Continental cichlid radiations: functional diversity reveals the role of changing ecological opportunity in the Neotropics

Abstract

Adaptive radiations have been hypothesized to contribute broadly to the diversity of organisms. Models of adaptive radiation predict that ecological opportunity and ecological release, the availability of empty ecological niches and the response by adapting lineages to occupy them, respectively, drive patterns of phenotypic and lineage diversification. Adaptive radiations driven by 'ecological opportunity' are well established in island systems; it is less clear if ecological opportunity influences continent-wide diversification. We use Neotropical cichlid fishes to test if variation in rates of functional evolution is consistent with changing ecological opportunity. Across a functional morphological axis associated with ram-suction feeding traits, evolutionary rates declined through time as lineages diversified in South America. Evolutionary rates of ram-suction functional morphology also appear to have accelerated as cichlids colonized Central America and encountered renewed opportunity. Our results suggest that ecological opportunity may play an important role in shaping patterns of morphological diversity of even broadly distributed lineages like Neotropical cichlids.

Keywords: Cichlidae; adaptive radiation; freshwater fish; macroevolution; morphology; phylogenetics.

Figure 1.

Diversity and distribution of Neotropical cichlids in South (dark grey/blue) and Central America (light grey/green). (a) Phylogeny of genera represented in this study [18,22]. (b) Examples of convergent ecomorphs (p, piscivore; d, detritivore/algivore; s, substrate sifter; i, rheophilic invertivore) in Neotropical cichlids (clockwise from top = Petenia, Herichthys, Satanoperca, Crenicichla, Teleocichla, Cichla, Symphysodon, Theraps and Astatheros). (c) Phylogenetic PC scores of functional morphology in 75 species of Neotropical cichlid [29]. Morphological variation associated with the positive (right) and negative (left) extremes of each axis illustrated below. Image credits to: Jessica Arbour, Hernán López-Fernández, Michael Tobler. (Online version in colour.)

Figure 2.

Changes in evolutionary rates of ram–suction morphology in South and Central America ((a) pPC1 and (b) pPC2) on the MCC relative time-tree (electronic supplementary material, figure S1) of 75 species of Neotropical cichlids. Evolutionary rate estimates (absolute value of standardized independent contrasts) through time for South American (blue, circles) and Central American (green, triangles) taxa, including the regression line (shaded region = 95% CI) from the NHT. Outliers are given by an open circle. (Online version in colour.)

Figure 3.

DTT analysis of pPC1 and pPC2 of Neotropical cichlid feeding functional morphology. DTT plots generated based on the MCC relative time-tree (electronic supplementary material, figure S1). Solid black lines, observed DTT curve; dashed lines, median simulated DTT curve; shaded region, 95% range of simulated DTT curves. Lighter region shows the area excluded from MDI calculations to account for incomplete taxonomic sampling. (a) Cichlinae, (b) primary South American taxa, (c) Central American taxa. (Online version in colour.)

Figure 4.

Results of BAMM analysis of functional morphology ((a) pPC1 and (b) pPC2) on the MCC phylogeny. Branches are coloured by evolutionary rates estimated under the highest posterior probability (given below each tree) evolutionary rate regime. Inset figures show the BAMM median evolutionary rates from the posterior distribution of BAMM calculated through time, with 95% CI as series of shaded polygons (5% intervals). (Online version in colour.)