Do exaggerated chelicerae function as weapons or genitalia in a long-jawed spider? Functional allometric analysis...

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Morphology

Background:

• Extreme traits in animals often arise from natural or sexual selection.
• The exaggerated chelicerae of long-jawed spiders (Tetragnatha) have been hypothesized to function as holdfasts during mating.
• This hypothesis has remained largely untested in the Tetragnatha genus.

Purpose of the Study:

• To investigate the function and development of extreme chelicerae in the long-jawed spider Tetragnatha elongata.
• To test the hypothesis that Tetragnatha chelicerae function as holdfasts during mating.
• To explore the roles of natural and sexual selection in shaping cheliceral morphology.

Main Methods:

• Functional allometry was used to analyze cheliceral development and scaling in Tetragnatha elongata.
• Comparative analysis of male and female cheliceral morphology.
• Fieldwork to assess operational sex ratio, male-male competition, and sexual cannibalism.

Main Results:

• Chelicerae were longer in adult males than females, with elongation occurring only in the adult stage.
• Male chelicerae exhibited positive allometry, suggesting scaling beyond a simple holdfast function.
• Female chelicerae showed negative allometry, correlating with increased foraging efficiency.

Conclusions:

• The study supports the holdfast hypothesis but proposes a dual function for male chelicerae, potentially for mechanical meshing with larger females.
• Female cheliceral shortening is likely driven by natural selection for enhanced foraging.
• The findings highlight the complex interplay of sexual and natural selection in the evolution of exaggerated traits.