Other communication mechanisms for courtship

Visual cues: UV light Bees Butterflies Fishes Lizards Songbirds

Bees and butterflies detect UV light Examples of UV signals emitted by certain flowers, above, and butterflies, below. Mating preference to males with brighter UV reflecting patches.

Testing role of UV in sticklebacks Important control experiment?

UV reflecting feathers influence mate choice in songbirds too In 13/16 paired trials, females approached the male whose UV reflecting feathers had not been treated with sunscreen. Evolution of a visual system tuned to UV wavelengths.

UV signals between males This threat display indicates how strongly a male can bite another lizard. Both the size of the gape and the size of the white patch signal aggression and “intimidation factor”.

Proportion of non-escalated (open) and escalated (shaded) contests and (b) mean log duration (seconds; ±s.e.) of non-escalated and escalated contests for manipulated and control males. Manipulated males initiated fights with longer ventral displays and more likelihood of escalation, probably due to misjudgment of their ability by their opponent. Stapley J , Whiting M J Biol. Lett. 2006;2:169-172

Signals Require a nervous system that can recognize important stimuli Modifications to the nervous system form the basis for selection Visual Auditory Touch Taste/Smell Motor patterns

How signals arise Co-option of an existing signal Aggressive “skrraa” adapted to a courtship “skrraa” Allow females to make choices between mates Produce new signal for which perceptual ability already exists Sensory exploitation Bowerbirds

Sensory exploitation in water mites Male trembling tricks the female into thinking there is prey inducing her to grab the male and release him. He then deposits his sperm and she picks it up, if she is receptive. Hungrier females are more receptive to this display, supporting but not firmly proving the notion that male trembling evolved to take advantage of a hungry female’s perceptual abilities.

DQ 9.6 Female lays eggs in nest, takes eggs into her mouth. Male swims by, flashes anal fin with orange spots, which the female tries to eat. Male deposits sperm, fertilizes eggs. Is this exploitation? Is the female’s fitness reduced to the male’s advantage? Use sensory exploitation theory to explain the male’s behavior. Was the first male to use this signal taking advantage of the female? Is her fitness reduced?

Mate choice in guppies Males that eat enough fruits obtain carotenoids that turn their scales orange. Orange males are more attractive to females of this guppie species. Why? Females were already sensitive/preferring of orange because they too enjoyed the rare fruit? This is supported by the orange disc expt.

Ornamentation-size of crest correlates with female receptivity Use a stuffed bird with artificial crest of varying size. More displays to the largest crest. In all cases—frogs, fish, etc. the artificial features elicited stronger responses from females than the natural ones. Why would animals have the ability to respond to signals that they never see in the wild?

Role of novel stimuli Perhaps novelty plays a role in attraction So the positive response is not ancestral, or even specific to the stimulus, it is a response to novelty.

Role of ancestral signals Perhaps animals react strongly to artificial stimuli because their ancestors displayed these types of stimuli in a biologically relevant setting This particular species of lizard has lost the abdominal blue patch, but still responds appropriately to a conspecific male with an artificial blue patch painted on.

Evolution of sexual selection traits Occurs rapidly Traits gained and lost, sometimes more than once Hard to study Many interpretations Nutrition, health of male General preference for body size Head and tail “extensions” make the whole animal bigger

Summary: origin of signals Exploiting: stimulating a sensory apparatus that evolved for another purpose Proximate cause Bias: female prefers novel form of male attribute because of greater fitness to her Ultimate cause Adaptive value: signals (giving and receiving) that are advantageous are maintained, while those that are disadvantageous are lost Greater fitness may mean better able to provide for her and the offspring for example. Garter snake mating mechanism—repel predators, males use response for copulation.