Sexual Selection

1
Sexual Selection
2
Darwin Evolution

• Evolution by natural selection
• Struggle for existence
• Adaptations increase individual survival

3
Darwin
The sight of a feather in a peacocks feather,
whenever I gaze at it, makes me sick
4
Hmm whats that about
5
Darwin on Sex

• Why do males females of the same species differ
  from one another, with males exhibiting
  morphological and behavioral phenotypes more
  exaggerated than those of females?

6
Darwin on Sex

• Why do males of closely related species exhibit
  much greater differences in morphology and
  behavior than the females of closely related
  species?

7
He also noticed that .

• Exaggerated characteristics were more prevalent
  in males
• Why are they adaptive for male not female
• Characteristics like, color, behavior, morphology
  are correlated to but not essential for
  reproduction

8
And that

• May or may not involve physical competition
• Adaptation not always beneficial to an
  individuals survival

9
Sexual Characteristics

• Primary sexual characteristics
• Structures needed for reproduction
• Ex Genitalia
• Secondary sexual characteristics
• Structures not necessarily needed for
  reproduction
• Large peacock tail, beard
• Aids in attracting mate
• Often energetically costly

10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Darwins Theory of Sexual Selection

• "struggle between the individuals of one sex,
  generally the males, for the possession of the
  other sex
• The Origin of Species
• Reduced survivorship of males with elaborate
  characteristics is more than compensated for by
  increased advantage in mating
• Mechanisms
• Male-male competition
• Sexual characteristics are driven by male
  competition for less common females
• Female choice
• Females passively stand by and mate with winning
  males
• Victorian perspective

16
Wallace

• Co-discovered natural selection sexual
  selection
• Agreed with Darwin about importance of male-male
  competition
• Elaborate structures adaptive to attain mates
• Recognized the importance of female choice
• Crypsis is adaptive

17
Sexual Selection vs Natural Selection

• Sexual selection is different than natural
  selection
• Evolutionary selection forces specific to sexual
  reproduction
• Characteristics not always adaptive
• Ex. Peacock tail
• Individuals are favored by their fitness relative
  to other members of the same sex
• Natural selection works on the fitness of a
  genotype relative to the whole population

18
Sexual Selection Works 2 Ways

• Selection on mating behavior, either through
  competition among members of one sex (usually
  males) for access to members of the other sex
• Or
• Though choice by members of one sex (usually
  female)

19
Sexual Selection Mechanisms

• Intrasexual selection
• Male competition
• Males compete for access to females
• Phenotype with competitive advantage selected for
• Physical, behavioral, physiological
• Intersexual selection
• Female choice
• Females prefer males with elaborate traits
• Preferred males mate more often

20
Intrasexual Selection
Direct competition among individuals of one sex.
21
Intrasexual Selection
Indirect competition among individuals of one sex.
22
Intrasexual Selection
23
Intrasexual Selection
24
Intrasexual Selection
http//www.youtube.com/watch?v989uJug7zrg
25
Intrasexual Selection
26
Intrasexual Selection
27
Intrasexual Selection
28
Intrasexual Selection
29
Intrasexual Selection

• http//www.spike.com/video/flatworms-penis/2458366
  

30
Intersexual Selection

• aka Female choice
• Individuals of one sex are choosy in selecting
  their mates from individuals of the opposite sex
• Results in secondary sexual characteristics that
  are not used for competition

31
Female Choice
Figure 23.16x2 Male peacock
32
Marion Petrie the Blasted Peacock

• Male peacock have an average of 150 eyes
• Males with fewer than 130 eyes rarely mate
• Illustrated female choice

33

• www.birdsandbushtours.com.au/ gallery.htm

34
Female Choice

• www.naturalhistorymag.com/ 0302/0302_feature.html

35
(No Transcript)
36
(No Transcript)
37
http//www.youtube.com/watch?vmNXgh333ihQ http//
www.youtube.com/watch?v7l79rgG9bDkfeaturerelate
d
38
Cryptic Female Choice
39
Cryptic Female Choice
40
(No Transcript)
41
(No Transcript)
42
Why Male Competition Female Choice?

• Female gametes
• Few
• Large
• Costly
• Limiting factor is resource availability

• Male gametes
• Many
• Small
• Cheap
• Limiting factor is female availability