Effective Population Sizes and Temporal Stability of Genetic Structure in Rana Pipiens, the Northern Leopard Frog

Abstract

Abstract. Although studies of population genetic structure are very common, whether genetic structure is stable over time has been assessed for very few taxa. The question of stability over time is particularly interesting for frogs because it is not clear to what extent frogs exist in dynamic metapopulations with frequent extinction and recolonization, or in stable patches at equilibrium between drift and gene flow. In this study we collected tissue samples from the same five populations of leopard frogs, Rana pipiens, over a 22-30 year time interval (11-15 generations). Genetic structure among the populations was very stable, suggesting that these populations were not undergoing frequent extinction and colonization. We also estimated the effective size of each population from the change in allele frequencies over time. There exist few estimates of effective size for frog populations, but the data available suggest that ranid frogs may have much larger ratios of effective size (N e ) to census size (N c ) than toads (bufonidae). Our results indicate that R. pipiens populations have effective sizes on the order of hundreds to at most a few thousand frogs, and N e /N c ratios in the range of 0.1-1.0. These estimates of N e /N c are consistent with those estimated for other Rana species. Finally, we compared the results of three temporal methods for estimating N e . Moment and pseudolikelihood methods that assume a closed population gave the most similar point estimates, although the moment estimates were consistently two to four times larger. Wang and Whitlock's new method that jointly estimates N e and the rate of immigration into a population (m) gave much smaller estimates of N e and implausibly large estimates of m. This method requires knowing allele frequencies in the source of immigrants, but was thought to be insensitive to inexact estimates. In our case the method may have failed because we did not know the true source of immigrants for each population. The method may be more sensitive to choice of source frequencies than was previously appreciated, and so should be used with caution if the most likely source of immigrants cannot be identified clearly.Key words. Anuran, genetic structure, microsatellite, Rana pipiens, temporal stability, temporal variation, variance effective size. A fundamental goal of population genetics is to understand the relative importance of microevolutionary forces in determining the existing patterns of genetic variation within a species. Consequently, using molecular markers to estimate parameters such as the effective sizes of, and migration rates among, natural populations has become a major focus in the field of evolutionary biology. However, elucidation of past processes and the prediction of future patterns from molecular data requires that a state of equilibrium have developed between genetic drift and gene flow in the populations of interest. Demographic instability can disrupt that equilibrium (Whitlock 1992), rendering single ''snapshot'' estimates of population struc...

Effective number of breeding adults in Oregon spotted frogs (Rana pretiosa): genetic estimates at two life stages

“…The N e /N ratio estimated for the adult population was 0.086, which again is in the general range of DNA-based estimates for other ranid frogs (Hoffman et al 2004;Schmeller and Merila 2007). Thus, our data are consistent with previous suggestions that N e /N ratios in ranid frogs are in the typical range for vertebrates (e.g., *0.1-0.4), while those for bufonids are much lower (Hoffman et al 2004;Brede and Beebee 2006). Our main objective was to test a hypothesis about what features of the life cycle of R. pretiosa cause N e to be reduced relative to N. By obtaining separate N b estimates using egg and metamorph samples we could determine if these N b estimates differed from each other and from the simple estimate from counting egg massesN ab À Á .…”

“…Estimates from these various methods are listed along with their 95% confidence intervals (Bayesian credible intervals for the TL estimates) and N b /N ratios Beebee 2006). The N e /N ratio estimated for the adult population was 0.086, which again is in the general range of DNA-based estimates for other ranid frogs (Hoffman et al 2004;Schmeller and Merila 2007). Thus, our data are consistent with previous suggestions that N e /N ratios in ranid frogs are in the typical range for vertebrates (e.g., *0.1-0.4), while those for bufonids are much lower (Hoffman et al 2004;Brede and Beebee 2006).…”

“…What features of the life histories of different species might predispose them to have different ratios? For example, there is some intriguing evidence that toads of the genus Bufo have N e /N ratios an order of magnitude lower than those of frogs of the genus Rana (Hoffman et al 2004;Brede and Beebee 2006). Understanding what factors in the life cycle of amphibians are most responsible for reductions in N b or N e could be very useful for managing loss of genetic diversity in these taxa.…”

Estimating effective population size of guanacos in Patagonia: an integrative approach for wildlife conservation

“…Genetic N e /N ratios as low as ours (0.027-0.069), though not common, have been reported for fish (Miller and Kapuscinski 1997) and amphibians (Rowe and Beebee 2004;Easteal 1985;Hoffman et al 2004;Miller and Kapuscinski 1997;Scribner et al 1997 (Waples et al 2013)] are mostly appreciably higher than those of guanacos.…”

Genetic rescue of an inbred captive population of the critically endangered Puerto Rican crested toad (Peltophryne lemur) by mixing lineages

“…Peltophryne lemur is moderately variable at the six microsatellite loci. Within-population genetic diversity (H E ) is similar to or greater than that found for microsatellite loci in several other amphibians (Rowe et al 1998;Palo et al 2003;Brede and Beebee 2004;Martinez-Solano et al 2005;Arens et al 2006), while only a few have been found to have substantially greater H E (Austin et al 2003;Burns et al 2004;Hoffman et al 2004). Allelic diversity for P. lemur is comparable to several species examined over similar and larger geographical scales, despite much larger sample sizes for some (Rowe et al 1998;Palo et al 2003;Brede and Beebee 2004;Kraaijeveld-Smit et al 2005;Arens et al 2006).…”