Mass predicts web asymmetry in Nephila spiders

Area of Science:

• Zoology
• Biomechanics
• Ecology

Background:

• Vertical orb web architecture is influenced by spider size, gravity, and available space, alongside phylogenetic and developmental factors.
• Previous studies on orb web asymmetry primarily focused on adult spiders or used size parameters without considering mass, which is crucial for gravity's effect.
• Juvenile spiders may prioritize optimal web construction for foraging more than adults.

Purpose of the Study:

• To investigate the relationship between spider mass, size, and vertical web asymmetry in the giant orb web spider, Nephila pilipes.
• To test the hypothesis that gravity significantly affects vertical web asymmetry, measured by hub displacement.

Main Methods:

• Studied 100 vertical orb webs of Nephila pilipes across various size classes and developmental stages.
• Measured vertical web asymmetry using hub displacement and quantified web shape with the ladder index.
• Correlated asymmetry with spider mass, carapace length, leg lengths, and developmental stage.

Main Results:

• Spider mass was a better predictor of vertical web asymmetry than other size measurements.
• Heavier and larger juvenile spiders showed significantly more displaced hubs.
• Unlike other nephilid species, growing Nephila orb webs did not exhibit vertical elongation.

Conclusions:

• The ontogenetic pattern of vertical web asymmetry in Nephila is likely driven by optimal foraging strategies influenced by gravity.
• High web-building costs in the lower orb may act as a counteracting selective force.
• Alternative explanations like the size limitation hypothesis and biogenetic law lack strong support in recent literature.