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Date of Award

5-6-2021

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Dr. Kristine Grayson

Abstract

One impact from climate change is the potential for alterations to the geographic ranges of species. Thermal tolerance creates constraints that may restrict or widen the territory a given species can occupy. The study of the tolerance limits for extreme temperatures is important for invasive species given the concern that warming temperatures may alter their regional boundaries. Given the overall pattern of climate warming, more attention has been given to the study of upper thermal tolerances, but understanding cold temperature tolerance can be important in early developmental stages. These stages can be more vulnerable and most likely to encounter periods of extreme cold, particularly for spring hatching or emerging species. Chill coma recovery time is a common non-lethal metric of lower thermal tolerance. It can be used on species covering a broad geographic range to determine if physiological responses to extreme cold have intraspecific differences. We used this measure to compare cold tolerance in populations of the invasive European gypsy moth (Lymantria dispar) in the Eastern United States from long established areas and the extremes of the current northern and southern extent. In two chill coma recovery experiments, we exposed early instar larvae to a short period of nonlethal cold temperature and monitored recovery time. This exposure is representative of cold temperature extremes experienced by larvae after hatching during spring cold snaps. We also tested a subset of populations for growth responses 10-days post chill coma recovery, to examine sublethal effects of cold exposure. Our results support that individuals from the northern part of the invasive range recover more quickly, indicating higher cold tolerance, than those from warmer southern climates of the invasion. The growth study indicates that exposure to near freezing temperatures induces physiological stress comparable to that of a 24-hour starve period, while exposure to temperatures below freezing negatively impacts future growth. Studying the potential for intraspecific variation in cold tolerance increases our understanding of climatic factors that can influence the physiology of an invasive species. The findings of our study provide us with information that is helpful for predicting further expansion of this invasive forest pest.

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