Morphological Distance Matrices Research Articles

Shrews (Soricidae, Eulipotyphla) from the Russian Far East and Siberia: Combination and search for congruence of molecular genetic and morphological data

The distance joining (DJ) method has been used to combine morphological and molecular genetic (cytb) data on 19 species of Siberian and Far Eastern shrews. It has been found that morphological distances between the species do not correspond to molecular genetic distances (Mantel’s test, r = 0.336) due to the size component of morphological variation. Data on the relationships between taxa of generic and species levels according to the molecular marker (cytb) are incongruent to those based on morphometric characters of the Soricidae, since the cytb gene is a recorder of neutral mutations, whereas the size of morphological characters is a reflection of adaptive evolution. The correlation between the two types of data has noticeably increased (r = 0.799) after the size component was excluded from the morphological distance matrix. The combination of morphological and molecular distance matrices with subsequent nonmetric two-dimensional scaling and dendrogram construction has provided a basis for conclusions about the generic and sub-generic structure of the family Soricidae, which basically correspond to current views on the taxonomy of this group, and for hypotheses concerning the taxonomic status of S. mirabilis and S. minutissimus.

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

The ability of cranial morphology to reflect population/phylogenetic history, and the degree to which it might be influenced by environmental factors and selection pressures have been widely discussed. Recent consensus views cranial morphology as largely indicative of population history in humans, with some anatomical cranial regions/measurements being more informative on population history, while others being under selection pressure. We test earlier findings using the largest and most diverse cranial dataset available as yet: 7,423 male specimens from 135 geographic human population samples represented by 33 standard craniometric linear measurements. We calculated Mahalanobis D(2) for three datasets: complete cranial dataset; facial measurement dataset; and neurocranial measurement dataset; these morphological distance matrices were then compared to matrices of geographic distances as well as of several climatic variables. Additionally, we calculated Fst values for our cranial measurements and compared the results to the expected Fst values for neutral genetic loci. Our findings support the hypothesis that cranial, and especially neurocranial morphology, is phylogenetically informative, and that aspects of the face and cranium are subject to selection related to climatic factors. The Fst analysis suggest that selection to climate is largely restricted to groups living in extremely cold environments, including Northeast Asia, North America, and Northern Europe, though each of these regions appears to have arrived at their morphology through distinct adaptive pathways.

Microsatellite Markers to Complement Distinctness, Uniformity, Stability Testing of Brassica chinensis (Xiao Baicai) Varieties

Brassica chinensis varieties are mostly consumed as vegetables. In order to assess utility of microsatellite markers for testing distinctness, uniformity and stability of B. chinensis varieties, we used nine polymorphic microsatellite marker loci (with a total of 131 alleles) to evaluate four open pollinated and four hybrid varieties of B. chinensis. Each va- riety was represented by 48 randomly sampled individuals from a population of 150. Morphological evaluations were also conducted to the same samples. Compared with morphological evaluations, the microsatellite analysis provided a higher degree of separation and reflected greater uniformity for the three hybrid varieties by cluster analysis, Principal Coordi- nates Analysis (PCA) and assignment test. Average pair-wise Jaccard similarities and statistical tests by AMOVA (analy- sis of molecular variance) also suggested higher levels of intra-variety uniformity. It was also noted that there was no sig- nificant correlation between the genetic and morphological distance matrices (Mantel test). We conclude that microsatel- lite genotyping can be a valuable tool to complement morphological assessment of Brassica vegetable varieties for dis- tinctiveness and uniformity.

Patterns of phenotypic covariation and correlation in modern humans as viewed from morphological integration.

Proportionality of phenotypic and genetic distance is of crucial importance to adequately focus on population history and structure, and it depends on the proportionality of genetic and phenotypic covariance. Constancy of phenotypic covariances is unlikely without constancy of genetic covariation if the latter is a substantial component of the former. If phenotypic patterns are found to be relatively stable, the most probable explanation is that genetic covariance matrices are also stable. Factors like morphological integration account for such stability. Morphological integration can be studied by analyzing the relationships among morphological traits. We present here a comparison of phenotypic correlation and covariance structure among worldwide human populations. Correlation and covariance matrices between 47 cranial traits were obtained for 28 populations, and compared with design matrices representing functional and developmental constraints. Among-population differences in patterns of correlation and covariation were tested for association with matrices of genetic distances (obtained after an examination of 10 Alu-insertions) and with Mahalanobis distances (computed after craniometrical traits). All matrix correlations were estimated by means of Mantel tests. Results indicate that correlation and covariance structure in our species is stable, and that among-group correlation/covariance similarity is not related to genetic or phenotypic distance. Conversely, genetic and morphological distance matrices were highly correlated. Correlation and covariation patterns were largely associated with functional and developmental factors, which probably account for the stability of covariance patterns.

SEED MORPHOMETRICS AND ADAPTIVE GEOGRAPHIC DIFFERENTIATION.

Adaptive geographic differentiation is documented for seed morphology of 36 populations of Heterosperma pinnatum Cav. (Asteraceae), a seed heteromorphic annual plant in the central highlands of Mexico. Achenes (single-seeded fruits) vary continuously within heads but are classified by shape and position as central, intermediate, or peripheral morphs and as having adhesive awns or not. Here we quantify shape as a principal component score contrasting log length and width of achenes. Heads and their variation among populations are described in terms of maximum, minimum, and range of shape scores; the number of achenes per head; quantitative indices of the abruptness of shape shift; where in the head the most abrupt change in shape occurs; and what achene shapes have awns. First and second principal components of these descriptors summarize 86% of among-population variation in achene and head morphology and correlate strongly with percent central achenes per head (%C) and percent of achenes with awns (%A), respectively. Awns are associated with greater dispersibility and achene shape is correlated with speed of dormancy loss. We hypothesized that dispersal morphology would be associated with vegetation attributes indicative of population ephemerality and that dormancy morphology would be associated with precipitation patterns during the early germination season. Morphological distance matrices were calculated using Euclidean distances among populations in %A and %C. Geographic distances among populations were calculated, as were genetic distances based on isozyme frequencies from 29 bands of six enzymes. Vegetation was classified as open or closed and early spring (germination season) and summer precipitation means were determined for each site. Closed vegetation was assumed to provide only ephemeral habitats for H. pinnatum. Partial matrix correlations between morphology and environment controlled for geographic but not genetic distance among sites, since the latter was not significantly correlated with either morphology or geography. A significant relationship was found between %A and closed vegetation, lower spring, and higher summer precipitation. %C was only correlated with lower spring precipitation. Independence of isozyme and morphological traits is interpreted in terms of selection on the latter but not the former.

Patterns and causes of morphological population differentiation in the Tenerife skink, Chalcides viridanus

Abstract Recent studies indicate that differential selection between mesic and xeric habitats is the most plausible explanation of within-island geographic variation in the Gran Canarian skink, Chalcides sexlineatus . The island of Tenerife shows mesic/xeric heterogeneity similar to that on Gran Canaria, so we tested the prediction of parallel geographic patterns of morphological population differentiation in the Tenerife skink, Chalcides viridanus . Geographic variation was found to be complex; patterns of differentiation in body dimensions and scalation show evidence of both mosaic and latitudinal facets. Using randomization and regression methods, significant relationships were found between a hypothesized xeric/mesic model of population differentiation and geographic variation in female body dimensions, as well as with substantial proportions of the geographic variation in male and female scalation and, to a lesser extent, body dimensions. Matrix comparisons based on the entire morphological distance matrices show that the patterns of variation are not concordant with an alternative hypothesis of historical secondary contact, or with an isolation-by-distance model. It is argued that a substantial component of the geographic variation in body dimensions and scalation of C. viridanus is due to differential selection along an aridity gradient.