Animal migration How do animals orient Visual cues

Animal migration How do animals orient? Visual cues – orientation studies in birds using stars, sun Olfactory cues Magnetic fields Adjustments in magnetic field affect orientation What triggers migration?

Darwin: “The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!” Sexual selection: Selection for features that increase the likelihood of mating success.

Success at mating: Males: RS is typically limited by the number of females he can convince to mate with him. Females: RS is typically limited by the number of eggs/pregnancies she can produce. Why? How does this come about?

Anisogamy: asymmetry in gamete size found in all sexually reproducing animals Consequences: Female RS tends to be limited by egg production Male RS tends to be limited by # females

Disparity in potential LRS: Salmon: females lay ~3500 eggs males fertilize w/ 400, 000, 000 sperm Human females ~ 1 egg per month males can have 400, 000 sperm

Is there disparity in potential LRS?

Robert Trivers 1972: When one sex has more parental investment, the other will compete for access to them Parental investment – any effort spent for offspring that survival or RS of offspring at cost to parent. Gametes Nutrition to young or mate Protection of eggs, young

Disparity in parental investment leads to… If a gender has less parental investment, they will have higher mating investment These differences in types of investment in males vs. females leads to: Intrasexual competition (which tends to be male vs. male for access to females) Intersexual competition (which tends to be female choice for best quality males)

Intrasexual competition: Aggressive competition - prevent access, mate guarding Display competition Sperm competition if females have multiple mates

Intersexual selection Female choice (typical pattern) Males relatively indiscriminating Females are choosy

Wow…look at his snood!

Who is choosy? Can both be choosy? Mate choice and differences in relative parental investment Albatross vs. Bird of paradise displays

Who is choosy? Another influence is operational sex ratio OSR: the ratio of sexually competing males that are ready to mate to sexually competing females that are ready to mate If there is a large disparity in OSR, this can emphasize or even override investment differences depending on the ratio

Why choose males that are only slightly different than others? Call frequency Song repertoire Number of eyespots Tail height Tail length Stripe size

Can choice actually select for features? Is it really only tail length? Before Widowbird After p. 191

Ornamentation is often costly Extreme ornamentation temporary May be subject to physiological tradeoffs Box 7. 2 tail length vs. red ornamentation The expense of flashiness may suggest why females choose ornamentation