Research conducted at ELVER is focused on understanding morphological, physiological, and behavioral evolution. We have a special interest in studying the mechanisms guiding diversification in vertebrate clades whose members have evolved an elongate and limb-reduced (or complete loss) body plan such as snakes, anguilliform fishes, and other eel-like vertebrates.
When attempting to understand the evolution
of diversity in disparate vertebrate groups, I consider the functional interaction
between body plan and feeding behavior. Why I study feeding is pretty self-explanatory.
All organisms need to consume food to survive and some of the most fascinating
behavioral innovations have evolved for organisms to do just that-feed. Some
of the more awesome behaviors are tied to modifications of the hyobranchial
complex such as the ballistic tongue of bolitoglossine salamanders and chameleons
and moray eel pharyngeal jaws (see below). But why the elongate limb-reduce
body plan? This body plan has evolved multiple times across disparate vertebrate
groups and it poses many challenges related to feeding. These challenges include
an increase in surface area-to-volume ratio, a relatively small mouth that
must sustain a long mass, and no limbs or extremely reduced limbs so food
manipulation is challenging. My interests lie in documenting how these vertebrate
groups cope with these morphological and physiological challenges and understanding
what kinds of advantages these organisms my confer (physiologically or behaviorally)
from elongating their body and reducing their limbs.
Mehta Lab Research
Morphological and Functional Innovation: Raptorial jaws help moray eels swallow large prey
Moray eels are large predatory fish that are found on coral reefs world-wide and yet little is known about their feeding mechanics. In studies published in 2007 & 2008 I describe a novel prey transport mechanism in moray eels (pharyngeal transport, Fig. 1). My study revealed that morays have a reduced capacity to suction feed and apprehend their prey by biting. When the prey item is apprehended in their oral jaws, morays protract a pair of pharyngeal jaws, located behind the head, into their oral cavity. Once in the oral cavity, the pharyngeal jaws bite down on the prey item and transport the prey into the esophagus.
The moray transport mechanism is the first alternative prey transport mechanism to suction reported in an aquatic vertebrate and the first example of a vertebrate using a second set of jaws to grasp and transport prey from the oral jaws into the esophagus. The transport behavior of morays is also convergent with the prey transport mechanism used by snakes. Similar to snakes, moray eels are large elongate limbless predators that have evolved a strategy for ratcheting down large prey. However, rather than ratchet from side to side using independent movement of the left and right jaws like a snake, morays ratchet from front to back using independent movement of two separate jaw systems.
Since these papers, I have documented the biomechanical diversity of the oral jaws of various moray species. The majority of morays swallow large prey whole, although some morays process their prey in their oral jaws before ingesting them. One might imagine that swallowing large prey whole requires specialized adaptations of the digestive tract. My present goals are to understand the digestive physiology of consuming large prey whole versus consuming chunks of prey, two strategies seen in the feeding ecology of morays.
Fig 1. Pharyngeal transport in the reticulated moray, Muraena retifera. Arrows point to the pharyngeal jaws. Radiograph revealing position of the pharyngeal jaws in relation to the skull (a). Radiograph revealing extreme pharyngeal protraction during prey transport (b).
Fig 2. Lateral view of a radiograph of a snook skull, Centropomus undecimalis. The modules are in reference to the following developmental complexes: Module 1-oral jaws, Module-2 hyobranchial system,
and Module 3-opercular series.
The teleost skull is one of the most heavily studied functional units among
vertebrates and has been used as a model for numerous biomechanical studies,
however, the majority of these studies focus on suction feeding. Although suction
feeding is considered the most commonly used prey capture mechanism across aquatic
vertebrates, biting as a prey acquisition strategy has evolved independently
in several teleost clades. The evolution of biting appears to have had an effect
on the transport and respiratory complex for some of these biting taxa. For
example, during my postdoctoral research, I discovered that moray eels, a species
rich clade of anguilliform fishes, do not rely on suction to feed, but apprehend
their prey by biting. In addition to biting their prey, I found that morays
have evolved an alternative method of transporting their prey (see Recent Research
section). This functional innovation in moray transport behavior provides an
opportunity to examine how functional innovations
in integrated systems arise. I hypothesize that the evolution
of biting has had downstream effects on different modules comprising the cranio-musculoskeletal
system of teleosts.
My current research, funded by the National Science Foundation (IOS -0819009),
investigates trait correlation in the teleost skull. In this body of work
I examine three distinct modules, or developmental complexes, of the teleost
skull: the oral jaws, the hyobranchial system, and the opercular series (Fig.
2) in anguilliform fishes. I am specifically interested in documenting how
changes in the oral jaws (i.e. extreme elongation as seen in many biting taxa)
affects the hyobranchial and opercular system which may result in functional
specialization and novel prey transport and respiratory modes, as observed
Rita S. Mehta
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz