Habitat selection response of small pelagic fish in different environments. Two examples from the oligotrophic Mediterranean Sea.

A number of scientific papers in the last few years singled out the influence of environmental conditions on the spatial distribution of fish species, highlighting the need for the fisheries scientific community to investigate, besides biomass estimates, also the habitat selection of commercially important fish species. The Mediterranean Sea, although generally oligotrophic, is characterized by high habitat variability and represents an ideal study area to investigate the adaptive behavior of small pelagics under different environmental conditions. In this study the habitat selection of European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus is analyzed in two areas of the Mediterranean Sea that largely differentiate in terms of environmental regimes: the Strait of Sicily and the North Aegean Sea. A number of environmental parameters were used to investigate factors influencing anchovy and sardine habitat selection. Acoustic surveys data, collected during the summer period 2002-2010, were used for this purpose. The quotient analysis was used to identify the association between high density values and environmental variables; it was applied to the entire dataset in each area in order to identify similarities or differences in the "mean" spatial behavioral pattern for each species. Principal component analysis was applied to selected environmental variables in order to identify those environmental regimes which drive each of the two ecosystems. The analysis revealed the effect of food availability along with bottom depth selection on the spatial distribution of both species. Furthermore PCA results highlighted that observed selectivity for shallower waters is mainly associated to specific environmental processes that locally increase productivity. The common trends in habitat selection of the two species, as observed in the two regions although they present marked differences in hydrodynamics, seem to be driven by the oligotrophic character of the study areas, highlighting the role of areas where the local environmental regimes meet 'the ocean triad hypothesis'.

Under-representation of PolyA/PolyT tailed ESTs in human ESTdb: an obstacle to alternative polyadenylation inference.

Alternative polyadenylation is a key regulatory process which affects the 3' end formation of variants of the same transcription unit, thus altering gene expression pattern, and transcripts' cellular behaviour and characteristics. The common methodology for computational analysis of alternative polyadenylation signal utilization is based on EST data, specifically on PolyA/PolyT tailed ESTs. Studying the human ESTs dataset we detected a significant underrepresentation of PolyA/PolyT tailed ESTs, constituting only 10% of most libraries. Consequently, more than 50% of false-negative events are revealed in the analysis of alternatively polyadenylated variants' expression. We therefore argue that the ratios of PolyA/PolyT tailed ESTs, as represented in the human EST database, do not reflect the truepicture of 3' end variants formation of a given physiological situation. Thus the EST database should not be considered a reliable source for alternative polyadenylation signal usage inference.