Capitate hydrozoans are a morphologically and ecologically diverse hydrozoan suborder, currently including about 200 species. Being grouped in two clades, Corynida and Zancleida, these hydrozoans still show a number of taxonomic uncertainties at the species, genus and family levels. Many Capitata species established symbiotic relationships with other benthic organisms, including bryozoans, other cnidarians, molluscs and poriferans, as well as with planktonic dinoflagellates for mixotrophic relationships and with bacteria for thiotrophic ectosymbioses. Our study aimed at providing an updated and comprehensive phylogeny reconstruction of the suborder, at modelling the evolution of selected morphological and ecological characters, and at testing evolutionary relationships between the symbiotic lifestyle and the other characters, by integrating taxonomic, ecological and evolutionary data. The phylogenetic hypotheses here presented shed light on the evolutionary relationships within Capitata, with most families and genera being recovered as monophyletic. The genus Zanclea and family Zancleidae, however, were divided into four divergent clades, requiring the establishment of the new genus Apatizanclea and the new combinations for species in Zanclea and Halocoryne genera. The ancestral state reconstructions revealed that symbiosis arose multiple times in the evolutionary history of the Capitata, and that homoplasy is a common phenomenon in the group. Correlations were found between the evolution of symbiosis and morphological characters, such as the perisarc. Overall, our results highlighted that the use of genetic data and a complete knowledge of the life cycles are strongly needed to disentangle taxonomic and systematic issues in capitate hydrozoans. Finally, the colonization of tropical habitat appears to have influenced the evolution of a symbiotic lifestyle, playing important roles in the evolution of the group.

This paper discusses methods to take into account interactions between characters, in the context of parsimony analysis. These interactions can be in the form of some characters becoming inapplicable given certain states of other, primary characters; in the form of only certain states being allowed in some characters when a given state or set of states occurs for other characters; or in the form of transformation costs in some character being higher or lower when other characters have certain states or transformations between states. Character-state reconstructions and evaluation of trees under the assumption of independence may easily lead to ancestral assignments that violate elementary rules of biomechanics, well-established theories relating form and function or ideas about character co-variation. An obvious example is reconstructing an ancestral bird as wingless and flying at the same time; another is reconstructing a protein-coding gene as having a stop codon in some ancestors. If the characters are optimized independently, such chimeric ancestral reconstructions can occur even when no terminal displays the impossible combination of states. A set of conventions (implemented via new TNT commands and options) allows the definition of complex rules of interaction. By recoding groups of characters with proper step-matrix costs (and excluding impossible combinations from the set of permissible states), it is possible to find the ancestral reconstructions that maximize homology (and thus the degree to which similarities can be explained by common ancestry), within the constraints imposed by the rules specified by the user. We expect that considerations of biomechanics, functional morphology and natural history will be a source of many theories on possible character dependences, and that the present implementation will encourage users to take the possibility of character dependences into account in their phylogenetic analyses.

Informative and consistent taxonomy above the species level is essential to communication about evolution, biodiversity and conservation, and yet the practice of taxonomy is considered opaque and subjective by non-taxonomist scientists and the public alike. While various proposals have tried to make the basis for the ranking and inclusiveness of taxa more transparent and objective, widespread adoption of these ideas has lagged. Here, we present TaxonomR, an interactive online decision-support tool to evaluate alternative taxonomic classifications. This tool implements an approach that quantifies the criteria commonly used in taxonomic treatments and allows the user to interactively manipulate weightings for different criteria to compare scores for taxonomic groupings under those weights. We use the butterfly taxon Argynnis to demonstrate how different weightings applied to common taxonomic criteria result in fundamentally different genus-level classifications that are predominantly used in different continents and geographic regions. These differences are objectively compared and quantified using TaxonomR to evaluate the kinds of criteria that have been emphasized in earlier classifications, and the nature of the support for current alternative taxonomic arrangements. The main role of TaxonomR is to make taxonomic decisions transparent via an explicit prioritization scheme. TaxonomR is not a prescriptive application. Rather, it aims to be a tool for facilitating our understanding of alternative taxonomic classifications that can, in turn, potentially support global harmony in biodiversity assessments through evidence-based discussion and community-wide resolution of historically entrenched taxonomic tensions.

An algorithm is described for the optimization of character data (e.g. qualitative, nucleic acid sequence) on softwired phylogenetic networks. The algorithm presented here is an extension of those developed for trees under the parsimony criterion and can form the basis for phylogenetic network search procedures. Although the problem is (in general) an NP-Hard optimization, the resolution-based algorithm we describe here capitalizes on the significant amount of shared structure in sub-graphs containing network edges, reducing the execution time and allowing for the analysis of empirical datasets.

As it spread through time and into distinct areas of science-from comparative anatomy to evolutionary biology, cladistics, developmental and molecular biology-the homology concept has changed considerably, presenting various meanings. Despite many attempts at developing a comprehensive understanding of the concept, this context-sensitive notion of homology has been a subject of an ongoing debate. Inspired by that and following Kevin de Queiroz and Richard Mayden's view on species concept and delimitation, we presented in this article an attempt to systematize and advance the understanding of the homology problem. Our main goals were: (i) to present a comprehensive checklist of 'concepts of homology'; (ii) to identify which are really concepts with ontological definitions (theoretically rooted in structural correspondence and common ancestry), and which are, in fact, not concepts, but epistemological (empirical and methodological) criteria of homology delimitation; (iii) to provide a synonymy of the concepts and criteria of homology delimitation; (iv) to present a hierarchy of homology concepts within Hennig's hologenetic system; and (v) to endorse the adoption of a unified view of homology by treating homology as a correspondence of spatio-temporal properties (genetic, epigenetic, developmental and positional) at the level of the individual, species or monophyletic group. We found 59 'concepts of homology' in the literature, from which 34 were categorically treated as concepts, 17 as criteria of homology delimitation, Four were excluded from our treatment, and Müller's five concepts were rather treated as approaches to homology. Homology concepts and criteria were synonymized based on structural correspondence, replicability, common ancestry, genetic and epigenetic developmental causes, position and optimization. Regarding the synonymy, we conclusively recognized 21 different concepts of homology, and five empirical and four methodological criteria. Hierarchical ontological aspects of homology were systematized under Hennig's hologenetic system, based on the existence of ontogenetic, tokogenetic and phylogenetic levels of homology. The delimitation of tokogenetic and phylogenetic homologies depends on optimization criteria. The unified view of homology is discussed in the context of the ancestral angiosperm flower.

Figure18 of Hennig's Phylogenetic Systematics (University of Illinois Press, Urbana, IL, 1966) shows a phylogenetic tree (a generative hierarchy) and what appear to be nested sets (an inclusive hierarchy) that he stated were two representations of the same pattern of relationships. This essay questions whether this is correct or not, explores the meanings of different hierarchical patterns, reviews various interpretations of Hennig's figure, and discusses the conceptual path from systematic evidence to phylogenetic explanation. The crux of the argument is that systematic hierarchies as we know them scientifically are nested sets that group theoretical entities based on patterns of synapomorphy. The notions of phylogeny and common ancestry reflect this hierarchical pattern.