Species complexes and life cycles of digenetic trematodes from the family Derogenidae.

The best way to study digenean diversity combines molecular genetic methods, life-cycle studies and elaborate morphological descriptions. This approach has been barely used for one of the most widespread digenean taxa parasitizing fish ­ the superfamily Hemiuroidea. Here, we applied the integrative approach to the hemiuroideans from the family Derogenidae parasitizing fish at the White and Barents Seas. Analysis of 28S, 18S, 5.8S rDNA, ITS2 and cox1 gene sequences from sexually adult worms (maritae) showed genetic heterogeneity for 2 derogenid species known from this area: Derogenes varicus and Progonus muelleri. Thus, 2 pairs of genetic lineages were found: DV1 and DV2, PM1 and PM2, respectively. Data from other regions indicate that 2 more lineages of D. varicus probably exist. Based on previous records from the White and Barents Seas, we hypothesized that the cercariae found in the moonsnails (family Naticidae) belong to the Derogenidae and may help to differentiate these lineages as species. According to our results, Cercaria appendiculata from Cryptonatica affinis matched DV1, similar nameless cercariae from Euspira pallida and Amauropsis islandica matched DV2, and Cercaria octocauda from C. affinis matched PM1. We provide new data on the structure of these cercariae and discuss the life-cycle pattern of the studied digeneans.

First elucidation of the life cycle in the family Brachycladiidae (Digenea), parasites of marine mammals.

Digeneans of the family Brachycladiidae are cosmopolitan parasites restricted to marine mammals. Their life cycles are unknown. Phylogenetically, Brachycladiidae are closely related to Acanthocolpidae, parasites of marine teleost fishes. Acanthocolpida typically possess three-host life cycles with gastropods of the superfamily Buccinoidea acting as the first intermediate hosts for most species, and either fishes or bivalves acting as the second intermediate hosts. A few species previously identified as Neophasis differ from other Acanthocolpidae in having naticid gastropods as first intermediate hosts, and both fishes and bivalves as second ones. We assumed that this may indicate an incorrect life cycle description and revised previous data on rediae and cercariae of Neophasis spp. from Cryptonatica affinis (Naticidae) and metacercariae from cardiid bivalves at the White Sea using molecular and morphological approaches. Sequence comparison showed that rediae and cercariae from C. affinis resembling some representatives of the genus Neophasis and metacercariae from bivalves resembling Neophasis oculata belong to the brachycladiid species Orthosplanchnus arcticus. Thus, the life cycle of O. arcticus proceeds as follows: seals serve as the definitive host, C. affinis as the first intermediate host and cardiid bivalves as the second. We found one more type of redia and cercaria in C. affinis which, by molecular evidence, also belongs to Brachycladiidae and is closely related to O. arcticus. Here we refer to them as Brachycladiidae gen. sp. 1 WS. We suggest that Brachycladiidae gen. sp. 1 WS may belong to either Orthosplanchnus or Odhneriella, with beluga whales possibly being the definitive host. Morphological features of O. arcticus and Brachycladiidae gen. sp. 1 WS cercariae are summarised and matched with published data on putatively brachycladiid cercariae. We compare and discuss the diversity of life cycle patterns among Brachycladiidae and Acanthocolpidae, and show that they differ not only in the type of definitive host, but also in both intermediate hosts.

Multiparticle Brownian dynamics simulation of experimental kinetics of cytochrome bf oxidation and photosystem I reduction by plastocyanin.

A model of electron transport from cytochrome f to photosystem I mediated by plastocyanin was designed on the basis of the multiparticle Brownian dynamics method. The model combines events which occur over a wide time range, including protein diffusion along the thylakoid membrane, long-distance interactions between proteins, formation of a multiprotein complex, electron transfer within a complex and complex dissociation. Results of the modeling were compared with the experimental kinetics measured in chloroplast thylakoids. Computer simulation demonstrated that the complex interior of the photosynthetic membrane, electrostatic interactions and Brownian diffusion provide physical conditions for the directed electron flow along the photosynthetic electron transport chain.