Geographic Variation in Larval Metabolic Rate Between Northern and Southern Populations of the Invasive Gypsy Moth

Abstract

Thermal regimes can diverge considerably across the geographic range of a species, and accordingly, populations can vary in their response to changing environmental conditions. Both local adaptation and acclimatization are important mechanisms for ectotherms to maintain homeostasis as environments become thermally stressful, which organisms often experience at their geographic range limits. The spatial spread of the gypsy moth (Lymantria dispar L.) (Lepidoptera: Erebidae) after introduction to North America provides an exemplary system for studying population variation in physiological traits given the gradient of climates encompassed by its current invasive range. This study quantifies differences in resting metabolic rate (RMR) across temperature for four populations of gypsy moth, two from the northern and two from southern regions of their introduced range in North America. Gypsy moth larvae were reared at high and low thermal regimes, and then metabolic activity was monitored at four temperatures using stop-flow respirometry to test for an acclimation response. For all populations, there was a significant increase in RMR as respirometry test temperature increased. Contrary to our expectations, we did not find evidence for metabolic adaptation to colder environments based on our comparisons between northern and southern populations. We also found no evidence for an acclimation response of RMR to rearing temperature for three of the four pairwise comparisons examined. Understanding the thermal sensitivity of metabolic rate in gypsy moth, and understanding the potential for changes in physiology at range extremes, is critical for estimating continued spatial spread of this invasive species both under current and potential future climatic constraints.

Climate‐related geographical variation in performance traits across the invasion front of a widespread non‐native insect

“…May et al. (2018) did not find support for metabolic cold adaptation in L. d. dispar , but their study compared populations based on latitude rather than a measure of local climate. Further research on growth and metabolic rates across a broader environmental gradient and using a metric of climate rather than latitude would increase understanding of the physiological mechanisms underlying the patterns found in our study.…”

The Respiratory Metabolism of Polistes biglumis, a Paper Wasp from Mountainous Regions

“…However, as already stated by Terblanche et al [10], the generality of this hypothesis is contentious. While there is evidence that this may occur in aquatic [12] and terrestrial poikilothermic animals [9][10][11], May et al [22] could not find support in a comparison of northern and southern populations of gypsy moths (Lymantria dispar) introduced to America. Our comparison, between P. biglumis from colder mountainous habitats showing a considerably lower metabolic rate and sensitivity to temperature than P. dominula from the warmer lowlands (Figure 4), seems to call the generality of the metabolic cold adaptation theory in question.…”

“…The metabolic cold adaptation theory predicts that populations or species from cooler environments should have either a higher metabolic rate at a certain temperature, or a steeper relationship of respiratory metabolism with temperature (a greater sensitivity to temperature), see e.g., [9,10,21,22]. However, as already stated by Terblanche et al [10], the generality of this hypothesis is contentious.…”

“…These processes are considered similar in related species [19]. However, regarding the thermal sensitivity of insect metabolism (Q 10 ), i.e., the influence of ambient temperature on it, there nevertheless may occur differences in the energy demand of closely related species or even subspecies, living in different habitats, see e.g., [9,10,[20][21][22]. Indeed, we could detect such differences, when we compared the SMR of Polistes biglumis with that of Polistes dominula from the study by Käfer et al [5].…”

Validating measurements of acclimation for climate change adaptation

“…12]. Further, acclimation for other physiological and biochemical processes such as metabolic rate can help organisms maintain fitness under increasing mean temperatures [13]. Under climate change, increasing hot-cold temperature fluctuations, changing fire regimes, drought and flooding are also expected to influence populations [14].…”