Gene structure and larval expression of cnox-2Am from the coral Acropora millepora

We have cloned a Hox-like gene, cnox-2Am, from a staghorn coral, Acropora millepora, an anthozoan cnidarian, and characterised its embryonic and larval expression. cnox-2Am and its orthologs in other cnidarians and Trichoplax most closely resemble the Gsx and, to a lesser extent, Hox 3/4 proteins. Developmental northern blots and in situ hybridisation are consistent in showing that cnox-2Am message appears in the planula larva shortly after the oral/aboral axis is formed following gastrulation. Expression is localised in scattered ectodermal cells with a restricted distribution along the oral/aboral body axis. They are most abundant along the sides of the cylindrical larva, rare in the oral region and absent from the aboral region. These cells, which on morphological grounds we believe to be neurons, are of two types; one tri-or multipolar near the basement membrane and a second extending projections in both directions from a mid-ectodermal nucleus. Anti-RFamide staining reveals neurons with a similar morphology to the cnox-2Am-expressing cells. However, RFamide-expressing neurons are more abundant, especially at the aboral end of the planula, where there is no cnox-2Am expression. The pattern of expression of cnox-2Am resembles that of Gsx orthologs in Drosophila and vertebrates in being expressed in a spatially restricted portion of the nervous system.     

Zooplankton-trophic state relationships in some north and central Florida lakes

In a survey of eight lake systems located in north-central Florida, total zooplankton abundance showed a strong positive correlation (r²=0.87, a=0.01) with trophic state. Zooplankton abundance averaged 1.0 × 10⁵ organisms · m^–2 in oligotrophic systems and up to 8.2 × 10⁵ organisms · m^–2 in the eutrophic systems. Seasonal variations in total abundance were greatest in the eutrophic lakes where rotifers dominated and periodically produced sharp population peaks (approaching 2.0 × 10⁶· m^–2). In contrast, the more oligotrophic systems had relatively stable levels of total abundance and were dominated by copepods. Diversities of the major taxa in the lakes were variable with one to three species of copepods, zero to four species of cladocera, and two to seven species of rotifers dominant at any one time. Planktonic cladoceran communities were often composed of only one or two species. Low cladocera diversity in these subtropical systems was suggestive of increased predation pressure on this group of crustaceans. A comparison of the total crustacean abundance in the Florida systems to those of some of the Great Lakes indicated that lower standing crops of crustacean zooplankton in the Florida lakes may be a response to both predation and temperature.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.     

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

The renal morphology of 24 species of mormoopid and phyllostomid bats feeding on six different diets was examined to test evolutionary changes in several structural traits presumably led by dietary shifts from ancestral insectivorous diets. The kidneys of a fish-eating vespertilionid and an insect-eating emballonurid were also examined but not included in the phylogenetic comparison. The length, width, and breadth of the kidneys were used to calculate relative medullary thickness (RMT). Tissues were processed for stereological analysis, and the volumes of the kidney, nephron components, and vasculature were determined. RMT did not correlate with body mass in either animal-eating or plant-eating phyllostomid and mormoopid bats. The shift from insectivory to frugivory and nectarivory was accompanied by a reduction in RMT, a reduction in the percent of renal medulla, and an increase in the percent of renal cortex. No changes in these traits were observed in bats that shifted to carnivorous, omnivorous or sanguinivorous habits. No changes were observed in renal vasculature, in the percentage of cortical and medullary nephron components or of capillaries surrounding the nephrons in any feeding group. Vespertilionid and emballonurid species had similar values in all traits examined as compared to insectivorous phyllostomids and mormoopids. Our data suggest that diet does not influence a single area of the nephron, but rather the entire nephron such that the relative amounts of renal cortex and medulla are affected.     

Ultrastructure and distribution of microbodies in leaves of grasses with and without CO2-photorespiration

Summary A comparative study was made of the ultrastructure, distribution and abundance of leaf microbodies in four species of temperate grasses with high and four tropical grasses with low CO₂-photorespiration. The temperate grasses were all festucoid; the tropical grasses included two panicoid species and two chloridoid. Comparisons of relative abundance were made by computing the average numbers of microbody profiles per cell section.Although microbodies were present in the green parenchymatous leaf cells in all grasses examined, their average number per cell was in general severalfold greater in the grasses with high CO₂-photorespiration than in those with low. Furthermore, whereas in the grasses with high CO₂-photorespiration the microbodies were distributed through the mesophyll, in those with low CO₂-photorespiration they were concentrated in the vascular-bundle-sheath cells and were smaller and relatively scarce in the mesophyll cells. The leaf microbodies of the eight grass species resembled one another in general morphology, but differed to some extent in regard to size and type of inclusion. Microbodies of all four festucoid species contained numerous fibrils with a discernible substructure. Those of the two panicoid species contained clusters of round bodies with transparent cores. The equivalence of the microbodies to peroxisomes as biochemically defined was shown cytochemically by employing 3,3-diaminobenzidine for the localization of catalase, a marker enzyme for the peroxisome. This reaction was blocked by the catalase inhibitor, aminotriazole.The observations on the relative abundance and distribution of peroxisomes in leaves of grasses with high CO₂-photorespiration versus those with low are consistent with the published biochemical data on the levels and distribution of peroxisomal enzymes in representatives of plants with high and low CO₂-photorespiration, and may help explain the differences in apparent photorespiratory levels between these two groups of plants.     

Proterozoic phytoplankton and timing of Chlorophyte algae origins

Abstract: Morphological and reproductive features and cell wall ultrastructure and biochemistry of Proterozoic acritarchs are used to determine their affinity to modern algae. The first appearance datum of these microbiota is traced to infer a minimum age of the divergence of the algal classes to which they may belong. The chronological appearance of microfossils that represent phycoma‐like and zygotic cysts and vegetative cells and/or aplanospores, respectively, interpreted as prasinophyceaen and chlorophyceaen microalgae is related to the Viridiplantae phylogeny. An inferred minimum age of the Chlorophyte origin is before c. 1800 Ma, the Prasinophyceae at c. 1650 Ma and the Chlorophyceae at c. 1450 Ma. These divergence times differ from molecular clock estimates, and the palaeontological evidence suggests that they are older.