Abstract
Ecological speciation is well-known from adaptive radiations in cichlid fishes inhabiting lentic ecosystems throughout the African rift valley and Central America. Here, we investigate the ecological and morphological diversification of a recently discovered lotic predatory Neotropical cichlid species flock in subtropical South America. We document morphological and functional diversification using geometric morphometrics, stable C and N isotopes, stomach contents and character evolution. This species flock displays species-specific diets and skull and pharyngeal jaw morphology. Moreover, this lineage appears to have independently evolved away from piscivory multiple times and derived forms are highly specialized morphologically and functionally relative to ancestral states. Ecological speciation played a fundamental role in this radiation and our data reveal novel conditions of ecological speciation including a species flock that evolved: 1) in a piscivorous lineage, 2) under lotic conditions and 3) with pronounced morphological novelties, including hypertrophied lips that appear to have evolved rapidly.
Highlights
Species flocks are monophyletic assemblages of closelyrelated species that occur in sympatry and display high degrees of endemism [1] that are often in the process of radiating along an ecological gradient
Lower pharyngeal jaw shape is highly speciesspecific (CVA=91.9%, P
Neotropical cichlids represent multiple speciose adaptive radiations [40] and pharyngeal jaw morphology is often highly co-evolved with trophic function [39] and important components of resource-based ecological partitioning among closely related species [6,41]
Summary
Species flocks are monophyletic assemblages of closelyrelated species that occur in sympatry and display high degrees of endemism [1] that are often in the process of radiating along an ecological gradient. Resource segregation is often associated with cases of adaptive divergence among sister species [6,7] and among species flocks [8,9]. Examples of ecological differentiation among species flocks have been documented primarily in lentic fishes [9,10,11] and divergence is generally associated with habitat (i.e., pelagic-littoral zonation) heterogeneity. Pronounced habitat zonation (i.e., depth, temperature, dissolved oxygen) characterizes lentic ecosystems. Such habitat zonation may be limited in lotic environments, where water current seems to be the primary selective agent [15]. No prior studies have documented adaptive radiations of lotic species flocks
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