Ectotherm Size- and Age-At-Maturity in a Warmer, Variable and Resource-Poor World

Area of Science:

• Ecology
• Evolutionary Biology
• Aquatic Biology

Background:

• Ectotherms typically mature at smaller sizes and earlier ages with increasing temperatures, a phenomenon known as the Temperature-Size Rule (TSR).
• Natural environments present complex factors like thermal variability and fluctuating food resources that can influence ectotherm development.
• The interplay between temperature, food availability, and food quality on TSR expression remains incompletely understood.

Purpose of the Study:

• To investigate the combined effects of temperature, food concentration, and food quality on size and age at maturity in ectotherms.
• To determine how ecological factors modify the predictions of the Temperature-Size Rule.
• To assess the thermal limits for TSR expression under varying resource conditions.

Main Methods:

• Utilized a bioenergetic model to simulate ectotherm growth and development.
• Conducted factorial growth experiments using Daphnia magna as a model organism.
• Manipulated temperature, food concentration, and food quality (PUFA and sterol content) in experimental settings.

Main Results:

• Poor food quality reduced the upper thermal limit for TSR expression.
• Low food quantity constrained both the upper and lower thermal bounds for TSR.
• Increased thermal variability shifted the optimal temperature range for TSR towards cooler conditions.
• Combined stressors can lead to smaller yet older individuals at maturity.

Conclusions:

• The Temperature-Size Rule may not be universally applicable under ecologically realistic conditions.
• Resource limitation and temperature variability are critical factors modulating TSR.
• Warming scenarios with concurrent resource scarcity and increased thermal variability may result in smaller and older maturing ectotherms, challenging established TSR predictions.