# Carryover Effects on Reproduction Can Buffer Against Mortality‐Driven Population Declines at Elevated Developmental Temperatures

## TL;DR

Higher temperatures during development can boost insect reproduction, potentially preventing population declines despite lower survival rates.

## Contribution

The study reveals novel thermal carryover effects that influence mating and population dynamics in warming climates.

## Key findings

- Elevated developmental temperatures increase adult fertility, offsetting reduced juvenile survival.
- Mating between individuals from different developmental temperatures reduces mating success due to morphological mismatches.
- Thermal carryover effects can generate assortative mating and influence reproductive morphology.

## Abstract

Carryover effects broadly influence adult performance and population persistence. Although variation in developmental environments can have contrasting effects on survival and reproduction, current predictive models of vulnerability to environmental change typically ignore simultaneous changes in both fitness components. We tested how developmental temperatures shape survival and multiple aspects of reproduction in a plant‐living insect (Enchenopa binotata treehoppers) and used population dynamic models to examine the cumulative impact of these complex effects on population growth. We show that elevated developmental temperatures increase adult fertility, offsetting reduced juvenile survival and potentially forestalling population declines following global warming. Moreover, pairing mates from different developmental temperatures exacerbated morphological mismatches between sexes, reducing mating success and sperm transfer. Our findings thereby provide novel evidence that thermal carryover effects can generate assortative mating and selection on adult reproductive morphology, in addition to shaping the relative importance of survival and reproduction for persistence in warming climates.

We show that hotter juvenile temperatures can increase adult fertility in an emerging model insect system. These reproductive benefits may be crucial for insect populations to avoid extinction during global warming, which often reduces survival rates. Population dynamics estimated from lethal stress alone, or without considering carryover effects from developmental plasticity across animals' different life stages, may be unreliable for predicting extinction risk in response to climate change.