Estimate effect of introgressive hybridization on wild
populations
All three datasets (mitochondrial, microsatellites and SNPs) show that
captive stocks in both the UK and Greece have been predominantly derived
from birds of western origin (Perdix perdix perdix ). However,
there is also evidence of Eastern genotypes within both these captive
populations, signalling that birds of the eastern lineage (Perdix
perdix lucida ) have also been used for captive breeding. However,
considering that in both the UK and Greece, individuals from captive
stocks are released each year, very little evidence of hybrids within
the wild individuals has been found; one hybrid individual was
identified in the UK and five in Greece/North Macedonia based on
microsatellites (Figure 4). Although they provide insight, the use of
just eight microsatellites has limitations. As can be seen with the
known hybrid individuals, only three out of the six can be identified as
hybrids using this microsatellite data. However, even when considering
the robust SNP data, there is no evidence of F1 hybrids in the wild
(Figure 7), although the microsatellite data indicates that there may be
one wild F1 hybrid in the UK dataset (Figure 4).
Obviously, Greece would be predicted to have a larger number of hybrids,
considering the captive stocks being released are of Western origin,
however, there is very little evidence to suggest that hybridization has
occurred within the wild Greek birds. This contrasts with neighboring
North Macedonia where all our genetic datasets (mitochondrial,
microsatellite and SNPs) indicate that individuals of both eastern and
western genealogies are present in the wild population. However, as
already discussed, whether this is a natural transition zone betweenP. p. perdix and P. p. lucida or the result of captive
releases requires further investigation. The differences between levels
of hybridization in the captive stocks compared to the wild individuals
in both the UK and Greece are intriguing. Several reasons could explain
this: 1) Released birds do not survive and therefore do not contribute
to the wild gene pool, 2) Released hybrid individuals do not survive and
contribute to the wild gene pool, 3) Hybridization within the captive
stocks is a relatively recent phenomenon and not many hybrids have been
released yet, 4) The numbers of released birds have been very small
compared to the wild population. We argue that the last point is
unlikely, as the grey partridge has been the most important European
game bird for centuries and there is historical evidence that stocking
and translocations have been conducted throughout Europe as far back as
the 1560s (Andersen and Kahlert, 2012). The other common name of the
grey partridge (the Hungarian Partridge) is based on the widespread
exporting of captive stock from Hungary across Europe and to North
America during the 20th century (Browne, Buner and Aebischer, 2009).
Estonian and French birds were more recently imported into Ireland for
captive breeding between 2002-2005 (Buckley et al. , 2012). This
widespread sharing of game bird stock across Europe is of routine and
historical occurrence. However, the geographical origins of captive
stock are rarely known. Regarding the third point, it does seem that
captive populations are mainly of Western origin. This has been the
finding of our study in both the UK and Greece but also of the two
previous genetic studies in Finland and Denmark (Liukkonen-Anttilaet al. , 2002; Andersen and Kahlert, 2012) It is, therefore,
feasible that hybridization is of limited success or has not occurred
until recently. However, regarding the two first points, multiple
studies have found that released birds have very low survival (Brittaset al. , 1992; Mallord et al. , 2024). This is the most
likely explanation for Greece, where releases of captive birds have
occurred since the 1980s, but without evidence of western genotypes in
the wild populations yet. However, contrasting with Greece, in the UK we
failed to find evidence of genetic structure between wild populations
within the UK. These wild populations also share genetic similarities to
the captive population based on mitochondrial (Figure 3) and
microsatellite data (Figure S3_Appendix). Considering the low dispersal
of Grey Partridge, this is indicative of widespread historic
translocation of birds and/or the survival of captive releases.