Morphological Evolution in Muroid Rodents I. Conservative Patterns of Craniometric Covariance and Their Ontogenetic Basis in the Neotropical Genus Zygodontomys

Abstract

Analyses of craniodental measurement data from 15 wild-collected population samples of the Neotropical muroid rodent genus Zygodontomys reveal consistent patterns of relative variability and correlation that suggest a common latent structure. Eigenanalysis of each sample covariance matrix of logarithms yields a first principal component that accounts for a large fraction of the total variance. Variances of subsequent sample principal components are much smaller, and the results of bootstrap resampling together with asymptotic statistics suggest that characteristic roots of the covariance matrix after the first are seldom distinct. The coefficients of normalized first principal components are strikingly similar from sample to sample: inner products of these vectors reveal an average between-sample correlation of 0.989, and the mean angle of divergence is only about eight degrees. Since first principal component coefficients identify the same contrasts among variables as comparisons of relative variability and correlation, we conclude that a single factor accounts for most of the common latent determination of these sample dispersions. Analyses of variance based on toothwear (a coarse index of age) and sex in the wild-collected samples, and on known age and sex in a captive-bred population, reveal that specimen scores on sample first principal components are age- and sex-dependent; residual sample dispersion, however, is essentially unaffected by age, sex, or age × sex interaction. The sample first principal component therefore reflects the covariance among measured dimensions induced by general growth, and its coefficients are interpretable as exponents of postnatal growth allometry. Path-analytic models that incorporate prior knowledge of the equivalent allometric effects of general growth within these samples can be used to decompose the between-sample variance by factors corresponding to other ontogenetic mechanisms of form change. The genetic or environmental determinants of differences in sample mean phenotypes induced by such mechanisms, however, can be demonstrated only by experiment.

The Evolution of Sexual Dimorphism in the House Finch. I. Population Divergence in Morphological Covariance Structure

“…Decoupling of bill and body trait evolution in finches may be enabled by differential phenotypic and genetic patterns of growth between these groups of traits (Boag 1984;Bjö rklund 1993;Badyaev and Martin 2000b). Contrary to other studies (Johnston 1973;Voss et al 1990;Bjö rklund 1993Bjö rklund , 1994Bjö rklund , 1996Bjö rklund and Merilä 1993;Badyaev 1997), we found that most of the recent morphological divergence in the house finch involved small and relatively independent changes in individual traits (Table 3) and not changes in general size (e.g., eigenvectors I and II in Table 4). However, this result may be expected for traits with initially low integration (e.g., feather traits and body mass).…”

A new species of the rodent genus Hylomyscus from Angola, with a distributional summary of the H. anselli species group (Muridae: Murinae: Praomyini)

“…Directly pertinent to our taxonomic subject is the recent study by Demos et al (2014b), whose gene-sequencing results have supported the specific recognition of two members of the H. anselli group, H. anselli and H. arcimontensis as defined by Carleton & Stanley (2005), and justified the description of a third, H. kerbispeterhansi, from the Kenyan Highlands. Such findings reinforce the thesis developed by Voss and colleagues (Voss et al, 1990;Voss & Marcus, 1992), who demonstrated that covariation patterns commonly distilled from ordination of muroid craniodental measurements relate to underlying ontogenetic trajectories that account for such conserved patterns of size and shape and, by inference, to pronounced genetic divergence between the sampled populations. Of course, independent genetic evaluation of the specific status and relationship of H. heinrichorum is highly welcomed.…”

A Systematic Review of SulawesiBunomys(Muridae, Murinae) with the Description of Two New Species

“…Compared with samples from the westcentral mountain block, that from Pegunungan Mekongga differs by its average shorter and narrower skull, shorter basicranium, smaller bullae, and shorter molar row as reflected in the tables of summary statistics In an ordination bounded by first and second principal components, the usual pattern of scores representing two morphologically closely related but different species consists of two slightly overlapping and obliquely oriented elliptical clouds in which the major axes (regression lines) of the spreads are phenetically discrete-the regression lines of the second principal component on the first are clearly separate and their Yintercepts are significantly different between the two species (see Voss et al, 1990;Voss and Marcus, 1992). This is the pattern illustrated in the principal components ordination comparing samples of B. chrysocomus with the morphologically similar B. coelestis (fig.…”