MCMILLAN, D.M.*; FEARNLEY, S.L; STRODE, E.P; RANK, N.E; DAHLHOFF, E.P; Santa Clara University; Sonoma State University; Santa Clara University; Sonoma State University; Santa Clara Universtiy: Survival, growth and metabolic rate depends on environmental temperature, Hsp70 expression and PGI genotype in larvae of a montane leaf beetle
The willow beetle Chrysomela aeneicollis is found in thermally heterogenous habitats in the Eastern Sierra Nevada. Allele frequencies of the enzyme phosphoglucose isomerase (PGI) vary along latitudinal and altitudinal gradients and respond to climate change. In addition, expression of a heat shock protein (Hsp70) depends on PGI genotype. Here we examine differential effects of temperature on larval survival and performance among PGI genotypes. We focused on populations living in three isolated drainages in Eastern California, Bishop Creek (BC), Rock Creek (RC), and Big Pine Creek (BPC). We performed a reciprocal transplant for second-instar larvae from these drainages and monitored survival and developmental stage for 3 weeks. We also measured the effects of temperature on growth and metabolic rate of BC larvae in the laboratory. Larvae were acclimated at 20oC d 4�C n, with a 4h experimental treatment each day of 20, 27 or 34oC (growth) or 20, 34, or -4oC (metabolic rate). Hsp70 expression was measured after acclimation. Larval survival in nature was independent of source drainage and PGI genotype and was lowest in the coldest drainage (RC); however, larval growth was related to the frequency of the PGI-1 allele. In the laboratory, the effects of temperature on growth and metabolic rate depended on PGI genotype, and Hsp70 expression was correlated with growth and metabolic rate, independent of genotype. These data demonstrate differences in growth, survival and metabolic rate among PGI genotypes, which may provide a mechanism explaining the persistence of the PGI polymorphism in these populations.
