No abstract

This study investigated the composition of milt of the South American silver catfish (Rhamdia quelen) or jundia´. The semen was taken from jundia´in different periods during the four seasons. The biochemical composition of seminal fluid and the characteristics of sperm were analyzed. The semen quantity which can be extracted per fish in one day was 0.95±0.08 ml during spring (maximum) and 0.24±0.03 ml during winter (minimum). Sperm density (spermatocrit) showed higher values in the spring (75.1±1.3%) decreasing slightly afterwards and reaching 63.0±2.4% to 65.0±2.2% in the fall and winter. Immediately after water dilution, 90-100% of the spermatozoa presented vigorous straightforward motility that remained for at least 20 s. The total duration of the motility was 47.9±1.3 s in the spring and 38.6±0.6 s in the other seasons (P < 0.05). This pattern of motility is maintained for more than 2 h after storage of the milt at room temperature. The pH from 5 to 10 of the water dilution does not influence the sperm motility. The mean seminal pH and osmolality values were 8.7±0.07 and 274.8±11.2 (mOsm/kg), respectively. The ion concentration was: Na 153.7±2.4, K 10.7±2.4, Cl 139.4±2.1, Ca 4.2±0.2, Mg 0.9±0.05, P 0.9±0.08 (mEq/l). The total protein was 0.6±0.05 mg/dl and cholesterol concentration was 13.9±0.9 mg/dl.

The willistoni species subgroup has been the subject of several studies since the latter half of the past century and is considered a Neotropical model for evolutionary studies, given the many levels of reproductive isolation and different evolutionary stages occurring within them. Here we present for the first time a phylogenetic reconstruction combining morphological characters and molecular data obtained from 8 gene fragments (COI, COII, Cytb, Adh, Ddc, Hb, kl-3 and per). Some relationships were incongruent when comparing morphological and molecular data. Also, morphological data presented some unresolved polytomies, which could reflect the very recent divergence of the subgroup. The total evidence phylogenetic reconstruction presented well-supported relationships and summarized the results of all analyses. The diversification of the willistoni subgroup began about 7.3 Ma with the split of D. insularis while D.paulistorum complex has a much more recent diversification history, which began about 2.1 Ma and apparently has not completed the speciation process, since the average time to sister species separation is one million years, and some entities of the D. paulistorum complex diverge between 0.3 and 1 Ma. Based on the obtained data, we propose the categorization of the former "semispecies" of D. paulistorum as a subspecies and describe the subspecies D. paulistorum amazonian, D. paulistorum andeanbrazilian, D. paulistorum centroamerican, D. paulistorum interior, D. paulistorum orinocan and D. paulistorum transitional.

No abstract

The DNA methyltransferase 2 (DNMT2) protein is the most conserved member of the DNA methyltransferase family. Nevertheless, its substrate specificity is still controversial and elusive. The genomic role and determinants of DNA methylation are poorly understood in invertebrates, and several mechanisms and associations are suggested. In Drosophila, the only known DNMT gene is Dnmt2. Here we present our findings from a wide search for Dnmt2 homologs in 68 species of Drosophilidae. We investigated its molecular evolution, and in our phylogenetic analyses the main clades of Drosophilidae species were recovered. We tested whether the Dnmt2 has evolved neutrally or under positive selection along the subgenera Drosophila and Sophophora and investigated positive selection in relation to several physicochemical properties. Despite of a major selective constraint on Dnmt2, we detected six sites under positive selection. Regarding the DNMT2 protein, 12 sites under positive-destabilizing selection were found, which suggests a selection that favors structural and functional shifts in the protein. The search for new potential protein partners with DNMT2 revealed 15 proteins with high evolutionary rate covariation (ERC), indicating a plurality of DNMT2 functions in different pathways. These events might represent signs of molecular adaptation, with molecular peculiarities arising from the diversity of evolutionary histories experienced by drosophilids.