The reproductive behavior of six species of Namib desert tenebrionid beetles (Coleoptera: Tenebrionidae)

The reproductive behavior of six species of tenebrionid beetles (Coleoptera: Tenebrionidae) was studied in the Namib Desert of southern Africa. In three species, males follow closely behind females (following behavior), while in the other three species, males mount females and remain clasped to them for extended periods (riding behavior). Following behavior occurs before and sometimes after copulation, while riding behavior occurs primarily after copulation. Males of all six species guard females from contesting males, although the effectiveness of guarding is greater in riding species. The evolution of the two male mating strategies does not appear to be related to operational sex ratio differences but, rather, to differential tendencies of females to remate. Variation in total pair duration within following and riding species may be attributed partly to species differences in operational sex ratio. However, pair durations are not affected by experimental manipulations of sex ratio in each species.     

Developmental expression of syndecan, an integral membrane proteoglycan, correlates with cell differentiation

Syndecan is an integral membrane proteoglycan that behaves as a matrix receptor by binding cells to interstitial matrix and associating intracellularly with the actin cytoskeleton. Using immunohistology, we have now localized this proteoglycan during the morphogenesis of various derivatives of the surface ectoderm in mouse embryos. Syndecan is expressed on ectodermal epithelia, but is selectively lost from the cells that differentiate into the localized placodes that initiate lens, nasal, otic and vibrissal development. The loss is transient on presumptive ear, nasal and vibrissal epithelia; the derivatives of the differentiating ectodermal cells that have lost syndecan subsequently re-express syndecan. In contrast, syndecan is initially absent from the mesenchyme underlying the surface ectoderm, and is transiently expressed when the surface ectoderm loses syndecan. These results demonstrate that expression of syndecan is developmentally regulated in a distinct spatiotemporal pattern. On epithelia, syndecan is lost at a time and, location that correlates with epithelial cell differentiation and, on mesenchyme, syndecan is acquired when the cells aggregate in proximity to the epithelium. This pattern of change with morphogenetic events is unique and not duplicated by other matrix molecules or adhesion receptors.     

Phylogenetic relationships among four members of Stizostedion (Percidae) determined by mitochondrial DNA and allozyme analyses

Phylogenetic relationships among four Stizostedion species were examined using mitochondrial DNA (mtDNA) and allozyme analyses. Twenty-six allozyme loci were scored, and mtDNA variation was examined using 24 restriction endonucleases, yielding 48–57 restriction sites among the species. Genetic distance analyses show that the two North American species ( S. canadense and S. vitreum ) cluster in one group, while the two European species ( S. hciopercu and S. vogense ) form a second group. Nei's genetic distance between these two groups was 0.7 ± 0.2 for allozymes, while the corresponding mtDNA sequence divergence was 14.8 ± 2.0%, suggesting that these two groups diverged approximately 10 million years ago. Thus, these data are consistent with the hypothesis that Stizostedion colonized North America during the Pliocene.     

In Situ Analysis of Na,K-ATPase α1- and α3-Isoform mRNAs in Aging Rat Hippocampus

Abstract: Age-related changes in the expression of Na,K-ATPase α1- and α3-isoform mRNAs were analyzed by in situ hybridization in the Fischer-344 rat hippocampus. Quantification of signal density with cRNA probes in rat hippocampus at 3 months of age showed (a) α1 content is 1.5 times higher in granule than in pyramidal cell layers, whereas α3 content shows the opposite ratio and (b) α3 label is found in large clusters related to mossy cells and basket cells and in medium clusters corresponding to interneurons within the dendritic fields of CA1–3. In the 24-month-old rats as compared with the young animals, the α1 signal is increased more than sevenfold in the dendritic fields and is not significantly changed in perikaryal layers. The α3 signal is reduced about threefold ( p < 0.0001, ANOVA, n = 6) in perikaryal layers, is almost completely absent over the interneurons, basket cells, and mossy cells, and is not significantly changed in dendritic fields. These data indicate age-related, cell- and isoform-specific alterations in pretranslational regulation of Na,K-ATPase α isoforms. The striking changes in the dendritic fields, mossy cells, and GABAergic basket cells and interneurons may constitute early and sensitive markers for age-related alterations in hippocampal function, before cell loss.