Important Note About This Lecture

1
Important Note About This Lecture Please be sure
to review this web presentation for material on
altruism. This material will be covered on exam
even though not presented in class today.
2
From predator avoidance To sex
3
Darwin Sexual size dimorphism is common.
elephant seals
Many mammals males bigger
female
male
Many spiders males smaller
rainforest spider
4
Sexual differences include differences in
morphology and behavior.
Elephant tusks Beetle horns Bird head ornaments
Morphology
Male frigate bird inflating red pouch to
female Male moth antennae, elaborated for sex
pheromone Male frog calling by inflating vocal sac
Behavior
5
Sexual differences often reflect sexual selection.
sexual selection form of natural selection
relating to differences in reproduction by
different genotypes of the same sex
6
Darwin (1871, p. 256) We are, however, here
concerned only with that kind of selection, which
I have called sexual selection. This depends on
the advantage which certain individuals have over
other individuals of the same sex and species, in
exclusive relation to reproduction.
7

• Sexual selection involves two mechanisms
• Mate competition
• Mate choice

8
A. Mate competition members of one sex compete
with members of the same sex for access to mates
male marine iguanas
bull elephant males
9
B. Mate choice members of one sex choose mates
among members of the opposite sex
Male peacock display Male sparrow singing Male
frog calling
10
Male Courtship in Jumping Spiders
(video)
11

• Possible Functions for Mate Choice
• Nuptial gifts
• Genes for good health
• Genes for attracting the opposite sex

Examples of each type

• Roadrunner offering lizard to female
• Spring peeper calling to females
• Male stalk-eyed fly

12
Do sexes differ with respect to mate competition
and mate choice?
13
Generally, Males compete more intensely for
mates than do females. and Females are choosier
about their mates than are males. WHY?
14
Answer Anisogamy Anisogamy the occurrence of
Gametes of different sizesMales make many
small gametes, termed sperm.Females make few,
large gametes, termed eggs.
Optional material
15
Anisogamy suggests that male fitness will be
limited by number of mates, whereas female
fitness will be limited by quality of offspring.
Optional material
16
Consequently males should compete more for mates
than do females, and females should be choosier
about who they mate with.
We are!!
We do!!
Optional material
17
From sex To altruism
Required material!!
18

• Altruism
• behavior that benefits a recipient while
  incurring a cost to its donor
• alarm calls in prairie dogs
• helping behavior in birds mammals
• sterile castes in honey bees, ants and naked mole
  rats

19
Explanations for Altruism
Kin Selection propagating ones genes by helping
genetic relatives propagate genes shared by
descent
20
Concept of Inclusive Fitness W.D. Hamilton
(1964) an individual increases its fitness either
through own personal reproduction OR reproduction
of genetic relatives inclusive fitness is fitness
due to both forms of reproduction
21
Females fighting
Males playing
Cooperation between male chimpanzees is greater
than cooperation between females.
In chimps, females disperse from natal troop,
whereas males often stay.
Hence, males in a troop are more
genetically-related to each other.
22
Conditions for altruism towards genetic relatives
(kin) set by Hamiltons rule b/c gt 1/r b
benefits to recipient c cost to donor r
coefficient of relatedness
Relationship r mother-offspring 1/2 sister-brother
1/2 uncle-nephew 1/4 cousin-cousin 1/8
If r 1/2, then benefit b must ? 2c.
23
I would lay down my life for 2 of my brothers or
8 of my cousins.
-- J.B.S. Haldane
Reportedly making this statement in a British
pub, Haldane was referring the fact that we are
more closely related to our siblings than we are
to our cousins, And that altruism should be
adjusted accordingly.
24
Extremes in Altruism Darwin perplexed by sterile
castes in social insects. groups of individuals
within a colony that did not breed, instead
helping the queen to breed.
25
Kin Selection Sterile Castes Hamilton,
1964 haplodiploidy kind of sex determination in
which males are haploid (1N), females diploid
(2N). Ants, bees and wasps are haplodiploid.
26
Hamilton reasoned that haplodiploidy would affect
relatedness among kin. termed relatedness
asymmetry
Review Text, page 1033.
27
Relationship rDIPLODIPLOID rHAPLODIPLOID mother-
offspring 0.5 0.5 sister-sister 0.5 0.75
In haplodiploid system, sisters are more related
to one another than they would be to their own
offspring! Worker bees can benefit by foregoing
reproduction and helping queen rear.... more
sisters!
28

• Sterile Castes in Naked Mole Rats
• Naked mole rats are African mammals that live
  underground and feed on plant roots.
• Occur in colonies of up to 300 members.
• Breeding restricted to a single queen.

Watch naked mole rat webcam
http//nationalzoo.si.edu/Animals/AfricanSavanna/d
efault.cfm?cammr
29
Naked Mole Rats Not Haplodiploid But Still
Highly Genetically Related Extreme inbreeding in
mole rat colonies generates high degree of
genetic relatedness.