A paper I collaborated on with Christopher Martinez on Malawi and Tanganyikan cichlid kinematics was recently published in Evolution. This paper builds upon a kinematic dataset and paper I worked on that you can find more information about on my site here. Most fish (including cichlids) can be categorized as either suction feeders or biters. Suction feeders by protruding their jaws, depressing their hyoid bone, and abducting the operculum (gill plate) generate a suction force to suck their prey into their mouth. Biters directly contact and forcefully remove the prey with their jaws.
In this paper, we track how the feeding apparatus changes during a feeding event mapping its morphology (see below photo) and investigated how it relates to exploiting functionally different prey. The linearity of the mapped trajectory can then be used to assess how efficient the strike is, with a more linear strike being more efficient.
The above depicts how the craniofacial (head and face) morphology of Lamprologus lemairii, a fish and crustacean predator that employs suction feeding to capture prey, changes throughout prey capture. The figure shows how we tracked kinesis and the overall trajectory as the head moves from the beginning (teal dot) of a feeding event to the maximum expansion of the jaws during a feeding event (red dot). Light blue dots are individual morphological landmarks tracked throughout the strike while the yellow dots are along a curve tracked throughout the strike. Dark blue dots and associated photos show how these landmarks move at roughly evenly spaced out intervals throughout the strike. The dotted line depicts the overall kinematic trajectory.
We find that fish that feed on evasive prey items, fish that typically employ suction feeding to capture prey, have more cranial kinesis during a strike, as the jaws protrude to aid in generating suction force (see the below photo). While the jaws and other aspects of the head do undergo a vast amount of kinesis during feeding, we find that they have much more kinematically efficient (i.e. more linear) than species that employ biting (algae, sponge, mollusk feeders, etc.) and have far less jaw kinesis. Our study highlights underappreciated aspect of jaw protrusion, how it aids in kinematic efficiency, which may help in understanding the origins and diversity of jaw morphology in ray-finned fishes.
Phylogeny of Lake Malawi and Tanganyikan cichlids depicting the diet of species, the amount of cranial kinesis, and with representative photos showing how morphology changes during feeding. Branch colors of the phylogeny depict the amount of cranial kinesis, with species on cooler colored branches having more cranial kinesis and species on warmer colored branches having less cranial kinesis. Colored dots next to species names represent one of the six diet classifications used to categorize species (i.e. fish, zoobenthos, aufwuchs, etc.). From the various pictures of fish heads, it is easy to see that species that feed on more evasive prey items (fish, zoobenthos 2 (which includes shrimps) have more cranial kinesis than species that employ biting to feed on non-evasive prey items (aufwuchs, zoobenthos 1 (which includes snails and bivalves).
The citation and link to the paper:
Martinez CM, McGee MD, Borstein SR, and Wainwright PC. 2018. Feeding ecology underlies the evolution of cichlid jaw mobility. Evolution.