Preprint Hypothesis Version 2 Preserved in Portico This version is not peer-reviewed

The Daphnia Carapace and the Origin of Novel Structures

Version 1 : Received: 6 February 2021 / Approved: 8 February 2021 / Online: 8 February 2021 (16:36:20 CET)
Version 2 : Received: 12 February 2021 / Approved: 17 February 2021 / Online: 17 February 2021 (11:03:22 CET)
Version 3 : Received: 4 March 2021 / Approved: 5 March 2021 / Online: 5 March 2021 (11:32:56 CET)

How to cite: Bruce, H. The Daphnia Carapace and the Origin of Novel Structures. Preprints 2021, 2021020221. Bruce, H. The Daphnia Carapace and the Origin of Novel Structures. Preprints 2021, 2021020221.


Understanding how novel structures arise is a central question in evolution. The carapace of the waterflea Daphnia is a bivalved “cape” of exoskeleton that surrounds the animal, and has been proposed to be one of many novel structures that arose through repeated co-option of genes that also pattern insect wings. To determine whether the Daphnia carapace is a novel structure, the expression of pannier, the Iroquois gene aurucan, and vestigial are compared between Daphnia, Parhyale, and Tribolium. The results suggest that the Daphnia carapace did not arise by cooption, but instead represents an elongated ancestral exite (lateral lobe or plate) that emerges from a proximal leg segment that was incorporated into the Daphnia body wall. The Daphnia carapace therefore appears to be homologous to the Parhyale tergal plate and the insect wing. In addition, the vg-positive region that gives rise to the Daphnia carapace also appears to be present in Parhyale and Tribolium, which do not form a carapace. Thus, rather than a novel structure resulting from gene co-option, the carapace appears to have arisen from an ancient, conserved developmental field that persists in a cryptic state in other arthropod lineages, but in Daphnia became elaborated into the carapace. Cryptic persistence of serially homologous developmental fields may thus be a general solution for the origin of many novel structures.


novelty; arthropod; appendages; Parhyale; Tribolium; Daphnia; carapace


Biology and Life Sciences, Biochemistry and Molecular Biology

Comments (1)

Comment 1
Received: 17 February 2021
Commenter: Heather Bruce
Commenter's Conflict of Interests: Author
Comment: corrected a label on Fig. 2 (mouth -> rostrum), minor wording changes, added more references
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