Ecology Behavioral Today's questions: T d ' ti I. What are ecology and behavioral ecology? II. What is sexual selection? II Wh i l l i ? III. How does sexual selection act when males compete for mates? t f t ? IV. How does sexual selection act when females choose mates? choose mates?
II. What is sexual selection?
Darwin wanted to explain why, in some species, males look different than females. (Beyond genitalia) 1. There is heritable variation in appearance and/or 1 Th i h it bl i ti i d/ courtship behavior. 2. Individuals experience differential success in obtaining mates--individuals with certain traits do better.
In most species, females invest MUCH more in offspring than males do. For example: Female red deer average kg. and are pregnant for kg and are pregnant for months, over the winter. Calves average Calves average kg at kg at birth and nurse for two months; they weigh about kg at weaning. Males average kg, they contribute
III. How does sexual selection act when males compete for III How does sexual selection act when males compete for mates? In red deer, intense malemale competition occurs. 1. Which sex has higher variation in RS? 2. In which sex would alleles associated with increased associated with increased mating success increase faster?
Question: In some human cultures, men control access to jobs and other resources required to start a family, and marriages are arranged. As a result, females have little or no ability to choose their mates. In these cultures, how might men react to efforts to 1) increase the education level of women, or 2) help women increase the education level of women, or 2) help women start businesses through microlending or other programs?
Question: In the U.S., there is an extremely strong correlation between amount of education and lifetime income. And traditionally, men have been the i A d t diti ll h b th "breadwinner" in families. But currently, 57% of U.S. college students are female. college students are female g In culture, this how might men and women react to the new asymmetry in level of education?
In China in 1996, there were 121 boys aged 14 for every In China in 1996 there were 121 boys aged 1 4 for every 100 girls aged 14. This cohort is almost of marriageable age. age. How likely is it that all men in this cohort will be able to marry and have a family? Will hi i Will this situation make men happy or crabby? i k h bb ? Are they likely to remain celibate all their lives? Are they likely to remain celibate all their lives? Boys are esteemed far above girls in traditional Chinese y g culture. Is this likely to change or remain the same?
IV. How does sexual selection act when females choose mates? What do females choose? A. "Good alleles"
B. Resources required to produce offspring. Sexual selection in Australian redback spiders.
During copulation, male During copulation male redbacks insert a sperm transfer organ into the female Then they do a somersault, which places their abdomen in front of the female's f f h f l ' mouthparts. In many cases, the female proceeds to eat the male.
Hypothesis: Copulation lasts longer and more sperm are yp p g p transferred if males are eaten. Prediction: RS of cannibalized males is higher than RS of noncannibalized males. A test: Allow female redbacks to mate with two males. Document the proportion of young sired by each male.
Data: 2nd male Data: male 2nd male 2
rejected accepted
Females ate 1st male Females did not eat 1st male 1. What statistical test would you use to analyze these 1 Wh t t ti ti l t t ld t l th data? 2. For first males, is there a benefit to being cannibalized?
NC = average for non cannibalized 2 cannibalized 2nd males C = average for cannibalized 2nd males
Pa aternity of 2nd male f (fract tion of eggs fertiliz zed)
And more data:
Copulation duration of 2nd male (minutes)
2. For second males, is there a benefit to being cannibalized?