ECOLOGICAL BIOCHEMISTRY - Study Guide - V. M. Isaienko 2005

Chapter 6. ECOLOGICAL AND BIOCHEMICAL INTERACTIONS BETWEEN ANIMALS

6.3. Interactions between animals of different species

6.3.2. Allomones of parasitic organisms

Based on their MECHANISM OF ACTION, some of these substances cause a breach in the integrity of host Tissues through their enzymatic "Digestion" (histolysins). These compounds play a crucial role during the parasite's invasion of the host body, as well as during the migration and exit of the parasites themselves, their larvae, or Germ Cells.

In many parasite larvae, alongside mechanical means of penetrating the host's body and integument, gland-secreted substances are produced that compromise the integrity of the host's outer layers. For instance, trematode cercariae possess glands opening at the Base of the frontal organ or stylet that secrete hyaluronidase. This enzyme breaks down hyaluronic acid, the cementing matrix of the intercellular substance. Consequently, fluke cercariae are able to penetrate animal integuments and migrate through their bodies. Hyaluronidase is also produced by the larvae of nematodes and certain other parasites migrating within the host.

Certain substances produced and secreted by parasites are capable of "dissolving" host tissues. These include proteolytic, glycolytic, and lipolytic Enzymes. The breakdown products of Proteins, CARBOHYDRATES, and Lipids resulting from the action of these enzymes serve as nutrients for the parasites.

Some parasitic organisms secrete substances that inhibit the action of the host organism's enzymes. This prevents parasites from being digested by the enzymes in the gastrointestinal tract of the host animal, blocks phagocytosis, and suppresses other defense mechanisms. Certain parasites produce anticoagulants that delay Blood clotting. For example, leech saliva contains hirudin, which neutralizes the action of Thrombin and fibrinogen. A similar effect is produced by tabanin, found in the saliva of female horseflies (Tabanus bovinus). The saliva of ticks (Ixodes ricinus) contains a substance that inhibits The Effect of blood clotting factors on prothrombin, which are involved in The formation of thromboplastin.

The irritating substances present in the saliva of blood-sucking parasites (trophogones) stimulate an increased inflow of the host's BLOOD AND Lymph toward the parasite's mouthparts.

Among the substances produced by parasitic organisms are those that induce the overgrowth of host tissues at the site of parasite localization (thylacogens), leading to the formation of galls that ensure the long-term normal physiological activity of the parasites.

The formation of galls can be induced by A wide variety of parasites, including Sporozoans, flukes, tapeworms, and other animals. Examples include the formation of spherical swellings on the stems of polyp colonies by the larvae of the pantopod *Phoxichilidium*, galls in sea anemones (*Anemonia sulcata*) caused by copepods *Staurosoma parasiticum*, galls on the inner surface of the sea urchin body wall (*Phormosoma uranus*) induced by the copepod *Pionodesmotes phormosomae*, and leather-like "pouches" in fish formed by isopods *Livoneca amurensis*, among others.

Encapsulation is particularly frequent in vertebrates. Distinctive double-layered capsules form around tapeworm larvae within mammalian tissues. When nematode larvae are delayed in the host tissues during migration, a fibrous capsule forms around them, much like the reaction to standard foreign bodies. Encapsulation also occurs around the larvae of the dog roundworm (Toxocara canis), though these capsules exhibit certain structural differences from typical foreign-body capsules. In the bodies of reservoir hosts where they undergo no further development, the larvae of the nematode Physocephalus sexalatus become enclosed in capsules whose Structure resembles the tissues of various host species.

Aside from parasites, encapsulation can be induced by certain commensals—organisms that live off the resources of another species without causing it harm. For instance, the young coral crab Hapalocarcinus marsupialis, living on various corals (Sideropora, Pocillopora, Seriatopora), gradually becomes surrounded by coral branches until it is essentially en-

tombed within, maintaining contact with the external environment through only two narrow slits.

Certain parasites produce substances that directly or indirectly affect the host's Gonads, causing underdevelopment and characteristic dystrophic changes. For example, the bivalved isopod Liriopsis pygmaea causes ovarian degeneration in the barnacles of the genus Peltogaster upon which it parasitizes.

In males of the crab Inachus mauretanicus infected by the bopyrid isopod or sacculinid parasite Drepanorchis neglecta, secondary sexual characteristics undergo varying degrees of feminization.

In insects as well, parasite-derived substances can induce morphological changes associated with the loss of the host's secondary sexual characteristics and the acquisition of traits typical of the opposite sex. For instance, in solitary bees of the genus Andrena infected by stylopids (Strepsiptera), both males and females differ markedly from healthy bees, exhibiting smaller heads, expanded abdomens, altered wing venation, and other anomalies. Notably, secondary sexual characteristics in insects develop independently of the state of their reproductive Organs. Consequently, in stylopized bees, the reproductive organs generally function normally.

METABOLISM/18.html">The Influence of parasite-derived substances on host behavior has also been documented in ants, lepidopteran caterpillars, and other insects.

Allomones of myrmecophiles and termitophiles. Specialized glands of myrmecophiles and termitophiles (permanent inhabitants of ant and termite nests) produce and secrete substances that induce specific behaviors in ants and termites, occasionally triggering narcotic-like excitation. These are not nutritive substances, as they cannot serve as a food source. In this regard, these compounds differ fundamentally from the secretions of aphids and scale insects, which are similarly licked by ants but serve as nutritional resources.

Some ant queens that lack their own worker force live within the nests of other ant species. The workers of these host species lick the substances produced by the foreign queen, which triggers an instinctive drive to feed her and tend to her brood. A classic example is the interaction between the queens of the ant Wheeleriella santschii and the host species Monomorium salomonis, within whose nests these queens reside. Immediately after mating, the Wheeleriella queen detaches her wings and crawls into a Monomorium nest. The allomones she produces and secretes attract the worker ants, which lick them off. The workers then begin tending to the queen, her eggs, larvae, and subsequently the pupae and adult individuals. Before long, the worker ants become hostile toward

the reproductive queens of their own species and may even kill them. Thus, the Wheeleriella queen becomes the sole egg-laying female in the Monomorium nest.

A comparable situation is observed in the ants Anergates atratulus and Teleuteromyrmex schneideri, whose queens inhabit the nests of Tetramorium caespitum.

Worker ants of certain species are also capable of producing similar allomones. For instance, ants of the genus Megalomyrmex symmetochus feed on Fungi yet do not cultivate them. Instead, within the nests of Sericomyrmex amabilis, they co-opt the fungus-growing ants. To prevent the host colony from attacking them, the Megalomyrmex ants secrete a substance that the Sericomyrmex ants readily lick.

Myrmecophilous allomones are also secreted by beetles belonging to the families Pselaphidae, Staphylinidae, Nitidulidae, Histeridae, and others. For example, the larvae of beetles of the genera Atemeles and Lomechusa secrete a substance that mimics the allomones of the larvae of the specific ant species in whose nest they live. Upon infiltrating the ant nest, adult Atemeles and Lomechusa beetles secrete a substance licked by the ants, ensuring the beetles are left unharmed.

Bugs of the species Ptilocerus ochraceus secrete a substance that attracts Hypoclinea bituberculata ants. The ants lick this secretion, which intoxicates them, allowing the bug to feed on their fluids.

Larvae and adult beetles of the families Staphylinidae and Rhyssopaussidae, flies of the family Termitoxeniidae, and several other insects inhabit termite nests, secreting substances that compel worker termites to tend to them and their offspring. These secretions likely mimic the scent and taste of sex pheromones of reproductively active termites, exerting a powerful attraction on the workers. A similar phenomenon occurs among ants.