Estimation of divergence time between two sibling species of the Anopheles (Kerteszia) cruzii complex using a multilocus approach

Abstract

Background: Anopheles cruzii is the primary human Plasmodium vector in southern and southeastern Brazil. The distribution of this mosquito follows the coast of the Brazilian Atlantic Forest. Previous studies indicated that An. cruzii is a complex of cryptic species.

Results: A multilocus approach using six loci, three circadian clock genes and three encoding ribosomal proteins, was implemented to investigate in more detail the genetic differentiation between the An. cruzii populations from Santa Catarina (southern Brazil) and Bahia States (northeastern Brazil) that represent two sibling species. The analysis revealed very high FST values and fixed differences between the two An. cruzii sibling species in all loci, irrespective of their function. An Isolation with Migration model was fit to the data using the IM program. The results reveal no migration in either direction and allowed a rough estimate of the divergence time between the two sibling species.

Conclusions: Population genetics analysis of An. cruzii samples from two Brazilian localities using a multilocus approach confirmed that they represent two different sibling species in this complex. The results suggest that the two species have not exchanged migrants since their separation and that they possibly diverged between 1.1 and 3.6 million years ago, a period of intense climatic changes.

Figure 1

Posterior probability distributions of demographic parameters. Posterior probability distributions for each of the six demographic parameters estimated using IM: effective population size for an ancestral and two descendent populations (theta), divergence time between Florianópolis and Itaparica, and migration rates in both directions. Four IM simulations (a, b, c and d) using different seed numbers were plotted for each parameter estimate (see also Additional file 7). All curves are shown including the range of the priors.

Figure 2

Neighbor-joining trees of clock genes. Neighbor-joining trees using the three clock gene nucleotide sequences of the two An. cruzii sibling species obtained with Jukes and Cantor distance for Clock gene, and Kimura 2-parameter distance for the others. Numbers on the nodes represent the percentage bootstrap values based on 1,000 replications. Flo: Florianópolis; Bah: Itaparica.

Figure 3

Neighbor-joining trees of ribosomal protein genes. Neighbor-joining trees using the three ribosomal protein gene nucleotide sequences of the two An. cruzii sibling species obtained with Kimura 2-parameter distance. Numbers on the nodes represent the percentage bootstrap values based on 1,000 replications. Flo: Florianópolis; Bah: Itaparica.