Heterotopic expression of respiratory-associated genes suggests a developmental basis for pleopodal gill evolution in isopod crustaceans

Heterotopic expression of trachealess (trh) and ventral veins lacking (vvl) in developing pleopodal regions is linked to pleopodal gill evolution in Gnorimosphaeroma cf. hoestlandti and Porcellio scaber.

• Why it matters: Organ relocation during evolution can reshape morphology, but the developmental basis for isopod pleopodal gill placement versus thoracic gills in other crustaceans is unclear.
• What they did: The authors combined comparative anatomy with multiplex in situ hybridization chain reaction to map embryonic expression of trh and vvl, and assessed posterior patterning using abdominal-A and Abdominal-B (AbdB).
• The result: In both species, trh and vvl mark developing pleopodal gill-bearing tissues; trh is more restricted than vvl, with posterior domains overlapping AbdB regions, suggesting developmental contributions and later spatial shifts in pleopod gill evolution.

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