The cichlid Labeotropheus: fish eater? Or algae grazer?

Conith and Albertson 2021
illustrated a series of three images (Fig. 1, here animated) to show a schematic “cichlid” that looks that looks like Labeotropheus (Fig. 2), a genus also mentioned in their text. The caption reads, “C – Schematic illustrating the relative positions of the oral (red) and pharyngeal (blue) jaws within the skulls of cichlid fishes. D – Schematic illustrating the relative roles of each jaw complex in prey capture and prey processing.”

So, we’re left guessing which one of 500 to 1000 species of cichlid from three African lakes we’re looking at in the authors’ diagram. Labeotropheus (Fig. 2) seems reasonably close if not right on the money.

Figure 1. Labeotropheus animation from three images in Conith and Albertson 2021, eating a fish. According to Wikipedia Labeotropheus is an algae grazer.

Wikipedia reports on Labeotropheus,
“These cichlids are popular ornamental fish and are ideally suited to the cichlid aquarium. Like many Malawi cichlids, these species are algal grazers.”

So… which is correct? Fish-eater? Or algae grazer? Or were the authors purposefully being nebulous when writing their caption?

Figure 2. Labeotropheus x-ray and graphic from Conith and Albertson 2021, colorized here. Circumorbital ring added. Note the position of the mandible in the x-ray. Compare to figure 1.

Evidently diet is not germane.
Conith and Albertson wrote: “Ray-finned fishes have broken functional constraints by developing two jaws (oral-pharyngeal), decoupling prey capture (oral jaw) from processing (pharyngeal jaw). It is hypothesized that the oral and pharyngeal jaws represent independent evolutionary modules and this facilitated diversification in feeding architectures. Here we test this hypothesis in African cichlids. Contrary to our expectation, we find integration between jaws at multiple evolutionary levels.”

It would have been ideal to show the fish eating type of cichlid eating the fish, rather than the algae grazer eating the fish, but their point was made. Some cichlids do eat little fish. And when one body part changes, so do others (contra the modular hypothesis).

Conith and Albertson wrote,
“Cichlids that hunt elusive prey typically pair slender, mobile oral jaws with gracile pharyngeal jaws, while cichlids that feed on algae or other tough foods typically pair robust, compact oral jaws with strong pharyngeal jaws.”

Gracile or robust? (Fig. 1) You be the judge. There’s no doubt a fish eating a fish is more interesting than an algae grazer. Remember, professors sometimes play by different rules. In academia you gotta get published! Or perish. Or so the saying goes…

Or headline grabber? Co-author Conith was quoted in, “Remember the movie ‘Alien,’ when the alien is about to eat Sigourney Weaver’s character? It opens its mouth and out comes a second set of jaws. Fast forward twenty years, and here I am, studying animals that have jaws in their throats.”

Quoting Conith,It opens its mouth and out comes a second set of jaws.” Funny. Their own diagram (Fig. 1) shows the second set of ‘jaws’ remaining way back in the throat. My guess is reporters for might not have published this report if the subject was a 30cm algae grazer, “best kept in aquariums with volumes greater than 120L or 31.5 gallons.”

Albertson concludes, “This tells us that we need to rethink the fundamentals of evolutionary mechanisms.”

Do we? Or should we just be more specific when writing captions? Or less hyperbolic when speaking with reporters. Science is science, not show business. Stick with the fundamentals.

The first cichlid, Labeotropheus, entered
the large reptile tree (LRT, 1937 taxa) today nesting alongside Paleocene Massamorichthys and extant Monocentris. It is derived from an ancient sister to extant Polydactylus. Labeotropheus fuelleborni (Ahi 1926; 30cm) is the blue mbuna, endemic to Lake Malawi in eastern Africa.

Ahi E 1926. Einige neue Fische der Familie Cichlidae aus dem Njassa-See. Sber. Ges. naturf. Freunde, Berl. : 51-62.
Conith AJ and Albertson RC 2021. The cichlid oral and pharyngeal jaws are evolutionarily and genetically coupled. Nature Communications



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