hybrids of the two Coptotermes species using microsatellite and mitochondrial analyses. Out of 27,601 alates collected over three years, 4.4% were con rmed as hybrid alates, and some advanced hybrids (>F1 generations) were identi ed. The hybrid alates had a dispersal ight season that overlapped with the two parental species 13 out of 15 times.Most of the hybrid alates were female imply that backcross mating opportunities beyond F1 may primarily be possible through female hybrids. However, the incipient colony growth results from all potential mating combinations suggest that only backcross colonies with hybrid males could sometimes lead to brood development. The observed asymmetrical viability and fertility of hybrid alates may critically reduce the probability of advanced-hybrid colonies being established in the eld.
The endpoint of speciation has been viewed as complete isolation and the absence of gene flow between species. If the influx of genes from another species is maladaptive because species have different adaptations and genetic backgrounds, selection should favour the closing of species boundaries and zero gene flow, a process known as reinforcement. Recently, numerous cases of gene flow between species have been identified, many of which involved adaptive introgression of beneficial alleles. These cases could reflect transient states on the way to closed species boundaries or the result of declining strength or efficacy of selection for reinforcement as the level of gene flow approaches zero. An alternative hypothesis, however, is that selection favours porous species boundaries that allow beneficial alleles to cross, especially in changing environments. This perspective evaluates the conditions that would be needed for selection to favour porous species boundaries and the evidence for them. A contrast is made between hybridization in sexual eukaryotes and gene transfer via homologous recombination in bacteria. Current evidence is inconclusive on whether non-zero gene flow is favoured by selection. Studies are needed that quantify selection gradients on rates of gene flow and test for evolution towards intermediate values, especially experiments that manipulate conditions and track evolution for multiple generations. Estimation of gene flow networks for more clades and regional assemblages using emerging genome data will also allow the evolutionary determinants of interspecific gene flow to be better understood.
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