The bearings of genetic correlation on the independent evolution of body mass and skeletal dimensions in mammals

Date Published: December 2, 2014

Source: BMC Evolutionary Biology

Summary: Mice were selectively bred to test the hypothesis that a genetic correlation with body and mass compels evolutionary change in the tibia length of mammals. The results of the test showed that the rate of independent evolution of tibia length is hindered by its correlation with body mass (and vice versa).

Mammals typically display a scaling relationship between limb bone size and body mass.

The scaling of limb bone dimensions with body mass ensures proper musculoskeletal function, prevents bones from failing under increased strain from gravity or motion, and serve many other crucial purposes. The correlation between body mass and limb bone dimensions is so significant, in fact, that any major mismatches between the two traits in a populations can have negative impacts on the ability of a mammal to survive (thus, they should be selected against). The exact reason for how the genetic correlation between these two traits impacts a mammal’s ability to evolve independently remains unclear.

The focus of this study was to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length. Researchers at the University of Calgary in Calgary selectively bred 14 generations of laboratory mice (which came to be known as the Longshanks line) and looked for increases in tibia length independent of body mass.

The results of the experiment showed that tibia length can change quickly and independently from body mass. The quantitative genetic analyses of the test showed that phenotypic correlations were around 0.52, while genetic correlations were 0.4-0.48. In other words, roughly 20% of the genetic variation in tibia length is tied to variation in body mass (the rest of the genetic variance in tibia length evolves independently of body mass). This explains why it responded relatively rapidly to selection and why, over the 14 generations, the mean tibia length increased by 9-13%, while mean body mass remained the same.

This artificial selection experiment exhibited the impact of genetic correlations on the independent evolution of body mass and skeletal size in a mammals. It showed that the independent changes in these complex traits are possible and quick. The results further suggested that the frequent and convergent evolution of relatively longer hind limbs among rodents may also have happened at a quick pace on a geological timescale (possibly due to adaptive radiations, niche partitioning in heterogeneous environments, etc.). Moreover, the simulated evolution indicated that this independent evolution is to some extent compelled by a genetic correlation (which most likely evolved due to natural selection).

Specifically, the experiment displayed that the rate of the independent evolution of tibia length is largely impeded by its correlation with body mass (and vice versa).

Citation:

Marchini, M., Sparrow L. M., Cosman, M. N., Dowhanik, A., Krueger, C. B., Hallgrimsson B., and Rolian, C. 2014. Impacts of genetic correlation on the independent evolution of body mass and skeletal size in mammals. BMC Evolutionary Biology 2014, 14:258 doi:10.1186/s12862-014-0258-0.