BLAKE, MA*; ANGILLETTA, MJ; Indiana State University; Indiana State University: Growth of the German cockroach at constant and fluctuating temperatures

Growth rate is temperature sensitive in all ectotherms, but most of our estimates of sensitivity are based on measurements of the growth of animals at constant temperatures. Fluctuating temperatures, which are similar to those experienced in nature, have seldom been used in comparisons of growth rate. To determine whether there is any significant difference in growth rate at constant and fluctuating temperatures, we incubated German cockroaches (Blatella germanica) for 28 days in one of four thermal treatments. Fluctuating thermal treatments (27 ±5 °C and 22 ±5 °C) were designed such that the mean temperature equaled constant temperature treatments (27 °C and 22 °C). Virgin parents were mated and the offspring were divided randomly among the four treatments. Each nymph was weighed at hatching and again after 28 days. We compared growth at high and low mean temperatures to quantify the thermal sensitivity of growth. Individuals at higher mean temperatures grew faster regardless of thermal fluctuation. We compared growth in fluctuating temperatures to growth in constant temperatures to show the effect of thermal fluctuation on growth rate. Fluctuating temperatures decreased the growth rate for roaches in the first 28 days of life. Recently published theories cannot be used to predict the outcome of a comparison of growth in constant versus fluctuating temperatures. Our study, combined with previous ones, indicate that the effects of thermal fluctuations on organismal performance can be complex. The thermal factor that primarily determines growth rate may be maximal temperature, minimal temperature, the relative duration of thermal exposures, the rate of temperature change, or a combination of all of these.