Genetic and environmental contributions to variation in baboon cranial morphology

Abstract

The development, function, and integration of morphological characteristics are all hypothesized to influence the utility of traits for phylogenetic reconstruction by affecting the way in which morphological characteristics evolve. We use a baboon model to test the hypotheses about phenotypic and quantitative genetic variation of traits in the cranium that bear on a phenotype’s propensity to evolve. We test the hypotheses that: 1) individual traits in different functionally and developmentally defined regions of the cranium are differentially environmentally, genetically, and phenotypically variable; 2) genetic covariance with other traits constrains traits in one region of the cranium more than those in others; 3) and regions of the cranium subject to different levels of mechanical strain differ in the magnitude of variation in individual traits. We find that the levels of environmental and genetic variation in individual traits are randomly distributed across regions of the cranium rather than being structured by developmental origin or degree of exposure to strain. Individual traits in the cranial vault tend to be more constrained by covariance with other traits than those in other regions. Traits in regions subject to high degrees of strain during mastication are not any more variable at any level than other traits. If these results are generalizable to other populations, they indicate that there is no reason to suppose that individual traits from any one part of the cranium are intrinsically less useful for reconstructing patterns of evolution than those from any other part.

The relative correspondence of cranial and genetic distances in papionin taxa and the impact of allometric adjustments

“…ranging from r = 0.35 to 0.86), suggesting that, in general, the correlation between cranial distances and genetic distances is stronger in hominoids than in papionins. This result is also consistent with the findings of Roseman et al (2010) who found no differences in the heritability or conditional evolvability of different cranial regions in a captive population of baboons. This suggests that there may be few differences across the papionin cranium in terms of phylogenetic efficacy, with all regions being equally useful (or problematic) when attempting to reconstruct phylogenetic relatedness across taxa.…”

“…In guenons, the morphology of several masticatory regions, the mandible, oral cavity, and zygomatic region, all yielded morphological matrices significantly correlated with genetic distances among taxa, but the non-masticatory chondrocranium did so with a higher correlation coefficient (Cardini and Elton, 2008). Therefore, despite the intuitive link between masticatory strain, plasticity, and homoplasy, the relationship between these factors is complex, and this phenomenon does not necessarily negatively affect the correspondence between cranial morphology and genetic patterns (von Cramon-Taubadel, 2009b;Roseman et al, 2010).…”

“…Recently, a quantitative genetic study of captive baboons found no significant differences in heritability across traits from different cranial regions (Roseman et al, 2010), suggesting that there is no a priori reason to suspect that cranial regions will perform differently in terms of their phylogenetic efficacy. Moreover, and in contrast with previous studies of wild papionin taxa (e.g., Lycett and Collard, 2005), they find no disparity in intrinsic phenotypic variation among cranial traits that could be attributable to differences in either additive genetic or environmental variation.…”

“…Nevertheless, empirical studies of wild primates from across a range of taxa have demonstrated differences in terms of both phenotypic variability and phylogenetic efficacy of different craniomandibular and dental traits (see von Cramon-Taubadel, 2014 for review), even if heritability, phenotypic variability, and phylogenetic efficacy are not evidently causally related (von Cramon-Taubadel, 2009b;Roseman et al, 2010).…”

“…One misconception that lies at the heart of hypotheses regarding homoplasy is the assumption that morphological traits with higher heritability will be more "reliable" for reconstructing phylogeny due to the notion that such traits reflect underlying genetic information more accurately and are less influenced by the environment (i.e., will be less plastic). These misconceptions have been discussed at length previously (von Cramon-Taubadel, 2009b;Roseman et al, 2010) and the problem lies with a general misunderstanding of how additive genetic variance and environmental variance combine and interact to produce observable phenotypic variance. Moreover, while the response to selection of a single quantitative trait is directly related to its heritability (i.e., the proportion of phenotypic variance due to underlying additive genetic variance), the relationship between heritability and the propensity for a multivariate morphological structure to respond to selection is more complex.…”