Читать книгу The Behavior of Animals - Группа авторов - Страница 44

Scent perception in many insects involves receptor cells best tuned to chemical sign-stimuli. In the silk moth, Bombyx mori, scent hairs on the male’s antennae are equipped with “olfactory specialist receptor cells.” These respond maximally to a female’s key pheromone bombykol, as mentioned above (Figures 2.6 and 2.7a). A bombykol receptor is also somewhat sensitive to chemically related compounds, however, at 10- to 1000-fold higher concentrations (Kaissling 2014).

Figure 2.6 Male silk moth in alerted position, with combed antennae elevated (top). (Courtesy of R.A. Steinbrecht.) Bottom: schematic section through a scent hair with pore tubuli and two scent receptor cells. Arrangement for recording impulses from bombykol receptor. (Modified after R.A. Steinbrecht).

Figure 2.7 Principles of scent detection in moths by specialist receptor cells and interneurons. (a) In male silk moths a receptor channel is specialized for female’s sex pheromone bombykol. (b) In male nun moths a receptor channel is specialized for the sex pheromone (+)-disparlure. (c) In male gypsy moths two types of receptor channel are specialized for two pheromone compounds: (+)-disparlure stimulates interneurons, whereas (−)-disparlure inhibits their response to (+)-disparlure. (d) In male leaf-roller moths the concurrent excitatory influences of the two receptor channels specialized for the two sex pheromone stereoisomers (Z)-11-tetradecenyl-acetate and (E)-11-tetradecenyl-acetate are essential to activate interneurons. (Compiled from data in Hansen 1984; Kaissling 2014.) Note that a behavioral response requires activation of many specialist receptor cells and corresponding interneurons.

Other examples of such narrow-band olfactory specialists are the meat receptor in Necrophorus beetles, the rotten-meat receptor in blow-flies Calliphora erythrocephala, and the grass receptor in the locust Locusta migratoria. Grass receptors respond to chemically related components of fresh grass, such as hexenol, hexenal, and hexenic acid (Kafka 1970).

In leaf-roller moth species, as mentioned above, the males have two types of specialized receptor cells, each one tuned to a different pheromone, both emitted by the conspecific female in a characteristic proportion (e.g., Figure 2.7d), which minimizes the risk of mating with males of inadequate species.

Another way of species separation are interspecific inhibitors. Females of the nun moth, Lymantria monacha, and the gypsy moth, L. dispar, produce the male-attracting compound (+)-disparlure (Figure 2.7b, c). However, the female nun moth also produces (−)-disparlure, which stimulates a specialist receptor cell in the male gypsy moth to inhibit its behavioral response to (+)-disparlure (Figure 2.7c) (Hansen 1984). This kind of species separation would function in one direction, since a male nun moth could be attracted by (+)-disparlure of the female nun or gypsy moth. Presumably, female gypsy moths are less attractive to male nun moths because of the high emission concentrations of (+)-disparlure (Figure 2.7c ).

In addition to specialist receptors there are “generalist receptor cells.” These—showing partly overlapping response spectra—respond differently to various odor compounds. Such cells may be suitable to distinguish odorous substances by individual experience.