Detecting introgressive hybridisation in rock partridge populations (Alectoris graeca) in Greece through Bayesian admixture analyses of multilocus genotypes

Abstract

The nominal subspecies of rock partridge (Alectoris graeca graeca) is widely distributed in Greece, where populations are declining due to overhunting and habitat changes. Captive-reared chukars (A. chukar) have been massively released throughout the country, raising fear that introgressive hybridisation might have disrupted local adaptations leading to further population declines. In this study we used mtDNA control-region sequences and Bayesian admixture analyses of multilocus genotypes determined at eight microsatellite loci, to assess the extent of introgressive hybridisation in 319 wild rock partridges collected in Greece. A neighbour-joining tree split the mtDNA haplotypes into three strongly supported clades, corresponding to rock, red-legged (A. rufa) and chukar partridges. We did not detect any case of maternal introgression. In contrast, admixture analyses of microsatellite genotypes identified from four to 28 putative hybrids (according to different assignment criteria), corresponding to 1.2-8.8% of the samples, which were widespread throughout all the country. Power and limits of admixture analyses were assessed using simulated hybrid genotypes, which revealed that a small number of markers can detect all first and second generation hybrids (F 1 and F 2 ), and up to 90% of the first generation backrossess. Thus, the true proportion of recently introgressed rock partridges in Greece might be ca. 20%. These findings indicate that introgressive hybridisation is widespread, suggesting that released captive-bred partridges have reproduced and hybridised in nature polluting the gene pool of wild rock partridge populations in Greece.

Mitochondrial DNA and microsatellite markers evidence a different pattern of hybridization in red-legged partridge (Alectoris rufa) populations from NW Italy

“…The Bayesian clustering procedure identified seven putative introgressed individuals (6.5 % of the total sample) in comparison to 34 cases of maternal introgression (19.3 % of the total sample) directly found by discordant mtDNA and morphological traits. As previously reported by Barilani et al (2007b), the low levels of nuclear introgression (all specimens showed ^>90 %) and the presence of chukar haplotypes suggest that the admixed individuals could have had a hybrid ancestry with exotic partridges over the second past generation. In the BC subpopulation, both markers suggest the exclusion of recent admixture events with the chukar genome.…”

“…If an individual did not fit this requirements, it was classified as putative hybrid. A more rigorous threshold with respect to Barilani et al (2007b) was chosen to improve the accuracy of hybrid detections (Vaha and Primmer 2006). In so doing, we used Structure to estimate the posterior probability that each individual belonged to each species or that it had fractions of its genome from two parental species.…”

“…The hybrids between black grouse Tetrao tetrix and capercaillie Tetrao urogallus are the most common patterns of grouse hybridization (Porkert et al 1997). A growing body of evidence suggests that the introduction of exotic species and the translocation of captive-reared animals or artificial hybrids have a negative impact on the integrity of local populations, leading to disruption of coadapted gene complexes and loss of local adaptations (Allendorf et al 2001;Randi 2005Randi , 2008Williams et al 2005;Barilani et al 2007b;Barbanera et al 2010;De Haan et al 2010). These detrimental effects may result in reduced fitness and demographic decline (outbreeding depression; Templeton 1986), concurring to the disappearance of wild populations.…”

Detection of hybrids in nature: application to oaks (Quercus suber and Q. ilex)

“…Similarly, some uncertainty is involved in the identity of the 10 remaining individuals (Figure 2). Our simulations indicated that the identification of backcrosses is more problematic than that of F1 hybrids, because they can be confused with pure individuals and Detection of hybrids in oaks C Burgarella et al vice versa, as already shown with other hybrid systems (Barilani et al, 2007). The extent of incorrect classification can be minimized by choosing an appropriate threshold to improve accuracy (and reduce error), whereas accepting the associated trade off of loss of power (Vähä and Primmer, 2006).…”

Hybridization versus conservation: are domestic cats threatening the genetic integrity of wildcats (Felis silvestris silvestris) in Iberian Peninsula?

“…The risk of introgression of domestic cat genes into wildcat gene pools is a big concern to conservation biologists, since most wildcat populations are now in juxtaposition with the urban ranges of feral domestic cats (Stahl & Artois 1994). Cross-breeding with domesticated forms may culminate in the homogenization of gene pools and result in outbreeding depression, reduced fitness and, consequently, severe population declines of wild populations (Barilani et al 2007). Especially for closely related (sub)species, identifying the ecological and biological driving forces of this phenomenon can be exceptionally challenging.…”