The Origin of Morphological Characters and the Biological Basis of Homology

Abstract

Abstract, -A homolog is a part of the phenotype that is homologous to equivalent parts in other species. A biological homology concept is expected to explain three properties of homologs: I) the conservation of those features that are used to define a homolog, 2) the individualization of the homolog with regard to the rest ofthe body, and 3) the uniqueness of homologs, i.e., their specificity for monophyletic groups. The main obstacle to describing a mechanistic basis for homology is the variability of the developmental pathways of undoubtedly homologous characters. However, not all aspects of the developmental pathway are ofequal importance. The only organizational features of the developmental system that matter are those that have been historically acquired and cause developmental constraints on the further evolutionary modification of the characters. Two main factors contribute to historically acquired developmental constraints: generative rules of pattern formation and ontogenetic networks. In particular, hierarchical and cyclical inductive networks have the required properties to explain homology. How common such networks are is an open empirical question. The development and variation of pectoral fin hooks in blenniid fishes is presented as a model for the study of a simple ontogenetic network.

Taxonomic revision and phylogenetic hypothesis for the jumping spider subfamily Ballinae (Araneae, Salticidae)

“…M. longicauda is the only species known from both sexes. Judging from illustrations of male genitalia in Proszynski (2003) and Cutler & Wanless (1973: figs 5–7) they are probably correctly placed in Ballinae. Their genitalia show Ballinae synapomorphies: presence of ec and a terminally coiled embolus.…”

“…The same can be said for Padilla , a genus of seven species, all from Madagascar. Judging from illustrations in Proszynski (2003) they may be included in Ballinae, as male genitalia show Ballinae synapomorphies: presence of ec ( 2‐1 ) and spiralling embolus ( 4‐1 ). Unfortunately, drawings are only available for P. armata Peckham & Peckham, 1894, and P. cornuta (Peckham & Peckham, 1885).…”

“…They need to be confirmed by congruence with other characters (Patterson, 1982; Brooks & McLennan, 1991; de Pinna, 1991; Wenzel, 1992). The consideration of characters as operationally equivalent to putative synapomorphies enables the discovery of common patterns among taxa (de Pinna, 1991; but see Wagner, 1989a, b and references therein, for a different opinion). Codings were checked against as many species as possible for each genus.…”

The Phylogenetic Significance of Anthropoid Paranasal Sinuses

“…How can this be avoided? Ideally, the criterion for delimiting character states would be Wagner's (1989a, b) criterion for identifying “individualized” structures or potential homologs, which are, after all, character states. On this basis, most sinuses would be coded as simply present or absent, although the various forms of the cupular sinus would warrant some subdivision, not simply because they differ in their final adult form, but rather because they appear to be produced by a second set of diverticula that, although in direct continuity with the cupular sinus proper, possesses a morphogenetic potential of their own.…”

Behavioural evolution in penguins does not reflect phylogeny

“…Thus a major challenge for those who championed use of behavioural characters was to demonstrate the homology of behavioural characters. Only characters that have arisen once can be considered to be homologous (Wagner, ), that is, traits are shared due to common ancestry (Nixon and Carpenter, ). As suggested by Japyassu and Machado (), and following Brower and Schawaroch (), assigning behavioural homology is a three‐stage process where comparable features are discovered among taxa, then character variability is partitioned into subunits.…”