Phylogenetic Relationships of the Spinolai Complex and Other Triatomini Based on Mitochondrial DNA Sequences (Hemiptera: Reduviidae)

Introduction

W ithin the subfamily Triatominae (Hemiptera: Reduviidae), the genus Mepraia is endemic from the semiarid and arid regions of northern and central Chile. It is mainly found amongst rock piles, but occasionally it enters and colonizes domestic and peridomestic habitats (Frías et al. 1998). This genus was first described with the inclusion of Triatoma spinolai Porter 1934, as Mepraia spinolai by Mazza et al. (1940), synonymized by Lent and Wydogzinsky (1979), but then revalidated by Lent et al. (1994). Lent and Wygodzinsky (1979) described the spinolai complex as a taxonomic group composed of Triatoma eratyrusiformis Del Ponte 1929, Triatoma breyeri Del Ponte 1929, and Triatoma (Mepraia) spinolai Porter 1934. T. eratyrusiformis and T. breyeri occur in Argentina, and are geographically separated from spinolai by the Andean Range (Lent and Wygodzinsky 1979). Carcavallo et al. (2000) described the breyeri complex formed by breyeri and eratyrusiformis, as a group related to the T. (M.) spinolai, while Hypsa et al. (2002), on the basis of molecular studies using 16S rDNA, postulated that this complex should be assigned to the Mepraia genus. Recently, Schofield and Galvão (2009) indicated that is necessary to establish the relationships within the spinolai complex to decide the inclusion or exclusion of Mepraia from the genus Triatoma.

Until 1998, Mepraia spinolai was the only species of the genus, distributed in coastal and interior valleys from Chile between parallels 18° and 34° S (Lent and Wygodzinsky 1979). However, on the basis of karyotype, morphological characters, and experimental crosses, coastal desert populations between parallels 18°and 26° S were ranked as a new species named Mepraia gajardoi (Frías et al. 1998). The remaining populations, from 26° to 34° S, distributed in the interior mountains from the Atacama to the Metropolitan Regions, maintain the name M. spinolai (Frías et al. 1998). Recently, genetic studies using nuclear and mitochondrial markers on Mepraia sp. populations suggest the possible existence of introgression due to past hybridization events or the retention of ancestral polymorphisms, in the geographical intersection zone between these two taxa (Calleros et al. 2010). The goal of our study is to clarify the systematic uncertainties of Mepraia sp. and the Argentinan T. eratyrusiformis and T. breyeri. To this end, we constructed a phylogeny of Triatominae species belonging to the Triatomini tribe (Lent and Wygodzinsky 1979) by means of currently available mitochondrial gene sequence data of 16S ribosomal DNA and cytochrome b (Cyt b), adding the missing sequence data of the spinolai complex.

Materials and Methods

Results and Discussion

The phylogenetic analysis showed a clustering for the members of the spinolai complex, with support of 69% for this node (Fig. 1), which is marginally significant according to Hillis and Bull (1993). Within the complex, M. gajardoi and M. spinolai show a close relationship with significant nodal support values, close to T. breyeri and T. eratyrusiformis. Considering this phylogeny, we suggest that the species of the spinolai complex form a monophyletic group and that Mepraia corresponds to a clearly established genus and the phylogenetic relationship between T. eratyrusiformis and T. breyeri with M. spinolai and M. gajardoi reframes the debate to include these species in a single genus as proposed (Hypsa et al. 2002). According to our phylogeny, it would not be appropriate to synonymize Mepraia with Triatoma because a clear node supporting the genus Triatoma is lacking. In fact, species from the genera Panstrongylus and Dipetalogaster are also included within the genus Triatoma, suggesting a polyphyletic origin. However, it is necessary to include more gene sequence data from other species of the genus Triatoma to perform a more complete phylogenetic analysis.

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FIG. 1.

Maximum likelihood (ML) phylogenetic tree of Triatomini species based on 16S ribosomal DNA and Cyt b concatenated gene sequences, inferred with the model GTR+G (G=0.2060, −lnL=8298.59467). Numbers above the branch are the ML support values derived from bootstrap resampling with 1000 replicates and numbers under the branches are parsimony bootstrap values. Gray branches indicate the spinolai complex members.

The detected clustering of the spinolai complex members agrees with the classical studies proposed by morphological studies (Lent and Wygodzinsky 1979, Moreno et al. 2006). Moreno et al. (2006) compared the phenotype of the antennae among the species of the spinolai complex and found that Mepraia species and T. eratyrusiformis shared similarities in bristles and receptors that are not present in T. breyeri. In the same vein, it has been reported that T. eratyrusiformis shows multiple sex chromosomes like spinolai and gajardoi, but unlike most other South American Triatoma species (Panzera et al. 1998). It is necessary to complete the information provided by cytogenetic studies to have the whole scenario of the relationships of spinolai complex.

The monophyletic relationships between the taxa of the spinolai complex suggest that the Argentinian T. breyeri and T. eratyrusiformis could have had a common ancestor with the Mepraia genus. It has been proposed that the species of spinolai complex were separated with the uplifting of the Andes mountains during the Miocene in the Tertiary geological era about 20 million years ago (Moreno et al. 2006). It would be interesting to perform studies of the most recent common ancestor to estimate dates of divergence among the taxa to be compared with geological events. The spinolai complex appears related to South American species of triatomines. The relationship between M. spinolai and T. eratyrusiformis with South American species of the infestans complex were previously reported (Hypsa et al. 2002, de Paula et al. 2005). Interestingly, North American species seems to form a distictive group from South American species, even though not supported by high bootstrap values, which agrees with de Paula et al. (2005). This topology could be explained by the polyphyly of the Triatomini and the radiation pattern of these species (Schofield and Galvão 2009).

In conclusion, our phylogenetic evidence suggests that all the members of the spinolai complex constitute a monophyletic group corresponding to an established genus.