Abstract
Interbreeding of two species in the wild implies introgression of alleles from one species into the other only when admixed individuals survive and successfully backcross with the parental species. Consequently, estimating the proportion of first generation hybrids in a population may not inform about the evolutionary impact of hybridization. Samples obtained over a long time span may offer a more accurate view of the spreading of introgressed alleles in a species’ gene pool. Common quail (Coturnix coturnix) populations in Europe have been restocked extensively with farm quails of hybrid origin (crosses with Japanese quails, C. japonica). We genetically monitored a common quail population over 15 years to investigate whether genetic introgression is occurring and used simulations to investigate our power to detect it. Our results revealed that some introgression has occurred, but we did not observe a significant increase over time in the proportion of admixed individuals. However, simulations showed that the degree of admixture may be larger than anticipated due to the limited power of analyses over a short time span, and that observed data was compatible with a low rate of introgression, probably resulting from reduced fitness of admixed individuals. Simulations predicted this could result in extensive admixture in the near future.
Highlights
Interspecific hybridization and its evolutionary consequences are often studied by analysis of samples obtained over a relatively short time period, without aiming to monitor genetic changes over time
Since mitochondrial DNA (mtDNA) is maternally inherited and common quail and Japanese quail have well differentiated sequences (Barilani et al, 2005), this marker is useful for establishing directionality in hybrid matings
We found that increased introgression of farm alleles would not be consistently detectable unless the proportion of potential breeders coming from farms was above 3%, higher than the proportion observed in our study area
Summary
Interspecific hybridization and its evolutionary consequences are often studied by analysis of samples obtained over a relatively short time period, without aiming to monitor genetic changes over time. This approach may allow identification of admixed individuals, but it may not be informative about the evolutionary impact of introgressive hybridization. When hybrids have reduced fitness or are infertile, hybridization might not have a large impact on the genetic composition of the parental species Hybridization in such cases will still imply a loss of intraspecific mating opportunities, reducing the effective breeding population (accelerating genetic drift). If alien alleles do introgress into the gene pool of the native population, hybridization can have long-term fitness consequences (Rhymer and Simberloff, 1996; Haygood et al, 2003)
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