Hybrids and Phylogenetic Systematics I. Patterns of Character Expression in Hybrids and Their Implications for Cladistic Analysis

Abstract

Abstract. -Interspecific hybridization is considered common among plants, but the methods of cladistic systematics produce only divergently branching phylogenetic hypotheses and thus cannot give the correct phylogeny ifan analysis includes hybrids. Empirical studies ofthe impact ofknown hybrids on phylogenetic analysis are lacking, and are necessary to begin to understand the problems that we face if hybrids are often included in cladistic analysis. Examination of the implications of hybrids for cladistics must begin with patterns of character expression in hybrids. This study includes 17 hybrids and their nine parental taxa that are Central American species ofAphelandra (Acanthaceae), analyzed using a set of50 morphological characters. The hybrids are overwhelmingly intermediate as quantitatively scored for phylogenetic analysis. They express maternal and paternal, and primitive and derived characters in equal frequencies, showing no evidence of predominant inheritance of derived character states as has been assumed by most cladists who have considered hybrids theoretically. Because oftheir known genetic constitution, hybrids were useful in homology assessment and ordering character states. The parental character set was generally robust, but some changes were made to reflect the special evidence offered by the hybrids. These hybrids suggest that the inclusion of hybrids in phylogenetic analysis will not lead to unresolved cladograms with rampant homoplasy, as has been predicted by other authors. Instead, the patterns of character inheritance in these hybrids lead to the prediction that a hybrid will be placed by phylogenetic analysis as a basal lineage to the clade that includes its most derived parent, with relatively little effect on homoplasy. These predictions will be evaluated by incorporation of the hybrids in phylogenetic analyses, to be reported in a subsequent paper.

Polymorphism and concerted evolution in a tandemly repeated gene family: 5S ribosomal DNA in diploid and allopolyploid cottons

“…As hybrid taxa are expected to occupy phylogenetically basal positions in cladistic analyses (McDade 1990(McDade , 1992, we interpret these results as additional support for the hybridization and introgression hypothesis advanced by Wendel et al (1995b).…”

Assessing the monophyly of polyploid Gossypium species

“…In both cases, the PCR, cloning, and sequencing were repeated to verify the conversion. Because conversion events can influence the phylogeny by shifting the phylogenetic placement of the converted sequence to the base of the clade (McDade 1990(McDade , 1995, alignments were constructed and analyzed that either included or excluded the affected regions (Fig. 1).…”

Molecular Evidence for the Compilospecies Model of Reticulate Evolution in Armeria (Plumbaginaceae)

“…longiaristata ), which presents polymorphic sites for five of the informative positions (367, 388, 389, 517, and 599), all of them supporting major clades (see below). This sample jumps between different branches in the most-parsimonious trees and shows behavior typical of a recent hybrid (McDade, 1990). Because this sample can be detected as a recent hybrid both by the five relevant polymorphic positions and by its effects on the most-parsimonious trees, we removed it from the data set (Humphries and Funk, 1984;Funk, 1985) to see what would be the effects on the analysis.…”