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have complex gene architectures, intron-rich and with high protein domain diversity. We find that such enrichments occur in differentially-timed innovation bursts. For example, the most important premetazoan intronization event occurred in the last common ancestor of choanoflagellates and animals (>80% homologous introns when compared to the urme-tazoan). Conversely, animal-specific protein domain arrangements often appear before, in the urholozoan (~12% ofnovel arrangements, compared to frequent contractions in later-branching lineages). Our results support a scenario of sudden innovation processes within holozoans followed by gradual simplifications in extant protistan lineages, while Metazoa retain most novelties and develop more of their own. This is observed for both intronization and protein rearrangements. Yet, these aspects of gene architecture are decoupled in time and mechanis-tics: non-coding and coding gene elements are under different evolutionary pressures, and innovation bursts are identified in different ancestors.
THE ROLE OF CAEDIBACTER-INDUCED KILLER TRAITS IN PARAMECIUM INTER-STRAIN AND INTERSPECIES COMPETITION Grevtseva I.1, Nekrasova I.1, Lanzoni O.2, Lebedeva N.3, Petroni G.2, Potekhin A.1
1 - Faculty of Biology, St Petersburg State University, Saint Petersburg, Russia
2 - Department of Biology, University of Pisa, Pisa, Italy
3 - Centre of Core Facilities "Culture Collections of Microorganisms", St Petersburg State University, Saint Petersburg, Russia [email protected]
Some species of Paramecium (Ciliophora) present killer traits when inhabited by bacterial endosym-bionts belonging to the genus Caedibacter. These bacteria are occasionally released by killer strains to the environment, get engulfed by other paramecia, and secrete a not yet characterized toxin, which kills symbiont-free ciliates. We studied three Paramecium biaurelia strains bearing cytoplasmic symbionts Caedibacter caryophilus. The killer strains originated from St Petersburg region, Russia, and from Sicily, Italy. All strains were characterized by different rate and dynamics ofkiller effect manifestation; sensitive paramecia displayed various lethal and malfunction symptoms. The killer cells were resistant to their own killer trait even after antibiotic-induced removal of symbionts, thus allowing to assume that resistance is genetically determined. Also killer strains appeared to be relatively reciprocally resistant for the other killers. We made a series of tests to reveal resistance or sensibility to killer effects for a number of strains
representing several Paramecium species. The results indicated that the strains of the P. aurelia species complex and P. caudatum were generally rather sensitive, while the strains ofphylogenetically distant species were almost always resistant. Thus, Caedibacter might give a significant advantage for the host, providing it with a powerful weapon for competition with uninfected paramecia normally present in the same environment. Several strains of symbiont-free P. biaurelia also appeared to be resistant, thus allowing to speculate that this species might be genetically adapted to be the host of C. caryophilus. Supported by RFBR 16-04-01195.
HIDDEN DIVERSITY IN MALLOMONAS MATVIENKOAE SPECIES COMPLEX Gusev E.S.1, Kapustin D.A.1, Doan Nhu-Hai2, Nguyen Ngoc-Lam2
1 - Papanin's Institute for Biology of Inland Waters Russian Academy of Sciences, Russia, 152742 Yaroslavl, Nekouz., Borok
2 - Institute of Oceanography, Viet Nam Academy of Science and Technology, 01 Cau Da, Vinh Nguyen, Nha Trang, Viet Nam
Mallomonas matvienkoae B. Asmund & Kristi-ansen is considered as a widespread taxon (Kristi-ansen & Preisig 2007) from the order Synurales, class Chrysophyceae. This species have been described from Ukraine under the name Mallomonopsis ellip-tica Matv. (Matvienko 1941) and later redescribed and transferred into the genus Mallomonas (Asmund & Kristiansen 1986). Mallomonas matvienkoae is a polymorphic species; it includes five varieties and forms. An investigation of the clonal cultures of M. matvienkoae representing populations from subtropics resulted in descriptions of three new species using both morphological features and molecular data (Jo et al. 2013). The authors also described a fossil species of this group. Our studies of this species complex in the tropics (Vietnam and Indonesia) revealed at least four new taxa for science confirmed by molecular methods. One of them has been already described as M. paragrandis E.S. Gusev (2015). Additionally, five new morphotypes ofscales have been found which can be considered as new species for science. Three taxa, recently described by Jo et al. (2013), were also found in Vietnam (Mallomonas hexareticulata, M. sorohexareticulata and M. pseudomatvienkoae). Thus, Mallomonas matvienkoae species complex is a rather diverse group of pseudocryptic taxa, which needs further studies using polyphasic approach. This study was supported by RFBR grants 15-04-04181 and 1634-60099.
