title: Functional and physiological consequences of genetic variation at phosphoglucose isomerase: heat shock protein expression is related to enzyme genotype in a montane beetle.
abstract: Allele frequency variation at the phosphoglucose isomerase (PGI) locus in Californian populations of the beetle Chrysomela aeneicollis suggests that PGI may be undergoing natural selection. We quantified (i) apparent Michaelis-Menten constant (K(m)) of fructose 6-phosphate at different temperatures and (ii) thermal stability for three common PGI genotypes (1-1, 1-4, and 4-4). We also measured air temperature (T(a)) and beetle body temperature (T(b)) in three montane drainages in the Sierra Nevada, California. Finally, we measured 70-kDa heat shock protein (Hsp70) expression in field-collected and laboratory-acclimated beetles. We found that PGI allele 1 predominated in the northernmost drainage, Rock Creek (RC), which was also significantly cooler than the southernmost drainage, Big Pine Creek (BPC), where PGI allele 4 predominated. Allele frequencies and air temperatures were intermediate in the middle drainage, Bishop Creek (BC). Differences among genotypes in K(m) (1-1 > 1-4 > 4-4) and thermal stability (4-4 > 1-4 > 1-1) followed a pattern consistent with temperature adaptation. In nature, T(b) was closely related to T(a). Hsp70 expression in adult beetles decreased with elevation and differed among drainages (BPC > BC > RC). After laboratory acclimation (8 days, 20 degrees C day, 4 degrees C night) and heat shock (4 h, 28-36 degrees C), Hsp70 expression was greater for RC than BPC beetles. In RC, field-collected beetles homozygous for PGI 1-1 had higher Hsp70 levels than heterozygotes or a 4-4 homozygote. These results reveal functional and physiological differences among PGI genotypes, which suggest that montane populations of this beetle are locally adapted to temperature.
authors.affiliation: Department of Biology, Santa Clara University, Santa Clara, CA 95053, USA.
authors.forename: E P
authors.initials: EP
authors.lastname: Dahlhoff
authors.forename: N E
authors.initials: NE
authors.lastname: Rank
mesh_terms: D000064:Acclimatization; D000818:Animals; D002980:Climate; D001517:Coleoptera / Q000235:genetics* / Q000378:metabolism; D004795:Enzyme Stability; D005786:Gene Expression Regulation; D005787:Gene Frequency; D014644:Genetic Variation; D005838:Genotype; D005956:Glucose-6-Phosphate Isomerase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D007700:Kinetics; D013696:Temperature; D013816:Thermodynamics
chemical_list: D018840:HSP70 Heat-Shock Proteins; D005956:Glucose-6-Phosphate Isomerase