RESUMEN
Finding optimal sample sizes is critical for the accurate estimation of genetic diversity of large invasive populations. Based on previous studies, we hypothesized that a minimal sample size of 3-8 individuals is sufficient to dissect the population architecture of the harlequin lady beetle, Harmonia axyridis, a biological control agent and an invasive alien species. Here, equipped with a type IIB endonuclease restriction site-associated (2b-RAD) DNA sequencing approach, we identified 13,766 and 13,929 single nucleotide polymorphisms (SNPs), respectively, among native and invasive H. axyridis populations. With this information we simulated populations using a randomly selected 3000 SNPs and a subset of individuals. From this simulation we finally determined that six individuals is the minimum sample size required for the accurate estimation of intra- and inter-population genetic diversity within and across H. axyridis populations. Our findings provide an empirical advantage for population genomic studies of H. axyridis in particular and suggest useful tactics for similar studies on multicellular organisms in general.
RESUMEN
Analysis of population genetics provides insights into the evolutionary processes, among which the sample size choice is per se a crucial issue in the analysis. Genome-wide high-throughput techniques based on RADseq have been increasingly used in studies on the population genomics of invasive species. However, there is little information available regarding optimal sample sizes for analyzing population genomics of invasive species. In this study, we first use type IIB endonucleases restriction site-associated DNA (2b-RAD) to mine thousands of single nucleotide polymorphisms (SNPs) for native and introduced populations in Q1 clade (SPB and 17JN) and Q2 clade (ISQ and UAS0601) of the whitefly, Bemisia tabaci (Gennadius) MED (also known as B. tabaci biotype Q). Then, we used resampling techniques to create simulated populations with a random subset of individuals and 3,000 SNPs to determine how many individuals should be sampled for accurate estimates of intra- and interpopulation genetic diversity. We calculated the intrapopulation genetic diversity parameters (unbiased expected heterozygosity, observed heterozygosity, and the number of effect alleles) and pairwise genetic differentiation F ST; finally, an ad hoc statistic, ΔK, was used to determine the optimal value. Our results showed that a sample size greater than four individuals (n ≥ 4) has little impact on estimates of genetic diversity within whitefly populations; moreover, precise estimate of F ST can be easily achieved at a very small simple size (n = 3 or 4). Our results will provide in-depth understanding of the optimization of sampling schemes in population genomics of invasive species.