Biology 3300- Sexy Sons Hypothesis & Female Choice

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BIOL 3300
Theresa Burg

Biology 3300 th Mar.5 , 2014 Good Genes - Different direct indicators that females can use to determine if males have good genes - Speaker placed in front of the females and played male calls - Below 1 – lower score and moved away from the speaker - Above 1 – higher score and moved closer to the speaker - Looked at fitness of offspring o Fertilized the eggs either from a short-calling male or a long-calling male o Looked at larval growth, survival, time to metamorphosis o Found no difference or offspring of males with long calls did better o Higher, stronger growth rate with long-calling males, they were also more aggressive - MHC: major histocompatibility complex o Molecule from class 1 & class 2 combine to produce antigen o Humans average 6 class 1, 8 class 2 o Chose mate to maximize diversity in offspring o Sticklebacks (fish) have 2-8MHC alleles class 2  Found offspring with 5-7 alleles have a lower parasite load  Increasing genetic diversity, decreasing parasite load Sexy Sons Hypothesis: - Stalk-eyed flies - Size of the stalk is correlated to the size of the individual; also larger in males than females in relative size - IF variation in eyestalks and preferences are correlated we should lead to assertive mating o Preference for short you will mate with short male eyestalks - Both traits are heritable - Assortative mating is not random. They are choosing who to mate with. - Selection experiment - Runaway selection o Can get a change in evolution o When selecting for long stalks there was no difference from the control group o When selecting for short stalks the females began to prefer males with short stalks o This shows that females are choosy o Female preference and male eye stalk length is heritable o Selection on one trait can affect pattern of female preference o There is an x-linked gene that can increase the amount of female offspring How did sexual dimorphism originate? - No male-male competition is seen – such as in harbor seals – we see no sexual dimorphism - Elephant seals where there is male-male competition begins to produce sexual dimorphism Female choice: responsible for producing sexual dimorphism in barn swallows? - Length of tail can show good genes, or has many nutrients and thus large access to food - Huge variation between male size - Experiments where they altered the tail length - “mock” altered  cut and reglued - Males with the longer tail found a mate more quickly compared to the males with shorter tails - Males with elongated tails have a higher chance of second clutches - Males with the longer tails had more offspring - Males with longer tails had extra copulation - Males with shortened tails lost paternities to other males - All that was changed wa
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