ABSTRACT. Within the Meliponini, a widely distributed group of stingless bees, Melipona rufiventris has been considered as a single, cohesive species. Recently, analysis of morphological characters led to the splitting of this species into two species, M. mondury and M. rufiventris. The former occurs in the Atlantic Rain Forest ranging from Santa Catarina to Bahia States, while the latter is found in other parts of Brazil. We used PCR + RFLP to identify genetic marker patterns of the mtDNA between these species. Nine mtDNA regions were amplified and digested with four restriction enzymes (EcoRI, EcoRV, HindIII, and HinfI). Six species-specific restriction sites were identified for M. mondury and M. rufiventris with all enzymes, except for HindIII. The molecular data agree with the morphological classification.

Key words: Meliponini, Melipona rufiventris, Melipona mondury, RFLP, Mitochondrial DNA, Polymorphic site

INTRODUCTION

The stingless bee Meliponini tribe comprises several hundred (400 to 500) species that are restricted to the Neotropical region (Velthuis, 1997; Costa et al., 2005). According to Michener (2000), the total number of species is still not well established because of the many cryptic species. In Brazil more than 300 stingless species have been described from several regions (Kerr et al., 1996). Besides playing a very important ecological role, some species are commercially exploited for honey production and pollination of various cultivated crops (Del Sarto et al., 2005).

Melipona rufiventris Lep. was considered to be a stingless bee species widely distributed in several regions of the Brazil (Vasconcelos, 1998). However, Moure (1975) and Camargo and Pedro (1992) suggested the separation of some M. rufiventris populations as different species. Melo (2003) found some morphological differences in populations considered to be M. rufiventris and separated these populations into two species, M. mondury and M. rufiventris. The former is currently located in the Atlantic Rain Forest, ranging from Santa Catarina to Bahia States, whereas the latter is found in other parts of Brazil (Melo, 2003).

Mitochondrial DNA (mtDNA) has been widely used as a molecular genetic marker in vertebrates and invertebrates due to its characteristics, such as high-mutation rates, maternal inheritance, absence of recombination, and small molecular size (Brown et al., 1979; Moritz et al., 1987; Harrison, 1989). Analysis of mtDNA polymorphism has been used in several animal studies, such as population dynamics, species and subspecies characterization, systematics, and phylogeny (Moritz et al., 1987; Patarnello et al., 1994; Weinlich et al., 2004).

Biodiversity of bees was first assessed using morphometric analyses. Ruttner et al. (1978) recognized 24 Apis mellifera subspecies and suggested that they could be grouped into three or four evolutionary “branch groups”. Later mtDNA analyses confirmed the existence of these four evolutionary branches, with slight modifications to subspecies composition (Estoup et al., 1995; Franck et al., 2000). Since mtDNA is inherited maternally, it has been used in biogeographic studies of A. mellifera to investigate the ancestry of individual colonies, and for studies of gene flow patterns among hybridizing populations, such as the spread of African-derived honey bees from Brazil to other parts of South, Central and North America (Sheppard and Smith, 2000).

Among non-Apis bees, mtDNA has been used to study genetic variability in the Bombini and Meliponini tribes. In bumble bees (Bombinae), analyses of sequences from the cytochrome b and COI regions of the mtDNA were used to determine the genetic structure of several Bombus species (Estoup et al., 1996; Widmer et al., 1998; Widmer and Schmid-Hempel, 1999).

mtDNA has also been used for the characterization of species and subspecies within the Meliponini. Restriction maps have been made for species belonging to the genera Plebeia and Melipona (Francisco et al., 2001; Weinlich et al., 2004), while Moretto and Arias (2005), through RFLP analyses, identified restriction size patterns for M. quadrifasciata quadrifasciata and M. quadrifasciata anthidioides.

There have been very few molecular studies of M. rufiventris and M. mondury. Recently, Costa et al. (2005) noted low genetic variability when they analyzed isoenzyme data of some M. rufiventris populations. We used PCR + RLFP methods to identify genetic marker differences in the mtDNA between M. rufiventris and M. mondury.

MATERIAL AND METHODS

The mitochondrial genome analyses were carried out with individuals from eight M. mondury colonies sampled in Blumenau, Santa Catarina State and five colonies of M. rufiventris, four collected in São Simão, São Paulo State and one in Brasília, the Brazilian capital.

Total DNA was extracted as described by Sheppard and McPheron (1991), using one thorax per extraction. One individual per colony was sampled. The mtDNA was analyzed by PCR + RFLP. PCR was carried out using 1 µL of the total DNA extraction, 5 µL of PCR buffer (Boehringer Mannheim), 1.5 µL of each primer (20 mM), 5 µL of the dNTPs (2 mM each), and 2.5 U of Taq DNA polymerase (Boehringer Mannheim) in a total volume of 50 µL. Each PCR reaction was submitted to an initial denaturation at 94°C for 5 min, followed by 35 cycles of 94°C for 1 min, annealing for 1 min and 20 s at the specific temperature for each pair of primers (Table 1), with elongation at 64°C for 2 min. A final elongation step at 64°C for 10 min was performed. Seven pairs of primers (Table 1) were used to amplify specific mtDNA regions of M. q. quadrifasciata. The PCR products were separated by electrophoresis on 0.8% agarose gels, stained with ethidium bromide, visualized under a UV light and photographed.

To look for restriction sites, the PCR-amplified mtDNA fragments were digested for a minimum of 6 h with the following restriction enzymes: EcoRI, EcoRV, HindIII, and HinfI. The digested products were analyzed on 1.0% agarose (Agarose 1000 Gibco) and were stained and visualized as above.

RESULTS

Most primer pairs (Table 1) gave amplification products of nine mtDNA regions in M. mondury and M. rufiventris. Only the tRNA^Leu/COII region was not amplified in any of the individuals. The sample from the single M. rufiventris colony collected in Brasília did not amplify the ND2/COI region. The sizes in base pairs of the amplified mtDNA regions and digestion fragments are shown in Table 2.

The four restriction enzymes recognized one or more restriction sites in the two bee species. Only one restriction site was detected with HindIII in the ATPases (6,8) - COIII region, which was not polymorphic between M. mondury and M. rufiventris. With each of the other enzymes, at least one restriction site polymorphic between the two bee species was detected. HinfI produced polymorphic restriction sites in three mtDNA regions. Fragments with 1200 and 700 bp were observed in the COI region in M. mondury, while in M. rufiventris a single 950-bp fragment and various small fragments for which the size could not be precisely estimated were detected. Another HinfI polymorphic site was observed in the ND4-ND5 region, where two fragments with 1800 and 650 bp were detected in M. mondury and in M. rufiventris from Brasília and another with 1900 and 550 bp in M. rufiventris from São Simão. In the ND1-16S region HinfI gave fragments with 630 and 120 bp in M. mondury and with 650 and 100 bp in M. rufiventris.

The enzyme EcoRI cut four mtDNA regions, but polymorphic sites were detected only in the CytB-ND1 region, with fragments of 1000 and 700 bp in the five M. rufiventris samples and no restriction site in M. mondury. Another polymorphic site between the two bee species was found with EcoRV. In the CytB-ND1 region, this enzyme gave a restriction site that was detected only in M. mondury; two fragments with 1400 and 300 bp in this species were not visualized in M. rufiventris.

DISCUSSION

The PCR + RFLP technique enabled us to determine some pairs of primers that can be used to amplify the mtDNA in M. mondury and M. rufiventris and to estimate the number of restriction sites and size of the fragments generated by the four restriction enzymes. The mtDNA amplification of M. rufiventris and M. mondury was conducted with 10 pairs of primers previously used to amplify specific mtDNA regions in other Meliponini (Table 1). These primers amplified nine mtDNA regions, which encompass approximately 80% of the mitochondrial genome of M. mondury and M. rufiventris. No amplification products were obtained with the mtD18 + COI-IIF primers, which amplified the region that contained the COII gene (approximately 950 bp), in Plebeia remota and M. quadrifasciata (Francisco et al., 2001; Moretto and Arias, 2005). Therefore, the COII gene and its control region were the only mtDNA regions not amplified in M. mondury and M. rufiventris.

Recent studies of mtDNA of Meliponini have provided additional insight into the Melipona. Restriction site patterns have been used to characterize subspecies and populations at a molecular level in the two M. quadrifasciata subspecies and among M. q. quadrifasciata populations (Moretto and Arias, 2005; Torres RR, Arias MC and Moretto G, unpublished results).

Weinlich et al. (2004) determined the mtDNA maps of M. rufiventris and six other Melipona species. Twelve restriction sites on the M. rufiventris map were determined by eight restriction enzymes. The HaeIII site mapped at the ND5 gene was exclusive for M. rufiventris, while the other sites were shared by at least one other species. Although we did not use the enzyme HaeIII, some different restriction sites were identified when our results were compared with this map. The EcoRI restriction site at the ND2-COI region, present in the two bee species that we studied, was absent in all species in Weinlich’s map. The EcoRI site detected in the CytB-ND1 region, absent in M. mondury and present in M. rufiventris in our study, was undetected in the M. rufiventris analyzed by Weinlich et al. (2004). While no restriction site was detected with EcoRV in the M. rufiventris map, we found three non-polymorphic restriction sites in both bee species (Table 2) and a restriction site in the CtyB-ND1 region that was present in M. mondury and absent in M. rufiventris, as well as in the seven species of the map determined by Weinlich et al. (2004).

The restriction enzyme HinfI, which has a 4-base recognition site, has been used to discriminate subspecies of A. mellifera and M. quadrifasciata (Sheppard et al., 1996; Moretto and Arias, 2005). We detected four restriction sites for HinfI polymorphic between M. rufiventris and M. mondury; in contrast only one polymorphic site was detected among M. quadrifasciata subspecies (Moretto and Arias, 2005). The enzymes EcoRI and EcoRV, both with six-base recognition sites, also revealed a polymorphic restriction site that was not detected in M. quadrifasciata.

The stingless bees M. mondury and M. rufiventris were previously considered as a single species (M. rufiventris), with a large geographic distribution across Brazil. Recently, Melo (2003), based on morphometric analyses, concluded that a part of this group of populations is a new species, M. mondury, which is found in the Atlantic Rain Forest from Santa Catarina to Bahia. Although our mtDNA analysis was limited to four restriction enzymes, the genetic variability detected between M. mondury and M. rufiventris supports Melo’s conclusions.

ACKNOWLEDGMENTS

The authors thank Dr. Paulo Noguiera Neto, Instituto de Biociências, USP, Joaquim Pires for provining the Melipona rufiventris samples from São Simão and Brasília, and also Lauro Mugge for providing the M. mondury, and CNPq and FAPESC for financial support.

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