Neotropical characiform fishes form one of the most diverse freshwater ichthyofauna in the world. Knowledge of evolutionary processes that generated and maintain the immense characiform lineage and morphological diversity is still poorly understood. When did characiform lineages diversify? How have major geological and environmental changes affected diversification? Why are some clades seemingly more morphologically diverse than others? I examine the characiform superfamily Anostomoidea to address these broader questions of Neotropical diversification.
The abundant Neotropical freshwater fish superfamily Anostomoidea contains two clades with seemingly disparate evolutionary strategies. The first group, the anostomids, represent ~150 species with a wide variety of body coloration, mouth position, tooth shape and trophic strategies ranging from generalist to herbivory to insectivory. The other major group, the families: Curimatidae, Chilodontidae and Prochilodontidae, contains around the same number of species but members are silvery with some pigmentation, have little variation in mouth position, possess reduced or no teeth and all feed mostly on detritus.
The Prochilodontidae are some of the most abundant fish by biomass in South America and participate in mass-migrations for spawning and feeding. This group is characterized by low morphological diversity, large-body size and is generally resilient to small-scale vicariance barriers. As such, I use this widespread family to investigate the influence of large-scale paleoecological events, such as the rise of the Andean Eastern Cordilleras, on diversification of Neotropical fishes. I estimated the first time-calibrated molecular phylogeny for the family Prochilodontidae and compared diversification rate and events with known paleoecological events. Vicariance barriers and other events significantly impacted the historical biogeography of Prochilodontidae, supporting their role in generating the astounding diversity of Neotropical fishes.
In the second part, I investigated whether the morphologically depauperate detritivore clade actually contains a high number of ecologically equivalent species or if they are diversifying in a previously unstudied manner. There is substantially more variation in the arrangement of the gill arches, which are used in processing food, within the detritivores than in the trophically-diverse anostomids. The two clades have evolved over similar amounts of time, but differ in how efficiently they developed new gill morphologies. Through cladogenesis, detritivorous lineages evolved significantly different morphologies more readily and potentially more frequently than the anostomids. The significant diversity and evolutionary pattern of detritivore gill arch shape indicates that selection is acting on how they process food and demonstrates that detritivory encompasses a spectrum of ecomorphological specialization.