Phenotypic differences in body size, body condition and circulating carotenoids between hybrid and “pure” red-legged partridges (Alectoris rufa) in the wild

Abstract

In the last decades, the release of large numbers of farmed-reared birds became a widespread management practice for game species. The red-legged partridge (Alectoris rufa) is a quarry species with a high economic impact in rural areas of southwest Europe. In order to increase productivity and produce heavier birds, farmed red-legged partridges have often been hybridized with Chukar partridges (A. chukar), although these species have allopatric distribution ranges. During restocking, hybrid birds may be released into wild populations and may subsequently successfully breed, thus threatening the genetic integrity of native A. rufa populations. In this study, we compared several phenotypic indicators (body size, body condition and physiological state) between “pure” and hybrid partridges in order to evaluate the possible consequences of A. chukar genetic introgression into A. rufa. For this purpose, we captured 115 wild red-legged partridges during the breeding seasons 2003–2005 in four game estates of central Spain. We observed a greater occurrence of hybrid A. rufa × A. chukar partridges nearby the sites where the release of farmed-birds took place. We also found that hybrid males were smaller and hybrid females had better body condition and lower plasma carotenoid concentration than pure partridges of the same sex. Low carotenoid levels in blood plasma might be a limitation for female reproduction (fewer carotenoids available for ornamentation or to allocate to eggs). Overall, our results showed a greater occurrence of hybrids near restocking areas and phenotypic differences between hybrids and “pure” partridge in the wild. Genetic controls of farm-reared partridges should be a key step to prevent the releases of hybrids and ensure the maintenance of the genetic integrity of wild red-legged partridge populations.