Relaxed Feeding Constraints Facilitate the Evolution of Mouthbrooding in Neotropical Cichlids

Abstract

Multifunctionality is often framed as a core constraint of evolution, yet many evolutionary transitions involve traits taking on additional functions. Mouthbrooding, a form of parental care where offspring develop inside a parent's mouth, increases multifunctionality by adding a major function (reproduction) to a structure already serving other vital functions (feeding and respiration). Despite increasing multifunctionality, mouthbrooding has evolved repeatedly from other forms of parental care in at least 7 fish families. We hypothesized that mouthbrooding is more likely to evolve in lineages with feeding adaptations that are already advantageous for mouthbrooding. We tested this hypothesis in Neotropical cichlids, where mouthbrooding has evolved 4-5 times, largely within winnowing clades, providing several pairwise comparisons between substrate brooding and mouthbrooding sister taxa. We found that the mouthbrooding transition rate was 15 times higher in winnowing than in non-winnowing clades, and that mouthbrooders and winnowers overlapped substantially in their buccal cavity morphologies, which is where offspring are incubated. Species that exhibit one or both of these behaviors had larger, more curved buccal cavities, while species that exhibit neither behavior had narrow, cylindrical buccal cavities. Given the results we present here, we propose a new conceptual model for the evolution of mouthbrooding, integrating the roles of multifunctional morphology and the environment.We suggest that functional transitions like mouthbrooding offer a different perspective on multifunctionality: increasing constraints in one trait may release them for another, generating new evolutionary opportunities.

Beyond the (geometric) mean: stochastic models undermine deterministic predictions of bet hedger evolution

“…Persister cells divide more slowly, thereby reducing the population’s mean fitness, but are able to survive longer periods of antibiotic pressure, increasing their fitness in the presence of antibiotics and thus lowering fitness variance across the two environmental conditions ([12], [13]). Other examples of bet hedging include variable germination phenology in plants ([14], variable egg hatching in crustaceans ([15]), mouthbrooding in cichlids ([16]), altruism in birds ([17]), amphicarpic seed production in annual plants ([18]), and diauxic shift in yeast ([19]).…”

A new species ofLethrinops(Cichliformes: Cichlidae) from a Lake Malawi satellite lake, believed to be extinct in the wild

“…All of these taxa have ventrally positioned mouths, and relatively flat lower jaws with thin mandibular bones and small teeth. This jaw structure is believed to be associated with their feeding behaviour, which, where known, largely consists of 'sediment-sifting' or 'winnowing' (Weller et al 2022), whereby loose sand or mud is picked up in the mouth, tumbled briefly and then ejected through the mouth and / or operculum, presumably with prey retained and swallowed (Fryer 1959;Fryer & Iles 1972;Konings 2016). Species in the genus Lethrinops are largely distinguished from Taeniolethrinops, Tramitichromis and Ctenopharynx by their lack of traits that distinguish those genera (Eccles & Trewavas 1989, Turner 2022.…”