Day Late, Dollar Short: Runts of Asynchronously Hatched Songbird Broods Have Reduced Survival, Body Size, and Persistent Energy Deficits.

Many songbirds begin active incubation after laying their penultimate egg, resulting in synchronous hatching of the clutch except for a last-hatched individual ("runt") that hatches with a size deficit and competitive disadvantage to siblings when begging for food. However, climate change may elevate temperatures and cause environmental incubation as eggs are laid, resulting in asynchronous hatching and larger size hierarchies among siblings. Although previous work demonstrated that asynchronous hatching reduces nestling growth and survival relative to synchrony, the physiological mechanisms underlying these effects are unclear.

Investigating relationships among stress, reproduction, and immunity in three species of watersnake.

Energy is a finite resource required for all physiological processes and must be allocated efficiently among essential activities to ensure fitness and survival. During the active season, adult organisms are expected to prioritize investment in reproduction over other energetically expensive processes, such as responding to immunological challenges. Furthermore, when encountering a stressor, the balance between reproduction and immunity might be disrupted in order to fuel the stress response.