Mitochondrial DNA variation among Anopheles albimanus populations.

Abstract

Abstract. Barriers to gene flow between Pacific and Atlantic coast populations of Anopheles albimanus were reported in an earlier study of variation in the intergenic spacer of the nuclear ribosomal DNA. We examined the distribution of mitochondrial DNA haplotypes among A. albimanus populations to test for gene flow barriers with an independent genetic marker. A region of the NADH dehydrogenase subunit 5 gene was amplified by the polymerase chain reaction (PCR) in 1,105 mosquitoes collected from 16 locations in Guatemala and in single collections from Mexico, Honduras, Nicaragua, Costa Rica, Panama, Colombia, and Venezuela. The PCR products were tested for variation using single strand conformation polymorphism analysis and 45 haplotypes were detected. Haplotype frequencies did not vary between coasts in Guatemala. Populations within ϳ200 km of one another were panmictic. However, at distances Ͼ 200 km, F ST and geographic distances were correlated suggesting that populations are isolated by distance.Anopheles albimanus is one of the major vectors of malaria in Central America, the Caribbean, and coastal regions of northern South America. It feeds more readily on animals than humans, 1-3 and is generally exophilic in host-seeking and feeding behavior. [4][5][6] Sporozoite rates are generally low, with the greatest reported rate at only 1.6% (1 of 63). 7 However, these behavioral characteristics and vector competence estimates vary greatly among A. albimanus populations. 8 We have been testing for the presence of cryptic species within A. albimanus because of the strong historical precedence for the existence of cryptic, isomorphic Anopheles species.In an earlier study of Guatemalan A. albimanus populations, we observed a high degree of variation both in the frequency and copy number of intergenic spacer (IGS) length variants among individual A. albimanus. 9 Regardless of the collection site, most of the variation either in frequency or intensity of IGS variants was detected among mosquitoes within a population. The next largest component of genetic differentiation was detected between populations on the Pacific and Atlantic coasts of Central America. In contrast, populations from the Atlantic coast of Central America and from South America had similar IGS patterns. We suggested that the many mountain ranges that run through northern Central America could form barriers to gene flow among Atlantic and Pacific coast populations. However, extreme local variation in rDNA IGS has been found in many population studies of other insect species and is consistent with a model whereby molecular drive rapidly gives rise to unique spacer patterns in populations and then drives them to high frequencies. [10][11][12][13] In the case of A. albimanus, molecular drive probably occurs through unequal crossing-over and gene conversion within and among the 100-basepair (bp) repeat units constituting the IGS. 14 In the present paper, we test the inferences arising from our earlier rDNA study using an independent marker: variation in t...

Evidence for Pleistocene Population Divergence and Expansion of Anopheles albimanus in Southern Central America

“…Hierarchical AMOVA tests attributed 33.99% ( P = 0.0005) of the total genetic variance to the western versus eastern group comparison, thus partially supporting previous findings, 21,22 whereas the Pacific versus Atlantic group comparison accounted only for 6.93% ( P = 0.711) of the total variance and was not statistically significant ( Table 2 ). Furthermore, the Mantel analysis to test for IBD among all populations was statistically insignificant ( R 2 = 0.0214, P = 0.577) suggesting little input of direct-line geographic distance as an explanatory factor of the observed spatial pattern of genetic diversity.…”

“…albimanus using mitochondrial DNA (mtDNA) ND5 sequences found low to moderate differentiation between Central and South American populations, attributed mainly to isolation by distance (IBD). 21 In contrast, analysis of microsatellite loci using the same sample localities showed a small effect of distance, but uncovered differences in allele frequencies between Costa Rica and eastern Panama. 22 The discrepancy in allele frequencies may be attributed either to the mountain range that crosses Costa Rica and western Panama, which may act as a barrier to gene flow, or to population contraction in Panama caused by intense insecticide use.…”

“…The mtDNA has proven to be extremely useful in identifying the population structure and demographic history in malaria vectors because of its lack of recombination and high levels of variability, and it has been used extensively to study anopheline mosquitoes in the Neotropics, allowing for comparison across species and geographic areas. 8,[21][22][23][24][25] In this study, we use partial sequences of the mitochondrial gene, cytochrome oxidase subunit I (COI), and extensive sampling throughout southern Central America, to address the following questions: 1) Is there genetic differentiation in An. albimanus at this micro-geographic scale?…”

“…albimanus as western (1-9) and central-eastern localities (10)(11)(12)(13)(14)(15)(16) ( Figure 1 ; Table 1 ) to test for congruence with previous studies. 21,22 Second, we grouped the sequences from localities in the Pacific (1, 2, 3, 8, 9, 10, 11, and 15) and the Atlantic coasts (4, 5, 6, 7, 12, 13, 14, and 16) ( Figure 1 ; Table 1 ) to test for genetic diver gence caused by potential ecological differences (e.g., precipitation and/or tide regimen). Hierarchical AMOVA tests using both haplotype frequencies and the number of mutations between haplotypes (Φ) partitioned the genetic variance within and among populations within groups (Φ SC , Φ ST ) and among groups (Φ CT ).…”

Untitled

“…albimanus. Previous studies of ribosomal DNA analysis 25,26 , cytogenetic analysis 23 , and isozyme frequency studies 23 of An. albimanus indicated the absence of cryptic species.…”