Karyotypes in two species of the genusHippocampus (Pisces: Syngnatiformes)

Diploid modal numbers of chromosomes 2n=48 forHippocampus ramulosus and 2n=44 forH. hippocampus, collected in the Gulf of Palermo in May 1985, are established. No sex-linked heteromorphic pairs are observed in the two species analyzed. The karyotype ofH. hippocampus seems to be a derived condition.     

The oxidation of octanoic acid by cultured amniotic fluid cells: The effect of cell type and passage number

We have measured the rate of oxidation of [1⁻¹⁴C]octanoate in cultured amniotic fluid (AF) cells at various passages and in AF cell lines with different clonal morphology. It is possible that both the passage number and the cell type may influence the outcome of prenatal diagnosis of fatty acid oxidation defects using this technique. We found that there was no significant difference between the three major AF cell types (epithelial, large epithelial, and fibroblast) when analysed at identical passage number but there was a significant reduction in octanoate oxidation in all cell types with increasing passage. For reliable prenatal diagnosis, cell lines of similar low passage number should be used.     

Modeling the Effects of Habitat Fragmentation on Source and Sink Demography of Neotropical Migrant Birds

Many songbird populations in the midwestem United States are structured as a network of sources and sinks that are linked by dispersal. We used a modeling approach to examine explicitly how populations respond to incremental fragmentation of source habitat and how this response may vary depending upon two life-history attributes: fidelity to natal habitat type and reproductive strength of the source. Fragmentation of source habitat led to a predictable decline in population for both attributes examined, but the manner in which populations declined varied depending upon the reproductive strength of the source and the level of fidelity. When the source was weak and produced few excess individuals, fragmentation of source habitats resulted in a predictable and parallel population decline of adults in both the source and the sink. In this situation high fidelity to natal habitats was important for maintenance of population size and structure. Low fidelity to weak sources resulted in population extinction; populations experienced a demographic cost by dispersing from high quality source habitat to low quality sink habitat. In contrast, when the source was strong and produced many excess individuals, fragmentation of the source led to population declines in both the source and the sink, but this decline was more abrupt in sink habitats. When the source was strong and produced a large excess of individuals, nonfidelity to natal habitats had little effect on metapopulation size and structure.