Congruence of molecules and morphology using a narrow allometric approach

Abstract

There are many cases of incongruence between phylogenetic hypotheses produced from morphological data and those produced from molecular data. In such instances, many researchers prefer to accept the results of molecular phylogenies. For example, in a recent analysis of primate phylogenies based on craniodental characters, Collard and Wood [Collard M, Wood BA (2000) Proc Natl Acad Sci USA 97:5003-5006] argued that, because craniodental data do not yield relationships concordant with molecular studies, the results of studies that employ such characters must be considered suspect. As most of our knowledge of mammalian evolution and phylogenetic history comes from craniodental fossils, these results have dramatic implications. However, the aforementioned analysis did not take into account the potentially confounding effects of allometry on quantitative craniodental characters. In this article, we employ a previously undescribed narrow allometric coding method that accounts for such confounding influences in phylogenetic analyses of craniodental morphology. By using essentially the same raw data set as Collard and Wood [Collard M, Wood BA (2000) Proc Natl Acad Sci USA 97:5003-5006], 65 quantitative craniodental characters were adjusted in a parsimony analysis for the primate tribe Papionini, a group of monkeys argued to display extensive homoplasy. The resulting phylogenetic tree was congruent with the phylogenetic tree based on molecular data for these species, thereby meeting the "criterion of congruence." These results suggest that morphological data, when treated properly, can be considered as reliable as molecular data in phylogenetic reconstruction. Rather than accepting phylogenetic hypotheses from one data source over another, cases of incongruence should be examined with greater scrutiny.

Fig. 1.

Heuristic comparison of narrow allometric coding and conventional coding of size-adjusted data for hypothetical character “relative snout length.” The study group exhibits positive allometry for the character relative snout length, and taxa within the group fall into two basic size groups, small and large. The black lines represent ranges of relative snout length within each size group. Conventional conversion of craniometric data into phylogenetic characters (depicted in dashed lines and numbers on the y axis) would divide the entire range of relative snout lengths (the y axis) into segments horizontally, in this case producing five states. Our method of narrow allometric coding (depicted by diagonally arranged numbers marked with a prime) performs the same segmenting procedure but applies it to the two size groups separately such that the shortest-snouted species in each group are coded as “short,” and the longest-snouted species in each group are coded as “long.”

Fig. 2.

Previous hypotheses of papionin phylogenetic relationships. (a) Hypothesized phylogenetic tree of the extant Papionini from molecular (mtDNA and Y chromosome) data (–74) compared with b, the most parsimonious tree derived from the craniodental data set of Collard and Wood (25, 26), using Macaca rather than Pan as the outgroup.

Fig. 3.

Most parsimonious phylogenetic tree of the extant Papionini from craniodental morphological data in the mixed-sex analysis. Note that this tree is congruent with the hypothesized phylogenetic tree for the extant papionins from molecular data in Fig. 2a.

Fig. 4.

Most parsimonious phylogenetic trees of the extant Papionini from craniodental data in the male analysis (a) and from craniodental data in the female analysis (b).