Crossing experiments supporting the specific status of Anopheles maculatus chromosomal form K

Genetic and morphological evidence for a new species of the Maculatus Group of Anopheles subgenus Cellia (Diptera: Culicidae) in Java, Indonesia

BACKGROUND

Anopheles maculatus, a species of the Maculatus Group of subgenus Cellia (Diptera: Culicidae), is an important vector of human malarial protozoa in Java, Indonesia. However, the identity of this species in Indonesia has been questionable because published reports and records are based mainly on morphological identification, which is unreliable for distinguishing members of the Maculatus Group due to overlapping characters.

METHODS

We performed morphological assessments, metaphase karyotype preparations, phylogenetic analyses of ITS2 and cox2 sequence data and cross-mating experiments to determine whether the Javanese form and An. maculatus (s.s.) from Thailand were conspecific.

RESULTS

The adults of the Java strain are similar to those of An. maculatus (s.s.), but the larvae and pupae exhibit significant differences. The metaphase karyotype of Javanese specimens includes a long acrocentric X chromosome and a small telocentric Y chromosome, which are distinct from other members of the Maculatus Group. Cross-mating of the Java strain with An. maculatus (s.s.) revealed genetic incompatibility. Phylogenetic analysis of ITS2 and cox2 sequences revealed that the Java strain forms a single clade that is distinct from clades of other members of the group (Kimura 2-parameter, K2P, genetic distances 3.1-19.2% and 1.6-9.6%, respectively).

CONCLUSIONS

This study provides evidence that the Javanese form of An. maculatus is not conspecific with An. maculatus (s.s.) and constitutes a previously unrecognized species of the Maculatus Group.

Cytogenetic, cross-mating and molecular evidence of four cytological races of Anopheles crawfordi (Diptera: Culicidae) in Thailand and Cambodia

Twenty-nine isolines of Anopheles crawfordi were established from wild-caught females collected from cow-baited traps in Thailand and Cambodia. Three types of X (X1, X2, X3) and four types of Y (Y1, Y2, Y3, and Y4) chromosomes were identified, according to differing amounts of extra heterochromatin. These sex chromosomes represent four metaphase karyotypes, i.e., Forms A (X1, X2, X3, Y1), B (X1, X2, X3, Y2), C (X2, Y3) and D (X2, Y4). Forms C and D are novel metaphase karyotypes confined to Thailand, whereas forms A and B appear to be common in both Thailand and Cambodia. Cross-mating experiments between the four karyotypic forms indicated genetic compatibility in yielding viable progenies and synaptic salivary gland polytene chromosomes. The results suggest that the forms are conspecific and A. crawfordi comprises four cytological races, which is further supported by very low intraspecific variation (mean genetic distance=0.000-0.018) of the nucleotide sequences in ribosomal DNA (ITS2) and mitochondrial DNA sequences (COI, COII).

Genetic compatibility between Anopheles lesteri from Korea and Anopheles paraliae from Thailand

To assess differentiation and relationships between Anopheles lesteri and Anopheles paraliae we established three and five iso-female lines of An. lesteri from Korea and An. paraliae from Thailand, respectively. These isolines were used to investigate the genetic relationships between the two taxa by crossing experiments and by comparing DNA sequences of ribosomal DNA second internal transcribed spacer (ITS2) and mitochondrial DNA cytochrome c oxidase subunit I (COI) and subunit II (COII). Results of reciprocal and F1-hybrid crosses between An. lesteri and An. paraliae indicated that they were compatible genetically producing viable progenies and complete synaptic salivary gland polytene chromosomes without inversion loops in all chromosome arms. The pairwise genetic distances of ITS2, COI and COII between these morphological species were 0.040, 0.007-0.017 and 0.008-0.011, respectively. The specific species status of An. paraliae in Thailand and/or other parts of the continent are discussed.

Evidence to support a conspecific nature of allopatric cytological races of Anopheles nitidus (Diptera: Culicidae) in Thailand

Metaphase karyotype investigation on two allopatric strains of Anopheles nitidus Harrison, Scanlon, and Reid (Diptera: Culicidae) was conducted in Thailand during 2011-2012. Five karyotypic forms, i.e., Form A (X1, Y1), Form B (X1, Y2), Form C (X2, Y3), Form D (X1, X3, Y4), and Form E (X1, X2, X3, Y5) were obtained from a total of 21 isofemale lines. Forms A, B, and C were confined to Phang Nga Province, southern Thailand, whereas Forms D and E were restricted to Ubon Ratchathani Province, northeastern Thailand. Cross-mating experiments among the five isofemale lines, which were representative of five karyotypic forms of An. nitidus, revealed genetic compatibility by providing viable progenies and synaptic salivary gland polytene chromosomes through F2 generations. The results suggest that the forms are conspecific, and An. nitidus comprises five cytological races. The very low intraspecific sequence variations (average genetic distances = 0.002-0.008) of the nucleotide sequences in ribosomal DNA (internal transcribed spacer 2) and mitochondrial DNA (cytochrome c oxidase subunits I and II) among the five karyotypic forms were very good supportive evidence.

Cytogenetic, hybridization and molecular evidence of four cytological forms of Anopheles nigerrimus (Hyrcanus Group) in Thailand and Cambodia

Thirteen isoline colonies of Anopheles nigerrimus were established from individual wild-caught females collected from cow-baited traps at locations in Thailand and Cambodia. Three types of X (X1 , X2 , X3 ) and 4 types of Y (Y1 , Y2 , Y3 , Y4 ) chromosomes were recovered, according to differing amounts of extra heterochromatin. Four karyotypic forms were designed depending upon apparently distinct figures of X and Y chromosomes, i.e., Form A (X1 , X2 , X3 , Y1 ), B (X2 , X3 , Y2 ), C (X1 , Y3 ), and D (X3 , Y4 ). Forms C and D were new metaphase karyotypes discovered in this study. Form A appeared to be common in both Thailand and Cambodia. Forms B and D were found to be rather specific to southern and northeastern Thailand, respectively, whereas Form C was confined to Cambodia. Hybridization experiments among the eight isoline colonies, which were representative of four karyotypic forms of An. nigerrimus, demonstrated genetic compatibility in giving viable progenies and synaptic salivary gland polytene chromosomes through F2 -generations. These results elucidated the conspecific relationship, comprising four cytological forms within this taxon. Supportive evidence was confirmed further by very low intraspecific sequence variations (average genetic distance = 0.002-0.007) of the nucleotide sequences in ribosomal DNA [second internal transcribed spacer (ITS2)] and mitochondrial DNA [cytochrome c oxidase subunit I (COI) and subunit II (COII)].

Evidence to support karyotypic variation of the mosquito, Anopheles peditaeniatus in Thailand

Eight isoline colonies of Anopheles peditaeniatus Leicester (Diptera: Culicidae) were established from wild-caught females collected from buffalo-baited traps at 8 localities in Thailand. They showed 2 types of X (X(2), X(3)) and 4 types of Y (Y(2), Y(3), Y(4), Y(5)) chromosomes based on the number and amount of major block(s) of heterochromatin present in the heterochromatic arm, and were tentatively designated as Forms B (X(2), X(3), Y(2)), C (X(3), Y(3)), D (X(3), Y(4)) and E (X(2), X(3), Y(5)). Form B was found in Nan, Ratchaburi, and Chumphon provinces; Form C was obtained in Chon Buri province; Form D was recovered in Kamphaeng Phet province; and Form E was acquired in Chiang Mai, Udon Thani, and Ubon Ratchathani provinces. Crossing studies among the 8 isoline colonies, which were representative of 4 karyotypic forms of An. peditaeniatus, revealed genetic compatibility in providing viable progenies and synaptic salivary gland polytene chromosomes through F(2)-generations, thus suggesting the conspecific nature of these karyotypic forms. These results were supported by the very low intraspecific sequence variations (0.0 - 1.1%) of the nucleotide sequences in ribosomal DNA (ITS2) and mitochondrial DNA (COI and COII) of the 4 forms.

Molecular phylogenetics and biogeography of the Neocellia Series of Anopheles mosquitoes in the Oriental Region

Molecular studies of population divergence and speciation across the Oriental Region are sparse, despite the region's high biodiversity and extensive Pliocene and Pleistocene environmental change. A molecular phylogenetic study of the Neocellia Series of Anopheles mosquitoes was undertaken to identify patterns of diversification across the Oriental Region and to infer the role of Pleistocene and Pliocene climatic change. A robust phylogeny was constructed using CO2 and ND5 mitochondrial genes and ITS2 and D3 nuclear ribosomal markers. Bayesian analysis of mitochondrial genes was used to date divergence events. The repeated contraction and expansion of forest habitat resulting from Pleistocene climatic fluctuations appears to have had a substantial impact on intraspecific diversification, but has not driven speciation within this group. Primarily early to mid Pliocene speciation was detected within the Annularis Group, whereas speciation within the Maculatus and Jamesii Groups occurred during the mid and late Pliocene. Both allopatric divergence driven by late Pliocene environmental changes and ecological adaptation, involving altitudinal replacement and seasonality, are likely to have influenced speciation in the Maculatus Group.