Drivers of resource allocation for breeding under variable environments in a bet hedger

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Ornithology

Background:

• Life history theory predicts survival-reproduction trade-offs, with higher adult survival in long-lived species leading to variable breeding investment.
• Understanding how organisms adapt breeding strategies, like clutch composition, in fluctuating environments is crucial for evolutionary success.

Purpose of the Study:

• To investigate how Audouin's gulls (Larus audouinii) allocate energy through clutch and egg size adjustments in response to environmental variability.
• To analyze the influence of food availability and breeder age on clutch size, egg volume, and intra-clutch egg size variation.

Main Methods:

• Analysis of 27-year data from 2847 clutches of known-age Audouin's gulls.
• Statistical examination of clutch size, total egg volume, and egg size asymmetries in relation to food availability and breeder age.

Main Results:

• Both food availability and breeder age significantly impacted clutch size and total egg volume.
• An interaction effect was observed: younger breeders' two-egg clutches showed less size variation with food, and clutch size patterns varied with age under harsh conditions.
• Females increased investment with more food by laying larger first eggs, while conserving resources for subsequent eggs; older females showed increased egg size asymmetry with higher food availability.

Conclusions:

• Audouin's gulls employ a flexible bet-hedging strategy, adjusting egg allocation based on food and age to optimize fitness in variable environments.
• Food availability influences overall energy allocation, while age affects the quantity of resources invested but not the pattern of allocation within the clutch.
• Egg size profiles suggest a potential shift from three-egg to two-egg clutches with a progressive reduction in the third egg's size.