• Read pp 407- 420 for next week• Discussion Reading for tomorrow• EXAM next Tuesday (no need for a blue book)• Office hours moved from this thurs to NEXT Monday 1-3pm• NEXT week’s Discussion section—bring in 2 papers relevant to your Independent ProjectAnnouncements1Imprinting•Imprinting: Time-Sensitive learning (occurs at a specific age or life stage) that becomes fixed (or independent of external influence) later on in life.•Occurs during a brief critical period early in life•Focused on particular kinds of stimuli•Usually irreversible by subsequent experience2Learned mating preferences in zebra finches (Vos, Anim. Behav. 1995)• Used albino zebra finches to eliminate plumage variation• Painted bill red or orange• raised young with red dad, orange mom and vice-versaMomDadMomDad3• Males sang more to females with same bill color as their mother• Males even preferred males with mom’s bill color over females with dad’s• Females failed to show a preference for bill color, selecting males on song and courtship4Oedipus Rex• Son-mother imprinting far more common than daughter-father• Why?• Males and Females are looking for different types of information when choosing a mate• Females may be looking for behavioral or Condition-dependent states of male• Mating is less costly for males? and they use imprinting as a “rough rule of thumb”5Avian sexual imprinting • Remember the Great tit and Blue tit cross-fostering experiment?• Great tits reared with blue tit parents prefer to mate with blue tit females, • These males also copy the blue tit songs & alarm calls, and treat them as competitorsBlue titGreat titMale zebrafinch courting a female Bengalese finch after cross-fostering experiment6Evidence that it is widespread across taxa• Over 100 different species of birds (from 15 different orders) exhibit sexual imprinting• Also found in some mammals (goats, sheep), fish and even frogs7Can sexual Imprinting lead to exaggerated sexual traits?• If offspring are always imprinting on their parental or sibling forms, then should trait evolution stay static?• Can the imprinting process lead to exaggeration?• Possibly, through a by-product of the learning process called “peak shift”8Peak Shift• Peak shift is a form of skewed preferences or overgeneralization produced by discriminative learning about two similar stimuli that are differentially reinforced S+ (reward), and S- (punishment or no reward).• For example, the stimuli may be two colored lights different in wavelength or two tones differing in frequency.• Usually the strongest response is to the training stimuli (S+, S-)….• BUT…if the stimuli are similar in appearance, then the response shifts in a direction that increases the difference between S+ and S-9Peak Shift• Typical Response learning response without peak shift• Found in many taxa,Birds, humans, fish, etcGhirlanda & Enquist, 2003, Animal Behaviour10Peak Shift• Now compare response where S+ and S- are similar• Both studies use S+ at 550nm• In study with S- = no light, the peak response is ~ 545nm• In study with S- = 560, the peak response has shifted to 538nm• The Peak Shift response is found across taxa Ghirlanda & Enquist, 2003, Animal Behaviour11Can sexual Imprinting lead to exaggerated sexual traits?• Can this Peak Shift Phenomena contribute to exaggeration of traits that offspring imprint on and mates discriminate among?• Testing this with Zebrafinch• In sexually dimorphic species with biparental care, offspring are exposed to two phenotypically different parental types (father, mother) as imprinting stimuli. • Basic attributes for Peak Shift to develop• Hypothesis: offspring should develop sexual preferences for mates that exaggerate the sexual dimorphism(ten Cate et al. 2006, Current Biology)12Can sexual Imprinting lead to exaggerated sexual traits?• Zebrafinch usually sexually dimorphic in plumage and beak color• They used all-white plumage color morph where beak color is the most conspicuous sexually dimorphic trait• Examined Male Mate preferences• Painted the parental beaks with nail polish• Control group (O): Mom’s beak= Orange, Dad’s = Red (this is close to natural conditions)• Experimental Group (R): Mom’s = Red, Dad = Orange• Mom’s Beak Color = S+ …. Dad’s Beak Color = S-(ten Cate et al. 2006, Current Biology)13Can sexual Imprinting lead to exaggerated sexual traits?• Results:• M & P arrows refer to the Maternal and Paternal Beak colors for each group• M+1 & M+2 refer to more extreme versions of the maternal beak color for each of the two groups• Males directed MORE songs at females with MORE extreme color version of their Mom’s beak color(ten Cate et al. 2006, Current Biology)Female beak color range14Geographic imprinting• Salmon hatch in small tributary streams• At ~16 months, they smolt: change color, adapt to saltwater physiology, and swim to ocean• Feed and grow in ocean for 2-3 years• Return to the same tributary, deposit eggs and die. 15How do salmon find their way home?• Use magnetic navigation to find general area• Use olfactory cues to find specific tributary• How was this determined?– blinded salmon locate tributary– salmon with plugged nostrils do not16How are these olfactory cues acquired?• Hasler et al. (1978) exposed groups of smolts to two organic odors not found in nature: PEA (phenethyl alcohol) and morpholine, plus a control.• Smolts raised in Lake Michigan water - no tributary water allowed to reach them• At spawning time, tributaries were “baited” with artificial odors 17Fish imprinted onStream baited onMorpholine PEA ControlMorpholine 659 20 76PEA 8 343 55Control 14 9 154Hasler et al.’s imprinting experimentSalmon go to the stream bearing the artificial cue they imprinted on.18Mechanism of olfactory imprinting•Olfactory epithelium contains different types of sensor cells, each responsive to specific chemical types19•This response is mediated by membrane receptors triggered by particular chemicals•Triggering receptors during smolt period results in increased expression of more receptors, and therefore increased sensitivity to these chemical types•Changes at the olfactory periphery mediate imprinting.20Imprinting• Influences future reaction to specific stimuli• Mechanism?• Positive Feedback on Sensory System (olfactory imprinting in salmon)• Mechanism for Sexual