Usefulness and limitations of thermal performance curves in predicting ectotherm development under climatic variability

Abstract

1. Thermal performance curves (TPCs) have been estimated in multiple ectotherm species to understand their thermal plasticity and adaptation and to predict the effect of global warming. However, TPCs are typically assessed under constant temperature regimes, so their reliability for predicting thermal responses in the wild where temperature fluctuates diurnally and seasonally remains poorly documented. 2. Here, we use distant latitudinal populations of five species of sepsid flies (Diptera: Sepsidae) from the temperate region (Europe, North Africa, North America) to compare estimates derived from constant TPCs with observed development rate under fluctuating temperatures in laboratory and field conditions.3. TPCs changed across gradients in that flies originating from higher latitudes showed accelerated development at higher temperatures, an adaptive response.TPCs were then used to predict development rates observed under fluctuating temperatures; these predictions were relatively accurate in the laboratory but not the field. Interestingly, the precision of TPC predictions depended not only on the resolution of temperature data, with daily and overall temperature summing performing better than hourly temperature summing, but also on the frequency of temperatures falling below the estimated critical minimum temperature. Hourly temperature resolution most strongly underestimated actual development rates, because flies apparently either did not stop growing when temperatures dropped below this threshold, or they sped up their growth when the temperature rose again, thus most severely reflecting this error. 4. We conclude that when flies do not encounter cold temperatures, TPC predictions based on constant temperatures can accurately reflect performance under fluctuating temperatures if adequately adjusted for nonlinearities, but when encountering cold temperatures, this method is more error-prone. 5.Our study emphasizes the importance of the resolution of temperature data and cold temperatures in shaping thermal reaction norms. K E Y W O R D SAltitude, chilling, climate change, latitude, Sepsidae, temperature variation, thermal adaptation 1902 |

Thermal performance under constant temperatures can accurately predict insect development times across naturally variable microclimates

“…Our results align with these expectations, but they also highlight the important role of micro–macroclimate decoupling in such linearization, as well as the gradual effects of decreasing temporal resolution in the form of temperature averaging (Figure 4). For example, Khelifa et al (2019) successfully employed rate summation in five species of Scatophaga flies under fluctuating temperatures in well‐controlled laboratory conditions. However, they overestimated development time when applying the method in the field using weather station data—particularly when temperatures often fell below the estimated minimum for development.…”

“…For example, behavioural thermoregulation could superficially cause deviations from the null hypothesis (given Jensen's inequality) by creating a discrepancy between measured temperatures and actual body temperatures (Ma et al, 2021; Woods et al, 2015). Indeed, with robust methodology (see Box 1), inherent effects of thermal fluctuations (Milosavljević et al, 2020) stand out as the exception rather than the rule (Khelifa et al, 2019; Ludwig & Cable, 1933; Martínez‐García et al, 2018). This is corroborated by the similarities between simulated and observed differences in development times between fluctuating and constant temperatures across a large number of studies, species and thermal regimes (Figure 5).…”

“…Mortality is not used to infer performance in other traits (e.g. 100% end mortality under constant temperatures is not assumed to imply a development rate of 0; Khelifa et al, 2019;Liu et al, 1995). 4.…”

Thermal Performance Curves of Multiple Isolates of Batrachochytrium dendrobatidis, a Lethal Pathogen of Amphibians

“…TPCs include measures of thermal optimum [i.e., temperature optimum (T opt )], critical thermal minimum (CT min ), critical thermal maximum (CT max ), and thermal tolerance range (also known as thermal breadth; T br ) (Figure 1). Temperature sensitive parameters that determine an organism's TPC frequently vary with geographic clines (e.g., latitude), reflecting local adaptation (34,35). TPC models (e.g., vertical or horizontal shifts) offer a framework to consider the adaptive potential for temperature-sensitive organisms (36,37).…”

Do endotherms have thermal performance curves?

“…2). As a result, several commentators have pointed out a host of conceptual and practical difficulties due to the broad array of assumptions that must be made about the relationships among performance, T b and environment (Stevenson et al, 1985;Sinclair et al, 2016;Khelifa et al, 2019). For example, even small ectotherms are able to behaviourally thermoregulate (Fig.…”