PHYLOGENETIC INTERRELATIONSHIPS AND REDUCTIVE EVOLUTION IN NEOTROPICAL CHARACIDIIN FISHES (CHARACIFORMES, OSTARIOPHYSI)

Abstract— Miniaturization, which results in the presence of numerous apparently paedomorphic characters associated with reduced size, is a common phenomenon among neotropical fishes, with over 85 miniature species distributed among the five major ordinal groups. Eleven species are recognized as miniatures within the Characidiinae, a monophyletic subunit of Characiformes. A reconstruction of characidiin phylogeny is used to analyze the history of miniaturization events. Former hypotheses of origin of miniaturization among characidiins are rejected, underscoring the need for phylogenetic frameworks in the study of ontogenetic changes associated with the phenomenon of miniaturization. The 11 instances of miniature species can be most parsimoniously attributed to three independent miniaturization events within the Characidiinae.
Reductive characters comprise a large proportion of phylogenetically informative characters within the Characidiinae. In the largest group of miniatures, reductive characters represent more than half of the character state transformations affecting supraspecific relationships among Elachocharax, Klausewitzia, Odontocharacidium and Microcharacidium . An analysis of patterns of character state distributions fails to reject the null hypothesis of character independence. A distinction is made between the concepts of character independence, defined as the origination of character states from different (non-simultaneous) evolutionary events, and character correlation, defined as the association of character states in terminal taxa. Character correlation is not a sufficient criterion to reject Hennig's auxiliary principle, according to which the "presence of apomorphous characters in different species is always reason for suspecting kinship, and their origin by convergence should not be assumed a priori". High values of character correlation are the expected result of congruent patterns of character distribution.