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Spermatogenesis in Triatoma melanica Neiva and Lent, 1941 (Hemiptera, Triatominae)

2014; Wiley; Volume: 39; Issue: 1 Linguagem: Inglês

10.1111/j.1948-7134.2014.12094.x

1948-7134

Kaio Cesar Chaboli Alevi, João Aristeu da Rosa, Maria Tercília Vilela de Azeredo‐Oliveira,

Insect Resistance and Genetics

Costa and collaborators proposed the Triatoma brasiliensis complex using many approaches, including egg morphology (Costa et al. 1997a), morphometry of the testis (Freitas et al. 2008), hybrid cross (Costa et al. 2003), isoenzymes (Costa et al. 1997b), molecular data (Monteiro et al. 2004), morphological data (Costa et al. 1997a), biological data, and ecological data (Costa et al. 1998). This complex is comprised of the subspecies T. b. brasiliensis and T. b. macromelanosoma, and also the species T. juazeirensis and T. melanica. By means of phylogenetic reconstruction, Mendonça et al. (2009) proposed the inclusion of T. sherlocki to this complex. This inclusion was recently confirmed through the use of both cytogenetic analysis (Alevi et al. 2013a) and cross-mating experiments (Correia et al. 2013). Although the T. brasiliensis complex is a monophyletic group, T. melanica is considered an independent evolutionary unit and is thought to be the most differentiated form of the complex, with a genetic composition that is incompatible and hybrids that are inviable with other members of the T. brasiliensis complex (Costa et al. 2003). In 1941, this species was described by Neiva and Lent as a subspecies of T. brasiliensis (T. b. melanica). Using different studies such as morphology, biology, ecology, crossing experiments, allozymes, and mtDNA sequences, Costa et al. (2006) increased the specific status of T. b. melanica to T. melanica (Costa et al. 2006). Because T. melanica has only been collected in natural ecotopes and was considered to be important in the maintenance of the wild cycle of Trypanosoma cruzi (an etiologic agent of Chagas disease) (Costa, 1999), all approaches used to study biology and reproduction of this vector are important. Thus, the present study aims to describe the spermatogenesis of T. melanica. Seminiferous tubules of two adult males of T. melanica from the Triatominae Insectarium within the Department of Biological Sciences, in the College of Pharmaceutical Sciences, at Sao Paulo State University's Araraquara campus, Brazil (FCFAR/UNESP) were first shredded, smashed, and set on a slide in liquid nitrogen. They were then stained using the cytogenetic technique of lacto-acetic orcein (De Vaio et al. 1985, with modifications according to Alevi et al. 2012). Spermatogenesis consists of three different phases: spermatocytogenesis, which is a phase of proliferation; meiosis, which is the multiplication phase; and spermiogenesis, which is the differentiation phase (Johnson et al. 1997). Spermatocytogenesis was represented only by mitotic metaphase (Figure 1). Note all 20 autosomes and two sex chromosomes (arrows). All stages of meiosis were observed (Figure 2), including the diffuse stage (prophase) (Figure 2A), metaphase I in polar (Figure 2B) and lateral view (Figure 2C), anaphase I (Figure 2D) and II (Figure 2E) and telophase (Figure 2F). In addition, the elongation of haploid cells was observed during spermiogenesis (Figure 3). Analyses of mitotic and meiotic metaphases made it possible to confirm the karyotype described for T. melanica (2n = 20A + XY) (Panzera et al. 2000). However, T. melanica presented a peculiar behavior during mitotic metaphase: the chromatids of sex chromosomes were visible. All species of the T. brasiliensis complex have the same chromosomal characteristics: namely, 22 chromosomes (2n = 20A + XY) with heterochromatic blocks at one or both chromosomal ends of all autosomal pairs and a large heterochromatic chromocenter formed by the association of both sex chromosomes plus two autosomal pairs and many heterochromatic blocks dispersed inside the nucleus (Panzera et al. 2000; Alevi et al. 2013a). The analysis of prophase revealed the same results described when the C-banding technique was used by Panzera et al. (2000). Thus, our analysis confirms the association of T. melanica with the species of the complex. Through molecular data (16S and Cytb), T. melanica was considered to be a sister to T. sherlocki (Mendonça et al. 2009). Alevi et al. (2013b, 2013c) propose the analysis of spermatids as a cytotaxonomic tool that can be used to compare related species. During spermiogenesis of T. melanica, two heteropycnotic filaments were noted in each of the haploid cells. These characteristics are quite different from those described for T. sherlocki, which presents early spermatids and which possesses a heteropyknotic corpuscle that becomes a periphery filament during cell elongation (Alevi et al. 2013b). Thus, this paper describes the spermatogenesis of T. melanica, confirms the relationship this species shares with members of the T. brasiliensis complex, and differentiates T. melanica from T. sherlocki (sister species). Although morphometric analyses were not performed, we noted that cells of T. melanica are relatively larger than those of other members of complex. In addition to genetic load, this phenomenon may be a factor that is related to reproductive incompatibility in experimental hybrid crosses, thus representing an important pre-zygotic barrier between these hematophagous insects. This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (Process number 2013/19764-0) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).