Panayiota Kotsakiozi

Animal Mitochondria, Positive Selection and Cyto-Nuclear Coevolution: Insights from Pulmonates

Pulmonate snails have remarkably high levels of mtDNA polymorphism within species and divergence between species, making them an interesting group for the study of mutation and selection on mitochondrial genomes. The availability of sequence data from most major lineages – collected largely for studies of phylogeography - provides an opportunity to perform several tests of selection that may provide general insights into the evolutionary forces that have produced this unusual pattern. Several protein coding mtDNA datasets of pulmonates were analyzed towards this direction. Two different methods for the detection of positive selection were used, one based on phylogeny, and the other on the McDonald-Kreitman test. The cyto-nuclear coevolution hypothesis, often implicated to account for the high levels of mtDNA divergence of some organisms, was also addressed by assessing the divergence pattern exhibited by a nuclear gene. The McDonald-Kreitman test indicated multiple signs of positive selection in the mtDNA genes, but was significantly biased when sequence divergence was high. The phylogenetic method identified five mtDNA datasets as affected by positive selection. In the nuclear gene, the McDonald-Kreitman test provided no significant results, whereas the phylogenetic method identified positive selection as likely present. Overall, our findings indicate that: 1) slim support for the cyto-nuclear coevolution hypothesis is present, 2) the elevated rates of mtDNA polymorphims and divergence in pulmonates do not appear to be due to pervasive positive selection, 3) more stringent tests show that spurious positive selection is uncovered when distant taxa are compared and 4) there are significant examples of positive selection acting in some cases, so it appears that mtDNA evolution in pulmonates can escape from strict deleterious evolution suggested by the Muller’s ratchet effect.

Mitochondrial phylogeny and biogeographic history of the Greek endemic land-snail genus Codringtonia Kobelt 1898 (Gastropoda, Pulmonata, Helicidae).

The aim of this work was to infer the phylogeny of the Greek endemic land-snail genus Codringtonia Kobelt 1898, estimate the time frame of the radiation of the genus, and propose a biogeographic scenario that could explain the contemporary distribution of Codringtonia lineages. The study took place in the districts of Peloponnese, Central Greece and Epirus of mainland Greece. Sequence data originating from three mtDNA genes (COI, COII, and 16S rDNA) were used to infer the phylogeny of the eight nominal Codringtonia species. Furthermore, the radiation time-frame of extant Codringtonia species was estimated using a relaxed molecular clock analysis and mtDNA substitution rates of land snails. The phylogenetic analysis supported the existence of six Codringtonia lineages in Greece and indicated that one nominal species (Codringtonia neocrassa) might belong to a separate genus distantly related to Codringtonia. The time frame of differentiation of Codringtonia species was placed in the Late Miocene-Pleistocene epoch. The dispersal-vicariance analysis performed indicated that most probably Codringtonia exhibited a north-to-south spread with the ancestral area being that of central Greek mainland, accompanied with duplication (speciation) and vicariance events.

The transcriptome of a “sleeping” invader: de novo assembly and annotation of the transcriptome of aestivating Cornu aspersum

BackgroundCornu aspersum is a quite intriguing species from the point of view of ecology and evolution and its potential use in medical and environmental applications. It is a species of economic importance since it is farmed and used for culinary purposes. However, the genomic tools that would allow a thorough insight into the ecology, evolution, nutritional and medical properties of this highly adaptable organism, are missing. In this work, using next-generation sequencing (NGS) techniques we assessed a significant portion of the transcriptome of this non-model organism.ResultsOut of the 9445 de novo assembled contigs, 2886 (30.6%) returned significant hits and for 2261 (24%) of them Gene Ontology (GO) terms associated to the hits were retrieved. A high percentage of the contigs (69.4%) produced no BLASTx hits. The GO terms were grouped to reflect biological processes, molecular functions and cellular components. Certain GO terms were dominant in all groups. After scanning the assembled transcriptome for microsatellites (simple sequence repeats, SSRs), a total of 563 SSRs were recovered. Among the identified SSRs, trinucleotide repeats were the predominant followed by tetranucleotide and dinucleotide repeats.ConclusionThe annotation success of the transcriptome of C. aspersum was relatively low. This is probably due to the very limited number of annotated reference genomes existing for mollusc species, especially terrestrial ones. Several biological processes being active in the aestivating species were revealed through the association of the transcripts to enzymes relating to the pathways. The genomic tools provided herein will eventually aid in the study of the global genomic diversity of the species and the investigation of aspects of the ecology, evolution, behavior, nutritional and medical properties of this highly adaptable organism.

Climatic conditions driving a part of changes in the biochemical composition in land snails: Insights from the endangered Codringtonia(Gastropoda: Pulmonata)

Abstract Most land snails in order to ensure their survival under adverse environmental conditions interrupt their activity entering a state of dormancy. The transition from activity to dormancy is accompanied by several changes in the animals’ physiology. To identify these changes we examined the seasonal patterns in the biochemical composition and the LDH activity of three different tissues in four endangered land snail species. Additionally, within a phylogenetic framework we investigated the correlation of the measured parameters with the spatial and climatic variables of the sampling sites. Our results indicate that there are both differences and similarities in the pattern exhibited by the four species, depending on the physiological parameter investigated and the climatic conditions of the sampling sites, which sometimes have a significant effect on the seasonal pattern exhibited. Snails can successfully deal with the winter dormancy by maintaining high metabolite concentrations and stable water content whereas there is no indication of anaerobic pathways’ activation. At the same time, they deal successfully with the low humidity and high temperatures during the summer, but they are forced to maintain low metabolite concentrations and seem to activate anaerobic pathways to meet their energy demands. Therefore, from a biochemical perspective, it seems that winter is a less stressful period for snails compared to summer. According to the prevailing climate change scenarios, the Mediterranean region is going to exhibit a sudden transition towards a dryer and longer summer. This transition will exert a very high adaptation pressure on the already vulnerable Codringtonia species. Thus, it could be that this endemic Greek genus is truly on the verge of extinction.