Lecture 2 (Mate Choice 1) - Slides Flashcards
0
Q
2 Ways to get a sexually selected trait
A
1) Vanquishing same-sex rivals (intrasexual selection)
2) Being chosen by the opposite sex (intersexual selection)
- May not operate indendently, mate may be more likely to be subject to intersexual selection after an intrasexual competition
- Example: Male deer and antlers are both for competition and are selected by females (Large antlers = better health and fewer parasites, and if they can use them in competitions = strength)
1
Q
Sexual Selection
A
- Differential access to mates (more important) or gametes
- Natural selection operates independently (differently) for the sexes
- Sexual selection may not aid survival, and may impeded it. But it does aid reproduction.
2
Q
Handicap Principle
What is the cost balance called and explain
A
- Only those individuals in good condition can afford to grow or develop larger more elaborate versions of these traits (does not have to be physical, can be psychological as well.
- Fitness trade-off occurs because it’s expensive to develop these signals which could be used for survival
- Everything has a trade-off
- Example: Heightened growth to be bigger and stronger faster heightens aging
3
Q
Sexual Dimorphism in size
(What is the name for increased intrasexual competition among males, why is there variation in size at all, why not all big?)
A
- Polygyny: Increased intrasexual competition among males
- Males are 1.06 times larger than females in humans on average
- Why variation? Bigger individuals die earlier - important for grandparenting, and females may mate for resources and other reasons, not just height, but tall males usually have more resources.
- Also depends on female height.
- Monogamous species have similar size/shape/colour between sexes
- The more promiscuous the sexual behaviour, the more dimorphism (Usually male is bigger than female in mammals)
- Size is as good of a threat as ACTUALLY fighting and if competition increases, size becomes more important (Height is an ornament and a weapon)
- Exaggerated ornaments and weapons can occur as part of sexual dimorphism if competition increases
4
Q
Salska (2008)
A
- What is your ideal partner height for a romantic relationship
- Women prefer taller males, males are more flexible but perfer shorter
- Preference for height depends on your height as well and average height of men in your potential mate pool
- Indirect benefit of height: Height in males is heritable and will increase likelihood offspring will be more rep
5
Q
Male tallness benefits and cost
A
- Intimidate rivals, win physical competitions, provide resources and may cue status
- Cost: Senescence, difficult to achieve
6
Q
Sex Differences in Reproductive rate
A
- Women are constained by pregnancy, gestation, and lactation, limited conception risk (can only get pregnant at certain times)
- Men is limited only by the access they have to mate (and puberty), but have higher variance/death rate due to competition.
- On average most have 2-3 children, in natural fertile non-industrial cultures it’s higher
7
Q
Bateman’s Principle
A
- The sex with more variance in reproductive success will compete for access to the sex with less variance in reproductive success
- In humans, females are not able to reproduce as often as males for many reasons and therefore are more selective and males will be more competitive - the OSR is skewed to males
- Results in some males mating with multiple females, and some males not at all.
8
Q
Operational Sex Ratio
A
- Ratio of sexually mature males to sexually mature females that are available to mate.
- Sex ratio = regardless of sexually mature available to mate (107-100 males-females in humans)
- Influenced by differences in: Reproductive rate, sexual maturation, mortality
- Causes men to compete more (not enough women to go around) and females to be choosy about mates (to have higher standards)
9
Q
Examples of OSR
Natural effects and cultural events
A
- Young male syndrome: more male offspring born, but they die more usually do to more risky behaviours (still will have a male skew in OSR)
- Single Child Law in China
10
Q
Triver’s Parental Investment Theory
A
- The sex that invests less in offspring will compete for the sex that invests more.
- The sex that invests more in offspring will be more discriminative in selecting mates than will the sex that invests less
- Not all women release an egg in an ovulatory cycle and there is variation in egg quality
11
Q
Factor’s Influencing Parental Investment
A
1) Anisogamy: - Differences in gametes (Sperm are smaller and produced in huge quantities (12mil/hour), Ova are larger and 400/lifetime)
2) Gestation: Huge maternal investment and women prefer/mated with men who gave them more resources. Lactation further suppresses fertility
3) Post-natal care: women tended to be in contact with infants more than fathers
12
Q
The Coolidge Effect
A
- Males exhibit renewed sexual interest if introduced to new receptive sexual partners even after refusing sex from prior but still available sexual partner
- Males produce more sperm in their ejaculate to a new partner
- Women going on dates are more preoccupied with looking different, may be related to this.
- Men are more likely than women to benefit from additional mate opportunities
13
Q
Desire for number of mates
Bride wealth
A
- Male reproductive success benefits from increase in wives
- Payment made by a groom or his kin to ratify a marriage
- In some cultures the dowry is about the same as ring
- Men want sex with a new partner earlier than women, want more partners over 30 years and consent to sex earlier.
- Africa is very low, likely due AIDS and sex education
- Bride wealth positively correlates to how early female was circumcised (when she hit puberty. Earlier puberty = more fertile)
14
Q
Clark and Hatfield 1989
A
- Asked attractive confederates to ask out strangers.
- Men and women will equally go on a date, but apartment/sex option was way more men, and men apologized when they did say no
