Correlated Evolution
In Longshanks, we selected for increased tibia length relative to body mass. However, selection on a single trait often impacts other traits, in part because of pleiotropy in development (i.e., one gene affecting many traits). In this line of research, we study how other parts of Longshanks' body have changed as a correlated response to selection on tibia length.
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Tibia shape changes: By selecting for increased tibia length, the Longshanks tibia (left) has become not only longer, but also more tapered than in controls (right), with a thinner cross-section relative to its length. See Cosman et al 2016 |
Changes in bone properties: Longitudinal growth of the Longshanks tibia is ~15% faster than in controls. This faster growth is associated with reduced spongy bone at the ends of the tibia. (Farooq et al 2017). We have also demonstrated that this increased growth rate is associated with altered mechanical properties of Longshanks' bone, including increased brittleness and rigidity, leading to reduced strength (resistance to fracture) (Cosman et al 2019). We are also currently investigating whether Longshanks' accelerated growth is associated with differences in bone fracture healing properties. |
Correlated changes in other skeletal elements: Selection on relative tibia length in Longshanks has caused other limb bones to increase in length, including those of the forelimb (e.g., the radius), but not to the same extent. It has also changed cranial shape in ways that suggest that the growth plates of the cranial base have increased in size, much like those of the tibia. See Unger et al 2021. |