Evidence for pleistocene population divergence and expansion of Anopheles albimanus in Southern Central America

Abstract

The micro-geographic structure of Anopheles albimanus was studied in southern Central America using partial sequences of the mtDNA cytochrome oxidase subunit I gene (COI). Analysis of molecular variance supported significant genetic structure between populations from Costa Rica and western Panama versus those from central-eastern Panama (Phi(CT) = 0.33), whereas the within group divergence was shallow and statistically insignificant (Phi(ST) = 0.08). Furthermore, a statistical parsimony network depicted three divergent groups of haplotypes that were not evenly distributed across the study area. Our findings are in partial agreement with previous studies, yet they do not support physical barriers to gene flow or contemporary isolation by distance in this region. Instead, three co-occurring groups of An. albimanus may be the result of multiple introductions, most likely caused by historical fragmentation and subsequent secondary contact. In addition, the molecular signature of population expansion of An. albimanus was detected in central-eastern Panama approximately 22,000 years ago (95% confidence interval [CI] 10,183-38,169). We hypothesize that the population structure of An. albimanus, as determined by our COI locus analysis, is the result of late Pleistocene climatic changes in northern South America.

Figure 1.

Geographic distribution of the COI haplotypes in Central America. The letters correspond to the haplotype(s) observed for each locality. The circled numbers correspond to the localities in Table 1, positioned on the map according to the longitude and latitude of the site. Underlined bold letters depict shared haplotypes, and plain letters depict private haplotypes. Circles represent the distribution of groups A (white), B (black), and C (shaded) in the network. The dotted rectangle shows the area of the former Panama Canal Zone. Dashed line divides Costa Rica and western Panama (localities 1–9), from central-eastern Panama (10–16). Inset map depicts the geographic position of the study area.

Figure 2.

Statistical parsimony network of 91 COI haplotypes of Anopheles albimanus. The letters correspond to the haplotypes observed for the 16 localities in Table 1. The solid black dots represent missing haplotypes. Dotted lines depict 7 mutational steps between groups A (labeled A1–A41); B (B1–B41); and C (C1–C9). The size of the circle is proportional to the frequency of the haplotype, which is indicated following the haplotype code, and the color indicates the geographic distribution.

Figure 3.

Mismatch distribution for groups A, B, and C of Anopheles albimanus. Bars are observed distribution, and the dashed line shows the distribution simulated under a model of sudden expansion.