Chromosomal mapping of glutamate dehydrogenase gene sequences to mouse chromosomes 7 and 14

Glutamate dehydrogenase (GLUD) plays an important role in mammalian neuronal transmission. In human, GLUD is encoded by a small gene family. To determine whether defects in Glud genes are associated with known neurological mutations in the mouse and to contribute to the comparative mapping of homologous genes in man and mouse, the chromosomal location of genes reactive with a mouse brain GLUD cDNA were determined. Genomic Southern analysis of a well-characterized panel of Chinese hamster x mouse somatic cell hybrids identified two GLUD-reactive loci, one residing on mouse Chromosome 14 and the other on Chromosome 7. Progeny of an intersubspecies backcross were used to map one of these genes, Glud, proximal to Np-1 on Chromosome 14, but no restriction fragment polymorphisms could be identified for the second locus, Glud-2.     

Low acclimation capacity of narrow‐ranging thermal specialists exposes susceptibility to global climate change

Thermal acclimation is hypothesized to offer a selective advantage in seasonal habitats and may underlie disparities in geographic range size among closely‐related species with similar ecologies. Understanding this relationship is also critical for identifying species that are more sensitive to warming climates. Here, we study North American plethodontid salamanders to investigate whether acclimation ability is associated with species’ latitudinal extents and the thermal range of the environments they inhabit. We quantified variation in thermal physiology by measuring standard metabolic rate (SMR) at different test and acclimation temperatures for 16 species of salamanders with varying latitudinal extents. A phylogenetically‐controlled Markov chain Monte Carlo generalized linear mixed model (MCMCglmm) was then employed to determine whether there are differences in SMR between wide‐ and narrow‐ranging species at different acclimation temperatures. In addition, we tested for a relationship between the acclimation ability of species and the environmental temperature ranges they inhabit. Further, we investigated if there is a trade‐off between critical thermal maximum (CTMax) and thermal acclimation ability. MCMCglmm results show a significant difference in acclimation ability between wide and narrow‐ranging temperate salamanders. Salamanders with wide latitudinal distributions maintain or slightly increase SMR when subjected to higher test and acclimation temperatures, whereas several narrow‐ranging species show significant metabolic depression. We also found significant, positive relationships between acclimation ability and environmental thermal range, and between acclimation ability and CTMax. Wide‐ranging salamander species exhibit a greater capacity for thermal acclimation than narrow‐ranging species, suggesting that selection for acclimation ability may have been a key factor enabling geographic expansion into areas with greater thermal variability. Further, given that narrow‐ranging salamanders are found to have both poor acclimation ability and lower tolerance to warm temperatures, they are likely to be more susceptible to environmental warming associated with anthropogenic climate change.