PSYC 311 1st EditionLecture 21April 14 – Sex, Mating, Parenting Evolution of Reproductive Behavior - Why sex?o Western whiptail lizards (WWTL) – display typical lizard mating; bites legs of female (foreplay) and mountso Desert-Grasslands Whiptail (DGWTL) – practices asexual reproduction (no malesin the species) Arguments Against Sex - Cost of Meiosis – cost of producing males o See slide 6: DGWTL can replicate her genes, atleast twice as fast o Takes 2 offspring for WWTL to have parent genes fully represented Only takes one DGWTL - Cost of Recombination o Might delete good genes, and advance bad ones o Survivors are successful and reproduce Possess good gene combinations- Cost of Mating o Mates must be courted, secured and protected More dominant individuals have an advantage (territorial control)o Courtship/mating rituals attract predators o Mating can wound one of the participants (usually female) o How do we know that sexual union is with a member of one’s own species and not with a similar species Pre-zygotic reproductive isolating mechanisms – knowing they are of yourspecies Post-zygotic RIM – cross breeding causes problems- Offspring is usually a sterile hybrid - Physical/behavioral features somewhat in between the two parent species o Unfit for either species (vigor)o **Sexual reproduction is much more common than asexual reproduction Arguments for Sex - Sexual populations can evolve faster due to recombination o Genetic diversity – greater probability of adaptation to environmental pressures Capacity for change enhanced by genetic diversity o Can result in mutations Allergies, lactose intolerance o **Dandelions are asexual reproducers that are stuck with the parts of sexual reproducers - Sexual reproduction provides resistance to effects of mutations o “Ratchet Effect” – cumulative deleterious effects of mutations (leads to loss of vigor)o some animals employ both – aphids, hydras Asexual reproduction favored when near-future environment is constant (spring, summer) Sexual reproduction favored when environmental change is impending (winter) - Why have different sexes?o Bacteria exhibit sexual reproduction but only have one gender o differential selection – eventually resulted in different sexes most fit sperm get the ovum o Sperm and ova contribute equally Ova contribute more cytoplasm, endoplasmic reticulum, Golgi, and MITOCHONDRIA - no mitochondria in sperm - we’re all a little more mom than we are dad (females contribute most) ova are much bigger than sperm - high cost for females, low cost for males o Why the uneven burden? Evolution favors increased ova size and decreased sperm size - disruptive selection Trivers – females have a greater parental investment than males - “inequity” true both before and after the child is born o Why don’t males have a greater investment? C/B ratio of increased investment for males is less - decrease in probability of passing on genes if investment were equal to female Are the offspring his?- Mothers are always sure that the baby is theirs, males are never sure Approaches to Reproduction - Epigamic element – differences between males and females in terms of mate selection o Different requirements and C/B analyses o Sexual dimorphism - Consequences for C/B in maleso Competition among males for females- Males have low threshold for sexual reproduction o Mistakes are more costly for females- Females are choosier (high threshold) - Are his genes neat? Does he have resources? Is he my species?- Epigamic selection in males (slide 33)o Use of strategies allowing males to copulate successfully o Slide 33- Evolutionary pressure led to (slide 34)o Competition to secure females- Low threshold- Dominance behavior – competition and territory - Lek System - Bower Birds Alternative Mating Strategies - Troops – less dominant males trail male guarding a group of females and coordinate displays as attractions - Satellite males – solitary males hang around and try to sneak in - Mimicry of females – rape?- Competition to ensure o Protection of inseminating femaleo Being last to copulate with female (“spatula scoop”)o Carrying eggs (male seahorse pregnant)o Use of vaginal plugs (rats)o Pair bonding – sometimes for life Could signal to rival males that female is inseminated- Wedding ringso Placement of repugnant chemicals that turn-off males - Competition by decreased reproductive fitness of rival males (slide 44)o Sexual interferenceo
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