Ecological and Phenotypic Diversification after a Continental Invasion in Neotropical Freshwater Stingrays

Abstract

Habitat transitions are key potential explanations for why some lineages have diversified and others have not - from Anolis lizards to Darwin's finches. The ecological ramifications of marine-to-freshwater transitions for fishes suggest evolutionary contingency: some lineages maintain their ancestral niches in novel habitats (niche conservatism), whereas others alter their ecological role. However, few studies have considered phenotypic, ecological, and lineage diversification concurrently to explore this issue. Here, we investigated the macroevolutionary history of the taxonomically and ecologically diverse Neotropical freshwater river rays (subfamily Potamotrygoninae), which invaded and diversified in the Amazon and other South American rivers during the late Oligocene to early Miocene. We generated a time-calibrated, multi-gene phylogeny for Potamotrygoninae and reconstructed evolutionary patterns of diet specialization. We measured functional morphological traits relevant for feeding and used comparative phylogenetic methods to examine how feeding morphology diversified over time. Potamotrygonine trophic and phenotypic diversity are evenly partitioned (non-overlapping) among internal clades for most of their history, until 20-16 mya, when more recent diversification suggests increasing overlap among phenotypes. Specialized piscivores (Heliotrygon and Paratrygon) evolved early in the history of freshwater stingrays, while later trophic specialization (molluscivory, insectivory, and crustacivory) evolved in the genus Potamotrygon. Potamotrygonins demonstrate ecological niche lability in diets and feeding apparatus; however, diversification has mostly been a gradual process through time. We suggest that competition is unlikely to have limited the potamotrygonine invasion and diversification in South America.

Shark mandible evolution reveals patterns of trophic and habitat-mediated diversification

“…This has important ramifications for palaeoecological studies. It validates the underlying assumptions of the relationship between morphological disparity and functional disparity through the time of early gnathostomes and the ecological diversity through jaw morphology and dental characteristics 29 – 31 , 67 , 68 .…”

The genetics‐morphology‐behavior trifecta: Unraveling the single greatest limitation affecting our understanding of chondrichthyan evolution

“…Sharks, rays, and chimaera form the clade Chondrichthyes, a group of cartilaginous fishes thought to have first arisen during the Paleozoic and thus to have survived all five mass extinctions (Guinot & Cavin, 2016; Soldo, 2013; Stiassny et al, 2004). Over the course of its long history the clade has undergone major transitions in diversity (Grogan et al, 2012; Guinot & Cavin, 2016; Kriwet & Benton, 2004; Kriwet & Klug, 2008) but remains a morphologically and ecologically diverse component of modern ecosystems (Cailliet et al, 2005; Compagno, 1990; Kolmann et al, 2022; Stein et al, 2018), performing various important ecological functions (Flowers et al, 2021; Heupel et al, 2014; Navia et al, 2010). Chondrichthyan taxa have long been influential in studies of vertebrate, and particularly gnathostome evolution (Gillis & Shubin, 2009; Smith, 2003).…”

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“…Evolutionary theory predicts that differing habitats will exert unique ecological selection pressures on organisms, resulting in associations between ecological and phenotypic traits. Indeed, species inhabiting differing habitats often display functional, behavioral, or phenotypic differences, that have presumably been the result of adaptive diversification in their respective ecological contexts [1][2][3][4][5].…”