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UvA-DARE (Digital Academic Repository) From the Amazonriver to the Amazon molly and back again Poeser, F.N. Publication date 2003 Link to publication Citation for published version (APA): Poeser, F. N. (2003). From the Amazonriver to the Amazon molly and back again. IBED, Universiteit van Amsterdam. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:05 Oct 2021 130 From the Amazon river to the Amazon molly and back again: Chapter 11 TAXONOMY OF POECILIA BLOCH AND SCHNEIDER, 1801 Abstract Both the supra-generic and infra-generic taxonomy of Poecilia Bloch and Schneider, 1801 are discussed and two major views on taxonomy, i.e., 'traditional' taxonomy and taxonomy based on the Phylo-Code, are compared. Based on the phylogenetic analysis in the present thesis, two subgenera are possible in Poecilia, viz., Poecilia and Curtipenis Rivas and Meyer, 1950. Incorporating traditional taxonomy, several morphological distinct species groups can be recognized, making more subgenera possible. However, the latter action will break up Poecilia into a paraphyletic array of species, which is not allowed in any cladistic taxonomy. A more complete view on Poecilia was obtained using molecular data (Ptacek and Breden, 1998; Breden et al., 1999) and biogeographical data (Chapter 10). However, these sources did not provide additional information: Poecilia cannot be broken up into smaller groups without creating paraphyletic or polyphyletic taxa. Consequently, I recognize only a single large genus, viz., Poecilia, consisting of 35 species at the present. Within this genus, however, groups of morphologically distinct species groups are described and recorded geographically (Section 11.2). Introduction The genus Poecilia was formerly defined by two synapomorphies (Rodriguez, 1997): (i) Serrated serrae subdistally on gonopodial ray 3; (ii) A protruding hook, distally on gonopodial ray 5p. This characterization is confirmed herein (Chapter 9), together with the additional feature (iii) Hook found distally on gonopodial ray 3. However, defining Poecilia by only these characters causes severe problems. Both the hooks on ray 3 and ray 5 are possible homoplasies with other genera (e.g., Limia also has a hook distally at ray 3), and are sometimes reduced and even lost in several South American species, whereas also the serrated side of gonopodial ray 3 is sometimes not present, e.g., in P. hispaniolana or is found in non- related genera, such as Brachyraphis (Chapter 9). Phylogenetic taxonomy The above problem can be reconceptualized within the framework of phylogenetic taxonomy. Phylogenetic taxonomy is a discipline in biological science concerned with the nomenclatural representation of phylogenetic relationships, i.e., the naming of cladistically based taxa (De Queiroz and Gauthier, 1990). De Queiroz and Gauthier distinguished between "phylogenetic systematics", which is the construction of cladograms that reveal ancestral relationships between taxa, and "phylogenetic taxonomy", which is the branch of systematics concerned with representing these relationships. From the Amazon river to the Amazon molly and back again: Chapter 11 131 The application of phylogenetic taxonomy to generic names De Queiroz and Gauthier (1990) argue that taxa in a phylogenetically based taxonomy shouldn't be defined by characters, but by their ancestry. The proposed alternative of De Queiroz and Gauthier consists of three ways to define taxa, i.e., node-based, stem-based, and apomorphy-based definition of monophyletic taxa. Since their taxonomy governs only species and clades, all superspecific categories disappear from their taxonomy including the generic rank. Species and clades are considered biological entities, not "ranks". Naming these biological entities requires specific rules. In a description of a taxon the justification of its differences suffice, but additionally a specified kind of definition must be given, with its phylogenetic definition and a list of "specifiers". This latter term, i.e., specifiers, refers to a species, a specimen or a synapomorphy as a point of reference. Clade names are always accompanied by a phylogenetic definition that links it explicitly with a particular clade. There are three kinds of definitions, exemplified as follows. • A node-based definition refers to a "clade stemming from the most recent common ancestor of taxa A and B", or, in other words, to "the least inclusive clade containing taxa A and B." In short: clade (A+B). • A stem-based definition refers to a "clade consisting taxon Y and all organisms that share a more common recent ancestor with taxon Y than with W" (provided W does not belong to the same clade), or to "the most inclusive clade containing taxon Y, but not W." In short: clade (Y<- W). • Finally, an apomorphy-based definition refers to a "clade stemming from the first species to possess character M synapomorphic with that in H." In short: clade (M in H). Every clade requires an hypothesized phylogeny to which it refers. It is recommended that this phylogeny was published prior to the application of the taxonomy via an explicit, reproducible analysis. Another recommendation is that pre-existing clade names are preferred. As a final remark, it is added that if a pre-existing genus is used as a clade name, the definition of that genus must be included in the definition of the clade. In retrospective, this method might have avoided some taxonomie disturbances in the taxonomy of the Poeciliini. In agreement of Pleijel (1999), I will apply an apomorphy-based definition for the taxonomy of the Poeciliini, i.e., the defining character can be cross-checked with a specimen deposited as a type. The clade Poeciliini (converted clade name, or nomen cladum conversum) is defined as the clade stemming from the first species that possesses two gonapophyses, clearly bend forward. With this definition, no other clade can be meant than the clade in a well-supported phylogeny, e.g., Chapter 9 (Fig. 9, the majority rule consensus tree, reproduced in this Chapter as Figure 1), containing the herein mentioned clades Poecilia, Limia, Pamphorichthys and Pseudolimia (not in italics, although they are represented in the cladogram as genera). In this cladogram the Poeciliini are a monophyletic group, including the monophyletic Poecilia. For a more inclusive clade, e.g., Poecilia, another definition must be used, because no generally applicable synapomorphy is evident (see above). Also a stem-based definition does 132 From the Amazon river to the Amazon molly and back again: Chapter 11 not qualify. As the biogeography indicated (Chapter 10), the relationships among the more inclusive clades (formerly genera) is not fully clear, e.g., Pseudolimia is the sistergroup of Poecilia (Fig. 1), but it seems more related to Limia (cf. Breden et al., 1999). I cannot, therefore, unambiguously indicate any clade to which Poecilia is more related to (referred as "but not to taxon W" in the definitions above). This yields the node based definition as suitable for Poecilia, i.e., the clade "stemming from the most recent common ancestor of Poecilia hispaniolana, Poecilia sphenops &cetera." Note that the species names are not underlined, they are converted names based on full pre-existing binomials (= method A, Cantino et al., 1999). In this approach Poecilia is not based on characters themselves, but are defined by the characters as they have developed during the phyletic history of the clade. Poecilia is exemplary for this definition; the type species of the traditional genus does not posses all synapomorphies of the clade, i.e., Poecilia vivipara does not have hooks or claws extending from the gonopodial tip. Characters as such are, therefore, not considered as static denominators in a node based definition, they are transitory objects in the shapes that we presently observe. Hence, homologies are considered as characters that merely resemble each other in their present state. The present state of the defining characters can be traced in the cladogram where either their original state (hooks that in the case of Poecilia vivipara are secondary lost) or the derived state (serrae on gonopodial ray 3 that in the case of Poecilia dominicensis are present in a primitive state) can be retrieved. The application of traditional taxonomy to generic names De Queiroz and Gauthier (1990) claimed that the use of phylogenetic taxonomy has made the rank of "genus" obsolete. Their magic word to renounce generic ranks seems to be 'mandatory'. The application of generic ranks does not, according to these authors, identify phylogenetic information. In my opinion, this is true only when genera are not defined as monophyletic units. However, ever since the days of Darwin, a genus is phyletically defined (see thesis 8 herein). Therefore, it is not the generic rank that is obsolete, it is more likely that the term 'mandatory' is overstated. Also a single genus can be monotypic, and in addition a tribe or family can encompass only one, perhaps monotypic, genus. Granted, in these cases the rank of genus is uninformative, but it is in no way a problem. By defining genera as monophyletic groups of species in combination with a presented tree, phylogenetic information is incorporated into any classification.

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