MORPHOMETRIC CORRELATION PATTERNS OF ADULT BIRDS (FRINGILLIDAE: PASSERIFORMES AND COLUMBIFORMES) MIRROR THE EXPRESSION OF DEVELOPMENTAL CONTROL GENES.

Abstract

Stimulated by the rapid progress in developmental genetics, recent approaches to evolutionary theory focus on the interface function of developmental processes in the study of genotype-phenotype mapping. From this viewpoint, the main result of the present analysis is that the expression patterns of developmental control genes are reflected in the infraspecific correlation patterns of phenotypic characters in the adult stage. The study is based on 42 logarithmically scaled skeletal measurements of two avian clades, finches (43 species, n = 313) and pigeons (27 species, n = 219). First, for each clade an "observed correlation matrix" was calculated by computing a bias-reduced pooled-species correlation matrix based on the clade-specific pooled within-species variance-covariance matrix between measurements. Second, the expression domains of diverse developmental control genes, that is, Hox, Msx, Pax, Mhox, Shh, Bmp, and Gdf, in characters were represented by "theoretical matrices." Finally, the observed and the theoretical matrices were compared by Mantel's test to test hypotheses about pattern similarities between phenotypic correlations and the expression of developmental control genes. Seventeen percent of the single matrix comparisons revealed significant (P ≤ 0.05) pattern correspondences in finches, whereas 63% were significant in pigeons. The multiple comparisons revealed correspondences at the highest significance level (P ≤ 0.001) in both clades and disclosed that 15% of the observed matrix patterns are explained in finches versus 22% in pigeons. Presumably, as finches have less pronounced correspondences between gene expression and phenotypic correlation, they are more derived than pigeons. Out of the significant single matrix comparisons, four correspondences are common to both clades: one of them is connected with the Gdf gene expression concerning limb length relations and also harmonizes with the dominant pattern within the infraspecific correlation matrices. The general implication is that the significant correspondences detected here between observed and theoretical matrices are based on a correspondence between phenotypic and genetic modules. Because the phenotypic modules are potential candidates for a direct impact of selection, the important role of genotype-phenotype mapping in molding the body plan becomes apparent.