'Reproductive energetic window' determines reproduction under climate change: Concept, latitude, and physiological mechanism

Public summary

* Reproduction is crucial for population sustenance but is increasingly threatened by climate change.

* We proposed and validated a concept of “reproductive energetic window,” presenting net energy for reproduction.

* Empirical data and a mechanistic model predicted that low-latitude females would reproduce less under climate change.

* Reduced reproduction is related to a shrunken reproductive energetic window by limited metabolic regulation.

* Reproductive energetic window is robust and effective for assessing vulnerability under climate perturbation.

Abstract

Unveiling the pattern, processes, and underlying mechanisms by which climate change threatens faunal biodiversity is crucial for biodiversity conservation. Reproduction is robust in predicting individual fitness and population dynamics under climate change. However, it has never been rigorously investigated in natural conditions across latitudes. To address this knowledge gap, we proposed a novel concept of “reproductive energetic window” (REW) to illustrate the net energy available for reproductive output. To validate this concept, we conducted temperature-manipulated experiments in semi-natural conditions using three Takydromus species across latitudes and developed a mechanistic model that translated empirical results into REW. By considering physiological plasticity under warming climates, we further predicted changes in reproductive output within the current distribution range and changes in suitability of habitat by reproductive output. We found that simulated warming climates enhanced the reproductive output of high- and medium-latitude lizards but not of low-latitude congeners. Correspondingly, high- and medium-latitude lizards significantly adjusted their REW by modifying physiological traits, including metabolic rates and locomotion. In contrast, low-latitude lizards showed limited metabolic plasticity, leading to a decreased REW under warming climates. Mechanistic models predicted that reproductive output would increase toward high latitudes under climate change. Integrating the changes in reproductive output and REW across latitudes, we predict that low-latitude species might lose more suitable habitats in the future. This study provides a novel theoretical and practical concept for understanding the pattern, processes, and mechanisms through which climate change threatens faunal biodiversity by linking physiological traits to reproduction and vulnerability.