Orphan gene in Littorina: An unexpected role of symbionts in the host evolution

Mechanisms of reproductive isolation between closely related sympatric species are of high evolutionary significance as they may function as initial drivers of speciation and protect species integrity afterwards. Proteins involved in the establishment of reproductive barriers often evolve fast and may be key players in cessation of gene flow between the incipient species. The five Atlantic Littorina (Neritrema) species represent a notable example of recent radiation. The geographic ranges of these young species largely overlap and the mechanisms of reproductive isolation are poorly understood. In this study, we performed a detailed analysis of the reproductive protein LOSP, previously identified in Littorina. We showed that this protein is evolutionary young and taxonomically restricted to the genus Littorina. It has high sequence variation both within and between Littorina species, which is compatible with its presumable role in the reproductive isolation. The strongest differences in the LOSP structure were detected between Littorina subgenera with distinctive repetitive motifs present exclusively in the Neritrema species, but not in L. littorea. Moreover, the sequence of these repetitive structural elements demonstrates a high homology with genetic elements of bacteria, identified as components of Littorina associated microbiomes. We suggest that these elements were acquired from a symbiotic bacterial donor via horizontal genetic transfer (HGT), which is indirectly confirmed by the presence of multiple transposable elements in the LOSP flanking and intronic regions. Furthermore, we hypothesize that this HGT-driven evolutionary innovation promoted LOSP function in reproductive isolation, which might be one of the factors determining the intensive cladogenesis in the Littorina (Neritrema) lineage in contrast to the anagenesis in the L. littorea clade.

[Interaction between Steinernema carpocapsae with the arthropode fauna and natural populations of entomopathogenic nematodes in orchard biotope]

The introduction of a novel entomopathogenis nematode Steinernema carpocapsae strain "agriotos" (Rhabditida: Steinernematidae) into the soil of an orchard resulted in the reduction (up to 50 %) of total amount of phytophagous insects. No negative effect on the groups of beneficial arthropods, caused by the nematode, has been found. Recommended optimal application rate is 500 thousand invasive nematode larvae per 1 m2 of the soil. Increase or decrease of the application rate resulted in the rise of the abundance of phytophagous insects. This fact proved the existence of regulating factors determining optimal ratios of the amounts of parasites at micro- and macro-levels. Activation of native populations of entomopathogenic nematodes in soil surface layer has been observed after the introduction of the novel parasite species.

[A novel subspecies of entomopathogenic nematode Steinernema feltiae protense subsp. N.(Nematoda: steinernematidae) from Iakutiia]

A new subspecies of entomopathogenic nematode, Steinernema feltiae protense subsp. n., isolated from Yakutia grasslands is described. These nematodes demonstrate a high invasion activity to insect-hosts at 6 degrees C, maximum infestation of insect-hosts was registered at 13-21 degrees C.

[The distribution of entomopathogenic nematodes of the families Steinernematidae and Heterorabditidae in Russia and their morphological characteristics]

The data on a distribution of nematode species of the families Steinernematidae and Heterorabditidae in the northern and southern regions of the Russian Federation are given. Morphological characters of geographic isolates of some nematode species are not different, while their invasive activities in dependence of a temperature are different. Steinernema feltiae occurs in all climate zones, S. carpocapsae is restricted in distribution, nematode species of the family Heterorabditidae were found in southern regions only.