Convergent Evolution of Cichlid Fish Pharyngeal Jaw Dentitions in Mollusk-Crushing Predators: Comparative X-Ray Computed Tomography of Tooth Sizes, Numbers, and Replacement

Abstract

Synopsis Dental convergence is a hallmark of cichlid fish adaptive radiations. This type of repeated evolution characterizes both the oral jaws of these fishes as well as their pharyngeal jaws that are modified gill arches used to functionally process prey like hard-shelled mollusks. To test several hypotheses regarding the evolution of cichlid crushing pharyngeal dentitions, we used x-ray computed tomography (CT) scans to comparatively examine dental evolution in the pharyngeal jaw of a diversity of New World Heroine cichlid lineages. The substantial variation in erupted tooth sizes and numbers as well as replacement teeth found in these fishes showed several general patterns. Larger toothed species tended to have fewer teeth suggesting a potential role of spatial constraints in cichlid dental divergence. Species with larger numbers of erupted pharyngeal teeth also had larger numbers of replacement teeth. Replacement tooth size is almost exactly predicted (r = 0.99) from the size of erupted teeth across all of the species. Mollusk crushing was therefore highly associated with not only larger pharyngeal teeth, but also larger replacement teeth. Whether dental divergence arises as a result of environmental induced plasticity or originates via trophic polymorphism as found in the species Herichthys minckleyi, there appear to be general rules that structure interspecific divergence in cichlid pharyngeal erupted and replacement dentitions.

Ecological Speciation Promoted by Divergent Regulation of Functional Genes Within African Cichlid Fishes

“…and extent of LPJ divergence was comparable to divergence patterns in species pairs in older, more established cichlid radiations (Muschick et al 2012;Kusche et al 2014;Burress 2016;Hulsey et al 2020). We also report the first evidence of niche-specific differences in parasite load, and divergent expression regulation of major adaptive immune response networks between ecomorphs in Lake Masoko (Supplementary Fig.…”

Ecological speciation promoted by divergent regulation of functional genes within African cichlid fishes

“…1). We found that the observed direction and extent of LPJ divergence was comparable to divergence patterns in species pairs in older, more established cichlid radiations 34, 35, 37, 41 . We also report the first evidence of niche-specific differences in parasite load, and divergent expression regulation of major adaptive immune response networks between ecomorphs in Lake Masoko (Supplementary Fig.…”

“…1i; Supplementary Fig. 2), including body depth, head depth and length, size and position of the pectoral fin (important for manoeuvring [38][39][40] ), and size and position of the mouth (associated with feeding modality 41,42 ).…”

“…1i; Supplementary Fig. 2), including body depth, head depth and length, size and position of the pectoral fin (important for manoeuvring 38–40) , and size and position of the mouth (associated with feeding modality 41, 42 ). Taken together, these results indicate a substantial and consistent shift in feeding behaviour and trophic niche specialisation between the benthic and littoral ecomorphs.…”

The transcriptional state and chromatin landscape of cichlid jaw shape variation across species and environments

“…More specifically, our data suggest that pelagic foraging "drives" species-and environment-specific DE. This may seem counterintuitive as diets that involve large/hard prey items are generally considered to be the more mechanically demanding compared to small/soft food (Muschick et al, 2011;Gunter et al, 2013;Hulsey et al, 2020). However, Navon et al (2020) showed that in MZ bone matrix was deposited at a fast rate under pelagic foraging conditions, and speculated that suction feeding imposes mechanical load on the feeding apparatus as animals repeatedly open and protrude their jaws.…”