Variation in Hsp70 Levels after Cold Shock: Signs of Evolutionary Responses to Thermal Selection among Leptinotarsa decemlineata Populations

Anne Lyytinen,Johanna Mappes,Leena Lindström,Suzannah Rutherford

doi:10.1371/journal.pone.0031446

Abstract

Individuals of widely spread species are expected to show local adaption in temperature tolerance as they encounter a range of thermal conditions. We tracked thermal adaptations of the Colorado potato beetle (Leptinotarsa decemlineata) that invaded Europe within the last 100 years. It has occupied various conditions although, like the majority of invasive species, it lost a measurable amount of neutral genetic variation due to bottleneck effect when it invaded Europe. We exposed diapausing beetles originated from three different latitudes (54°N, 59°N, 60°N) to cold shock (−5°C, 1.5 hrs) in order to test if beetles from the northern populations express differential levels of cold-induced and constitutive Hsp70 compared to the beetles from milder temperature regime. The level of cold-induced Hsp70 was lowest in the northernmost beetle populations while the level of constitutive Hsp70 did not differ with the population. Moreover, the southernmost beetles were more plastic in their response to cold shock than the northernmost beetles. These results suggest that physiological adaptation, like the synthesis of Hsp70, can evolve very quickly.

Highlights

Why certain species occupy wide geographical areas whereas others are found in relatively small areas is a fundamental question in ecology
We studied the within species variation in the level of the Hsp70 in the diapausing Colorado potato beetles, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae, Say), of different geographic origin
As no significant differences in the Hsp70 level were found between the field and laboratory-derived populations from Lodeynoye Pole (2-way-ANOVA: F1, 26 = 0.305, p = 0.858), the two years were pooled for the further statistical analyses

Summary

Introduction

Why certain species occupy wide geographical areas whereas others are found in relatively small areas is a fundamental question in ecology. Harmful to insects are even brief exposures to sub-zero temperatures, i.e. cold shock, which can cause chill injuries [1]. Organisms have evolved several mechanisms to prevent these harmful changes. Heat shock proteins (Hsps, referred to as stress proteins) are an example of adaptive phenotypic plasticity in inducible tolerance to environment. They can be induced by high or low temperatures [3] when they prevent aggregation of stressdenatured proteins and assist in refolding proteins to their native state [4,5] thereby enhancing tolerance to various thermal stressors [6,7]

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Results

Conclusion