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顏士清、林致綱、王韋政、廖昱銓呂翊維、高詩豪、陳禹勛

Human sperm competition: testis size, sperm production and rates of extrapair copulations Simmons, L. W., R. C. Firman, G. Rhodes, and M. Peters Animal Behaviour, 2004, 68, 297-302. 顏士清、林致綱、王韋政、廖昱銓呂翊維、高詩豪、陳禹勛. INTRODUCTION.

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顏士清、林致綱、王韋政、廖昱銓呂翊維、高詩豪、陳禹勛

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  1. Human sperm competition: testis size, sperm production and rates of extrapair copulationsSimmons, L. W., R. C. Firman, G. Rhodes, and M. PetersAnimal Behaviour, 2004, 68, 297-302 顏士清、林致綱、王韋政、廖昱銓呂翊維、高詩豪、陳禹勛

  2. INTRODUCTION • When sperm from two or more males are present within the reproductive tract of a single female, there will be competition between them to fertilize available ova (Parker, 1998) • Increased risk and intensity of sperm competition are expected to favour increased male expenditure on sperm production (Parker, 1998)

  3. Sperm competition Body size dimorphism Canine size Testes size (Hacourt et al., 1995)

  4. AIMS Do human males adopt alternative reproductive tactic? (examined the relation between EPC behaviour and expenditure on sperm production) Testis variation Risk of sperm competition EPCs Sperm production

  5. Methods Subjects: 194 women and 222 men Questionnaire: age, sex, sexual orientation, and lifetime sexual behaviour (provided details on the occurrence and number of EPCs) permissive attitude (1:strong agree - 9:strong disagree) 1.sex without love is OK. 2.casual sex outside of existing relationships is OK. 3.sex on the first date is OK. 4.I would need to know my partner emotionally and psychologically before having sex.

  6. Methods • Measure the width and length of both the left and right testis. • Fifty person were recruited specifically to provide a semen sample for analysis.

  7. Results • There were no significant differences in the proportion of men and women who reported having engaged in EPCs (P =0.176) • There is no significantvariation in combined testis volume caused by male age, height, weight or ethnic grouping.(p=0.469)

  8. Results • There was no significantdifference in combined testis volumes between men who reported engaging in EPCs and those who reported not to have engaged in EPCs. • Testis size was not related to a man’s permissive attitude (p=0.70).

  9. DISCUSSION

  10. DISCUSSION The important data from the perspective of sperm competition risk is the probability that women will engage in EPCs. Only where women’s behaviour has the potential to generate extrapair paternity, the risk of sperm competition will be a selective force.

  11. DISCUSSION The population-wide rate of EPC of about 20% is expected to generate a rate of extrapair paternity of about 0.6% - 1.2%.

  12. DISCUSSION If the selection pressure from sperm competition risk lies somewhere between 2% and 22%, then we should expect male expenditure on testis size to be greater than for a monogamous species, consistent with the position of human relative testis size lying between those of gorillas and chimpanzees.

  13. DISCUSSION Neither was there a relation between the numbers of EPC partners reported by men who had engaged in EPC activity and their combined testis volume, or between testis volume and men’s attitudes towards permissive sexual behaviour. No evidence to support the claim that men adopt alternative reproductive strategies of sperm competition and monogamy.

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