Habitat fragmentation: island v landscape perspectives on bird conservation

Fragments of habitat are often viewed as islands and are managed as such; however, habitat fragmentation includes a wide range of spatial patterns of environments that may occur on many spatial scales. Fragments exist in a complex landscape mosaic, and dynamics within a fragment are affected by external factors that vary as the mosaic structure changes. The simple analogy of fragments to islands, therefore, is unsatisfactory. Understanding how birds respond to these complexities of fragmentation requires mechanistic studies focused on habitat selection and movement behaviour. Conservation efforts must be based on viewing fragmentation as a range of conditions that occurs in a landscape mosaic, and management should be directed toward the mosaics rather than focusing solely on reserves.     

Complete Elimination of Mitosis and DNA Synthesis in the Lens of the Hypophysectomized Frog: Effects on Cell Migration and Fiber Growth

Three weeks after hypophysectomy mitosis and DNA synthesis are absent in the lens of the leopard frog ( Rana pipiens ). By labeling germinative zone cells in their last DNA synthetic period we were able to follow them in the absence of further proliferation. By this means it has been demonstrated that migration of epithelial cells to the equator of the lens is stopped. Based on indirect measurements it seems that lens fiber formation also ceases. A correlation coefficient of 0.86 was computed between average labeling index and average distance migrated. In hypophysectomized animals the correlation coefficient between time and migration was 0.02 while in intact animals it is 0.87.     

Isolation of highly polymorphic microsatellite markers from the intertidal barnacle Chthamalus montagui Southward

This study reports the isolation and characterization of seven highly polymorphic microsatellite loci in Chthamalus montagui (Crustacea, Cirripedia). The loci were isolated from a library constructed from genomic DNA enriched for CA repeats. The markers yielded three to 43 alleles per locus (mean 16.7) in samples averaging 49 individuals. Observed heterozygosity ranged from 0.08 to 0.58 (mean 0.39). These microsatellite loci will be valuable tools for population genetic studies of this species.     

Ultrastructure of the Tubificid Acrosome (Annelida, Oligochaeta)

The later morphogenesis of the acrosome of Limnodriloides winckelmanni and Rhyacodrilus arthingtonae is compared with that in Enchytraeus and in earthworms. After superposition of the acrosome on the tip of the nucleus the manchette continues apically beyond the nucleus to ensheath the acrosomal tube. At the posterior limit of, and probably contained in, the spacious/ terminal primary acrosomal vesicle is an electron-dense ring. A domed protrusion into the floor of the primary vesicle is tentatively regarded as the secondary acrosome vesicle. The axial rod when first observed is attached to the vesicle complex. Later, the rod detaches and extends deeply into the acrosome tube. A membrane ensheathes the tubificid axial rod but its exact homology with the complex layers surrounding the lumbricid or megascolecid axial rod is not clear. The domed apical region of the tubificid acrosome is probably a persistence of the primary acrosome vesicle and it is deduced that the acrosome vesicle surrounding the axial rod in lumbricids and megascolecids is a product, by invagination, of the secondary acrosome vesicle only.     

An orb‐weaver spider eludes plant‐defending acacia ants by hiding in plain sight

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