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

Abstract

Aim Invasive species are ideal systems for testing geographical differences in performance traits and measuring evolutionary responses as a species spreads across divergent climates and habitats. The European gypsy moth, Lymantria dispar dispar L. (Lepidoptera: Erebidae), is a generalist forest defoliator introduced to Medford, Massachusetts, USA in 1869. The invasion front extends from Minnesota to North Carolina and the ability of this species to adapt to local climate may contribute to its continuing spread. We evaluated the performance of populations along the climatic gradient of the invasion front to test for a relationship between climate and ecologically important performance traits. Location Eastern United States of America Taxon Lymantria dispar dispar L. (Lepidoptera: Erebidae) Methods Insects from 14 populations across the US invasion front and interior of the invasive range were reared from hatch to adult emergence in six constant temperature treatments. The responses of survival, pupal mass and larval development time were analysed as a function of source climate (annual mean normal temperature), rearing temperature and their interaction using multiple polynomial regression. Results With the exception of female development time, there were no significant interactions between source climate and rearing temperature, indicating little divergence in the shape of thermal reaction norms among populations. Source population and rearing temperature were significant predictors of survival and pupal mass. Independent of rearing temperature, populations from warmer climates had lower survival than those from colder climates, but attained larger body size despite similar development times. Larval development time was dependent on rearing temperature, but there were not consistent relationships with source climate. Main Conclusions Thermal adaptation can be an important factor shaping the spread of invasive species, particularly in the context of climate change. Our results suggest that L. d. dispar is highly plastic, but has undergone climate‐related adaptation in thermal performance and life‐history traits as it spread across North America.

Using simulated temperature regimes to test growth and development of an invasive forest insect under climate change

“…We found evidence that source populations responded differently to experimental treatments (Figure 2c). However, evidence for local adaptation of larval growth and development was equivocal overall, in contrast to other recent studies (Faske et al, 2019; Friedline et al, 2019; Thompson et al, 2017, 2021). Among-population variation in larval growth rates in the baseline and CC4.5 treatments was not discernibly related to a “home field advantage” as was seen in the CC8.5 treatments.…”

“…We focus here on data from third and fifth instars because fungal contamination of the artificial diet increased mortality between fifth instar and adulthood in individuals raised in one of the laboratories (Figure S2). Data from this and a previous experiment (Thompson et al, 2021) showed that larval masses were strongly correlated with pupal masses (Table S1), which in turn, are an excellent proxy for fecundity (Faske et al, 2019; Honěk, 1993).…”

“…Individuals used in this experiment were sourced from seven populations in the Eastern US, a subset of those used in Thompson et al (2021). These populations represent areas of active range expansion and the current climatic extremes of the L. dispar invasive range in the US (Figure 1a).…”

“…For example, egg masses sourced from warmer climates had higher viability when reared at warm range-edge temperatures relative to populations from cooler regions (Faske et al, 2019). In constant temperature experiments, warmer climate populations had lower mortality rates and smaller reductions in fitness-associated traits when reared at supraoptimal temperatures than those sourced from cooler climates (Thompson et al, 2017, 2021). Additionally, genomic evidence is consistent with a genetic basis for phenotypic differences in temperature-related performance traits (Friedline et al, 2019).…”

Diversity and distribution of cytochrome oxidase I (COI) haplotypes of the brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera, Pentatomidae), along the eastern front of its invasive range in Eurasia

“…In addition, climatic factors in some regions may permit more rapid population growth (and increased agricultural impacts) due to multiple generations of any given successfully-established haplotype (Musolin et al 2019;Stoeckli et al 2020). However, variation in performance traits in invasive insect species can be an important predictor of their success in establishment and spread across a broad geographic range (Thompson et al 2021). Future research investigating the different H. halys haplotypes would be of interest to determine whether there is any validity to the observation that H1 appears to be a more successful invader and to determine whether this success is linked to intraspecific variation in biological traits, such as phenology, thermal performance, flight capacity, overwintering survival or fecundity.…”