Mosaic evolution

Abstract: The mammalian brain comprises a number of functionally distinct systems. It might therefore be expected that natural selection on particular behavioural capacities would have caused size changes selectively, in the systems mediating those capacities. It has been claimed, however, that developmental constraints limited such mosaic evolution, causing co-ordinated size change among individual brain components. Here we analyse comparative data to demonstrate that mosaic change has been an important factor in brain structure evolution. First, the neocortex shows about a fivefold difference in volume between primates and insectivores even after accounting for its scaling relationship with the rest of the brain. Second, brain structures with major anatomical and functional links evolved together independently of evolutionary change in other structures. This is true at the level of both basic brain subdivisions and more fine-grained functional systems. Hence, brain evolution in these groups involved complex relationships among individual brain components.

Abstract: Mickevich, M. F., and M. S. Johnson (Ceutre de Recherches Mathe6matiques, Universit' de Montr6al, Montreal, P.Q., Canada and Department of Ecology and Evolution, State University of New York, Stony Brook, N. Y. 11794) 1976. Congruence between morphological and allozyme data in evolutionary inference and character evolution. Syst. Zool. 25:260-270. -In view of the growing concern that evolutionary information obtained from morphological data may differ in content from evolutionary information from molecular data, we have asked whether morphological data yield phyletic interpretations consistent with those inferred from allozymes. Minimum length Wagner trees were calculated from sets of morphometric and allozyme data on sixteen populations representing five nominal species of Menidia (Teleostel, Atherinidae). The two sets of characters yield nearly perfectly congruent evolutionary trees, despite the fact that phenetic analyses reveal very great disparity between the similarity structures of the morphometrics and the allozymes. A quantitative method for estimating convergence and parallelism was developed and revealed no significant differences in the proportions of these types of homoplasy for the two data sets. This cladistical method for estimating convergence is contrasted with partially phenetic methods used in the past; the later are shown to be incorrect. Mosaic evolution between morphometrics and allozymes is demonstrated statistically, and shown to result from heterogeneous rates of apomorphy, rather than from a preponderance of plesiomorphy in one data set. This mosaicism is the probable source of the large phenetic disparity. We conclude that 1) cladistical, rather than phenetic, methods are required for the analysis of character evolution, and 2) that the ease of obtaining sufficient information, rather than presumed inherent differences between characters, should determine which characters are used for evolutionary taxonomic inference. [Cladistical character analysis; taxonomic congruence; morphometrics; allozymes; Menidia.] During the past decade, studies of proteins have had an increasingly important influence on evolutionary biology and systematics. An important question arising from these studies is whether molecular characters are evolutionarily concordant with anatomical characters. The impression of some authors has been that proteins and morphological characters have evolved concordantly (summaries in Lewontin, 1974; Avise, 1974). Recently, however, several studies have indicated a high degree of evolutionary independence of molecular and morphological evolution (Turner, 1974; Gould et al., 1974; Maxson and Wilson, 1974, 1975; Johnson, 1974, 1975; Avise et al., 1975; King and Wilson, 1975; Kornfield and Koehn, 1975; Johnson et al., 1976). These 1Present address: Department of Zoology, University of Western Australia, Nedlands, Western Australia 6009. examples of disparity add to the already substantial evidence against the non-specificity hypothesis (Rohlf, 1965; Sneath and Sokal, 1973). It is not clear from such studies, however, whether there are differences between proteins and morphological characters in their reliability as indicators of evolutionary relationships, because characters which are completely independent genetically, and highly disparate in their rates of divergence, may be perfectly concordant in their indications of phylogenies. In other words, phenetically disparate characters may show taxonomic congruence (Farris, 1971). Either explicitly or implicitly, the suggestion has been made that molecular data are more reliable as phyletic indicators than are morphological data (Anonymous, 1974; Avise, 1974; Maxson and Wilson, 1974, 1975; Nei, 1975). However, to answer the

Abstract: Considerations of Homology and the Visual System.- Some Questions and Problems Related to Homology.- Reconstructing the Evolution of the Brain in Primates through the Use of Comparative Neurophysiological and Neuroanatomical Data.- Allometric Considerations.- Some Cautionary Notes on Making Inferences about Relative Brain Size.- Allometric Approaches to the Evolution of the Primate Nervous System.- The Relativity of Relative Brain Measures and Hominid Mosaic Evolution.- Allometry, Brain Size, Cortical Surface, and Convolutedness.- Ontogenetic Perspectives.- Encephalization and Obstetrics in Primates with Particular Reference to Human Evolution.- The Role of Brain Maturation in the Evolution of the Primates.- The Development of the Primate Pulvinar.- Approaches from Cytoarchitectonics.- Mosaic Evolution in the Primate Brain: Differences and Similarities in the Hominid Thalamus.- Brain Organization and Taxonomic Relationships in Insectivora and Primates.- Quantitative Cytoarchitectonics of the Cerebral Cortices of Several Prosimian Species.- Role of Architectonics and Connections in the Study of Primate Brain Evolution.- A Paleoneurological Perspective.- Mapping Fossil Endocasts.- Early Primate Brain Evolution.- A Study of Cerebral Vascular Evolution in Primates.- Asymmetries of the Brains and Skulls of Nonhuman Primates.- Theoretical Overviews.- Neurobiological Aspects in the Phylogenetic Acquisition of Speech.- On the Origin and Progressive Evolution of the Triune Brain.- List of Contributors.- Author Index.

Abstract: Mosaic evolution, which results from multiple influences shaping morphological traits and can lead to the presence of a mixture of ancestral and derived characteristics, has been frequently invoked in describing evolutionary patterns in birds. Mosaicism implies the hierarchical organization of organismal traits into semiautonomous subsets, or modules, which reflect differential genetic and developmental origins. Here, we analyze mosaic evolution in the avian skull using high-dimensional 3D surface morphometric data across a broad phylogenetic sample encompassing nearly all extant families. We find that the avian cranium is highly modular, consisting of seven independently evolving anatomical regions. The face and cranial vault evolve faster than other regions, showing several bursts of rapid evolution. Other modules evolve more slowly following an early burst. Both the evolutionary rate and disparity of skull modules are associated with their developmental origin, with regions derived from the anterior mandibular-stream cranial neural crest or from multiple embryonic cell populations evolving most quickly and into a greater variety of forms. Strong integration of traits is also associated with low evolutionary rate and low disparity. Individual clades are characterized by disparate evolutionary rates among cranial regions. For example, Psittaciformes (parrots) exhibit high evolutionary rates throughout the skull, but their close relatives, Falconiformes, exhibit rapid evolution in only the rostrum. Our dense sampling of cranial shape variation demonstrates that the bird skull has evolved in a mosaic fashion reflecting the developmental origins of cranial regions, with a semi-independent tempo and mode of evolution across phenotypic modules facilitating this hyperdiverse evolutionary radiation.