Anatomical Specializations For Insectivory

Although eating insects is a dominant part of many diets, anatomical and behavioral specializations for insectivory are not as widespread. Many lizards, for example, feed on whatever suitable prey item might be available. Nevertheless, there are several anatomical specializations that seem to assist in the capture of insect prey. Perhaps the most obvious and remarkable trait is a highly projectile tongue. This sort of tongue evolved many times, in many different lineages, and in many different ways. Most frogs have a projectile tongue whose intrinsic muscles attach to the lingual edge of the symphysis of the jaw. The tongue is flipped out of the mouth, in the same way that a catapult works, so that the back of the tongue after it is extruded contacts the prey first. Salamanders have evolved several different types of projectile tongues. One group of lungless salamanders, the plethodontids, uses the hyobranchial skeleton and associated muscles, once used to ventilate lungs, in a tongue protrusion mechanism that is quite spectacular. Contraction of these muscles results in protrusion of the tongue as well as large parts of hyobranchial skeleton, resulting in an extruded tongue that can reach 80% of body length.

Chameleon lizards have an unmatched ability to accurately aim, project, and hit arboreal insect prey. The muscles that chameleons use to accomplish this ballistic feat contract faster than any other vertebrate muscle. Furthermore, the tongue

TABLE I Examples of Frog, Lizard, and Mammal Lineages in Which Termites and/or Ants Are a Significant Part of the Diet

Frogs

Dendrobatidae—poison frogs Microhylidae—narrowmouth frogs and toads Pelobatidae—spadefoot toads Rhinophrynidae—Mesoamerican burrowing toads Lizards

Agamidae—angelheads, calotes, dragon lizards, and allies

Amphisbaenia—wormlizards

Gekkonidae—geckos and pygopods

Iguaninae

Lacertidae—wall lizards, rock lizards, and allies

Phrynosomatinae

Scincidae—skinks

Teiidae—whiptail lizards, tegus, and allies Tropidurinae Snakes

Anomalepididae—early blindsnakes Leptotyphlopidae—threadsnakes and wormsnakes Typhlopidae—blindsnakes

Mammals

Canidae—dogs and foxes

Cercopithecidae—Old World monkeys

Cricetidae—New World mice, hamsters, etc.

Dasypodidae—armadillos

Didelphidae—opposums

Herpestidae—mongooses

Lorisidae—lorises

Manidae—pangolins

Muridae—Old World rats

Myrmecobiidae—marsupial anteaters

Myrmecophagidae—anteaters

Orycteropidae—aardvarks

Sciuridae—squirrels

Tachyglossidae—echidnas

Talpidae—moles

Thylacomidae

Vespertilionidae—bats

Note. Not all the taxa that are a part of these lineages eat only ants and/or termites. There are many other lineages not listed that eat insects.

can be accurately projected up to 200% of body length. The tongue has a large tip covered with viscous mucous. A muscle in the large fleshy tip contracts just after the tongue tip strikes a prey item, creating a slight vacuum that assists in prey capture.

Mammals eat insects and the most distant ancestors of mammals may have been insectivores. Generalized features derived from the primitive amniote condition are associated with mammalian feeding, including a longer secondary pallate, heterodont dentition, higher metabolic rates and more active foraging behaviors. Several of these features are reversed in obligate ant- and termite-eating mammals. For example, anteaters, pangolins, and the echidna, numbat, and aardvark possess highly simplified teeth few in number or lack teeth entirely. Some ant and termite specialists have lower metabolic rates, but it is not clear if these rates are retained from a primitive mammalian ancestor or if they are a response to prey that may present chemical challenges to typical mammalian digestive systems. A long, sticky, and protrusible tongue is a common feature among ant- and termite-feeding mammals. Details of tongue anatomy confirm that many of these lineages evolved these specializations independently.

See Also the Following Articles

Food, Insects as • Predation

Further Reading

Cushing, C. E., and Allan, J. D. (2001). "Streams: Their Ecology and Life."

Academic Press, San Diego. Gerking, S. D. (1994). "Feeding Ecology of Fish." Academic Press, San Diego.

Schwenk, K. (ed.) (2000). "Feeding: Form, Function, and Evolution in

Tetrapod Vertebrates." Academic Press, San Diego. Thorp, J. H., and Covich, A. P. (eds.) (2001). "Ecology and Classification of North American Freshwater Invertebrates," 2nd ed. Academic Press, San Diego.

Zug, G. R., Vitt, L. J., and Caldwell, J. P. (2001). "Herpetology: An Introductory Biology of Amphibians and Reptiles," 2nd ed. Academic Press, San Diego.

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