Latitude‐associated evolution and drivers of thermal response curves in body stoichiometry

Abstract

1. Trait-based studies are needed to understand the plastic and genetic responses of organisms to warming. A neglected organismal trait is elemental composition, despite its potential to cascade into effects on the ecosystem level.2. Warming is predicted to shape elemental composition through shifts in storage molecules associated with responses in growth, body size and metabolic rate. Our goals were to quantify thermal response patterns in body composition and to obtain insights into their underlying drivers and their evolution across latitudes.3. We reconstructed the thermal response curves (TRCs) for body elemental composition [C (carbon), N (nitrogen) and the C:N ratio] of damselfly larvae from highand low-latitude populations. Additionally, we quantified the TRCs for survival, growth and development rates and body size to assess local thermal adaptation, as well as the TRCs for metabolic rate and key macromolecules (proteins, fat, sugars and cuticular melanin and chitin) as these may underlie the elemental TRCs. 4. All larvae died at 36°C. Up to 32°C, low-latitude larvae increased growth and development rates and did not suffer increased mortality. Instead, growth and development rates of high-latitude larvae were lower and levelled off at 24°C, and mortality increased at 32°C. This latitude-associated thermal adaptation pattern matched the 'hotter-is-better' hypothesis. With increasing temperatures, lowlatitude larvae decreased C:N, while high-latitude larvae increased C:N. These patterns were driven by associated changes in N contents, while C contents did not respond to temperature. Consistent with the temperature-size rule and the thermal melanism hypothesis, body size and melanin levels decreased with warming. While all traits and associated macromolecules (except for metabolic rate that showed thermal compensation) assumed to underlie thermal responses in elemental composition showed thermal plasticity, these were largely independent and none could explain the stoichiometric TRCs. 5. Our results highlight that thermal responses in elemental composition cannot be explained by traditionally assumed drivers, asking for a broader perspective including the thermal dependence of elemental fluxes. Another key implication is that thermal evolution can reverse the plastic stoichiometric thermal responses Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Van Dievel M, Tüzün N, Stoks R. Latitude-associated evolution and drivers of thermal response curves in body stoichiometry.

Genetic compensation rather than genetic assimilation drives the evolution of plasticity in response to mild warming across latitudes in a damselfly

“…Combining current transcriptomic results and the phenotypic companion study (Van Dievel et al, 2019) suggests that southern populations can increase their growth rate with mild warming despite a lack of major plastic gene expression responses as observed in the northern populations. Unfortunately, our functional analysis does not pinpoint pathways crucial for southern populations to thermally adapt to warming.…”

“…Several studies have shown latitude-associated thermal adaptation in I. elegans for life history, behaviour and physiology with cold-adapted northern populations and warm-adapted southern populations (e.g. De Block et al, 2013;Debecker & Stoks, 2019;Van Dievel et al, 2019).…”

“…Females were sampled during the summer of 2015 and allowed to oviposit on wet filter paper. Per population, larvae from 10 females (total of 60 females, 1,756 larvae) were used for the rearing experiment described in the companion study of Van Dievel et al (2019).…”

“…In the companion study of Van Dievel et al. (2019), the focus was on the thermal evolution of phenotypic reaction norms with particular emphasis on body stoichiometry. Here we reconstruct thermal reaction norms in gene expression and also test whether certain reaction norm patterns are enriched for specific biological pathways.…”

Live fast, die old: oxidative stress as a potential mediator of an unexpected life‐history evolution

“…Given that the lifespan of the study species is ca 10 days (Cordero et al ), the loss of a few days has strong fitness implications. The study species shows striking latitudinal differences in life history, with higher larval growth rates in the multivoltine (3–4 generations per year), low‐latitude populations compared to the semivoltine (2 years per generation), high‐latitude populations (Stoks and De Block , Shama et al , Stoks et al , Debecker et al , Debecker and Stoks , Van Dievel et al , Verheyen and Stoks ). Moreover, we have recently shown in separate studies that the low‐latitude populations of the species have a longer adult lifespan (reported as Supporting Information in Debecker et al ) and higher levels of antioxidant enzymes in the larval stage (Debecker and Stoks ).…”