A rangewide population genetic study of trumpeter swans

Abstract

For management purposes, the range of naturally occurring trumpeter swans (Cygnus buccinator) has been divided into two populations, the Pacific Coast Population (PP) and the Rocky Mountain Population (RMP). Little is known about the distribution of genetic variation across the species' range despite increasing pressure to make difficult management decisions regarding the two populations and flocks within them. To address this issue, we used rapidly evolving genetic markers (mitochondrial DNA sequence and 17 nuclear microsatellite loci) to elucidate the underlying genetic structure of the species. Data from both markers revealed a significant difference between the PP and RMP with the Yukon Territory as a likely area of overlap. Additionally, we found that the two populations have somewhat similar levels of genetic diversity (PP is slightly higher) suggesting that the PP underwent a population bottleneck similar to a well-documented one in the RMP. Both genetic structure and diversity results reveal that the Tri-State flock, a suspected unique, non-migratory flock, is not genetically different from the Canadian flock of the RMP and need not be treated as a unique population from a genetic standpoint. Finally, trumpeter swans appear to have much lower mitochondrial DNA variability than other waterfowl studied thus far which may suggest a previous, species-wide bottleneck.

Conservation genetics of the alligator snapping turtle: cytonuclear evidence of range-wide bottleneck effects and unusually pronounced geographic structure

“…For microsatellites, number of alleles per locus per population was much lower than reported in a comparable study of nine populations (n = 11-22; 5 loci) of diamondback terrapin (1.4-3.9 vs. 6.5-12.7;Hauswaldt and Glenn 2005) and well below the average (8.2; range = 1.5-18.0) in a review of turtle microsatellite DNA studies (FitzSimmons and Hart 2007). The range for alligator snapping turtles is well within that reported for populations showing bottleneck effects, including the review by Garza and Williamson (2001;2.1-5.3; 7 mammals, 1 fish), and a more recent report for trumpeter swan (2.4-3.2;Oyler-McCance et al 2007). Finally, the M-test detected potential past bottlenecks for 10 of 12 tested populations of alligator snapping turtle, and five populations showed evidence of past bottlenecks on the basis of at least two of the three tests (M-test, heterozygosity excess, allele size-class frequency).…”

Genetic consequences of trumpeter swan (Cygnus buccinator) reintroductions

“…Findings from a recent range-wide genetic study supported these delineations, revealing significant genetic differentiation at both microsatellite loci and mitochondrial sequence data between the RMP and the PP with the Yukon Territory as an area of admixture (Oyler-McCance et al 2007). Results indicated a non-significant trend of lower genetic diversity in the RMP relative to the PP.…”

“…Over-harvest and habitat destruction in the early part of the 1900s led to a significant reduction in trumpeter swan numbers, with the most dramatic decline being the complete extirpation of the species from the eastern portion of its range (Banko 1960). Through habitat protection and a moratorium on hunting migratory birds, trumpeter swans rebounded to total over 34,000 individuals forming the Rocky Mountain Population (RMP) and the Pacific Coast Population (PP) (Moser 2006;Oyler-McCance et al 2007; Fig. 1).…”

“…This may be explained by the fact that a severe population bottleneck occurred in the RMP in the early part of the twentieth century reducing the number of known breeding birds to 57 individuals (Bellrose 1976;Banko 1960). Additionally, Oyler-McCance et al (2007) found that trumpeter swans possessed lower than average mitochondrial diversity when compared with other waterfowl. This low genetic diversity is consistent with a study by Marsolais and White (1997) using minisatellite probes that found that trumpeter swans had higher band sharing coefficients, i.e.…”

“…Translocation events are well documented and studies evaluating the success of translocations based on demographic factors exist (Engelhardt et al 2000). The wild populations are genetically well characterized (Oyler-McCance et al 2007), allowing direct comparisons between source populations and restoration flocks. Further, reintroduced individuals originated from different numbers of sources (single or multiple disjunct populations) and include different types of flocks (wild-released and captive), providing an opportunity to assess the impact of alternative translocation strategies.…”