Читать книгу The Behavior of Animals - Группа авторов - Страница 35

The notion that the releasing values of sign-stimuli often depend on characteristic relationships between features accords with examples from other sensory modalities, such as chemical or auditory signals used in communication.

Female moths use sex-attractant pheromones to invite their males. In many moth species these consist of blends of two chemical compounds (Kaissling 2014). Whereas the same two components can be emitted by phylogenetically related species, a species-specific signal is produced by a characteristic mixture: “principle of parsimony.” Among species of the North American female leaf-roller moth the proportion of the pheromone compounds [Z]-11-tetradecenyl-acetate: [E]-11-tetradecenyl-acetate is:

 90:10 in Archips mortuanus

 60:40 in Archips argyrospilus

 17:83 in Archips cerasivoranus

In various species of frogs, to choose another example, the females are attracted by the advertisement calls of the conspecific males if certain low-frequency and high-frequency components of sufficient energy in the call power-spectrum coincide (Capranica 1976):

200 Hz and 1400 Hz, bullfrog, Rana catesbeiana

500 Hz and 1500 Hz, leopard frog, Rana pipiens

900 Hz and 3000 Hz, green tree frog, Hyla cinerea.

Male adult bullfrogs among themselves evoke advertisement calls in a chorus. However, if young males start to take part, the adults become mute. Although immature, the young display sort of advertisement call, albeit a bit unsounded: high-frequency peak at 1400 Hz, but the low-frequency peak not at 200 Hz rather around 600 Hz. This 600-Hz component inhibits adult male’s mating-calling and female`s interest to follow. With age the vocal cavities of young males increase, so that the low-frequency peak shifts perfectly to 200 Hz (Capranica 1976). Hence, females are protected twofold from meeting an immature partner.

Unlike Rana or Hyla, the advertisement call of the Puerto Rican male treefrog, Eleuterodactylus coqui, is made up of a sequence of two notes with different conspecific addressees: the “Co”-note of 1100 Hz is addressed to males in male–male territorial interactions; it is followed by the “Qui”-note, upward sweeping from 1800 to 2100 Hz, to attract females (Narins 1981). The advertisement call of male tungara frogs, Engystomops pustulosus, too, consists of a sequence of different notes: a whine followed by several lower-pitched chucks (Ryan & Rand 1995). Whereas the whine serves species recognition, the chucks enhance the call’s attractiveness to females. Males of the related species E. coloradorum whine but do not chuck. If given a choice, their females prefer E. pustulosus calls (Chapter 12).

Enhancing effects may also result from combining features of different sensory channels. When prey is difficult to carry for Aphenogaster ants, they recruit help from workers by emitting a pheromone. If food competitors are present and time is short, ants also deliver a vibrational stimulus. Vibration alone has no effect on worker recruitment, but in combination it enhances the pheromone’s efficacy (Markl & Hölldobler 1978). Workers of leaf-cutting ants, Atta cephalotes, respond to a pheromone or vibration with recruitment behavior. If these ants are given a choice, they choose the combination, suggesting a kind of summation effect.