Fish larval patterns across the Reykjanes Ridge

Fish larvae and hydrography were surveyed in summer 2005 in the upper 500 m from the Iceland Basin across the Reykjanes Ridge [as part of the Mid-Atlantic Ridge (MAR)], and into the Irminger Sea. Fish larval abundance was highest in the Iceland Basin, followed by the eastern slope of the ridge. Among 22 identified taxa, larvae of mesopelagic boreal and boreal-subarctic species prevailed, with Maurolicus muelleri contributing 80.9% to the total abundance, followed by Benthosema glaciale and Protomyctophum arcticum. Four subtropical species were first recorded for these latitudes, linked with the positive sea surface temperature anomaly encountered. Furthermore, larvae of demersal species were caught, mainly above the ridge and eastern slope of the Greenland Basin, enhancing species richness there. Changes in fish larval abundances, species richness and vertical distributions of larvae coincided with hydrographic fronts and bottom topography. MAR bottom topography guides currents in midwater. The role of these and surface currents for larval dispersal is discussed.     

Concordance of species richness patterns among multiple freshwater taxa: a regional perspective

Geographical gradients in species richness and the degree to which different taxa show congruent patterns remain unknown for many taxonomic groups. Here, I examined broad-scale species richness patterns in five groups of freshwater organisms; macrophytes, dragonflies, stoneflies, aquatic beetles and fishes. The analyses were based on provincial distribution records in Denmark, Norway, Sweden and Finland. In general, variation in species richness across provinces was concordant among the groups, but stoneflies showed weaker negative relationships with the other taxonomic groups. Species richness in most groups decreased with increasing latitude and altitude, and a considerable part of the variation was explained by mean July temperature. However, stoneflies showed a reversed pattern, with species richness correlating positively, albeit more weakly, with mean provincial altitude. Nevertheless, combined species richness of all five taxa showed a strong relationship with mean July temperature, accounting for 74% of variation in provincial species richness alone. Such temperature-controlled patterns suggest that regional freshwater biodiversity will strongly respond to climate change, with repercussions for local community organization in freshwater ecosystems in Fennoscandia.     

Evolution of mixed maturation strategies in semelparous life histories: the crucial role of dimensionality of feedback environment

We study the evolution of age at maturity in a semelparous life history with two age classes. An individual may either breed in the first year of its life and die, or delay breeding to the second year. In this setting a mixed strategy means that a fraction of the individual''s offspring breed in the first possible breeding event, while the remaining fraction delay breeding. Current theory seems to imply that mixed strategies are not evolutionarily stable strategies (ESSs) under a steady-state population dynamical regime. We show that a two-dimensional feedback environment may allow the evolution of mixed age at maturity. Furthermore, different phenotypes need to perceive the environment differently. The biological reasoning behind these conditions is different resource usage or predation pressure between two age classes. Thus, the conventional explanations for the occurrence of mixed strategies in natural populations, environmental stochasticity or complex dynamics, are not needed. <br>     

Evolution of resource allocation between growth and reproduction in animals with indeterminate growth

We review the recent theoretical developments explaining the evolution of age-schedules of reproduction in animals with indeterminate growth. Indeterminate growth, i.e. growth that continues past maturation and may continue until the end of life, is characteristic for a large number of invertebrate taxa (e.g. clams, cladocerans and crayfish) and ‘lower’ vertebrate taxa (e.g. fish, amphibians, lizards and snakes). Many plants also exhibit indeterminate growth, and we liberally include studies focused on plants when they can be interpreted in terms of animal life histories. We focus on different measures used to determine the fittest life histories, on indeterminate growth as a problem of resource allocation and on the effects of environment to the evolution of the resource allocation schemes.     

Changes in the expression of cell surface sialoglycoproteins during transition of human monocytes into macrophages

Cell surface sialoglycoproteins of human mononuclear phagocytes in different maturation stages were labelled by the periodate/borohydride method and separated by SDS-polyacrylamide gel electrophoresis. The main surface glycoproteins of peripheral blood monocytes had molecular masses of 115 and 95 kDa. During in vitro transition into adherent macrophages, the monocyte-characteristic surface glycoproteins disappeared. Most of the changes in the surface glycoprotein pattern occurred during the first 24 h and after 96 h the changes were completed. The major sialoglycoproteins of the macrophage cell surface had molecular masses of 130 and 55 kDa. The macrophage cell surface showed further changes when cultured in the presence of synovial fluid (10%). These results may reflect the in vivo maturation of monocytes into tissue macrophages. In synovium, tissue-derived factors may also take part in differentiation.     

Linear analysis solves two puzzles in population dynamics: the route to extinction and extinction in coloured environments

In this paper, we give simple explanations to two unsolved puzzles that have emerged in recent theoretical studies in population dynamics. First, the tendency of some model populations to go extinct from high population densities, and second, the positive effect of autocorrelated environments on extinction risks for some model populations. Both phenomena are given general explanations by simple, linear, sto-chastic models. We emphasize the predictive and explanatory power of such models.