Sperm dimorphism in the Triatoma brasiliensis species complex and its applications

Sperm ultrastructure of Pycnoderes incurvus (Hemiptera: Miridae)

The sperm morphology can provide helpful information about sexual selection, phylogeny, and the evolutionary history of a given animal group. However, there is limited or no knowledge of many taxa, especially those belonging to insects, a vast and highly diverse group. An example is the Miridae, or plant bugs, which belong to the infraorder Cimicomorpha (Heteroptera), where only three out of 17 families have published data on their sperm morphology. Here we described the Miridae sperm structure by analyzing Pycnoderes incurvus sperm under light and transmission electron microscopy. In this species, the spermatozoa were as long and slender as those of most insects. However, the anterior-most region was twisted, a characteristic first reported for Heteroptera. The acrosome was coated with electron-dense material, most likely extra-acrosomal. The centriole adjunct was a notably long, cylindrical and compact structure connecting the nucleus to the flagellar elements, with just clove-like electron-lucent points in cross-section, also features unique to Miridae so far. The flagella exhibited an axoneme of 9 + 9 + 2 microtubules and two symmetrical mitochondrial derivatives. The latter two partially embrace the axoneme, and each exhibits two paracrystalline areas and a bridge connecting it to the axoneme; these are considered Heteroptera synapomorphies that support their monophyly. RESEARCH HIGHLIGHTS: The P. incurvus sperm showed a twisted acrosome, the first reported for Heteroptera. The centriolar adjunct is a sole structure linking the nucleus and flagellum. The flagella presented the synapomorphies supporting Heteroptera monophyly.

Germ cells: a useful tool for the taxonomy of Rhipicephalus sanguineus s.l. and species of the Amblyomma cajennense complex (Acari: Ixodidae)

The systematics of several ticks species (Acari: Ixodidae) remains controversial. Many species, including those of the Amblyomma cajennense complex and Rhipicephalus sanguineus s.l., are given special attention since they are cryptic species complexes and are also important in human and veterinary medicine. The A. cajennense complex was recently reorganized into six valid species, among which Amblyomma patinoi and Amblyomma mixtum have been confirmed in Colombia. On the other hand, the taxonomic status of R. sanguineus s.l. is controversial since it is a cosmopolitan cryptic species complex with a high reproductive capacity and a broad range of hosts (including man). To address this challenge, the germ cells of male ticks display a diverse morphology that offers novel opportunities for taxonomy. This study describes the events of spermatogenesis in A. mixtum and R. sanguineus s.l. individuals collected during active feeding on domestic hosts in the department of Caldas, Colombia. The individuals were identified using dichotomous keys and through PCR amplification of a fragment of the mitochondrial 16S ribosomal DNA gene. The male reproductive systems of A. mixtum and R. sanguineus s.l. were fixed in 2.5% glutaraldehyde for 48 h and dehydrated in increasing dilutions of ethanol. The samples were then embedded and mounted in historesin to obtain sections of 3 μm that were stained with hematoxylin-eosin (HE), photographed, and visualized through optical microscopy. The results show that the morphology of mature germ cells displays excellent diagnostic traits that can be used for tick taxonomy.

Spermatological Morphology of Triatoma Species (Hemiptera: Reduviidae: Triatominae)

Spermatozoa are among the most diverse cell types, and their morphologies often provide data that can be used to reliably evaluate phylogenetic relationships. They can also help to clarify the nature of 'specific complexes', which are common among triatomines. In the present study, we evaluated the copulation behavior of Triatoma rubrovaria Blanchard 1843 (Hemiptera: Reduviidae: Triatominae) and the structural morphology of sperm from T. carcavalloi Jurberg Rocha & Lent, 1998, T. infestans Klug, 1834, T. pintodiasi Jurberg Cunha & Rocha, 2013, and T. rubrovaria. Copulatory behavior was described from the moment males and females genitalia joined until they separated. Insemination was confirmed by the presence of a spermatophore in the female's bursa copulatrix. To measure their sperm, males were dissected and their seminal vesicles were removed, squashed on glass slides, and then spread, fixed, and observed under a photomicroscope. The images obtained were analyzed to measure the sperm. Seminal vesicles were also prepared for transmission electron microscopy. We performed K-means clustering separately for each species to group their sperm based on morphology. The differences in spermatozoa length among species of Triatominae, sperm types, and the interaction between species and sperm type were assessed with a two-way analysis of variance (ANOVA). The copulation time in T. rubrovaria was 3 to 5 min, which was sufficiently long for spermatophore transfer. All taxa showed polymorphic (short and long) sperm, with significant differences in the lengths of sperm among taxa. Using electron microscopy, the sperm cells of the four taxa examined were found to have similar ultrastructural morphology, confirming the hypothesized synapomorphies of sperm within the suborder Heteroptera (Hemiptera).

Sperm morphology of predatory pirate bugs Amphiareus constrictus and Blaptostethus pallescens (Heteroptera: Anthocoridae) with phylogenetic inferences

The sperm morphology of two predatory bugs Amphiareus constrictus and Blaptostethus pallescens, representing the tribes Dufouriellini and Blasptostethini, respectively, was described using light and transmission electron microscopy. The spermatozoa of Amphiareus constrictus and Blaptostethus pallescens are fine and long, each measuring 216.6μm and 181.0μm in length, of which 37.0μm and 11.6μm, respectively, comprise the nuclei. When stained with DAPI (for DNA), the posterior half of the nucleus in B. pallescens exhibited low fluorescence, while in A. constrictus this feature was observed only in the last 6μm. In both species, as in Heteroptera in general, the spermatozoa have, in the head region, an acrosome and nucleus, and in the flagellar region, an axoneme with 9 accessory tubules, 9 peripheral doublets and 2 central microtubules (9+9+2 microtubules), 2 mitochondrial derivatives (MDs), and a centriolar adjunct in the nucleus-flagellum transition. However, unlike most Heteroptera, in these species, the MDs are asymmetric, and the centriolar adjunct is quite long and encompasses completely the posterior nuclear end and the anterior tips of the MDs. These features are considered as derived, thus supporting the condition derived of Anthocoridae within Cimicomorpha. In addition, several traits of the spermatozoa of these two species easily distinguish one species (and probably a tribe) from the other; for example, the difference of formats in the MDs, and the long anterior projection of the centriolar adjunct parallel to the nucleus in B. pallescens.