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Origin of evolutionary novelties and elimination of plesiomorphic alleles: Some comments on limitations of the concept of synapomorphy
Dalton de Souza AmorimI; Maria Elisabeth AraújóII; Antonio M. SoleIII
IDepartamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto/USP, Av. Bandeirantes, 3900, 14040-901 Ribeirão Preto, SP, Brasil. Send correspondence to D.S.A.
IISUDENE E/CE, Rua Rodrigues Jr., 840, 60060 Fortaleza, CE, Brasil
IIIDepartamento de Genética, Instituto de Biologia, Universidade Federal do Rio de Janeiro, 21941 Rio de Janeiro, RJ, Brasil
ABSTRACT
The intuitive concept of synapomorphy involves the idea of modified (apomorphic) features shared by a set of organisms. From the evolutionary point of view, the origin of new features involves at least two processes of completely different nature. One of them is the molecular process of modification of a pre-existing gene at a given locus; the other is the process of plesiomorphic allele elimination at that locus in the population. These two events do not occur at the same time in the history of a "synapomorphy". Actually, they may occur in the history of a phyletic stem separated by one or more cladogenetic events. In these cases, the result is the inheritance of polymorphisms between ancestral-descendent species. The radical differences between these two processes recommend a conceptual discenunent between them. Shared evolutionary novelties (apomorphic alleles) and shared absence of plesiomorphic alleles are named herein, respectively, syntrepty and synapousy. Many cases understood as homoplasies - more than one origin of the same evolutionary novelty - may correspond to more than one independent event of elimination of the plesiomorphic allele. One of the most important consequences for the phylogenetic analysis is that syntreptic and synapousic events are not directly comparable as probabilistic entities. This has important effects on the application of the parsimony concept on allele matrix analysis.
Keywords: Plesiomorphic alleles; Synapomorphy;
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