1. Evolution of Reproductive Tactics
Chapter 10 Or
Sexual Selection

2. Types of Selection Natural Selection Sexual selection
Favors traits that enhance survival, production of young, etc.
Sexual selection
Favors traits that enhance ability to mate.
These traits may lead to lower individual survival
A subset of natural selection that acts through inter- and intra-sexual interactions

3. Types of Selection Natural Selection Sexual selection
Favors traits that enhance survival, production of young, etc.
Sexual selection
Favors traits that enhance ability to mate.
These traits may lead to lower individual survival
A subset of natural selection that acts through inter- and intra-sexual interactions

4. Intra-sexual selection
Favor traits to get mates
Fighting and other interactions
Inter-sexual Selection
Favors traits that females (the choosy sex) prefers.
Ex. - Females like red cardinals – shows males eat well.

5. Inter-sexual Selection
Favors traits that females
(the choosy sex) prefers.
Ex. - Females like red cardinals
– shows males eat well.

6. Bateman’s Principle Male fitness increases as # of matings increase.
Female fitness is weakly correlated with # of matings.
Consequences:
Females are the limiting sex
Therefore the choosy
Males will compete for females
Sexual selection acts on males.

7. Modern Version of Bateman’s Principle
The gender making the greatest investment is the limiting sex
Typically females are limiting
Males are main investors for seahorses and some frogs
Shown at the
cellular level
Large egg
and small sperm

8. Differential reproductive investment patterns
Potential sexual partners are traders and sex is an exchange
Trades must be equitable
Value is based on supply and demand
Male investment in sperm is far lower than female investment in eggs
Male investment in rearing offspring tends to be low
Male reproductive potential far higher than female
Therefore: The operational sex ratio is male biased
Males have surplus supply but high demand
copyright © Dennis Kunkel.

9. 10.11(2) Phylogenetic relationship between complex parental care by males and sex role reversal
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10. Intra-sexual Selection and Sexual Dimorphism
Generally, males are bigger than females, or are better defended.
Big males are energetically expensive
Affects foraging and anti-predatory costs

11. Alternate mating tactics
Males in a population can use > 1 tactic to get mates
Some can be genetically determined
Others are environmentally driven (size due to food availability)

12. Basic Mating Tactics Submissiveness to dominate males Satellite males
Wait and grow tactic
Satellite males
Sneaky males that try to intercept females on the way to mate with dominate males
Female mimics
Males that look like females, get close in territory, and mate with guarded females.
Female mimicry can avoid dominant male aggression.

13. Alternative mating strategies
Genetic vs Conditional strategies
Les Bourgeois
Invest in territoriality
Satellite males
Loiter around bourgeois males and intercept surplus females
Mildly territorial
Sneaker males
Invest in large ejaculate volume, not body size
Steal fertilizations from bourgeois and satellites
Frequency-dependent selection when strategy genetic

14. Territorial (bourgeois) male
Sneaker males
poised in ambush
Territorial male
Sneaker male
Female

15. Evolutionary Maintenance of Alternate Male Tactics
Territory and satellite males in pupfish
Determined by size, not genetics

16. Genetically Determined Tactics
Imagine two morphs, A and B
At “evolutionary stability” – a stable mixture of both types of males, the fitness of A must equal B.
This is achieved with frequency dependant selection
When B is rare, their fitness is > A
When A is rare, then fitness is > B

17. Salmon Normal males – 3-4 years in ocean before returning to spawn
Sneaker males – 1-2 years in ocean
Smaller size, basically bags of sperm
All energy put into sperm production rather than growth.

18. Sponge Isopods 3 types of males Genetically distinct
Territorial, female mimic, and sneaker
Genetically distinct
Determined by 3 different alleles
Fitness based on distribution of females.

19. Male inherited alternative sexual strategies: Paracerceis sculpta
The 3 male morphs with distinct reproductive tactics:
-males are largest possess elongated uropods and comprise 81% of the male population
-males are smaller than a-males, comprise 4% of male population
resemble females in their behavior and external morphology
invade spongocoels by mimicking female behavior;
-males are smallest, comprise 15% of aggregate male population
Use their small size and rapid movements to invade spongocoels (From Shuster 1992).
Male morph differences are the result of genetic differences.
In order for three morphs to exist they MUST exhibit equal reproductive success

20. Growth-based alternative tactics
Satellite and callers in frogs
Marine Iguanas

21. Scorpion Flies Final size determines tactic
Large males – control large dead insect prey as nuptial gift
Medium males – produce saliva balls
Small males – forced copulation (generally not successful)

22. 10.12 Mormon cricket males give their mates an edible nuptial gift
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23. Mate Choice by Females Inter-specific Selection
Fact – Females do not mate randomly, they exhibit nonrandom choice
Assume there is an adaptive basis.
Choice occurs in the sex with the higher parental investment (normally females)

24. Mate Choice by Females Males will offer material benefits to females
Females choice largest nuptial gift
Weaver finches judge male quality by quality of the nest he builds

25. 10.36 Sperm transfer and the size of nuptial gifts
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26. 10.44 Do male ornaments signal good genes? (Part 1)
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27. 10.44 Do male ornaments signal good genes? (Part 2)
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28. 10.15 Sexually selected “ornaments” of males
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29. Monopolization of Resources by Males
Males fight to control resources
Females mate with winner
For genes and access to resources
Bullfrogs
Red Wing Blackbirds

30. 10.9 Male sex drive is intense
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31. Male Parental Care
Fact: Male parental care is very unusual in animal kingdom except for birds
Females chooses males based on ability to feed offspring, ie. quality to be a parent.
Mechanisms:
Courtship feeding
Nest building

32. Examples House Finches Common Moorhen Cichlidfish
Choose males by redness of feathers
Common Moorhen
Polyandrous, females prefer short squat males
Cichlidfish
Females like big males that are better defenders
Males like females that are big egg producers
Both sexes “choose”

33. Female Choice Very common Females very choosy in this situation
Leads to extreme sexual selection
Sometimes results in run away sexual selection

34. Examples

35. Reproductive behavior
Bower birds:
Males build elaborate structures
Females are attracted to these structures
A female will mate with a male after inspecting his bower
After mating the female leaves never to return

36. Reproductive behavior
Boys and bowers: build them bigger build them better

37. 10.2 Evolutionary relationships among 15 populations of bowerbirds
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38. 10.4 Bower building may be an indicator of brain size
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39. 10.43 Male satin bowerbirds provide females with multiple signals (Part 2)
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40. 10.8 Sexual behavior differences between sexes may arise from differences in parental investment
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41. 10.18 Dominant male baboons fail to control fertile females as completely as expected (Part 1)
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42. 10.26 A male black-winged damselfly removes a rival’s sperm before transferring his own
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43. 10.27 Sperm competition has shaped the evolution of the black-winged damselfly’s penis
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