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

Pond-breeding amphibians are deme-structured organisms with a population ge netic structure particularly susceptible to demographic threats. We estimat ed the effective number of breeding adults (N-b) and the effective populati on size (N-e) of the European urodele amphibians Triturus cristatus (the cr ested 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. ma rmoratus, albeit with high frequencies of null alleles at two loci. Three p onds in western France were sampled, situated 4-10 kilometres apart and inh abited by both species. Parent-offspring cohort comparisons were used to me asure N-b; samples collected at time intervals of nine or 12 years, respect ively, were used to measure N-e. The adult population census size (N) was d etermined by mark-recapture techniques. With one exception, genetic distanc es (F-ST) between temporal samples were lower than among populations. N-b r anged between 10.6 and 101.8 individuals, N-e ranged between 9.6 and 13.4 i ndividuals. For the pond where both parameters were available, N-b/N (overa ll range: 0.10-0.19) was marginally larger than N-e/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, N- b/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 b y T. cristatus only some decades ago, no significant genetic bottleneck cou ld be detected. Our findings give rise to concerns about the long-term demo graphic viability of amphibian populations in situations typical for Europe an landscapes.