The successful founder: genetics of introduced Carduelis chloris (greenfinch) populations in New Zealand

Abstract

The amount and distribution of genetic variation in seven introduced New Zealand populations of Carduelis chioris were assessed at 40 loci using starch gel electrophoresis and compared with those in native European populations. Fewer alleles (1.45) and fewer polymorphic foci (33 per cent) were detected across the introduced populations than across native populations (1.75, 55 per cent), reflecting the narrow geographical origin of the introduced populations. There was no evidence for severe inbreeding or genetic drift as the levels of average heterozygosity (H = 0.025), percentage polymorphic loci (P = 16.9) and average number of alleles per locus (A = 1.22) were indistinguishable from levels observed within European populations (H = 0.025, P 14.1, A = 1.19). Furthermore, introduced populations were genetically less weakly differentiated (FST = 0.022) than native populations (FST = 0.041), indicating that little genetic drift has been involved in the colonization of the new range.Similar levels of genetic variability in native and introduced greenfinch populations are consistent with theoretical expectations as the founder population size was relatively large (>60 individuals) and a rapid increase in population size directly after colonization was documented.A review of earlier studies on introduced birds also revealed that reductions in levels of genetic variability seem to be inversely proportional to the size of the founder population, and that less variation has been lost if the rate of population growth directly after introduction was fast.

Rescue of a severely bottlenecked wolf (Canis lupus) population by a single immigrant

“…Moreover, the genetic variability is signi cantly lower in the contemporary Scandinavian wolf population than in the eastern or historical wolves (table 2; Wilcoxon's signed rank test for the expected heterozygosity and number of alleles, p , 0.05 in both cases). Low genetic diversity and strong differentiation are consistent with a very small number of individuals founding the Scandinavian population and stress the in uence of genetic drift (Barton & Charlesworth 1984;Merilä et al 1996;Tarr et al 1998). The founding effect may have formed, in just 15 years, a population that is highly differentiated from the source population.…”

Origin and colonization history of the white-clawed crayfish, Austropotamobius pallipes, in Ireland

“…The loss of genetic variation could be extremely rapid throughout the genome in small or localized populations founded by a few individuals and cut off from gene exchange with the main body of the species (Planes and Lecaillon, 1998). In a review of studies of introduced birds, Merilä et al (1996) noted that reductions in genetic diversity tended to be inversely correlated with the number of individuals released. Thus, according to our results, it seems likely that Irish white-clawed crayfish are derived from a low number of introduced individuals translocated from populations in western France.…”

Hatching failure increases with severity of population bottlenecks in birds

“…3). A review of genetic variation in introduced bird species between their native and introduced ranges (including five species from New Zealand) found that more severe bottlenecks indeed reduced genetic variability in the resulting populations (34). Further genetic studies are required to confirm this pattern in both the native and introduced species in this study, but our results suggest that severe bottlenecks result in measurable fitness costs and that this result is consistent with that expected by increased inbreeding and the loss of genetic diversity when populations drop to small numbers.…”