Contemporary gene flow and the spatio‐temporal genetic structure of subdivided newt populations (Triturus cristatus,T. marmoratus)

Abstract

Gene flow and drift shape the distribution of neutral genetic diversity in metapopulations, but their local rates are difficult to quantify. To identify gene flow between demes as distinct from individual migration, we present a modified Bayesian method to genetically test for descendants between an immigrant and a resident in a nonmigratory life stage. Applied to a metapopulation of pond‐breeding European newts (Triturus cristatus, T. marmoratus) in western France, the evidence for gene flow was usually asymmetric and, for demes of known census size (N), translated into maximally seven reproducing immigrants. Temporal sampling also enabled the joint estimation of the effective demic population size (Ne) and the immigration rate m (including nonreproductive individuals). Ne ranged between 4.1 and 19.3 individuals, Ne/N ranged between 0.05 and 0.65 and always decreased with N; m was estimated as 0.19–0.63, and was possibly biased upwards. We discuss how genotypic data can reveal fine‐scale demographic processes with important microevolutionary implications.

Estimating the propagule size of a cryptogenic crested newt population

“…A single inseminated female (newts are characterized by internal fertilization) would contribute four chromosomes into the newly founded population, and multiple matings (a regular occurrence in newts, Halliday, 1998) could increase this number. On the other hand, it is likely that not all introduced individuals would have reproduced (evidenced through N e /n ratios for large-bodied newts being well below unity, Jehle et al, 2005), and the census propagule size would probably have been larger that the estimated number of 58 (116/2) diploid individuals. Louis Vall´ee's introduction was presumably not a deliberate attempt to establish a new T. cristatus colony, but rather the semi-accidental release of a few animals redundant from morphological studies.…”

“…The introduced 30-50 individuals represent an N e of 21-33, so N e /n is in the 0.4-1.0 range, and N K is in the range of 200-500. However, the N e /n ratio is not necessarily linear, with small populations having a larger proportion of breeders (Ardren & Kapuscinski, 2003;Jehle et al, 2005;Ficetola et al, 2009) and, as noted, N e estimates are accompanied by large confidence intervals. Because of the uncertainty involved, we evaluated the effect of N K on the estimate of c over a large range (20oN K o500).…”

“…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).…”

“…The population census size (n) of the colony is unknown, but estimates have been made in two similar field ponds in the same study area over the last three decades (ponds 278 and 2D5; see fig. 2 in Arntzen et al, 2009), where large-bodied newts population size (including T. cristatus and T. marmoratus) has been fairly stable in the range of 200-300 adults (Jehle et al, 2005;J. W. Arntzen, unpubl.…”

“…We used the eight polymorphic microsatellite loci and associated genotyping procedures outlined in Krupa et al (2002) and Jehle et al (2005) to genetically characterize our study populations. Polymerase chain reactions (PCRs) were performed in Hybaid thermal cyclers (Hybaid Ltd, Basingstoke, UK), and PCR products were separated on an Applied Biosystems model 377 semi-automated sequencer (Foster City, CA, USA).…”