Re‐evaluating the morphological evidence for the re‐evolution of lost mandibular teeth in frogs

Abstract

Dollo's law of irreversibility states that once a complex structure is lost, it cannot be regained in the same form. Several putative exceptions to Dollo's law have been identified using phylogenetic comparative methods, but the anatomy and development of these traits are often poorly understood. Gastrotheca guentheri is renowned as the only frog with teeth on the lower jaw. Mandibular teeth were lost in the ancestor of frogs more than 200 million years ago and subsequently regained in G. guentheri. Little is known about the teeth in this species despite being a frequent example of trait "re-evolution," leaving open the possibility that it may have mandibular pseudoteeth. We assessed the dental anatomy of G. guentheri using micro-computed tomography and histology and confirmed the longstanding assumption that true mandibular teeth are present. Remarkably, the mandibular teeth of G. guentheri are nearly identical in gross morphology and development to upper jaw teeth in closely related species. The developmental genetics of tooth formation are unknown in this possibly extinct species. Our results suggest that an ancestral odontogenic pathway has been conserved but suppressed in the lower jaw since the origin of frogs, providing a possible mechanism underlying the re-evolution of lost mandibular teeth.

Multiple transitions between realms shape relict lineages of Proteus cave salamanders

“…Complex traits have re-evolved in other cases after their loss (Collin & Miglietta, 2008;Paluh et al, 2021;Recknagel et al, 2018). This has also been suggested to be the case in olms (Bizjak Mali & Sket, 2019;Sessions et al, 2015).…”

“…While we consider an evolutionary reversal from cave to surface phenotype in the Parkelj lineage unlikely, it is not impossible. Complex traits have re‐evolved in other cases after their loss (Collin & Miglietta, 2008; Paluh et al, 2021; Recknagel et al, 2018). This has also been suggested to be the case in olms (Bizjak Mali & Sket, 2019; Sessions et al, 2015).…”

Blocking endogenous retinoic acid degradation induces oral tooth formation in zebrafish

“…This re-emergence requires an external intervention which is the suppression of endogenous RA degradation and is therefore not a natural occurring re-emergence of a lost trait. This however did happen in nature in the Guenther’s marsupial frog, where unlike other frog species, teeth can form on the lower jaw, making this example a similar challenger to Dollo’s Law ( 15 ). The results of this study, coupled with previous reports in other animal species, strongly challenges Dollo’s Law of Irreversibility of Evolution ( 6 ) and illustrates how slightly modifying the action of a single signaling pathway or molecule can be helpful in testing the reversibility of character loss in fish and other animals.…”

‘Evolutionary poker’: an agent‐based model of interactome emergence and epistasis tested against Lenski's long‐term E. coli experiments

“…From a statistical or entropy perspective, such a reversal would be analogous to allowing a drop of perfume to diffuse throughout a room and then, somehow, coaxing all the perfume molecules back into a drop at the original place in the room. The difficulty is that although Dollo's law seems generally to be valid, such that evolution is rarely reversed (see Domes et al., 2007; Galis et al., 2010; Paluh et al., 2021 for some possible exceptions), historical contingency does not appear generally to be valid. Experimental evidence to be reviewed below tends to show that rerunning the tape usually produces very similar or identical genetic adaptations.…”