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Asymmetry in parental investment between male and females: between male and females: Before fertilization: Asymmetry in size and number of gametes, and.

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Presentation on theme: "Asymmetry in parental investment between male and females: between male and females: Before fertilization: Asymmetry in size and number of gametes, and."— Presentation transcript:

1 Asymmetry in parental investment between male and females: between male and females: Before fertilization: Asymmetry in size and number of gametes, and in the rate that gametes are released. MALES Small gametes Large numbers Energetically cheap FEMALES Large gametes Small numbers Energetically costly

2 Asymmetry in parental investment between male and females: between male and females: Before fertilization: Asymmetry in size and number of gametes, and in the rate that gametes are released. After fertilization: Asymmetry in incubation (some birds), in gestation (mammals), and in care and feeding of young (mammals, some birds)

3 Because the fastest rate that a female can reproduce is slower than the fastest rate that a male can reproduce (especially in birds and mammals) Females are a scarce resource for males ** Female RS is limited by food, condition. ** Male RS is limited by females.

4 Maximum number of offspring produced during lifetime: Male Female Elephant seal Red deer Human >

5 Females Males Number of offspring No. of individuals There is often greater variance in male RS than in female RS

6 Parental investment: Any effort by a parent to increase the chances of survival of an existing offspring at the expense of the parent’s ability to produce future offspring. Parental investment involves a trade-off between current and future offspring.

7 For females:For males: Few gametesFew gametes Each mating is a largeEach mating is a large % of lifetime RS RS depends on theRS depends on the % of offspring raised to maturity Many gametes Each mating is a small % of lifetime RS RS depends on the number of females fertilized Females put most of their reproductive effort into parental effort, while males put theirs into mating effort.

8 Female reproductive success Female reproductive success depends on nutrition Male reproductive success Male reproductive success depends on females

9 In many species, there is male parental investment (PI): Direct male PI: Feeding and protection of young (birds, canids, many fish) Indirect male PI: Provide and defend territory, female or young

10 Mating systems and parental care in mammals in mammals - Internal gestation, lactation - Over 90% of species are polygynous - Male parental care is rare

11 Monogamy: 1 male, 1 female Polygamy: > 1 mate Polygyny: 1 male, >1 female. Or fewer males than females Polyandry: 1 female, >1 male

12 DEGREES OF POLYGYNY IN MAMMALS Slight polygyny: lions More polygynous: gorillas Extreme polygyny: Elephant seals

13 Mating systems and parental care Mating systems and parental care in birds and mammals in birds and mammals Mammals: Internal gestation, lactation. - Over 90% of species are polygynous. - Male parental care is rare. Birds: Eggs must be incubated, chicks must be fed (in most species). - Over 90% of species are monogamous. - Male parental care is often essential.

14 Maximum number of offspring produced during lifetime: Male Female Elephant seal Red deer Human > Kittiwake gull 26 28

15 Parental care in fish Parental care in fish MaleFemaleBoth carecarecare External fertilization Internal fertilization

16 Factors that influence male parental care: 1.External vs. internal fertilization/gestation 2.How effective is care by 1 or 2 parents? 3.Can a deserting male improve his RS? 4.Paternal certainty


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