The test statistics SSD (0.0092; P = 0.37) and rg (0.047; P = 0.44) were small and not statistically significant, indicating that the sudden expansion model ZD1839 could not be rejected. The value found for ��, the time to the population expansion, where �� = 2ut, u is the mutation rate for the entire gene segment, and t is the number of generations since the expansion [34], was 3.029 (95% confidence intervals: 1.023, 4.896). Assuming 2.3% pairwise divergence per million years in the COI gene in insects [33], the mean mutation rate per site per generation in the 624bp segment for a single lineage is (624) �� (1.15 �� 10?8) or 7.176 �� 10?6. Based on these values, the estimated time to the population expansion in Cx. tarsalis (with 95% confidence intervals) was 211,050 (71,279�C341,140) generations ago.

Figure 4Demographic history of Culex tarsalis from the Sonoran Desert inferred from the mismatch distribution (a) and Bayesian skyline analysis (b). Vertical bars of the mismatch distribution show the observed distribution of pairwise differences among COI haplotypes, … Bayesian skyline analysis (Figure 4) showed that Cx. tarsalis showed a clear signature of an historical population expansion, consistent with the results from FLUCTUATE and the mismatch distribution. Given the untested assumptions of a neutral mutation rate per site per generation (��) of 1.15 �� 10?8 and a single generation per year, the timing of the expansion shown in the Bayesian skyline plot is only a rough approximation.

Nonetheless, the mismatch distribution and Bayesian skyline plot both suggest that the expansion began approximately 200,000 generations ago, which places it within the timeframe of the Pleistocene, unless improbable estimates of �� and generation time are assumed.4. Discussion4.1. Genetic DiversityA major finding of this study was that genetic diversity in the COI gene segment of Cx. quinquefasciatus from the Sonoran Desert was much lower than that seen in Cx. tarsalis and Culex sp. 1 and sp. 2 (Table 1). One possible explanation for this difference is that Cx. quinquefasciatus has preferentially undergone repeated cycles of population fluctuations, resulting in a much lower genetic diversity, owing to vector control measures in urban areas in northwestern Mexico which are primarily aimed at controlling Ae. aegypti and the dengue virus.

Subtle ecological differences in microhabitat preferences that result in less exposure Cilengitide to insecticides might explain why the Sonoran Desert Cx. tarsalis and Culex sp. 1 and sp. 2 maintain a relatively high genetic diversity. These three species, or putative species, show diversity indices similar to native dipterans from the Sonoran Desert region, including the cactophilic Drosophila (with the exception of D. nigrospiracula) and Odontoloxozus longicornis and O. pachycericola [38, 41�C43].