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Developmental system drift in the patterning of the arthropod tarsus
Benjamin Klementz1, Sophie Neu1, Ethan Laumer1
1Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI53706, USA.
Proceedings. Biological Sciences
|February 10, 2026
Summary
Harvestman clawless gene knockdown disrupts tarsal development, unlike in insects where it specifies the claw. This suggests a shift in gene function during arthropod leg evolution.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Genetics
Background:
- Proximodistal axis patterning in arthropod legs is primarily studied in insects.
- A conserved gene regulatory network for leg patterning is hypothesized across arthropods.
- Chelicerates show divergent appendage patterning, with limited functional data.
Purpose of the Study:
- To investigate the function of the clawless gene in the harvestman Phalangium opilio.
- To compare clawless gene function between insects and chelicerates.
- To infer the ancestral function of clawless in Chelicerata.
Main Methods:
- RNA interference (RNAi) to knock down clawless expression in Phalangium opilio.
- Analysis of tarsal growth, patterning, and tarsomere formation after knockdown.
- Expression surveys of clawless homologues across diverse chelicerates.
Main Results:
- Clawless knockdown in harvestmen disrupted tarsal growth and proximal boundary patterning.
- No effect on claw formation was observed in knockdown experiments.
- Expression patterns suggest a conserved tarsal-patterning role for clawless in Chelicerata.
Conclusions:
- Harvestman clawless has a distinct function in tarsal patterning compared to insect clawless.
- The ancestral function of clawless in Chelicerata likely involved tarsal patterning.
- Developmental system drift contributes to the diversity of panarthropod appendage patterning.
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