32.6 Thursday, Jan. 5 Divergence in the functional morphology and feeding kinematics of threespine stickleback MCGEE, M.D.*; WAINWRIGHT, P.C.; Univ. of California, Davis; Univ. of California, Davis email@example.com
Studies of adaptive radiation rarely examine divergence across functional systems. We examined functional morphological divergence between benthic and limnetic threespine stickleback from British Columbia. We measured eleven morphological variables from four functional feeding systems: Suction Index, the opercular four-bar linkage, and the components of the jaw opening lever and the jaw closing lever. These morphological variables were then used to calculate a functional index variable for each the four systems. Benthics exhibit a higher Suction Index and a higher mechanical advantage of jaw opening than limnetics. Limnetic fish exhibit a higher opercular four-bar kinematic transmission coefficient. This functional divergence was driven largely by two components of Suction Index, epaxial height and epaxial width, and the jaw opening inlever. We then performed a principal component analysis separately on the morphological and functional variables. The major source of both functional and morphological variation in the dataset was benthic-limnetic divergence. Benthics and limnetics show strong separation with little overlap in the morphological PCA and no overlap in the functional PCA. To better understand divergence in this system, we filmed benthic and limnetic fish at 500 Hz feeding on cladoceran prey, a resource consumed by both species in the wild. We digitally tracked eleven landmarks which were then used to derive 18 kinematic variables characterizing motion of the head, body and jaws. Benthics and limnetics exhibit divergence in several kinematic traits, with limnetics exhibiting faster ram speed during the strike. Overall, benthics appear to possess morphological and kinematic traits geared towards generating high suction pressures, while limnetics possess morphology and kinematics better adapted to the capture of evasive prey.