5.13. Introductions – work for hunting or conservation?

Hand-rearing and releasing can be used for conservation of endangered species or biodiversity (Kleiman et al. 1994, Cade & Temple 1995). On the other hand, conservation efforts may fail because maladaptive traits are introduced into populations when hand-reared individuals are released into the wild. Despite the previous releasing actions of grey partridges (Putaala & Hissa 1998), only five grey partridges of the western lineage were found in the wild population in Finland, which, in general, represented the eastern mtDNA lineage. On the other hand, the farm stocks represented the western lineage as well. The Irish and Swedish populations consisted of both mtDNA lineages, which was probably an evidence of historical releases of imported birds (Westerskov 1958).

The wild population in Italy consisted of two different haplotypes, while the Italian farm stock consisted mainly of the basic western haplotype. According to Lovari (1975) the native Italian P. p. italica still existed back in 1975 in the district of Tuscany, the same area from where the samples of this study were collected in 1998. P. p. italica as its purest form is presumed extinct (Matteucci 1988), because of the intensive releasing of farm birds in Italy (Matteucci 1988, Montagna et al. 1990). Both P. p. italica and P. p. hispaniensis are listed as endangered subspecies of the grey partridge in the Annex I (http://europa.eu.int/comm/environment/nature/directive/perdix_perdix_hispaniensis_en. htm, and http://europa.eu.int/comm/environment/nature/directive/perdix_perdix_italica_ en.htm, 10.5.2001) of the European Union (EU).

Despite the numerous releases of grey partridges, amazingly few marks of these could be seen in continental Europe. One possible explanation, in addition to natural selection (Darwin 1859), may be found in the Haldane’s rule (Haldane 1922), which states: “when in the F₁ offspring of two different animal races one sex is absent, rare or sterile, that sex is the heterozygous [heterogametic]; sex”. Haldane based his rule on a study of 45 Lepidopteran, 10 bird and six mammalian crosses. In birds, female is the heterogametic sex (ZW) and will show sterility in interspecific matings, even though males were still fertile. In twenty-one avian species hybrid female offspring is known to be partially or completely inviable, and in thirty species hybrid female offspring is sterile (for review, see Laurie 1997). Because mtDNA is maternally inherited, the possible reduced viability or even sterility of the hybrid female offspring of two different subspecies may explain the slight expression of the massive releasing activity in mtDNA in the present populations. However, this aspect remains to be studied.

Unsuccessful introductions may result from the maladaptation of birds to climatic or environmental conditions of the introduction areas. In hand-rearing for conservation purposes, the genetic origin of the animals should be compatible with the wild ones of the releasing site (Rave et al. 1994, Glenn et al. 1999). The genetic similarity of wild and hand-reared birds should preserve local adaptation and avoid harmful effects of outbreeding (Templeton 1986). Even though animals are released only for hunting purposes, without any target for increasing the population size, this does not totally remove the risk for outbreeding depression. Some of the released individuals may survive in the wild and breed later. The hybridisation between the released alien and local subspecies may reduce fitness and adaptation to local conditions by a disruption of adaptive gene complexes (Templeton 1986).