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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

9) By separating vertebral count evolution from vertebral shape evolution, we highlight distinct developmental and evolutionary processes underlying one of the most important axes of fish morphological diversity!

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

8) This suggests that body elongation isn't achieved through simple geometric scaling of vertebrae. Rather, it requires integrated, multivariate changes across the axial skeleton that maintain function while body form evolves.

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

7) Surprisingly, however, body elongation is not explained by elongating individual vertebrae or increasing intervertebral spacing. Instead, vertebral number remains the main predictor of elongation. Therefore, coordinated vertebral shape evolution occurs alongside, or is driven by body elongation.

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

6) But what drives these coordinated shape changes? Body elongation! More elongate species have proportionally larger centra, posteriorly displaced neural & haemal spines and increased rib curvature. These changes occur across both vertebral regions, simultaneously.

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

5) However, we find no evolutionary relationship between precaudal and caudal counts. More simply, precaudal or caudal vertebrae can be gained or lost independently of the other domain. Therefore, the specification of vertebral identity and the subsequent shape development is decoupled.

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

4) We find that vertebral shape evolution is strongly integrated. Precaudal vertebrae, caudal vertebrae, and pleural ribs all covary along shared evolutionary axes, suggesting coordinated evolution across the axial skeleton rather than independent modules.

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

3) The cichlid vertebral column can broadly be separated into two regions: the precaudal, comprised of vertebrae associated, but not directly connected with, pleural ribs; and caudal domains (tail vertebrae that have a haemal arch).

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

2) Using geometric morphometrics on 3D vertebral shape and rib morphology from uCT-scans from my previous paper (www.nature.com/articles/s41...), we asked how axial skeleton evolution relates to whole-body elongation in the remarkable adaptive radiation of Lake Malawi cichlid fishes.

nature.com

A whole-body micro-CT scan library that captures the skeletal diversity of Lake Malawi cichlid fishes - Scientific Data

Scientific Data - A whole-body micro-CT scan library that captures the skeletal diversity of Lake Malawi cichlid fishes

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Callum Bucklow @callumbucklow.bsky.social · 18/06/2026

1) Vertebral columns are a classic example of a structure that's both repeated and regionalised. But when body shape evolves, do different vertebral regions change independently, or do they evolve together?

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Reposted by Callum Bucklow

Berta Verd @bertaverd.bsky.social · 21/04/2026

New Pre-Print Alert! Evolving initial conditions: an alternative developmental route to morphological diversity with Shannon Taylor and @jamesehammond.bsky.social www.biorxiv.org/content/10.6...

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Reposted by Callum Bucklow

James Hammond @jamesehammond.bsky.social · 08/09/2025

Out now in Seminars in Cell & Dev Biol! doi.org/10.1016/j.se... With thanks to co-authors @callumbucklow.bsky.social and @bertaverd.bsky.social

doi.org

Redirecting

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

That's great, thank you. Also just read the article you posted, fantastic summary and breakdown of the evidence.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

This is an absolutely amazing picture of a mouthbrooder -- I've only been able to get pics of eggs. Would you mind if I used this image for presentations and for teaching? Full credit given, of course.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Our findings reveal the dynamic interplay between somitogenesis and homeotic transformations driving vertebral diversity, reinforcing cichlids as an incredible model for unraveling axial evolution in teleosts. Not to mention exciting work bridging developmental biology, evo bio, and macroevolution!

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

We previously showed vertebral addition drives body elongation in African cichlids. But intraspecific variation in vertebral count doesn’t predict body shape, having more vertebrae doesn’t mean you’re more elongate. So, intraspecific variation is decoupled from macroevolutionary body shape patterns.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Therefore, evolutionary modification of somitic 'fidelity' (at least in African cichlids) has not been important in driving evolution of total counts and the intraspecific variation has not changed as African cichlids diversified... in other words, somite counts within species are highly canalised.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Despite high evolvability, vertebral counts in African cichlids show low intraspecific variation. Correcting for phylogeny: (1) variation doesn't scale with count (no sign of selection), and (2) doesn't differ between lakes & rivers, even if each system is subject to its own rate of count evolution.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Intraspecific variation in vertebral count is common across vertebrates, including in teleosts (and cichlids). The presence of intraspecific variation suggests developmental lability in somitogenesis, how has this variation evolved? What might it tell us about the evolution of somitogenesis?

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Using vertebral count data from >4,500 African cichlids (~500 species), we show that axial regionalisation can shift via changes to AP patterning. However, most variation reflects differences in somite number, with homeotic transformations emerging mainly as a consequence of these somitic changes.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

Interspecific differences in vertebral count and axial regionalisation reflect evolutionary shifts in somite number and homeotic identity post-divergence. By mapping these traits across clades, we can infer how somitogenesis and AP patterning have evolved alongside lineage diversification.

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Callum Bucklow @callumbucklow.bsky.social · 29/05/2025

The total number of vertebrae and their morphological identity along the anterior–posterior (AP) axis are established during development, through the processes of somitogenesis and subsequent regionalisation of the somites which is governed by Hox gene patterning.

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Reposted by Callum Bucklow

George Turner @dlimnothrissa.bsky.social · 26/05/2025

Lake Malawi cichlids: even common, big, spectacular species are often a taxonomic mess, like these Taeniolethrinops species. Much work needed!

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Reposted by Callum Bucklow

Berta Verd @bertaverd.bsky.social · 19/05/2025

Experimental embryology postdoc available in my lab at the @biology.ox.ac.uk @ox.ac.uk working on the evolution of vertebral counts. Reach out if you’re passionate about EvoDevo, enjoy lab work and microscopy and are into or could get into cichlid fishes. Deadline on the 16th June. Please share!

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Reposted by Callum Bucklow

Virtual Gastrulation Zoom Talks @vgzt2021.bsky.social · 16/05/2025

Please join next week‘s Western 🌙 VGZT: 🗓️ Thursday, May 22 ⏰ 9:30 PDT / 12:30 EDT / 16:30 UTC / 17:30 BST / 18:30 CET @aliseleit.bsky.social 👉Developmental heterochrony & evolution of segmentation in eels @laura-rustarazo.bsky.social 👉Rigidity transitions & epithelial organization in 🐟 embryos

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Our work highlights the need for comparative approaches to understand cichlid evolution and demonstrates that African cichlids can be very powerful models for the study of vertebral column evolution. More cichlid-related research to come!!

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Finally, we show that the common ancestor of African cichlids had a distinctly riverine axial morphology—deep-bodied with relatively few vertebrae and equal proportions of precaudal and caudal vertebrae. Axial diversity in lakes radiated outward from this ancestral form.

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Interestingly, axial morphospace correlates with radiation age—Tanganyikan cichlids (oldest) show the widest occupation. But rates of vertebral evolution vary between lake radiations and accumulated variation is not just a function of divergence time! Lake-specific dynamics??

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

However, despite the focus on the lacustrine radiations, riverine taxa occupy a much wider axial morphospace than the lacustrine species. Which is partly being driven by a stochastic rate of total vertebral count evolution twice that of the highest lacustrine rate.

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Elongation of the body is important for ecological adaptation. Lacustrine cichlids (those living in lakes) have repeatedly (and independently) evolved elongate, fusiform bodies supported by higher total vertebral counts, linked to demersal, pelagic, and piscivorous lifestyles.

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Consistent with other teleosts, cichlid body elongation often involves adding vertebrae—but it's not the only route. Cranial and post-cranial elongation have co-evolved, revealing multiple axes of morphological change.

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

Despite its critical role in locomotion, the evolution of the vertebral column in cichlids has rarely been studied. We set out to change that—with the first macroevolutionary analysis of axial morphology across 4861 individuals from 583 species.

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Callum Bucklow @callumbucklow.bsky.social · 16/05/2025

African cichlids are a powerful system in evolutionary biology, with over 1800 species and iconic radiations in Lakes Tanganyika, Malawi, and Victoria. But one feature has been overlooked: their axial skeletons.

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