Collaborator: John S. Sparks (AMNH)
For biomechanical systems consisting of multiple parts, different morphological configurations can often achieve the same functional output. This is known as many-to-one mapping (MTOM) of form to function and it has potential to influence the distribution and nature of morphological diversification within clades. In cichlids, and many other ancanthomorph fishes, the mechanics of the anterior jaw can be modeled with a fourbar linkage (Fig. 1-left), which has been shown to display MTOM with respect to a functional output, maxillary kinematic transmission (MKT).
For this project, we evaluated evolutionary relationships between body shape (Fig. 2) and jaw functional morphology (Fig. 1) in two subfamilies of endemic Malagasy cichlid, Etroplinae and Ptychochrominae. We were interested in testing whether the ability of jaws to vary in morphology but not function (i.e., exhibit MTOM) would influence the relationships between cranial and post cranial components of the body plan.
We found that the two subfamilies used different strategies to mitigate impacts of body shape variation on MKT. Ptychochromines displayed modularity, or a level of evolutionary independence, between cranial and post cranial morphologies. In contrast, etroplines maintained a strong relationship between body and jaw shapes (i.e., integration), with jaw morphologies varying in a manner that limited change in MKT (Fig 3.). This research showed that, unlike modularity, MTOM can allow traits to retain strong evolutionary covariation while still reducing impacts on functionality. These results suggest that MTOM, and its influence on the evolution of correlated traits, is likely much more widespread than is currently understood.
Martinez CM & Sparks JS. 2017. Malagasy cichlids differentially limit impacts of body shape evolution on oral jaw functional morphology. Evolution.71(9), 2219-2229.
Martinez CM, Arroyave J & Sparks JS. 2015. A new species of Ptychochromis from southeastern Madagascar (Teleostei: Cichlidae). Zootaxa. 4044, 79-92.
Gerstner Scholarship & Lerner Gray Postdoctoral Fellowship (AMNH)
NSF grants, IOS-0749943 and DEB-1257555 (awarded to JSS)