Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.     

Environmental networks,compensating life histories and habitat selection by white-footed mice

Summary Analysis of 6 years' data on a population of free-living white-footed mice documents both phenotypic and environmental control of litter size. Litter size was positively correlated with maternal body size. Maternal size depended upon both seasonal and annual variation. Paradoxically, the proportion of small versus large litters varied among habitats independently of the effects of body size. The result is an influence of habitat on life history that yields patterns of reproduction and survival opposite to the predictions of demographic theory. The habitat producing the largest litters had a relatively high ratio of adult/juvenile survival. Litter size was small in the habitat where the adult/juvenile survival ratio was smallest. All of these anomalous patterns can be explained through density-dependent habitat selection by female white-footed mice. Life-history studies that ignore habitat and habitat selection may find spurious correlations among traits that result in serious misinterpretations about life history and its evolution.     

Molecular cloning,nucleotide sequence and expression of a cDNA encoding an intracellular protein tyrosine phosphatase,PTPase-2, from mouse testis and T-cells

The PTP-2 cDNA encoding an intracellular protein tyrosine phosphatase (PTPase-2) was isolated and sequenced from mouse testis and T-cell cDNA libraries. This PTP-2 cDNA was found to be homologous to human PTP-TC and rat PTP-S, and contained 1,551 nucleotides, including 1,146 nucleotides encoding 382 amino acids as well as 5 (61 nucleotides) and 3 (344 nucleotides) non-coding regions. Northern blot analysis indicated that PTP-2 mRNA of 1.9 Kb was most abundant in testis and kidney, although it was also present in spleen, muscle, liver, heart and brain.Abbreviations PTPase Protein Tyrosine Phosphatase (EC3.1.3.48) - PTKase Protein Tyrosine Kinase (EC2.7.1.112)     

Tunicamycin,puromycin and brefeldin A influence the subcellular distribution of neuropeptides in hypothalamic magnocellular neurones of rat

Summary Magnocellular neurones in the supraoptic nuclei of normal Long Evans and homozygous Brattleboro rats were examined electron-microscopically after intracisternal injections of tunicamycin, puromycin, or brefeldin A. Moderate (50 g) or high (200 g) doses of tunicamycin caused the formation of electron-dense filamentous accretions in the endoplasmic reticulum (ER) cisterns of vasopressin neurones, but only the high dose of tunicamycin also caused accretions to form in the ER of some oxytocin neurones. Immunogold labelling of ultrathin sections from tunicamycin-treated rats revealed that, in about 5% of vasopressin neurones, the accretions could be immunogold-labelled for vasopressin and its associated neurophysin. However, in the majority of vasopressin neurones, the sections required trypsinisation before immunolabelling of the accretions could be detected. Small accretions in the ER of oxytocin neurones did not label for oxytocin or its neurophysin without prior trypsinisation, whereas larger accretions in other oxytocin cells could be labelled without prior trypsin treatment. Administration of puromycin resulted in the formation of small ER accretions in both vasopressin and oxytocin neurones. These accretions were immunolabelled with antisera, respectively, to vasopressin and oxytocin, but neurophysin-immunoreactivity was in most cases absent and was not revealed by treatment with trypsin, suggesting that neurophysin-immunoreactive epitopes were absent from truncated peptides forming the accretions. Brefeldin A caused dilatation of ER cisterns and disruption of the Golgi apparatus in both oxytocin and vasopressin neurones, but did not cause accretions to form in the ER.     

In situ hybridization of corticotropin-releasing factor-encoding messenger RNA in the hypothalamus of the white sucker,Catostomus commersoni

Summary In situ hybridization procedure with a ³²P-labelled synthetic oligonucleotide probe was used to detect corticotropin-releasing factor-encoding messenger RNA (CRF mRNA) in the hypothalamus of the white sucker, Catostomus commersoni. Adjacent sections were immunostained by a sucker CRF-specific antiserum. CRF mRNA-containing neurons were identified by autoradiography in the magnocellular and parvocellular subdivisions of the preoptic nucleus (PON). Many of these neurons were also immunostained by sucker antiserum, showing the same distribution patterns. These results confirm the presence of CRF mRNA and CRF peptide in the white sucker hypothalamus and support the view that the magnocellular and parvocellular neurons of the PON may be involved in the control of adrenocorticotropic hormone secretion from the pituitary in the white sucker.     

A non-alphoid repetitive DNA sequence from human chromosome 21

Summary A non-alphoid repetitive DNA from human chromosome 22, consisting of a 48-bp motif, shows homology to both G-group chromosomes in the gorilla, thus indicating the presence of additional repeat family members on further human chromosomes. Therefore, we screened a chromosome-21-specific cosmid library using this repetitive sequence from chromosome 22 (D22Z3). Some 40–50 cosmid clones were positive in tests for hybridization. One of the clones giving the strongest signals was digested with EcoRI/PstI, which we knew to cut frequently within the repeats; this resulted in fragments containing repeat units only. The fragments were subcloned into plasmid vector pTZ 19. Sequence-analysis of a 500-bp insert showed ten copies of a 48-bp repeat similar to D22Z3, with about 15% sequence deviation from the chromosome 22 consensus sequence. In situ hybridization of the newly isolated recombinant established its chromosome 21 specifity at high stringency. Physical mapping by pulsed field gel electrophoresis placed this new repeat in close vicinity to the chromosome 21 alphoid repeat. No cross-hybridization with other mammalian genomes except for those of apes was observed. The locus has been designated D21Z2 by the Genome Data Base. A gel mobility shift assay indicated that this repetitive motif has protein-binding properties.     

Mode of action studies on a Manduca sexta diuretic hormone

The mode of action of a diuretic hormone from pharate adult Manduca Sexta heads, which triggers fluid loss in M. sexta larvae and Pieris rapae adults, was studied. In vivo, Mas-DH (M. sexta diuretic hormone) decreased fluid absorption from larval recta, and increased levels of the second messenger cAMP in recta and Malpighian tubules (Mt) from larvae, and in fat body of larvae and adult M. sexta. In vitro, Mas-DH triggered minor changes in fluid loss from adult Mt, but did not affect levels of cAMP in Mt from larvae, pharate adults, or adults, though it elevated cAMP levels in fat body of these stages. © 1992 Wiley-Liss, Inc.     

Mapping of FMR1, the gene implicated in fragile X-linked mental retardation, on the mouse X chromosome

A genetic map of the Cf-9 to Dmd region of the mouse X chromosome has been established by typing 100 offspring from a Mus musculus x Mus spretus interspecific backcross for the four loci Cf-9, Cdr, Gabra3, and Dmd. The following order and genetic distances in centimorgans were determined: (Cf-9)-2.4 +/- 1.7-(Cdr)-2.0 +/- 1.4-(Gabra3)-4.1 +/- 2.0-(Dmd). Six backcross offspring carrying X chromosomes with recombination events in the Cdr-Dmd region were identified. These recombination events were used to define the position of Fmr-1, the murine homologue of FMR1, which is the gene implicated in the fragile X syndrome in man, and that of DXS296h, the murine homologue of DXS296. Both Fmr-1 and DXS296h were mapped into the same recombination interval as Gabra3 on the mouse X chromosome. These findings provide strong support for the concept that the order of loci lying in the Cf-9 to Gabra3 segment of the X chromosome is highly conserved between human and mouse.