Abstract:In Tanaidacea morphological identification of male individuals to the species level is complicated by two factors: the presence of multiple male stages/instars confuse the assessment of sexual stage while strong sexual dimorphism within several families ob− scures the morphological affinities of undescribed males to described females. Males of Paratanaoidea are often morphologically quite different from females and have not been discovered for most genera so far, which has led to the assumption that some tanaidaceans might have parthenogenetic reproduction or simply have undeveloped secondary sex traits. As a part of the IceAGE project (Icelandic marine Animals: Genetics and Ecology), with the support of molecular methods, the first evidence for the existence of highly dimorphic (swimming) males in four families of the superfamily Paratanaoidea (Agathotanaidae, Cryptocopidae, Akanthophoreidae, and Typhlotanaidae) is presented. This study suggests that these males might be the next instars after juvenile or preparatory males, which are morphologically similar to females. It has been assumed that "juvenile" males with a re− stricted ability for swimming (e.g., undeveloped pleopods) have matured testes, are capable of reproduction, and mate with females nearby, while swimming males can mate with dis− tant females. Our explanation of the dimorphism in Tanaidomorpha lies in the fact that males of some species (e.g., Nototanais) retain the same lifestyle or niche as the females, so secondary traits improve their ability to guard females and successfully mate. Males of other species that have moved into a regime (niche) different than that of the female have acquired complex morphological changes (e.g., Typhlotanais).
The activity of microorganisms was investigated in sediment samples of the Norwegian Sognefjord at a 1260 m depth. The enzymatic potential (measured, using the cleavage of fluoresceindiacetate FDA) ranged between 11 and 29 nmol FDA cm -:~ h ~. Labeled Anacystis sp. (Cyanobacteria) were degraded (measured as liberation of ~4C-labeled CO=) at a rate of 0.67-1.24 % day 1. The assays were run at 1 atm and at 126 atm pressure. In both cases, activity was higher when samples were incubated under 1 atm than under simulated in-situ conditions. This indicates that the sediment community of the fjord is adapted only to a limited extent to the elevated pressure at the bottom. The results are compared and discussed with data from other deep marine environments.
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