In the intricate tapestry of evolutionary biology, the origin and development of paired fins in jawed vertebrates have long posed a captivating puzzle. A fresh and compelling study from the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, spearheaded by associate scientist Andrew Gillis, has shed new light on this enigma. Drawing on nearly two decades of meticulous research initiated during his doctoral studies with Neil Shubin at the University of Chicago, Gillis and colleagues challenge conventional notions about serial homology and offer a transformative developmental perspective on the evolutionary links between gill arches and paired fins.
Published in the prestigious Proceedings of the National Academy of Sciences, this groundbreaking work advances a novel conceptual framework centered on “shared competence” — the ability of two distinct embryonic cell lineages to give rise to analogous adult structures. The research zeroes in on the little skate (Leucoraja erinacea), a cartilaginous fish whose paired fins and gill arches serve as model serial homologs, structures repeated along the body that share evolutionary and developmental origins.
Traditionally, serial homology—where one body part repeats or transforms into another—has been viewed through the lens of gradual evolutionary transformations. For instance, insect wings are believed to have evolved through modifications of leg segments, an idea supported by recent genetic and developmental insights. Similarly, 19th-century biologist Karl Gegenbauer proposed that the paired appendages of jawed vertebrates might have originated via transformation of gill arches, the bony supports of fish gills. However, defining serial homology precisely has remained elusive due to the complex interplay between anatomy, genetics, and development.
One perplexing aspect has been the embryonic origin of these structures. Gill arches are generally known to derive from the neural crest, a multipotent embryonic cell population famous for its versatility. In contrast, paired fins and limbs arise from the lateral plate mesoderm, a separate germ layer. This dichotomy raises the question: How can structures emanating from such distinct origins exhibit serial homology?
A pivotal insight emerged from a 2020 study led by Gillis’s former postdoc Victoria Sleight, which utilized advanced fate-mapping techniques to examine the early skate embryo’s cellular composition. They discovered that rather than a strict boundary between neural crest and lateral plate mesoderm, there exists significant cellular intermingling at the head-trunk boundary. This blending creates a mesenchymal field composed of cells from both germ layers, collectively competent to generate either gill arches or paired fins.
The latest experimental investigations, conducted by University of Chicago PhD candidate Michael Wen under co-advisors Gillis and Victoria Prince, rigorously tested the functional equivalence of these embryonic populations. Wen performed precise cell transplantation experiments, moving neural crest-derived cells intended for gill arch formation into developing fin fields, and reciprocally transplanting mesodermal cells into gill arch territories. Remarkably, transplanted cells integrated seamlessly and contributed normally to the new skeletal environment.
This interchangeability means that despite their differing embryonic origins, the cells share intrinsic developmental “competence.” They respond similarly to local signaling cues, allowing them to build serially homologous structures with comparable cartilage architectures. Essentially, the environmental context guides cell fate more decisively than their embryonic heritage.
This shared competence model reframes the understanding of serial homology by shifting emphasis from historical morphological transformations to contemporary cellular developmental potentials. It suggests that homologous repeating structures may arise not solely through evolutionary modification of one structure into another, but through the evolutionary conservation of cellular responsiveness within overlapping developmental fields.
Complex genomic regulatory landscapes likely underlie this phenomenon. Wen hypothesizes that the genomic architecture governing neural crest and lateral plate mesoderm cells shares key elements enabling their reciprocal plasticity. Future research is poised to dissect these gene regulatory networks to elucidate the molecular basis of shared competence.
While these findings deepen the developmental narrative, the evolutionary origin question of paired fins remains incompletely resolved, mainly because of gaps in the fossil record. Unlike the well-documented fin-to-limb transition, evidence for how paired fins themselves emerged is sparse, limiting direct paleontological corroboration of these developmental insights.
Nevertheless, Gillis and collaborators emphasize the broader applicability of their findings. If similar principles hold true across various vertebrate structures—such as vertebrae or digits in mammals—it could revolutionize how biologists conceptualize serial homology and morphological evolution.
The study also exemplifies the power of integrative approaches combining embryology, genetics, and experimental manipulations to address enduring evolutionary questions. It highlights the little skate as a valuable non-traditional model organism for uncovering cellular and molecular dynamics inaccessible in classical systems.
Outside of this focal inquiry, Gillis’s lab has begun expanding into other spheres of developmental biology, though this line of research yielded numerous foundational discoveries and conceptual frameworks that will undoubtedly influence future studies across evolutionary developmental biology.
Supporting this research were prominent funding sources including the National Science Foundation and the Owens Family Foundation, along with institutional fellowships from the University of Chicago and the Marine Biological Laboratory. These grants underscore the vital role of sustained investment in basic science discoveries.
To visualize these concepts, detailed skeletal preparations of little skate hatchlings exhibit the intricate arrangements of cartilage and mineralization within paired fins and gill arches, affirming the anatomical relevance of the shared competence principle. Fluorescent imaging of early embryos reveals the overlapping germ layer contributions, providing a vivid developmental context for these findings.
In sum, this innovative research upends traditional views by revealing an unexpected developmental equivalence between neural crest and mesodermal cell populations that undergird serially homologous structures. This paradigm opens new avenues to unravel how complex morphological patterns are repeated and evolved throughout vertebrate history, framing serial homology in terms of developmental plasticity and genomic regulation rather than mere evolutionary transformations.
Subject of Research: Animals
Article Title: Shared competence forms the basis of gill arch and paired fin serial homology
News Publication Date: 16-Mar-2026
Web References:
https://www.pnas.org/doi/10.1073/pnas.2529365123
References:
M.T.C. Wen, V.E. Prince, & J.A. Gillis (2026). Shared competence forms the basis of gill arch and paired fin serial homology. Proceedings of the National Academy of Sciences of the United States of America. DOI: 10.1073/pnas.2529365123
Image Credits:
Andrew Gillis, Marine Biological Laboratory (MBL); Michael Wen, University of Chicago/MBL
Keywords:
Developmental biology, serial homology, paired fins, gill arches, neural crest, lateral plate mesoderm, little skate, evolutionary biology, embryonic cells, morphogenesis, gene regulation
