1. Evolution III - contents
Sexual selection vs. natural selection
Male and female strategies
Alternative mating tactics

2. Sexual dimorphism
The large, male California sea lion, is distinctive from the surrounding, smaller females (from Kardong).

3. Sexual dimorphism
e.g. in peacock

5. Sexual selection
Differential reproduction owing to variation in the ability to obtain mates (as opposed to natural selection, which is related to the differential survival of individuals in nature, depending on non-sex related traits) – see Futuyma – Evolutionary Biology

6. Males are often less selective than females
Australian
jewel
beetle
male
toad

7. Biologists exploiting animal desire
sea
elephant

8. Anisogamy - Sperm and oocyte of hamsters (enlarged 4000 times – from Alcock)

9. Differential reproductive success in males and females
Female oocytes are a limited reproductive resource, whereas male sperm is not
Therefore, males have the potential to sire many more offspring than females
In humans, the male world record is held by Moulay Ismail the Bloodthirsty (Sultan of Morocco ), who is said to have fathered 888 children
Men produce between
100 and 300 million
sperm per day.

10. Female reproductive success in humans
According to Guinness World Records 2001, the highest officially recorded number of children born to one mother is 69. This was the first wife of Feodor Vassilyev ( ) of Shuya, Russia. Between 1725 and 1765, in a total of 27 confinements, she gave birth to 16 pairs of twins, seven sets of triplets, and four sets of quadruplets. 67 of them survived infancy.

11. Females must be more choosy because
costs of producing female gametes are higher
costs of pregnancy are higher (e.g. in mammals)
females often invest more into parental care
costs of mating with partner of poor genetic quality are higher in females

12. Thus, a general pattern across the animal kingdom is
males compete for females and try to mate with as many as possible (emphasis often on quantity)
females are choosy and try to find the highest quality partners (emphasis on quality)

13. How to impress females
1. look nice

14. How to impress females 2. bring them presents
(as e.g. in scorpion flies (right)
and Bittacus (below))

15. How to impress females
3. offer yourself as a present (e.g. preying mantids, some spiders: females cannibalise
males during or after mating –
thus detracting attention
from other possible sex
partners. also you give your
body as a resource for offspring)

16. How to impress females 4. sing them songs (picture from Alcock)
European warblers
Days to
finding
partner
Number of songs in repertoire

17. If none of this works - cheat
Satellite strategies – younger or “weaker” males often position themselves strategically near an attractive male, then sneaking up on females when the large male is un-attentive or otherwise engaged
Great Plains toads,
longhorn sheep,
horseshoe crabs

18. Alternative male mating tactics
different males in the same species use different strategies to gain access to females
satellite strategies are one example

19. Alternative male mating tactics – “rape”
In scorpion flies, some
males will not bring
presents, but mate with
unwilling females.
Usually “losers”,
fertilisation success
typically low.

20. FIGURE 7.12 Barn Swallows (Kardong, after Andersson, Moller)
Females often prefer exaggerated male traits
FIGURE 7.12 Barn Swallows (Kardong, after Andersson, Moller)

21. Why do females prefer exaggerated male traits?
“Good genes hypothesis” – extravagant traits indicate biological fitness (because less fit males would be less able to afford such traits).
One special case of this hypotheses is that such traits indicate ability to cope with parasites.
“Runaway selection hypotheses” – females prefer sexually attractive traits which they pass on to sons, which makes sons more fit (but only because the sons in turn will also be more attractive to females).