Effects of historical climate change, habitat connectivity, and vicariance on genetic structure and diversity across the range of the red tree vole (Phenacomys longicaudus) in the Pacific Northwestern United States

Phylogeographical analyses conducted in the Pacific Northwestern United States have often revealed concordant patterns of genetic diversity among taxa. These studies demonstrate distinct North/South genetic discontinuities that have been attributed to Pleistocene glaciation. We examined phylogeographical patterns of red tree voles (Phenacomys longicaudus) in western Oregon by analysing mitochondrial control region sequences for 169 individuals from 18 areas across the species' range. Cytochrome b sequences were also analysed from a subset of our samples to confirm the presence of major haplotype groups. Phylogenetic network analyses suggested the presence of two haplotype groups corresponding to northern and southern regions of P. longicaudus' range. Spatial genetic analyses (samova and Genetic Landscape Shapes) of control region sequences demonstrated a primary genetic discontinuity separating northern and southern sampling areas, while a secondary discontinuity separated northern sampling areas into eastern and western groups divided by the Willamette Valley. The North/South discontinuity likely corresponds to a region of secondary contact between lineages rather than an overt barrier. Although the Cordilleran ice sheet (maximum approximately 12,000 years ago) did not move southward to directly affect the region occupied by P. longicaudus, climate change during glaciation fragmented the forest landscape that it inhabits. Signatures of historical fragmentation were reflected by positive associations between latitude and variables such as Tajima's D and patterns associated with location-specific alleles. Genetic distances between southern sampling areas were smaller, suggesting that forest fragmentation was reduced in southern vs. northern regions.     

Suppression of feeding by cholecystokinin but not bombesin is attenuated in dorsomedial hypothalamic nuclei lesioned rats

Rats with dorsomedial hypothalamic lesions (DMN-L) or sham operations were injected IP with saline or the satiety peptide cholecystokinin (CCK) at 3.0 and 6.0 micrograms/kg at the onset of the dark phase. Food consumption was then measured 15, 30 and 60 min later. Compared to saline baseline intake, CCK suppressed feeding during the first 30 min following injection in the sham operated group but not in the DMN-L group. Bombesin (BBS), another satiety peptide was also injected (4.0 and 8.0 micrograms/kg) into the two groups. BBS produced significant and comparable suppression of feeding in both DMN-L and sham operated rats. In a third trial a large dose of CCK (12.0 micrograms/kg) was injected into the two groups as described above. The CCK suppressed feeding for 60 min in the control group. CCK also attenuated feeding in the DMN-L group, but for only 30 min. However, even this suppression was reduced compared to the control group. The data suggest that the DMN may play a role in CCK induced satiety.