Variations in stress resistance and adaptive plastic responses during ontogeny have rarely been addressed, despite the possibility that differences between life stages can affect species' range margins and thermal tolerance. Here, we assessed the thermal sensitivity and hardening capacity of
Drosophila melanogaster
across developmental stages from
larval
to the adult stage. We observed strong differences between life stages in heat resistance, with adults being most heat resistant followed by
puparia
,
pupae
and
larvae
. The impact of heat hardening (1 h at 35°C) on heat resistance changed during ontogeny, with the highest positive effect of hardening observed in
puparia
and
pupae
and the lowest in adults. These results suggest that immobile life stages (
puparia
and
pupae
) have evolved high plasticity in upper thermal limits whereas adults and
larvae
rely more on behavioural responses to heat stress allowing them to escape from extreme high temperatures. While most studies on the plasticity of heat resistance in ectotherms have focused on the adult life stage, our findings emphasize the crucial importance of juvenile life stages of arthropods in understanding the thermal biology and life stage-specific physiological responses to variable and stressful high temperatures. Failure to acknowledge this complication might lead to biased estimates of species' ability to cope with environmental changes, such as climate change.
Survival of heat stress with and without heat hardening in Drosophila melanogaster: interactions with larval density
