Signal polymorphism under a constant environment: the odd cross in a web decorating spider

Area of Science:

• Ethology
• Animal Behavior
• Evolutionary Biology

Background:

• Animal signal quality often varies, potentially due to context or to prevent exploitation.
• Orb weaver spiders (Argiope) create polymorphic visual signals using varied silk decorations in their webs.

Purpose of the Study:

• To investigate the pattern variation in Argiope mascordi web decorations under controlled laboratory conditions.
• To determine if intraspecific variation in web decorating behavior is intrinsic or an environmental response.

Main Methods:

• Observing Argiope mascordi spiders under invariant laboratory conditions.
• Recording and analyzing the frequency and switching patterns of circular and cruciate silk decorations.

Main Results:

• Argiope mascordi spiders are bimodal decorators, producing both circular and cruciate patterns.
• Circular decorations were most frequent, but spiders frequently switched patterns.
• Pattern variation remained consistent over time, indicating an intrinsic basis.

Conclusions:

• The intrinsic variability in Argiope mascordi web decorations challenges the notion of a single, adaptive signal function.
• This variation may be conserved to maintain signal function or may indicate that silk decorations are not adaptive signals.