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

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.

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!

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.

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.

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.

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?

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.

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.

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.

Thank you Ali!!

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!!

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.

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??

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.

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.

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.

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.

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.