GENETICS OF Anopheles paraliae

Abstract

Anopheles paraliae belongs to the Hyrcanus Group that is distributed widely along the coastal regions of southern Thailand, Malaysia (Malaysian peninsular, Sabah and Sarawak states), Brunei and Vietnam. The morphological characteristics of adult females of this species are similar to those of Anopheles lesteri, which are distributed in Palaearctic regions, but their immature habitats are obviously different. However, the true species status between An. paraliae and An. lesteri is still unclear. Furthermore, the cytological evidence and the genetic proximity among the karyotypic variants of An. paraliae has never been reported. Therefore, a systematic investigation of genetic proximity among karyotypic forms of An. paraliae, and between An. paraliae and An. lesteri were carried out in this study, based on cross-mating experiments related to DNA sequence variations of ribosomal DNA (second internal transcribed spacer, ITS2) and mitochondrial DNA (cytochrome c oxidase subunit I and II, COI and COII). A total of twenty-one isoline colonies of An. paraliae were established from wild-caught females collected from cow-baited traps in 4 provinces of Thailand, i.e., Chanthaburi, Ratchaburi, Songkhla and Nakhon Si Thammarat. The result of metaphase karyotype identification revealed 3 types of X (X1, X2, X3) and 5 types of Y (Y1, Y2, Y3, Y4, Y5) chromosomes, and they were designated as Forms A (X3, Y1), B (X1, X2, X3, Y2), C (X3, Y3), D (X1, X2, X3, Y4) and E (X3, Y5), based on Y chromosome. Form A was found in Songkhla province, Form B in Ratchaburi, Nakhon Si Thammarat and Songkhla provinces, Form C in Chanthaburi province, Form D in Ratchaburi and Songkhla provinces, and Form E in Ratchaburi province. Cross-mating experiments among the 7 isoline colonies, which represented the 5 karyotypic forms of An. paraliae, revealed genetic compatibility in providing viable progenies and synaptic salivary gland polytene chromosomes through F2-generations. These results were supported by the very low intraspecific variation (average genetic distance = 0.000-0.002) of the nucleotide sequences in ribosomal DNA (ITS2) and mitochondrial DNA (COI and COII), thus suggesting the conspecific nature of these 5 karyotypic forms of this species. Additionally, 3 and 5 isoline colonies of An. lesteri from South Korea and An. paraliae from Thailand, respectively, were used to assess their genetic relationships by cross-mating experiments and comparison of DNA sequences of ribosomal DNA (ITS2) and mitochondrial DNA (COI and COII). The results of reciprocal and F1-hybrid crosses between An. lesteri and An. paraliae indicated that they were genetically compatible by producing viable progenies and complete synaptic salivary gland polytene chromosomes, without inversion loops, in all chromosome arms. The low pairwise genetic distances of ITS2, COI and COII sequences between these species were 0.040, 0.007-0.017 and 0.008-0.011, respectively. Therefore, these results supported the conspecific relationships between An. paraliae within the taxon An. lesteri.