AGGRESSION, DENSITY, AND SEXUAL DIMORPHISM IN CHERNETID PSEUDOSCORPIONS (ARACHNIDA: PSEUDOSCORPIONIDA).

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Arachnology

Background:

• Sexual dimorphism, particularly in appendage size, is common in pseudoscorpions (false scorpions).
• The family Chernetidae exhibits variable degrees of dimorphism in pedipalp and chelae size between males and females.

Purpose of the Study:

• To investigate the evolutionary drivers of sexual dimorphism in false scorpions (Chernetidae).
• To determine the relationship between male combat ability, chela size, and mating success in relation to population density.

Main Methods:

• Comparative morphometric and habitat data analysis across Chernetidae species.
• Experimental manipulations with Dinocheirus arizonensis to assess the role of chela size in male combat and mating success.
• Statistical analysis of dimorphism patterns and correlation with behavioral and ecological factors.

Main Results:

• Sexual dimorphism in Chernetidae is highly variable and not strongly constrained by phylogeny.
• Enlarged male pedipalps are associated with pairing sperm-transfer behavior and male-male combat for mates.
• Male combat ability, linked to chela size, increases mating success primarily under high-density conditions.
• High population density favors larger males in spermatophore transfer by enabling them to interrupt and displace smaller competitors.

Conclusions:

• The evolution of enlarged male chelae in pseudoscorpions is driven by sexual selection related to combat and mating strategies.
• Population density is a critical factor mediating the advantage of male combat ability and associated dimorphism.
• A positive correlation exists between population density and enlarged male chela size across chernetid species.