Anales Del Jardín Botánico De Madrid 66(2): 263-277, Julio-Diciembre
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Anales del Jardín Botánico de Madrid Vol. 66(2): 263-277 julio-diciembre 2009 ISSN: 0211-1322 doi: 10.3989/ajbm.2224 Evolutionary analysis of five bryophyte families using virtual fossils by Richard H. Zander Missouri Botanical Garden, P.O. Box 299, St. Louis, MO 63166-0299 U.S.A. [email protected] Abstract Resumen Zander, R.H. 2009. Evolutionary analysis of five bryophyte fami- Zander, R.H. 2009. Análisis evolutivo de cinco familias de briofi- lies using virtual fossils. Anales Jard. Bot. Madrid 66(2): 263-277. tas empleando fósiles virtuales. Anales Jard. Bot. Madrid 66(2): 263-277 (en inglés). Traditional taxa paraphyletic or polyphyletic on a molecular Los táxones parafiléticos o polifiléticos tradicionales en un árbol phylogenetic tree may be interpreted as populations of surviv- molecular filogenético pueden interpretarse como poblaciones ing ancestors that are evolutionarily static in expressed traits de ancestros supervivientes que están evolutivamente estáticos though labile in DNA traits used to track genetic continuity. In en los caracteres expresados a través de lábiles en los caracteres those cases in which re-evolution (convergence) of such taxa is ADN que se emplean para seguir la continuidad genética. En deemed improbable, such heterophyly may be used to infer esos casos en los cuales la re-evolución (convergencia) de tales evolutionary series of virtual fossils reflecting macroevolution. táxones se considere improbable, la heterofilia puede usarse Descent with modification of taxa is here demonstrated by rein- para inferir series evolutivas de fósiles virtuales que reflejan la terpreting published cladograms of molecular studies of Di- macroevolución. El descenso con modificación de táxones se de- cranaceae, Pottiaceae, Grimmiaceae, Hypopterygiaceae, and muestra con la interpretación publicada de los cladogramas de Mniaceae as taxon trees. Given this argument, superimposed estudios moleculares de Dicranaceae, Pottiaceae, Grimmiaceae, inferred ancestors are support for the theory of punctuated Hypopterygiaceae y Mniaceae como árboles taxonómicos. En equilibrium. vista de este argumento, resulta que los ancestros inferidos su- perimpuestos apoyan la teoría del equilibrio puntuado. Keywords: virtual fossil, heterophyly, punctuated equilibrium, Palabras clave: fósil virtual, heterofilia, equilibrio puntuado, ár- taxon tree, evolution, autophyletic, Grimmiaceae, Hypoptery- bol taxonómico, evolución, autofilético, Grimmiaceae, Hypop- giaceae, Mniaceae, Pottiaceae. terygiaceae, Mniaceae, Pottiaceae. Introduction lution as descent with modification (Hall, 2003) of taxa because bioroles may be inferred from expressed It has long been recognized that phylogenetic analysis does not model evolution of sequences of trait combinations. In phylogenetic analysis, ancestral named ancestral and descendant taxa, i.e. genealo- mapped morphological or molecular traits, though gies, but demonstrates the evolution of characteristics presented as sequential, remain atomized. Attempts as branching lines of trait changes (e.g., Bowler, 1989: to infer soft tissues in geologic fossils also deal with in- 345-346; Farjon, 2007; Hörandl, 2006, 2007) for ex- dividual traits. For instance, in extant phylogenetic emplars of named terminal taxa. Of three particular bracketing (Witmer, 1995, 1998), a fossil lineage taxa, two are more likely to share an ancestor but that bracketed by two lineages each sharing one particular ancestor is generally not identified as a taxon different trait in their extant taxa would be expected to also from its descendants; it is simply represented in phy- have that trait, but features not present in both brack- logenetics by an unnamed node, or “common ances- eting lineages would be expected to be absent in the tor” of descendant lineages. When fossils are at hand, fossil. This method does not rely on and explain, how- however, they are potentially more informative of evo- ever, para- or polyphyly. 264 R.H. Zander Of particular importance for the present analysis is conservative, gapped phenotypic traits, and that total the idea that a split in a molecular lineage is not nec- convergence or crypsis is improbable or less probable essarily a speciation event. It could signal any isola- (Jardine & Sibson, 1971: 144) than other explana- tion event, sometimes followed by phenotypic stasis tions, simply enforcing monophyly by taxonomically of the isolated population, resulting in a surviving an- recognizing cryptic species, genera or families may be cestor. Identification of a surviving ancestor as a kind less productive scientifically than examining other ex- of living fossil may be done by (1) identification of a planations. The point of traditional taxonomy is to geologic fossil with an extant taxon; (2) biosystemat- make complete evolutionary convergence improbable, ic and cytogenetic studies, particularly in the case of and this applies at any taxonomic level. Classification “quantum” or local evolution (Lewis, 1962; Grant, is here presented as a major source of information 1971; Levin, 2001), the budding of a descendant about evolution needing only reliable information on species from a peripheral ancestral population, genetic continuity to reveal taxic steps. Even morpho- which are identifiable, for instance, as in the event of logical phenocopy involving two or more taxa that apparent daughter species being all more similar to lose traits when highly reduced (e.g. in high elevation an apparent parent than to each other; (3) the recent habitats) commonly allows retention of one or more method of Theriot (1992) inferring a surviving ances- conservative traits that allow accurate identification tor in a group of diatoms by evaluating a morpholog- (Zander, 1977: 261), or when unidentifiable, it is be- ically based cladogram and biogeographical informa- cause the reduced plants are intermediate or general- tion; (4) the somewhat more simplistic and problem- ist in form. Thus, Dollo’s Rule (Hall, 2003) is at least atic selection of a surviving ancestor as one lacking methodologically applicable at the organismal level of autapomorphies on a polytomous morphological a unified combination of traits, while many individual clade (Wiley & Mayden, 2000: 157; discussion by morphological characters may be quite homoplastic Zander, 1998); or (5) the method of virtual fossils (Endress, 1996: 313). used here. The null hypothesis is a fully nested set of pheno- When exemplars of different taxa are clustered to- taxa, without indication of descent with modification gether on a molecular tree, it is impossible to satisfac- of such taxa (Fig. 1). The null hypothesis for the torily infer the phenotype of the shared ancestor or evolution of expressed traits in a genus is that any ancestors. It could be the phenotype of any one of the phenospecies may be derived from any other in spite exemplars or even of a taxon of entirely different phe- of any inferred phylogenetic trees, which give no def- notype. When exemplars of the same taxon are clus- inite information on the phenotype of any ancestor. tered together on a molecular tree, it is straight-for- Falsification of that null is demonstration of one or ward to infer that the phenotype of the immediate more phenoancestors diagramed (e.g., Fig. 5) by mov- shared ancestor is that of the exemplars, rather than ing these (along with all descendants) out of the group all exemplars resulting from multiple convergences as a linked sequence, and leaving a “residuum” of un- from an ancestor of a different phenotype. If the ex- ordered taxa. By extension, with less resolution, one emplars are all one species, the ancestor is that phenogenus of a family may be derived from any oth- species. If they are of different species of one genus, er, unless an ancestor is demonstrable. the ancestor may be inferred to be that genus; or if When exemplars of the same taxon (particularly of genera, then their family, and so on. If two such clus- the same species) are distant from each other on a ters are sister groups, one may infer a particular an- molecular tree, being separated by other taxa at least cestor for each of both clusters, but the phenotype of as sister lineages, the homoplasy is commonly either the immediate shared ancestor of the two clusters is explained as (1) evidence of that taxon or something impossible to infer. It could be one or the other or a quite like it being basal or ancestral to a portion of the different extinct or unstudied taxon of perhaps inter- cladogram, or (2) cryptic or sibling taxa that need dif- mediate phenotype. ferent taxonomic names. Textbook examples of the A solution may be found if exemplars of the same former are given by Futuyma (1998: 456, 470), citing taxon are separated by a lineage of a different pheno- Moritz & al. (1992) where coastal and Sierran Cali- taxon. And in spite of such separation (phylogenetic fornian subspecies of the salmander Ensatina es- disjunction) on a cladogram the exemplars of the for- chscholtzii “appear to have been derived from” subsp. mer paraphyletic taxon, when examined for possible oregonensis, and citing Hey & Kliman (1993) and Kli- mistaken taxonomy, remain assuredly that taxon. Giv- man and Hey (1993) for the Drosophila melanogaster en that the circumscription of traditional phenotaxa, species group where the paraphyletic D. simulans at least those of modern studies, commonly involve “gene copies are traced back to a ‘deeper’ common Anales del Jardín Botánico de Madrid 66(2): 263-277, julio-diciembre. ISSN: 0211-1322.