An empirical test of the relationship between environmental variability and phenotypic plasticity in the pallid-winged grasshopper (Trimerotropis pallidipennis)

Phenotypic plasticity has been proposed as an adaptive mechanism by which organisms can maximize their fitness in response to short-term environmental variability. In this dissertation, I test one prediction that comes out of this idea: that populations from more variable environments should have higher levels of phenotypic plasticity than populations from less variable environments. I first analyzed precipitation variability and predictability across nine biomes in the Southwestern U.S. to determine a gradient of environmental variability. There was a non-linear negative relationship between precipitation variability and precipitation mean. In general, contrary to common belief, desert biomes were no more variable nor less predictable than nondesert biomes. I tested the relationship between environmental variability and phenotypic plasticity in seven populations of the pallid-winged grasshopper (Trimerotropis pallidipennis). Contrary to prediction, populations from more variable environments had lower, not higher, levels of phenotypic plasticity in development time. There was a significant convex quadratic relationship between plasticity for size at maturity and precipitation variability. In general, females in populations with more plasticity in development time had lower fitness. Plasticity in size at maturity generally did not affect fecundity, but increased survivorship. Plasticities in both traits conferred no significant costs or benefits in males. I tested the hypothesis that these results were due to constraints on the evolution of plasticity: either to a lack of genetic variation for plasticity or to antagonistic pleiotropy between size at maturity and development time. I found sufficient genetic variation for plasticity to evolve in all study populations and little evidence for antagonistic pleiotropy. I further tested whether selection for developmental stability or directional selection for short development time could explain the pattern of plasticity responses across the gradient. Low plasticity responses were apparently due to selection for developmental stability in deserts. I found weak evidence that antagonistic and synergistic selection could also explain the plasticity responses. I found no evidence that directional selection for short development time in all environments could explain the lower levels of phenotypic plasticity in the desert populations