Same Principles but Different Purposes: Passive Fluid Handling throughout the Animal Kingdom

Everything on earth is subject to physical laws, thus they influence all facets of living creatures. Although these laws restrain animals in many ways, some animals have developed a way to use physical phenomena in their favor to conserve energy. Many animals, which have to handle fluids, for example, have evolved passive mechanisms by adapting their wettability or using capillary forces for rapid fluid spreading. In distinct animals, a similar selection pressure always favors a convergent development. However, when assessing the biological tasks of passive fluid handling mechanisms, their diversity is rather surprising. Besides the well-described handling of water to facilitate drinking in arid regions, observed in, e.g., several lizards, other animals like a special flat bug have developed a similar mechanism for a completely different task and fluid: Instead of water, these bugs passively transport an oily defense secretion to a region close to their head where it finally evaporates. And again some spiders use capillary forces to capture prey, by sucking in the viscous waxy cuticle of their prey with their nanofibrous threads. This review highlights the similarities and differences in the deployed mechanisms of passive fluid handling across the animal kingdom. Besides including well-studied animals to point out different mechanisms in general, we stretch over to not as extensively studied species for which similar mechanisms are described for different tasks. Thus, we provide an extensive overview of animals for which passive fluid handling is described so far as well as for future inspiration.

Functional Morphology of Secretion by the Large Wax Glands (Sensilla Sagittiformia) Involved in Tick Defense

Ticks are protected against ants by release of an allomonal defense secretion from the large wax glands (or type 2 glands) that line their bodies. To explore how the large wax glands operate, before and after microscopic observations of these glands (nonsecreted versus secreted test groups), mass determinations were made forRhipicephalus sanguineusthat had been exhausted of secretion by repeated leg pinching to simulate attack by a predator. Prior to secretion, the glandular organ is fully intact histologically and matches thesensillum sagittiforme, a key taxonomic structure described in the 1940s. The large wax gland is innervated and responds to pressure stimulation as a proprioceptor that stimulates the secretory response. Histological observations after secretion has occurred show that the entire glandular contents and associated cells are jettisoned out of the gland like a syringe. The glandular cellular components are subsequently rebuilt by underlying hypodermal cells within a few days so that secretion can take place again. Presumably, the active allomonal ingredients (hydrocarbons) are released when these derived epidermal cells reach and burst onto the cuticular surface. Our conclusion is that the large wax glands are holocrine and feature intermittent regeneration.

Constituents of frontal gland secretion of peruvian termites Nasutitermes ephratae

The defense secretion of Nasutitermes ephratae soldiers was analyzed and its constituents were identified. The volatile fraction contains monoterpenic hydrocarbons α-pinene, camphene, sabinene, β-pinene, myrcene, 4-carene, 3-carene, α-terpinene, limonene, γ-terpinene, β-phellandrene, and terpinolene. From the non-volatile fraction four alcohols derived from trinervitane skeleton were isolated: 1(15),8(19)-trinervitadien-3α-ol (I), 1(15),8(19)-trinervitadien-2β,3α-diol (II) and its 2α,3α- (III) and 2α,3β- (IV) isomers. 3α-Hydroxy-1(15),8(19)-trinervitadien-2-one (V), which was also isolated, is probably an artefact formed during the work-up of the extract. The structure of 3β-hydroxy-1(15),8(19)-trinervitadien-2-one (VI) was determined on the basis of mass, IR and 1H NMR spectra, comparison with model compounds and analogy with the literature. The absolute configuration of the trinervitane skeleton was studied by CD spectra of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)praseodymium complexes of the 2,3-diols II-IV and by the 1H NMR spectra of esters of the alcohol I with (R)- and (S)-α-methoxy-α-(trifluoromethyl)phenylacetic acid. The results obtained by both methods are identical and confirm the earlier suggested absolute configuration of the trinervitane skeleton.