A bio-syringe mechanism and the pattern of genital correspondence in the weevil genus Sitona (Coleoptera: Curculionidae): an approach to the great interest of Sharp and Muir

The remarkable diversity in male and female genital morphology among the species of Sitona Germar might contribute to the understanding of the structural “lock-and-key” isolating mechanism. Recently, it has been found that in spite of the phallic sizes in male weevils of the genus Sitona, their internal sacs should precisely match with the vaginal infoldings of conspecific females. The present research also deals with the male transfer apparatus, which is a special organ for insemination procedure inside the female bursa copulatrix. A wedge-shaped structure with a fused ejaculatory pump was distinguished as the bio-syringe part of the transfer apparatus in the examined species. Two paired sclerites of the transfer apparatus support the bio-syringe, so that it would slide freely between them and lock precisely over the opening of the spermathecal duct inside the bursa copulatrix of the female. In this phenomenon, several new structures were also found, including a bursal sclerite (“bursal disc”) and a pair of miniature pouches (“bursal plugs”) which are embedded in the thickened wall of the female bursal lumen. These findings explain how the shapes of male and female copulatory organs are normally species-specific and provide an opportunity for understanding the role of the structural lock-and-key isolating mechanism.

Development of engineering calculation methods of a vibration isolation mechanism with stiffness compensation of the main elastic element

The design and verification calculation of the vibration-isolating mechanism of a pneumatic riveting hammer with stiffness compensation of the main elastic element is devoted. Graphs of the frequency response and amplitude-stiffness characteristics are given. Conclusions about the effectiveness of the vibration-isolating mechanism are made.

Species and sex divergence in vocalizations between hybridizing role-reversed shorebirds, Northern Jacana (Jacana spinosa) and Wattled Jacana (Jacana jacana)

ABSTRACTSpecies-specific vocalizations can act as a reproductive isolating mechanism between closely related populations. We analyzed vocal divergence between two hybridizing species of sex-role reversed polyandrous shorebirds, the Northern Jacana (Jacana spinosa) and Wattled Jacana (Jacana jacana). We found that J. spinosa calls have higher peak frequency and fundamental frequency than J. jacana calls. We also compared calls between males and females, as both jacana species are sex-role reversed and females compete for male mates. Males produce calls with a higher peak frequency, exhibit shorter note lengths and emit a greater number of notes within a calling bout than females, which could relate to mate attraction. These results suggest that vocal divergence could act as a behavioral barrier to limit hybridization between the species and vocalizations may function differently between male and female jacanas.

Hybridization experiments indicate incomplete reproductive isolating mechanism between Fasciola hepatica and Fasciola gigantica

SUMMARYExperiments on hybridization between Fasciola hepatica and Fasciola gigantica were carried out to clarify whether a reproductive isolating mechanism appears between the two Fasciola species. Molecular evidence for hybridization was based on the DNA sequence of the internal transcribed spacer 1 (ITS1) region in nuclear ribosomal DNA, which differs between the species. The results suggested that there were not pre-mating but post-mating isolating mechanisms between the two species. However, viable adults of the hybrids F1 and F2 were produced from both parental F. hepatica and F. gigantica. The hybrids inherited phenotypic characteristics such as ratio of body length and width and infectivity to rats from parental Fasciola hepatica and F. gigantica. These findings suggest that reproductive isolation is incomplete between Fasciola hepatica and F. gigantica. Adults of the hybrids F1 and F2 were completely different in mode of reproduction from aspermic Fasciola forms that occur in Asia and seem to be offspring originated from hybridization between F. hepatica and F. gigantica and to reproduce parthenogenetically.