Final answer:
True, fruit flies with strong heat shock responses or resistance to environmental stresses such as cold temperatures demonstrate lower fecundity as a trade-off for survival. Energy normally used for reproduction is instead diverted to other survival functions, exemplifying a classic energy budget trade-off.
Step-by-step explanation:
The statement that fruit flies with robust heat shock responses tend to have lower fecundities is true. This can be explained by the trade-off between survival and reproduction in the face of environmental stresses. In the context of fruit flies that are resistant to cold temperatures, we see decreased fecundity at early ages. This likely occurs because energy that could be used for reproduction is instead allocated to ensure survival under cold stress conditions.
A counterbalance of resources is crucial for these flies; in an environment where cold resistance is essential, the energy budget of an organism often dictates a trade-off where reproductive efforts are sacrificed for better survival traits. Thus, natural selection may favor flies that prioritize energy storage and survival in the cold over early reproduction, which manifests as a lower number of eggs laid, or lower fecundity.
This concept is supported by studies indicating that genetic selection for specific traits like resistance to DDT can result in a loss of fecundity, and that fruit flies' genetic expression can vary under different conditions, optimizing their survival strategies.