BECKER, B. A.; DARGIS-ROBINSON, V. R.; DAHLHOFF, E. P.; Santa Clara University; Santa Clara University; Santa Clara University: Effects of temperature on performance and fitness of two species of California willow beetle

We compared effects of temperature stress on running speed, fecundity and mating frequency for two species of California leaf beetle, Chrysomela schaefferi and C. confluens. C. confluens prefers warmer, inland locales and typically has higher body temperatures than C. schaefferi in nature. Differences in thermal tolerance between these species may explain differences in habitat use. To test this idea, we collected adults from sites in Sonoma, Santa Cruz and Santa Clara counties shortly after emergence from winter diapause. Individuals were sorted randomly into mating pairs and held in the laboratory at 20�C d, 4�C n. Each afternoon for 17 d, mating pairs were exposed to 20, 28 or 36�C for 4 h. Running speed, number of eggs laid (females) and mating activity (males) was assessed daily. We also quantified expression of a 70-kD heat shock protein (Hsp70) in beetles of known running speed. Fecundity was higher for C. confluens than C. schaefferi, especially at higher treatment temperatures. Male mating frequency did not differ between species, yet C. schaefferi males ran faster than C. confluens males after acute exposure to moderate temperatures (20�C), and slower after chronic exposure to elevated temperatures (28, 36�C). Running speed was correlated with fecundity and mating success and was fastest in beetles with lowest Hsp70 expression, implying beetles with better performance have better reproductive success, perhaps due to lower cost of Hsp expression. These results suggest a mechanism for temperature affecting habitat selection: C. schaefferi males may be more active in mild microclimates, resulting in higher mating success, but C. confluens females may have higher fecundity than their C. schaefferi counterparts in warmer microclimates.