Long-tailed dance flies Long-tailed dance fly – Rhamphomyia longicauda Trait preferences exist… Rhamphomyia longicauda
Preferences for exaggerated traits exist… Control I ! Control II (unmanipulated)
Peacocks Widowbirds
Number of matings Shortened ! Elongated
barn swallow Is tail length associated with mating success in barn swallows? Moller (1988) Nature 332:640 Control Elongated Control Shortened Do males with long tails mate more
frequently (compared to short-tailed males)? Do females prefer to mate with long tailed Change in number of matings Experimental males over short-tailed males? (remove eyesptos) ! ! ! !
barn swallow barn swallow
Moller (1988) Nature 332:640 Moller (1988) Nature 332:640
Males with elongated tails found Males with elongated tails mates more quickly re-mated more frequently
…but what is it that males (or females) choosing? Hypotheses for how mate choice evolves... ! ! • Honest advertisement • Individuals increase their fitness by selecting mates whose characteristics indicate that they are of high quality. • Direct benefits to individuals of the choosy sex
• Indirect benefits (e.g., good genes for offspring of choosy sex)
barn swallow
Females paired with short-tailed males more likely to accept extra matings Males with elongated tails had more offspring
long-tailed males were Extra pair copulations more successful at By males gaining extra matings By their female pair- mates Indirect benefits: Good genes hypothesis Direct benefits: food
In nature… Bittacus apicalis Exaggerated traits indicate the genetic quality of a mate
Handicap principle Costly signals likely to
be honest indicators of In laboratory… Bittacus apicalis genetic quality
Video: Spatuletail hummingbird
Direct benefits: spermatophores Direct benefits: spermatophores Some transferred directly to females
Mormon cricket Requena verticalis Female consuming spermatophore
Some deposited on substrate
Spermatophylax Sperm
Experimental manipulations show that spermatophylax increases sperm transfer time Sexual cannibalism: the ultimate nuptial gift Direct benefits: protection
praying mantis Newly rattlebox moth protected female moth being rejected by spider
redback spider
Male moth Cannibalized males copulate longer and fertilize more transfers eggs than those that survive copulation. Rattlebox moth feeding alkaloids to off rattlebox plant, Females are more likely to reject subsequent suitors female after consuming their first mate. obtaining alkaloids
Direct benefits: protection Direct benefits: protection Drosophila mojavensis Drosophila mojavensis (colonized dry SW habitats) (colonized dry SW habitats)
Figure 1. Desiccation resistance in females (measured in hours) (a) between mated (filled bars) and unmated (open bars) females, and (b) among populations. The relative contribution of mating in each population is identified by comparison with unmated females, indicated by the open bars. Direct and indirect benefits: male parental care Hypotheses for how mate choice evolves...
• Honest advertisement • • Males s/t responsible for nest ! Individuals increase their fitness by selecting mates whose characteristics construction, parental care indicate that they are of high quality. •!Female choice based on • Direct benefits to individuals of the choosy sex (e.g., food, protection) benefits to offspring Betta • Indirect benefits (e.g., good genes for offspring of choosy sex) splendens • Sensory exploitation • Traits evolve because they attract the attention of the opposite sex. There is a pre-existing bias that individuals will prefer mates with these traits. Some sounds, shapes, colors, odors, etc. are more noticeable to potential mates due to the way their sensory systems work.) sedge warbler
Swordtails & platyfish Preference for exaggerated NOVEL traits – small fish, genus Xiphophorus – males have elongated caudal fins (extensions), sometimes also brightly colored
Preference exists even if trait is novel
black-throated and zebra finches Basolo (1990) Science 250:808 Priapella (outgroup) Basolo (1990) Science 250:808 Priapella (outgroup) Basolo (1995) Proc R Soc 259:307 Basolo (1995) Proc R Soc 259:307 Basolo (1995) Anim Behav 50:365 Basolo (1995) Anim Behav 50:365
Platyfish Platyfish
species in which preference females prefer males with long swords
swords swords Swordtails Swordtails
In some cricket species, Sceloporus virgatus S. virgatus respond to lack blue ventral patches spermatophylax contains no nutrients artificial blue patches
Close relatives have them
Females in non-spermatophylax producing species accept them (sensory exploitation) Hypotheses for how mate choice evolves...
• Honest advertisement • Individuals increase their fitness by selecting mates whose characteristics indicate that they are of high quality. • Direct benefits to individuals of the choosy sex (e.g., food, protection)
• Indirect benefits (e.g., good genes for offspring of choosy sex)
Pisaura mirabilis • Sensory exploitation • Traits evolve because they attract the attention of the opposite sex. There is a pre-existing bias that individuals will prefer mates with these traits. Some sounds, shapes, colors, odors, etc. are more noticeable to potential mates due to the way their sensory systems work.)
• Runaway selection • Male traits evolve due to assortative mating between females with a preference for some trait and males who possess that trait. Such matings result in offspring both with the preference (daughters) and the trait (sons).
Runaway (Fisherian) selection (“sexy sons” hypothesis) Female guppies prefer males with orange spots...
! ! Slope is an indicator of preference
preference of F’s (higher slopes = greater preference)
orange spot size
Trait unrelated to male quality Trait passed to sons Preference passed on to daughters RA Fisher Female guppies prefer males with orange spots... Female control of copulation Male-orange & female preference are positively correlated across populations. In most cases, females retain control of mating
red junglefowl
Females from “big orange” populations had strong preference for orange spots
Houde & Endler (1990) Science 248:1405
Imposed artificial selection (directional) on the degree of orange in males.
High lines (males selected for more orange) Selection on males resulted in a correlated response in female preference for orange spots (!)
orange spot size Low lines (males selected for less orange)
Houde (1994) generations Proc Roy Soc 256:125
Cryptic female choice Cryptic female choice
Females of many species may store sperm Sperm storage: choice of sire?
ambrosia beetle Xiphophorus multilineatus
redback spider
Pulex spp.
Sperm storage an adaptation Female mollies mate with multiple males, for delayed conception but one sires ~70% of offspring