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W L Fink

Publications and source records attributed to W L Fink.

5 recordsLinked to original sources
PubMed2000

Spatiotemporal reorganization of growth rates in the evolution of ontogeny.

Heterochrony, evolutionary changes in rate or timing of development producing parallelism between ontogeny and phylogeny, is viewed as the most common type of evolutionary change in development. Alternative hypotheses such as heterotopy, evolutionary change in the spatial patterning of development, are rarely entertained. We examine the evidence for heterochrony and heterotopy in the evolution of body shape in two clades of piranhas. One of these is the sole case of heterochrony previously reported in the group; the others were previously interpreted as cases of heterotopy. To compare ontogenies of shape, we computed ontogenetic trajectories of shape by multivariate regression of geometric shape variables (i.e., partial warp scores and shape coordinates) on centroid size. Rates of development relative to developmental age and angles between the trajectories were compared statistically. We found a significant difference in developmental rate between species of Serrasalmus, suggesting that heterochrony is a partial explanation for the evolution of body shape, but we also found a significant difference between their ontogenetic transformations; the direction of the difference between them suggests that heterotopy also plays a role in this group. In Pygocentrus we found no difference in developmental rate among species, but we did find a difference in the ontogenies, suggesting that heterotopy, but not heterochrony, is the developmental basis for shape diversification in this group. The prevalence of heterotopy as a source of evolutionary novelty remains largely unexplored and will not become clear until the search for developmental explanations looks beyond heterochrony.

Animals↗
PubMed1998

Why morphometrics is not special: coding quantitative data for phylogenetic analysis.

Thorpe (1984) and Chappill (1989) argued that selection of a coding method should be [figure: see text] based on the purpose of coding. In our view, the purpose of coding is dictated by the principles of phylogenetic systematics. The foundation of phylogenetic systematics is the observation that monophyletic groups can be recognized if homologous character states, shared evolutionary novelties, can be identified (Hennig, 1966). Unfortunately, characters do not have labels indicating their homology. Instead, a systematist must propose a hypothesis of homology and evaluate its congruence with independent hypotheses based on other traits. In this context, the purpose of coding is to represent those hypotheses. The major obstacle to coding is that the a priori groups under analysis (i.e., taxa) often have ranges of variation that overlap to some degree. This is true whether traits are described qualitatively or quantitatively. One advantage of quantitative description is that it permits a more detailed analysis of how much the ranges of variation overlap. It may seem appropriate to use statistical methods to summarize the amount of overlap and even to decide objectively (on a priori grounds) whether taxa are similar or different. Above, we demonstrated some of the problems resulting from these uses of statistical analysis. In our view, the most important problem is the implication that similarity of the feature across taxa is the basis for inferring homology. The similarity that is relevant to phylogenetic analysis is not proximity in morphospace, but shared novelty. Statistical methods can describe proximity, but they cannot recognize novelty. The method of coding we recommend uses graphical displays of individual values. Coding decisions are based on all of the individuals in each taxon, not on summaries derived from models of expected distributions. Then, the evidence for inferring divergence is independently evaluated for each pair of overlapping taxa. Coding decisions are not based on a priori rules that have no bearing on recognition of evolutionary novelty. This is the same approach that is used to code qualitatively described traits.

Animals↗