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Images of Brachyistius aletes, courtesy of the California Academy of Sciences


I am happy to share that a study in which we determined how ecological specialization drives convergence in body shape and size among cleaner fishes is now available. Brachyistius aletes image 2

To trace the evolution of body shape, I collected morphological data from ~300 species of fishes. As part of this project, I got the chance to visit several museum collections across the US, including the Smithsonian National Museum of Natural History, the LA County Museum of Natural History, and the California Academy of Sciences.

After these visits, I realized I had missed one species: Brachyistius aletes, a type of surfperch. To my surprise, there were no clear photographs of this species available online - at least my frantic Google Images search yielded nothing.

Fortunately, Dave Catania (Senior Collections Manager of Ichthyology at the CAS) was able to hunt down a set of preserved specimens and snap a few photos for me. Here I’ll post these photos of Brachyistius aletes to make them available to others. Thanks again for sharing these, Dave!

Photos of Brachyistius aletes

First, I’ll share the three photos that Dave sent me. They all have the same (juvenile-sized) specimens but were shot under different lighting conditions.

(I have shrunk these images to reduce page loading times. Please feel free to email me if you’d like any of these in their original 4000 x 3000px glory.)

Natural history - we barely know anything

Relatively little is known about this species. It seems to be found only near Baja California, has little life history info available, and doesn’t even have a reliable common name [source].

It also looks like there has been some contention about its place among surfperches. It was originally assigned to the genus Micrometrus in the 50s, later reclassfied as a member of Brachyistius, but flagged as a species with uncertain taxonomy by Eschmeyer [source 1, source 2].

Genetic and morphological similarity between Brachyistius aletes and Brachyistius frenatus

A 2015 study (by my friends Gary Longo and Giacomo Bernardi!) determined that this species is indeed a very close sister taxon to Brachyistius frenatus [source]. With only ~0.025% genomic divergence between the two species (compared to an average ~0.32% difference found in other surfperch sister species) Brachyistius aletes and Brachysitius frenatus are so closely related, they may not be separate species according to some criteria.

The idea that we’re seeing incipient speciation between these two is reflected in what little morphological divergence we see in body shape. Below is a Procrustes superimposition of body shape landmarks between juvenile individuals of the two species.

By aligning and superimposing landmarks from the two species this way, we can see the (mostly minor!) differences in body shape.

Grey dots show the body shape of Brachyistius frenatus whereas the smaller black dots show the shape of Brachyistius aletes. B. frenatus is slightly more elongate, but otherwise the two really don’t look all that different!

With these photos (along with those for the other ~300 species), I was able to use geometric morphometric methods to show that cleaning promotes an elongate body shape, but really only among specialist cleaners [full paper here].

Brachyistius frenatus is an occasional cleaner whereas we know too little about B. aletes to say whether it exhibits this behavior as well. With B. frenatus having a slightly more elongate body, the patterns in body shape we see in these sister taxa match our overall findings across cleaners. But, the differences between these sister taxa really aren’t meaningful and there’s a decent chance Brachyistius aletes may also be a cleaner!

Thanks again to Dave Catania for supplying the three photographs included in this post! With any luck, these will pop up on Google Images and can be of help to anyone else interested in this genus. And special thanks to Gary for providing me the surfperch phylogeny from his 2015 study - it came in handy for my comparative analyses!

🐢

Written on May 24, 2019 by Vikram B. Baliga (vbaliga).