Age‐specific sensitivity of sperm length and testes size to developmental temperature in the bruchid beetle

In an era of global warming, the negative effects temperature stress on fertility could intensify predicted losses biodiversity. Male is particularly sensitive to stress, yet we have incomplete understanding when, during reproductive ontogeny, spermatogenesis most affected. Here, used a temperature-switch protocol identify when development affects expression sperm length and testes size in bruchid beetle Callosobruchus maculatus. Egg-to-adult took place at 17°C, 27°C or 33°C for either full duration pre-imago it was switched different stages development. Full 17°C resulted significantly shorter than 27°C. However, developing larvae were higher lower temperatures, observed switch-specific phenotypic size. Our key finding that high-temperature early ontogeny low-temperature latter ontogeny. Such age-specific developmental sensitivity suggests infertility resulting from transient heat (i.e. heatwaves) be mitigated by age-related heterogeneity within populations. Those individuals able avoid severe fertility, through serendipitously being less-sensitive development, potentially compensate loss experienced those more