{
  "id": 10435940,
  "title": "Age-specific Jensen contrasts reveal how ontogenetic responses to thermal variability shape lifetime performance in Daphnia magna",
  "url": "https://urgent.news/2026/09/28/age-specific-jensen-contrasts-reveal-how-ontogenetic-responses-to",
  "topic": "science",
  "section": "Science",
  "published": "2026-09-28T00:00:00.000Z",
  "source": {
    "name": "bioRxiv",
    "slug": "biorxiv",
    "url": "https://www.biorxiv.org/content/10.64898/2026.09.25.754440v1?rss=1"
  },
  "original_language": "en",
  "account": "Temperature plays a crucial role in shaping the life histories of organisms, particularly through its influence on energy allocation among growth, reproduction, and maintenance. Traditionally, the impact of temperature has been represented using thermal performance curves (TPCs), which are often viewed as static descriptors that apply uniformly throughout an organism's life. However, it is becoming increasingly evident that the response to thermal variability can change across different life stages, or ontogeny.\n\nIn this study, researchers examined the growth, reproduction, and survival of individual Daphnia magna under four distinct thermal regimes: Constant Low (15°C), Constant Rearing (20°C), Constant High (25°C), and Variable (15°C to 25°C). The Variable thermal regime closely matched the mean temperature of the Constant Rearing condition. To analyze the data, the researchers employed an allometric energy-allocation model, which enabled them to derive age-specific and lifetime performance measures while quantifying their uncertainty through a stratified individual-level bootstrap.\n\nA key metric derived from the study is the Jensen contrast, which represents the difference in performance between the Variable and Constant Rearing conditions. Surprisingly, the age-specific point estimates of the Jensen contrast changed signs across different life stages. Initially, a positive aggregate contrast in full trajectory growth was observed, followed by a negative mid-life contrast. Furthermore, the reproductive point estimates were positive during early and mid-life but turned negative later in life. The researchers found strong bootstrap support for these positive early life and negative mid-life growth contrasts, as well as the positive early life reproductive contrast.\n\nDespite the positive early life reproductive response, this did not translate into a positive lifetime outcome. When accounting for the weighting of survival over an organism's lifetime, the expected reproduction under Variable conditions was actually lower than under Constant Rearing. The strong bootstrap support for the negative lifetime contrast further highlights this discrepancy. As survival rates were lower under Variable conditions, the later stages of life contributed negatively to overall reproduction, outweighing the positive early life contributions.\n\nThe findings of this study emphasize the importance of considering ontogeny and temperature variability when forecasting life-history performance in organisms subjected to variable thermal environments. Relying solely on mean temperature, a single life stage, or an aggregate TPC may lead to inaccurate predictions of lifetime performance. By incorporating both ontogeny and temperature variability, researchers can improve their forecasts of life-history performance in the face of increasing thermal variability in the environment.",
  "summary": "1. Temperature shapes life histories through its effects on energy allocation among growth, reproduction and maintenance. The resulting temperature dependence of performance is commonly characterised using thermal performance curves (TPCs), which are often treated as static descriptions that apply uniformly throughout life. Yet the response to thermal variability may change across ontogeny. 2. We…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}