Morphological Differentiation Between Introduced and Native Populations of Three Species of Cichlid (Perciformes)
Fishes of the family Cichlidae are well known for their capacity to exploit trophic niches in their environments through rapid speciation and morphological diversification, with the best-documented cases of such diversification occurring in the lakes of the African Rift Valley. Numerous species of cichlids are established outside of their native ranges, with reproducing populations of many species occurring in southern Florida (U.S.). The purpose of this study was to examine morphological differences between native and non-native (Floridian) populations of three cichlid species (Pelmatolapia mariae, Parachromis managuensis, and Mayaheros urophthalmus) to better understand how these species have managed to invade so successfully. Using linear measurements, we found that all three species have diverged in multiple characteristics: Pe. mariae in head length (HL), snout length (NL), and interorbital width (IO), Pa. managuensis in maximum body depth (MD), NL, and IO, and M. urophthalmus in MD and IO. Analyses of 2D-landmark data also revealed that Pe. mariae and Pa. managuensis collected from non-native populations display morphological variation beyond the ranges of variation exhibited by specimens from native populations. The observed morphological differences may be the result of natural selection, morphological plasticity, or some combination of the two; further work is needed to test these hypotheses. This study suggests that the conditions exist to promote rapid morphological change in introduced populations of cichlids in Florida.
Measurements and landmarks used to collect data. (A) Linear measurements taken; adapted from Bergmann and Motta (2005). MD, maximum depth; NL; snout length; HL, head length; SL, standard length; FL, pectoral-fin length. (B) Landmarks recorded for each specimen analyzed; adapted from Fruciano et al. (2016). 1, Anterior margin of the snout; 2, center of the orbit; 3, convergence of the snout and forehead; 4, anterior insertion of the dorsal fin; 5, posterior insertion of the dorsal fin; 6, dorsal insertion of the caudal fin; 7, posterior extent of the lateral line canal at the caudal-fin insertion; 8, ventral insertion of the caudal fin; 9, posterior insertion of the anal fin; 10, anterior insertion of the anal fin; 11, pelvic-fin insertion; 12, ventral insertion of the opercular flap; 13, ventral margin of the maxillary articular joint; 14, posterior margin of the opercular cover; 15, dorsal insertion of the pectoral fin.
Principal component plots showing the morphospace occupations of introduced and native specimens of the following species: (A) Pelmatolapia mariae, (B) Parachromis managuensis, (C) Mayaheros urophthalmus.
Boxplots of linear morphometric ratio comparisons between introduced and native specimens for Mayaheros urophthalmus, Parachromis managuensis, and Pelmatolapia mariae. Only comparisons yielding significant differences are pictured. “Introduced” = non-native populations, “Native” = native populations. Plots A, B, and C: Pe. mariae, HL/SL, NL/SL, and IO/SL, respectively; plots D, E, and F: Pa. managuensis, MD/SL, NL/SL, IO/SL; plots G and H: M. urophthalmus, MD/SL, IO/SL. MD = maximum depth, NL = snout length, HL = head length, SL = standard length, IO = interorbital width.
Warp grid plots for the maximum and minimum value specimens plotted against the mean specimen for each species. Top: Pelmatolapia mariae, PC1 minimum (A, left) and PC1 maximum (A, right); center: Parachromis managuensis, PC2 minimum (B, left) and PC2 maximum (B, right); bottom: Mayaheros urophthalmus, PC1 minimum (C, left) and PC2 maximum (C, right).
Contributor Notes
Associate Editor: M. P. Davis