William L. Fink

The conceptual relationship between ontogeny and phylogeny

Studies of ontogenetic processes are fundamentally dependent on hypotheses of phylogeny. The model of Alberch et al. (1979) is reformulated in terms of phylogenetics and used to describe how heterochronic ontogenetic processes can be detected in nature. Heterochronic processes producing pae- domorphosis can result in morphologies which resemble primitive (retained ancestral) traits; the conditions under which paedomorphic and primitive features can and cannot be distinguished are described. The utility of ontogeny for determination of evolutionary character transformations and character polarity and for detection of convergence and parallelism are considered. The ontogenetic criterion for assessing polarity is independent of hypotheses of phylogeny and may be as effective as outgroup comparison. Ontogenetic analysis may aid in the detection of convergence but not in the detection of parallelism.

The ontogenetic dynamics of shape disparity

Abstract Disparity appears to decrease or remain stable over geological time in numerous groups. This pattern is sometimes explained in terms of developmental constraints, but labile developmental systems might produce the same pattern should novelties interact, counterbalancing their individual effects. We test the hypothesis that counterbalancing can reduce disparity by comparing ontogenies of shape among nine species of piranhas to identify the developmental novelties. All three parameters examined change multiple times, sometimes dramatically. By comparing levels of disparity between species at two developmental phases, at the transition from larval to juvenile phases, and at maximum adult body size, we find that disparity decreases significantly and substantially over ontogeny. That reduction occurs because of, rather than despite, novelties of postlarval morphogenesis. Some interacting novelties are historically independent and affect different developmental phases, others are historically independent and affect the same developmental phase, and still others are historically correlated and affect either the same or different developmental phases. By modeling hypothetical ontogenies, constraining developmental parameters mathematically to one of the observed values, we find that variation in each parameter, taken by itself, and combinations of them taken two at a time, tend to increase disparity. It is the interactions among all three that reduce disparity. In this group divergent ontogenies transform disparate larvae into similar adults.

Ontogeny and phylogeny of tooth attachment modes in actinopterygian fishes

There are four major tooth attachment modes in actinopterygians. Type 1 mode is characterized by complete ankylosis of the tooth to the attachment bone; it is the primitive attachment mode for actinopterygians. In Type 2 mode there is a ring of collagen between the tooth base and the bone. In Type 3 mode mineralization extends near or to the bone at the anterior tooth border, and there is a relatively large collagen area on the posterior surface of the tooth; Type 3 teeth are hinged with an anterior axis of rotation. Type 4 teeth also have a relatively large posterior collagen area, but there is no collagenous connection between the anterior basal tooth border and the attachment bone; Type 4 teeth are hinged, with a posterior axis of rotation. Types 2, 3, and 4 attachment modes appear to result from retardation of mineralization and resemble, with some modifications, ontogenetic stages in the development of Type 1 mode; they are considered to be paedomorphic features. Attachment modes 2, 3, and 4 are each associated with a major evolutionary lineage within the Teleostei. The degree to which paedomorphosis has been a factor in teleostean evolution is discussed.

Hemoglobin heterogeneity in Amazonian fishes

Abstract 1. The hemoglobin patterns of hemolysates from the lungfish,Lepidosiren paradoxa, four species of freshwater rays (Potamotrygon), and actinopterygian teleosts from 77 genera have been characterized by polyacrylamide disc gel electrophoresis. 2. These tropical fishes have hemolysates which are as complex as those reported from temperate zone fishes. 3. There are no obvious correlations between hemoglobin multiplicity and the fish behaviour or habitat preference. 4.Potamotrygon has blurred hemoglobin patterns,Lepidosiren shows a single hemoglobin, and the other teleosts show a mean of 4.0 hemoglobin bands per phenotype. 5. Ostariophysan fishes have a lower mean number of bands per phenotype than acanthopterygian fishes. 6. Patterns of a single hemoglobin band occurred in 8% of the phenotypes. 7. Two or more hemoglobin phenotypes were found in about 10 species. 8. SDS gel electrophoresis showed the fish hemoglobin chains to have molecular weights comparable to those of human Hb A.

Heterochrony and heterotopy: stability and innovation in the evolution of form

Heterochrony, change in developmental rate and timing, is widely recognized as an agent of evolutionary change. Heterotopy, evolutionary change in spatial patterning of develop- ment, is less widely known or understood. Although Haeckel coined the term as a complement to heterochrony in 1866, few studies have detected heterotopy or even considered the possibility that it might play a role in morphological evolution. We here review the roles of heterochrony and het- erotopy in evolution and discuss how they can be detected. Heterochrony is of interest in part because it can produce novelties constrained along ancestral ontogenies, and hence result in par- allelism between ontogeny and phylogeny. Heterotopy can produce new morphologies along tra- jectories different from those that generated the forms of ancestors. We argue that the study of heterochrony has been bound to an analytical formalism that virtually precludes the recognition of heterotopy, so we provide a new framework for the construction of ontogenetic trajectories and illustrate their analysis in a phylogenetic context. The study of development of form needs tools that capture not only rates of development but the space in which the changes are manifest. The framework outlined here provides tools applicable to both. When appropriate tools are used and the necessary steps are taken, a more comprehensive interpretation of evolutionary change in de- velopment becomes possible. We suspect that there will be very few cases of change solely in de- velopmental rate and timing or change solely in spatial patterning; most ontogenies evolve by changes of spatiotemporal pattern.

SPATIOTEMPORAL REORGANIZATION OF GROWTH RATES IN THE EVOLUTION OF ONTOGENY

Abstract. 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.

Allometry and developmental integration of body growth in a piranha, Pygocentrus nattereri (Teleostei: Ostariophysi)

Piranhas, like many teleosts, change their diets on both ontogenetic and phylogenetic time scales. Prior studies have suggested that pervasive morphological changes in body form on a phylogenetic time scale may be related to changes in diet, but previous reports have found little shape change in piranhas on an ontogenetic time scale. We re‐examine the post‐transformational allometry of body form in one piranha, Pygocentrus nattereri (Kner), using the method of thin‐plate splines decomposed by their partial warps. We find substantial evidence of allometry, primarily elongation of the mid‐body relative to the more anterior and posterior regions, elongation of the postorbital and nape regions relative to the more anterior head and posterior body, and deepening of the head relative to the body. In addition to these pervasive changes throughout the body, there are some that are more localized, especially elongation of the postorbital region relative to eye diameter and snout, and an even more localized elongation of the snout relative to eye diameter. Initial dietary transitions are associated with changes in head and jaw proportions, but rates of shape change decelerate through growth, so that the final transition to a diet increasingly dominated by small whole fish appears associated with change largely in overall body size.

Microcomputers and Phylogenetic Analysis

The programs discussed above show how microcomputers have added to the arsenal of systematic biologists. This is a rapidly developing field, and there are no doubt major changes on the horizon. Swofford is working on a new version of PAUP that will have some of the interactive features of MacClade (and will not require a math coprocessor) and there are efforts under way to make PAUP available on Macintosh. PHYLIP has undergone a steady evolution since its release, and Felsenstein has plans to continue that policy. A microcomputer descendant of the large mainframe program PHYSYS, authored by James S. Farris, is supposed to be forthcoming before the end of the year. Just as this review was being completed, J. Rohlf and R. Sokal of the State University of New York at Stony Brook unveiled a beta-test microcomputer version of their phenetic program package, NT-SYS. Inasmuch as it was not in release form and does not include algorithms specifically designed to do phylogenetic analysis, it has not been included here (although some phenetic techniques, such as UPGMA, produce results similar to parsimony trees under certain assumptions).

Central amazonia and its fishes

Abstract 1. The Amazon river system is characterized by its great size (it drains an area of about 6.5 million km 2 ), its great depth (to 90 m or more in some places), the flat topography of its drainage basin, the annual cycles of high and low water periods, and the geological structure of the drainage area. 2. The central Amazonian ecosystem is complex and the types of habitat within it are numerous, with broad overlap and intergradation of categories. An especially important factor in the aquatic habitat is water type (“white”, “black” or “clear”), a characteristic which is related to the geological character and the flora of the drainage area. 3. Cyclical changes in water level and associated fluctuations in the availability of oxygen are two factors which exert considerable influence over the biology of central Amazonian fishes. 4. The collection sites of Alpha Helix Phase IV are described briefly. 5. The systematics and evolution of most Amazonian fish groups are poorly known; the inability to identify all fishes examined and lack of well-tested evolutionary hypotheses of relationship on which to base comparisons pose problems for the comparative biologist. 6. A brief survey of general aspects of phylogeny and of the natural history of fishes examined by Phase IV is presented, including, when possible. information about habitat preferences, food and other aspects of the biology of the fishes.

Phylogenetic Analysis and the Detection of Ontogenetic Patterns

Some years ago an article in the journal Nature recounted a discussion which had occurred at a meeting of paleontologists at the British Museum (Halstead, 1978; see also Gardiner et al., 1979). Part of the debate concerned the differing classifications systematists of two schools might propose based on the same evidence about relationships. The schools were the phylogenetic (or cladistic) school and the “evolutionary” school. One discussant rose to claim that given a lungfish, a salmon, and a cow to classify, a phylogeneticist would perform the ridiculous action of grouping the lungfish and the cow together, exclusive of the salmon. A phylogeneticist replied “Yes, I cannot see what is wrong in that” (Halstead, 1978). Such exchanges exemplify some of the arguments that, until recently, were the stock in trade of gatherings concerning comparative biology and systematics. The debate has touched many areas of the biological sciences, from biogeography to developmental biology. What follows is a summary of the assumptions and methods of phylogenetic systematics, and how its practice can elucidate the relationship between ontogeny and phylogeny. I also address the problem of integrating studies of ontogenetic processes such as heterochrony into a modern comparative framework.