Sexual displays as amplifiers: practical examples with an emphasis on feather decorations

Abstract

Exact patterns of displays are not easy to explain on a functional basis. However, if displays evolve initially as amplifiers of previously perceived differences in quality, their patterns should correspond with patterns of quality cues that are amplified. Consequently, exact patterns of behavioral, morphological, and structural displays can be explained. I illustrate this with examples of some feather decorations. Furthermore, these examples indicate that, frequently, cues on which female choice is based cannot easily run away, whereas their amplifiers can. Finally, I present specific predictions of the amplifying theory of sexual selection.

Assessment of Potential Predation Costs of Male Decoration and Courtship Display in Wolf Spiders Using Video Digitization and Playback

“…It is apparently the combination of tufts and foreleg tapping that attracts predator attention. This supports earlier hypotheses that decorative tufts on the forelegs of S. ocreata function as amplifiers or attention signals (Hasson, 1991(Hasson, , 1997 increasing the efficacy of the leg-tapping display (McClintock and Uetz, 1996;Scheffer et al, 1996;Hebets and Uetz, 2000). Hebets and Uetz (2000) found a correlation between the presence of decorations and pigmentation on the forelegs of Schizocosa species males and the level of visual display they exhibited.…”

Leg ornamentation and the efficacy of courtship display in four species of wolf spider (Araneae: Lycosidae)

“…According to Hasson (1991), females should not respond to the presence of an "amplifier" unless it is enhancing a previously desired male quality, such as display rate. S. duplex males, which lack a leg-waving display, do not possess a visual quality indicator (such as rate of display) which ornamentation might amplify.…”

The use of multiple cues in mate choice

“…In the threespine stickleback (Gasterosteus aculeatus) for example, zig-zag movements during courtship expose the male's red ventral coloration to the female (McLennan & McPhail, 1990). Other examples are tail markings of birds that amplify tail length, shape or feather quality (Hasson, 1991;Fitzpatrick, 1998), and ornaments that amplify other ornamental traits, such as in guppies where black colours enhance areas of orange (Brooks, 1996).…”