Are Feeding Modes Concealing Morphofunctional Diversity? The Case of the New World Parrotfishes

Lucía Pombo-Ayora,Jose Tavera

doi:10.3389/fmars.2021.634046

Abstract

In functional ecology, morphology is expected to reflect function; however, occasional decoupling of these two can be found. In the case of feeding ecology, the diversity of the diet or diversity of the feeding modes within a clade is expected to be positively related to the diversity of the morphological traits involved in the feeding performance. Parrotfishes are separated into two main groups, the “reef” clade and the “seagrass” clade. Both groups have important differences in their evolutionary history. Still, more interestingly, they have important morphological and ecological differences. The generaScarusandSparisomaare the most specious genera of parrotfishes. They belong to each of those main groups, respectively. AllScarusspecies have the same feeding mode, while inSparisoma, there are three different feeding modes. We want to test if the morphological jaw diversity of these genera corresponds with the diversity in their feeding modes. Using a disparity analysis of feeding traits within a phylogenetical framework, we did not find a relationship between functional feeding morphology and feeding modes of the American parrotfishes of the generaScarusandSparisoma. Interestingly we found that some muscular traits are the source of the high disparity in the genusScarus. We explore some possible morpho-functional reasons for this phenomenon and reappraise the parrotfishes’ scraper feeding mode’s functional diversity. We also consider that there could be more ecological differentiation betweenScarusspecies that we are aware of. Using an ancestral reconstruction of feeding modes of 52 species of parrotfishes, we found that the scraping feeding mode exhibited by allScarusspecies is an evolutionary convergence with the scraping feeding modes performed by someSparisomaspecies. Different selective pressures or ecological conditions may have shaped the differences in the feeding ecology and the feeding morphology of these two genera. Probably, key novel structures and muscular properties found in theScarusspecies’ jaw played an essential role in this genus’s morpho-functional diversification. Finally, we propose that feeding modes may not fully capture the complexity of feeding ecology in parrotfishes.

Highlights

Parrotfishes (Scarinae, Labridae) are vital members of the herbivorous fish community within coral reef ecosystems (Russ, 1984; Lewis, 1986)
To answer our third question: Does the transitions between feeding modes across the parrotfish evolutionary history influence the ecological disparity between Scarus and Sparisoma? We modeled the ancestral transitions of feeding modes within the parrotfish phylogeny, using an equal rates transition matrix and Bayesian stochastic character mapping (Huelsenbeck et al, 2003) over a sample of 1000 trees randomly sampled from the posterior distribution of the Bayesian phylogenetic reconstruction, using the library phytools (Revell, 2012) included the software R (R Development Core Team, 2013)
The high morphological disparity exhibited by Scarus species that feed only by scraping, compared to Sparisoma parrotfishes that include scrapers, browsers, and excavators (Bellwood, 1994; Bruggemann et al, 1996; Bernardi et al, 2000; Streelman et al, 2002; Smith et al, 2008; Cardoso et al, 2009), indicates that there may be no correspondence between feeding mode diversity and feeding trait variation

Summary

Introduction

Parrotfishes (Scarinae, Labridae) are vital members of the herbivorous fish community within coral reef ecosystems (Russ, 1984; Lewis, 1986). Parrotfishes Feeding Morphological Diversity on epilithic algae, which grows on hard substrata like dead coral or rock, other species feed on seagrass and macroalgae (Bonaldo et al, 2014). The species of this family have a fundamental role in the resilience, maintenance, and recovery of coral reef ecosystems (Bonaldo et al, 2014; Clements et al, 2017). Species can be classified as (1) Browsers, which feed on macroalgae or seagrass without having direct contact with hard substratum, (2) Scrapers, which feed by scraping epilithic algae that grow on dead coral or rock, and (3) Excavators, which feed by breaking pieces of coral to obtain epilithic and endolithic algae (Bellwood and Choat, 1990; Bellwood, 1994; Green and Bellwood, 2009; Helfman et al, 2009; Bonaldo et al, 2014)

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Conclusion