The annual number of breeding adults and the effective population size of syntopic newts (Triturus cristatus, T. marmoratus)

Abstract

Pond‐breeding amphibians are deme‐structured organisms with a population genetic structure particularly susceptible to demographic threats. We estimated the effective number of breeding adults (Nb) and the effective population size (Ne) of the European urodele amphibians Triturus cristatus (the crested newt) and T. marmoratus (the marbled newt), using temporal shifts in microsatellite allele frequencies. Eight microsatellite loci isolated from a T. cristatus library were used, five of which proved polymorphic in T. marmoratus, albeit with high frequencies of null alleles at two loci. Three ponds in western France were sampled, situated 4–10 kilometres apart and inhabited by both species. Parent–offspring cohort comparisons were used to measure Nb; samples collected at time intervals of nine or 12 years, respectively, were used to measure Ne. The adult population census size (N) was determined by mark–recapture techniques. With one exception, genetic distances (FST) between temporal samples were lower than among populations. Nb ranged between 10.6 and 101.8 individuals, Ne ranged between 9.6 and 13.4 individuals. For the pond where both parameters were available, Nb/N (overall range: 0.10–0.19) was marginally larger than Ne/N (overall range: 0.09–0.16), which is reflected in the temporal stability of N. In line with the observed differences in reproductive life‐histories between the species, Nb/N ratios for newts were about one order of magnitude higher than for the anuran amphibian Bufo bufo. Despite of the colonization of the study area by T. cristatus only some decades ago, no significant genetic bottleneck could be detected. Our findings give rise to concerns about the long‐term demographic viability of amphibian populations in situations typical for European landscapes.

Amphibian molecular ecology and how it has informed conservation

“…Of particular importance for conservation has been accurately estimating population size and population structure across multiple scales. To get a sense of effective and census population sizes, Jehle et al (2001) analysed eight microsatellite loci in Triturus cristatus from three ponds. They found that effective population sizes were very small, on the order of 10 individuals.…”

Effective number of breeders and maintenance of genetic diversity in the captive bearded vulture population

“…with S 0 and S t being the number of individuals sampled at time 0 and t, respectively, and, N obs being the size of the population subject to sampling at time zero (Waples, 1989b;Jehle et al, 2001). If the changes in allele frequencies from parent to offspring are used to calculate F c , as was the case here, the result in equation (4) reflects the N erelated parameter N b , the effective number of breeders (Scribner et al, 1997).…”

“…We therefore used F ST for direct comparisons between temporal degrees of differentiation within the captive population (Jehle et al, 2001). Individual inbreeding coefficients from pedigree data were calculated with the studbook computer program (Zschokke, 2000).…”

Estimating the propagule size of a cryptogenic crested newt population

“…data). Effective population sizes (N e ) in total six ponds are more variable, with N e /n ratios ranging between 0.07 and 0.51 buffered against census sizes (small populations have a higher N e /n ratio than larger populations, Jehle et al, 2001Jehle et al, , 2005. Because of the uncertainty involved (N e estimates are accompanied by large confidence intervals), we allowed for a large range (50oN K o5000).…”