Silk elasticity as a potential constraint on spider body size

Area of Science:

• * Zoology
• * Biomechanics
• * Materials Science

Background:

• * Spiders utilize diverse silk types produced by specialized glands for various functions.
• * Major ampullate and capture spiral silks are well-researched, unlike minor ampullate silk used for bridging.
• * Spider silk's strength and extensibility are crucial for their ecological radiation and locomotion.

Purpose of the Study:

• * To investigate the biomechanical constraints of minor ampullate silk in spider locomotion.
• * To model the relationship between spider body mass, silk filament radius, and bridging efficiency.
• * To understand how silk properties influence spider size limitations and sexual dimorphism.

Main Methods:

• * Development of a biomechanical model incorporating existing data on spider silk and body mass.
• * Analysis of the relationship between required silk filament radius for bridging and spider body mass.
• * Examination of the implications of silk-based locomotion on spider morphology and size.

Main Results:

• * The minimum silk filament radius for efficient bridging scales with the square root of spider body mass.
• * Actual minor ampullate silk filament radii produced by spiders are smaller than model predictions for larger masses.
• * A negative correlation exists between body mass and displacement ability in spiders reliant on silk threads.

Conclusions:

• * Spider silk properties, particularly minor ampullate silk, impose size limitations on spiders.
• * The need for silk-based displacement restricts spider body size, especially when resource tracking is required.
• * Silk elasticity may drive sexual size dimorphism, limiting male spider growth due to the demands of female searching.