Diversification through gustatory courtship: an X-ray micro-computed tomography study on dwarf spiders

Area of Science:

• Evolutionary Biology
• Zoology
• Sexual Selection

Background:

• Sexual selection is theorized to promote species diversification.
• Dwarf spiders (Erigoninae) exhibit sexual dimorphism with male prosomal modifications linked to nuptial gifts.
• The evolutionary role of these dimorphic traits in speciation requires further investigation.

Purpose of the Study:

• To investigate the evolutionary lability of gustatory traits in dwarf spiders.
• To determine if modified male prosomata are linked to nuptial-gift-producing glands.
• To assess the role of these traits in species divergence and speciation.

Main Methods:

• Reconstruction of glandular tissue and muscular anatomy using X-ray micro-computed tomography in 76 erigonine spiders.
• Phylogenetic analysis incorporating gland and muscle data with existing morphological trait matrices.
• Comparative analysis of gland evolution relative to prosomal shape modifications.

Main Results:

• Modified prosomata are associated with gustatory glands in all but one species.
• Glandular equipment is the ancestral state; prosomal shape modifications evolved convergently multiple times.
• Seven cases of gland loss were identified, with differences in gland position observed between species.

Conclusions:

• Ancestral gustatory glands in sexually monomorphic ancestors facilitated the evolution of diverse dimorphic traits in dwarf spiders.
• The susceptibility of gland position to evolutionary change and multiple convergent modifications suggest divergent evolutionary patterns.
• Sexual selection acting on gustatory-courtship traits likely facilitates speciation in Erigoninae.