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:
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
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)
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.
Maximum number of offspring produced during lifetime: Male Female Elephant seal Red deer Human >
Females Males Number of offspring No. of individuals There is often greater variance in male RS than in female RS
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.
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.
Female reproductive success Female reproductive success depends on nutrition Male reproductive success Male reproductive success depends on females
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
Mating systems and parental care in mammals in mammals - Internal gestation, lactation - Over 90% of species are polygynous - Male parental care is rare
Monogamy: 1 male, 1 female Polygamy: > 1 mate Polygyny: 1 male, >1 female. Or fewer males than females Polyandry: 1 female, >1 male
DEGREES OF POLYGYNY IN MAMMALS Slight polygyny: lions More polygynous: gorillas Extreme polygyny: Elephant seals
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.
Maximum number of offspring produced during lifetime: Male Female Elephant seal Red deer Human > Kittiwake gull 26 28
Parental care in fish Parental care in fish MaleFemaleBoth carecarecare External fertilization Internal fertilization
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