Sympatric coexistence of recently diverged species raises the question of barriers restricting the gene flow between them. Reproductive isolation may be implemented at several levels, and the ...weakening of some, e.g. premating, barriers may require the strengthening of the others, e.g. postcopulatory ones. We analysed mating patterns and shell size of mates in recently diverged closely related species of the subgenus Littorina Neritrema (Littorinidae, Caenogastropoda) in order to assess the role of premating reproductive barriers between them. We compared mating frequencies observed in the wild with those expected based on relative densities using partial canonical correspondence analysis. We introduced the fidelity index (FI) to estimate the relative accuracy of mating with conspecific females and precopulatory isolation index (I
) to characterize the strength of premating barriers. The species under study, with the exception of L. arcana, clearly demonstrated preferential mating with conspecifics. According to FI and I
, L. fabalis and L. compressa appeared reliably isolated from their closest relatives within Neritrema. Individuals of these two species tend to be smaller than those of the others, highlighting the importance of shell size changes in gastropod species divergence. L. arcana males were often found in pairs with L. saxatilis females, and no interspecific size differences were revealed in this sibling species pair. We discuss the lack of discriminative mate choice in the sympatric populations of L. arcana and L. saxatilis, and possible additional mechanisms restricting gene flow between them.
Genus Littorina subgenus Neritrema (Mollusca, Caenogastropoda) includes the “obtusata” group of closely related species (Littorina obtusata and L. fabalis). The anatomy of the adult reproductive ...system (pallial oviduct) is the only reliable feature used for species identification in females of these species. Reproductive system anatomy and reproduction-associated proteins often diverge between sibling species. Despite being of high evolutionary interest, the molecular basis of this divergence remains poorly understood. We performed proteotranscriptomic comparison of oviducts of L. obtusata and L. fabalis by RNA-seq on Illumina HiSeq 2500 and two-dimensional protein electrophoresis (2D DIGE) with MS/MS identification of the species-specific proteins. The interspecies differences in the oviduct were associated with (1) metabolic proteins reflecting overall physiological differences between L. obtusata and L. fabalis, (2) receptor proteins, and (3) transcripts related to transposable elements (TEs). Various receptors identified may recognize a wide variety of ligands from pathogen-associated molecular patterns to specific carbohydrates on the sperm surface. Therefore, these may participate in immune defense as well as in sperm storage and regulation. Species-specificity of multiple TE sequences (coding for reverse transcriptase and ribonuclease H) may indicate the important role of these genomic elements in the Littorina species divergence, which has not been reported previously.
Reproductive isolation is the key attribute of biological species and establishment of the reproductive barriers is an essential event for speciation. Among the mechanisms of reproductive isolation, ...gamete incompatibility due to the variability of gamete interaction proteins may drive fast divergence even in sympatry. However, the number of available models to study this phenomenon is limited. In case of internally fertilized invertebrates, models to study gamete incompatibility and sperm competition mechanisms are restricted to a single taxon: insects. Here, we propose a group of closely related Littorina species as a new model for such studies. Particularly since periwinkles are already thoroughly studied in terms of morphology, physiology, ecology, phylogeny, and ecological speciation. Earlier, we have identified the first species-specific Littorina sperm protein (LOSP) with no known conservative domains or homologies. LOSP is relatively abundant component of sperm extracts and might be involved in gamete incompatibility. Here, we characterize its definitive localization and mRNA expression pattern in the male reproductive system by immunocytochemistry and RNA in situ hybridization. We demonstrate that LOSP distribution is limited to the parasperm cells. Losp gene expression occurs only at the early stages of parasperm development. The protein is stored within granules of mature parasperm and, most likely, is released after ejaculation inside female reproductive system. Thus, LOSP is the only described molluscan paraspermal protein to date, and there is a possibility for LOSP to be involved in gamete incompatibility since heterospermy is a common phenomenon among Littorina.
Romanenko, A. Ye., Finch, S. C., Hatch, M., Lubin, J. H., Bebeshko, V. G., Bazyka, D. A., Gudzenko, N., Dyagil, I. S., Reiss, R. F., Bouville, A., Chumak, V. V., Trotsiuk, N. K., Babkina, N. G., ...Belyayev, Yu., Masnyk, I., Ron, E., Howe, G.;thR. and Zablotska, L. B. The Ukrainian-American Study of Leukemia and Related Disorders among Chornobyl Cleanup Workers from Ukraine: III. Radiation Risks. Radiat. Res. 170, 711–720 (2008). Leukemia is one of the cancers most susceptible to induction by ionizing radiation, but the effects of lower doses delivered over time have not been quantified adequately. After the Chornobyl (Chernobyl) accident in Ukraine in April 1986, several hundred thousand workers who were involved in cleaning up the site and its surroundings received fractionated exposure, primarily from external γ radiation. To increase our understanding of the role of protracted low-dose radiation exposure in the etiology of leukemia, we conducted a nested case-control study of leukemia in a cohort of cleanup workers identified from the Chornobyl State Registry of Ukraine. The analysis is based on 71 cases of histologically confirmed leukemia diagnosed in 1986–2000 and 501 age- and residence-matched controls selected from the same cohort. Study subjects or their proxies were interviewed about their cleanup activities and other relevant factors. Individual bone marrow radiation doses were estimated by the RADRUE dose reconstruction method (mean dose = 76.4 mGy, SD = 213.4). We used conditional logistic regression to estimate leukemia risks. The excess relative risk (ERR) of total leukemia was 3.44 per Gy 95% confidence interval (CI) 0.47–9.78, P < 0.01. The dose response was linear and did not differ significantly by calendar period of first work in the 30-km Chornobyl zone, duration or type of work. We found a similar dose–response relationship for chronic and non-chronic lymphocytic leukemia ERR = 4.09 per Gy (95% CI < 0–14.41) and 2.73 per Gy (95% CI < 0–13.50), respectively. To further clarify these issues, we are extending the case-control study to ascertain cases for another 6 years (2001–2006).
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