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Reproductive Strategies. vs. Three types of comparisons: across species within species/ within a sex (alternative mating strategies). Reproductive Strategies.
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vs. • Three types of comparisons: • across species • within species/ • within a sex • (alternative mating strategies) Reproductive Strategies A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success. (more definitions later) specifically • Topics: • Why sex? • Male vs. female • Sexual selection
Why sex? vs. asexual reproduction (cloning) (sexual reproduction) Whiptail lizards some examples Aphids Portuguese man-o-war
Why Not Sex? Because Sex is Costly ! • Gonads are expensive organs to produce and maintain • Mating is risky, costly, time-consuming, often involving elaborate structures and behaviors • Cost of meiosis – this is the most significant cost
Why Not Sex? Sexual Reproduction:Cost of meiosis Asexual cloning Since each sexually-produced offspring only contains half the genetic material of each parent, there is a 50% reduction in fitness compared to asexual reproduction
Why sex? Benefits of Sexual Reproduction Natural selection is limited by fact that even as a species adapts to its biotic environment – its competitors, predators, parasites – that environment is also evolving. → “Arms Race” Genetic variability among offspring permits response to changing biotic environment Red Queen Hypothesis: whereas asexual reproduction is a ‘sitting duck’ target for competitors, pathogens, predators, sex and geneticrecombinationpresentamoving target “It takes all the running you can do to keep in the same place!”
Male and Female • ♂♀ • How define “male” and “female”? • Sex chromosomes not generally useful criterion: • Mammals: M - XY, F - XX • Birds: M – XX, F – XZ • Hymenopterans: M – N, F – 2N • Hermaphroditic species • Turtles, alligators: Facultative • (incubation temp dependent)
Male and Female Temperature-dependent Sex Determination
Male and Female • ♂♀ • How define “male” and “female”? • Male and female defined by relative size of their gametes (sex cells): • Females produce relatively few but expensive (provisioned) sex cells. • Males produce many more but cheap sex cells.
Anisogamy = “Unequal gametes” Eggs: few, large, energetically expensive Sperm: many, small, cheap Eggs and Sperm Fig 10.6 Alcock
Natural Selection Survival Parental Care
Natural Selection Survival Mating Success Parental Care
Natural Selection Survival Mating Success Parental Care Intrasexual Mate Choice Competition (Epigamic) Sexual Selection
Intrasexual Selection Epigamic Selection
SEXUAL SELECTION Occurs when (1) males compete among themselves for access to females (intrasexual selection) . . .
SEXUAL SELECTION Occurs when (1) males compete among themselves for access to females (intrasexual selection) and/or (2) try to attract females by flashy colors, behaviors etc (epigamic selection). Greater Sage Grouse 1 23
Black Grouse Norway Black Grouse Lek in Norway
What exactly do females see in these guys (besides a pretty face)? Epigamic Selection
Intrasexual selection → weapons, fighting National Geographic Wild America
Alternative Strategies come back to later Bluegill Sunfish
Epigamic Selection Flip side of epigamic selection: Female choice
Reproductive Strategies 1. A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success. 2. A set of behavioral and physical adaptations shaped by sexualselection.
Male-male competition (Intrasexual selection) Female Choice (Epigamic selection) Summing Up: • Sexual Selection tends to produce weapons and elaborate ornaments and displays • Sexual selection has two components: What drives sexual selection? Trivers: Key to sexual selection is parental investment (PI) = effort put into helping your offspring reach reproductive age.
Trivers: Differential Parental Investment drives Sexual Selection Female PI Sexual Selection ♂ - ♂
PARENTAL INVESTMENT (PI) • Initial PI • female's provisioning of egg cell • Specialized PI (mammary glands, incubation patches, etc) – usually supplied by one sex only, and that • is almost always the female • female’s nourishing of the embryo • female’s producing yolk-filled egg (reptiles and birds) • incubation (reptiles and birds) • female lactation • Generalized PI – usually behavioral and can be supplied by either sex • guarding the offspring • feeding the offspring • defending a territory/nest used for feeding and protecting young
Male-female difference in PI (mammals) Erick Greene
female’s producing yolk-filled egg (reptiles and birds)
Male Randall’s Jawfish Mouth-Broods Eggs
PARENTAL INVESTMENT (PI) 1. initial PI: females produce large egg cells, males produce small sperm 2. specialized adaptations directly related to reproduction (e.g., gestation, nursing): usually the female 3. behavioral adaptations (and costs): egg-guarding, protecting and feeding young: females or males (more commonly the female) Generally, female PI is much greater than male PI
SEXUAL SELECTION • Trivers: Key to sexual selection is parental investment (PI). • Trivers: Sexual selection = • Sex investing less will compete for sex investing more (intrasexual selection) • 2. Sex investing more will be discriminating in choosing mates (epigamic selection) • Typically: Female PI > Male PI • so usually its males competing among themselves for females and females choosing among males. • First: consider some consequences…
General Sex Differences in Behavior ♀ Male: ardent, indiscriminant Female: reluctant, discriminating ♀ • FEMALES – “Don’t you Dare.” • MALES – “Laissez Faire.”
