Sexual dimorphism in the Arachnid orders.

Area of Science:

• Evolutionary Biology
• Zoology
• Arachnology

Background:

• Sexual dimorphism (SD), differences between sexes in size and shape, is widespread in animals.
• Arachnids display extreme forms of SD, yet research often focuses on specific groups, neglecting broader patterns.
• Understanding SD in arachnids offers insights into sexual and natural selection pressures.

Purpose of the Study:

• To review current research on SD and sexual size dimorphism (SSD) trends in arachnid orders.
• To explore potential evolutionary drivers of SD across the Arachnida.
• To identify knowledge gaps and suggest future research directions for arachnid SD.

Main Methods:

• Comprehensive literature review of existing studies on sexual dimorphism in arachnids.
• Analysis of trends in body size, leg length, and pedipalp morphology across different arachnid orders.
• Synthesis of findings to identify common patterns and evolutionary hypotheses.

Main Results:

• Commonly observed trends include female-biased SSD in total body size.
• Male-biased SSD in relative leg length and SD in pedipalp length/shape are also prevalent.
• Phylogenetic uncertainties complicate the elucidation of evolutionary pathways for these traits.

Conclusions:

• Sexual dimorphism in arachnids is characterized by specific patterns in body size, leg proportions, and pedipalp morphology.
• Further research, particularly clarifying arachnid phylogeny, is crucial for understanding the evolution of these sexually dimorphic traits.
• Significant gaps remain in our understanding of SD drivers across the diverse arachnid orders.