Founder events and variation at microsatellite loci in an insular passerine bird, the Laysan finch (Telespiza cantans)

Abstract

Historically documented founder events provide opportunities to assess the effects of population size reductions on genetic variation, but the actual magnitude of genetic change can be measured only when direct comparisons can be made to the source or ancestral population. We assayed variation at nine microsatellite loci in the translocated population of the Laysan finch (Telespiza cantans) at Pearl and Hermes reef (PHR), and compared the level of variation to that in the source population on Laysan Island. Heterogeneity in allele frequencies was highly significant at eight of the nine loci, primarily as a result of fluctuations in allele frequencies in the three PHR populations. Intra‐ and interpopulational measures of genetic diversity generally matched predictions based on the well‐documented history of three islet populations at PHR: significantly lower numbers of alleles and polymorphic loci, as well as higher pairwise FST values and genetic distance, were observed for the two populations that underwent severe size reductions. Changes in heterozygosity at single loci were unpredictable, as both significant increases and decreases were observed in founder populations. A significant excess of heterozygotes was found in two populations and was highly significant over all four finch populations (P < 0.003). Estimates of effective population size from temporal changes in heterozygosity and allele frequencies were very small (Ne≤ 30) as a result of the founding events and the constraints of islet area on population numbers. We concluded that the PHR population is not adequate as a secondary genetic reserve for T. cantans, and an alternative refuge needs to be established.

Microsatellite variation and rare alleles in a bottlenecked Hawaiian Islands endemic: implications for reintroductions

“…The Laysan teal harbors low genetic diversity compared to other island endemics (e.g. Tarr et al 1998, Fowler et al 2009, Bowker-Wright et al 2012, likely due to its comparatively long isolation and radical range restriction from across the Hawaiian Archipelago to a 412 ha remote island. Long-term genetic management of reintroduced species is often a low priority when short-term population establishment is successful.…”

“…adaptation capacity in the face of new diseases or other biotic and abiotic environmental changes). If endangered species recovery strategies include reintroduction, translocations with small numbers of founders and no immigration can lead to loss of genetic variation over time via genetic drift or low initial genetic capture (Weeks et al 2011) and can potentially reduce the reintroduced population's long-term persistence or its potential to serve as a suitable source for future translocations (Tarr et al 1998, Groombridge et al 2012.…”

Genetic Variation in the Spread of Drosophila Subobscura From a Nonequilibrium Population

“…This comparison parallels ours in several respects, because the source island also experienced a founder effect earlier this century. Nine microsatellites with similar levels of variability (two to five alleles per locus) were identified and typed in a previous study (Tarr et al 1998). However, unlike our study, actual founder numbers are known for this invasion (30-50 surviving), so they can be compared with the maximum and minimum numbers derived from our methodology.…”

“…Second, because no alleles were lost in the founding of the Utah population (see below), one can also perform sim- To test the validity of our simulations, we also used our simulation program to study the 1967 invasion of Laysan finches (Telespiza cantans) from Laysan Island to Southeast Island in the Hawaiian archipelago (Tarr et al 1998). This comparison parallels ours in several respects, because the source island also experienced a founder effect earlier this century.…”

“…Standard techniques for studying founder events assume mutation-drift equilibrium and many survey the loss of rare alleles. In the case of secondary founder events, the secondary source population was likely not at equilibrium and it likely possessed fewer loci bearing rare alleles than the primary source population (e.g., Luikart et al 1998a;Tarr et al 1998). The most powerful tool available for studying these founder events, or others from nonequilbrium populations, may be to analyze allele frequency differences between secondary source and secondary founder populations.…”