The principles and theories of mate selection

1. Mate selection: Principles
and theories
Dr. Surjya Kumar Saikia
Department of Zoology
Visva-Bharati University

2. What we will learn………?
• We will be able to know and understand Bateman’s
Principle.
• We will be able to know and understand Fisher’s
Runaway Model.
• We will be able to know Fisher’s Sexy son
hypothesis.
• We will be able to know Zahavi’s ‘handicap’
hypothesis.

3. Sexual dimorphism
Mating systems
Monogamy Polygamy Promiscuity

4. The peacock’s tail
Extravagant male ornaments
The peacock’s tail greatly impairs his mobility…how could such a trait evolve?

5. Sex roles
The sex which invests the
most in offspring will
become a limiting resource
over which the other sex
competes ( = sexual
selection)
‘Males are promiscuous and females are choosy’
Angus John Bateman (1919–1996)
Bateman’s principle

6. Gametic investment:
sperm are consequently
cheaper than eggs
This predisposes females
to a greater level of
parental investment
Males can easily
produce enough sperm
to fertilize all of a
female’s eggs,
but the reverse is not
true
Mating opportunity
limits male
reproductive success
Fecundity limits female
reproductive success

7.  Pregnancy
 Care
 Nutrition
 Feeding

8. Sex-role reversal
Pipefish, sea horses, and
sea dragons belong to a
family in which the males
get pregnant
Here, males perform the
majority of the parental care,
while the females are highly
ornamented and territorially
aggressive

9. The number of males a female mates
determines her reproductive success
because she doesn’t care for eggs
Jacanas: One more example of sex role reversal
Most jacana species exhibit
harem polyandry
Males exhibit “sex role reversal”
Females mate with multiple males
and then leave eggs with males
Males maintain small territories and
perform all parental care

10. Polyandry- when male is a limiting resource
This often occurs when low offspring
survival requires male parental care
What is the
consequence?
Sexual selection is
stronger on females
than males
Saddleback TamarinsSpotted Sandpiper
Red-necked phalarope
Photo:
Commons.wikimedia.org

11. The peacock’s tail
Extravagant male ornaments
The peacock’s tail greatly impairs his mobility…how could such a trait evolve?

12. Andersson (1982) Nature 299:818
Male ornaments Long-tailed widowbird
1.Obtain mates more quickly
2.Have greater reproductive success
3.Experience a cost in tail size the
following year
Males with elongated tails:
Experimental manipulation
of tail length
Males with unnaturally long tails
attract females away from the nests
of “normal” males or males with
shortened tails

13. What is the hypotheses for male ornaments
Mate choice originally evolved to facilitate adaptive
choice for traits conferring a survival advantage
Once female preference evolved, any gene/s that
conferred survival advantage but compromised
attractiveness would not be passed on because
surviving males would fail to mate Ronald Fisher
Fisher’s “runaway” hypothesis

14. Fisher’s runaway modelFitness
Tail length
Total male fitness
(survival + mating)
Fitness due to survival
Survival Selection
Sexual Selection
Female choice
adaptive for survival

15. A female's ideal mate choice among potential mates is one
whose genes will produce male offspring with the best
chance of reproductive success
Fisher’s Sexy son hypothesis
Ronald Fisher

16. Amotz Zahavi
Zahavi’s “handicap” hypotheses
Extravagant male traits are costly to
develop and maintain
Choosing a mate with “good genes”
requires an honest signal of genetic
quality
Only males in good condition (those
with good genes) will be able to fully
develop and maintain an ornament

17. Handicap hypothesis
Note that the handicap itself need not be heritable. It needs only to provide a
reliable index of fitness, and fitness must be heritable
Condition dependent
Handicap: Traits that
encumber the
owner are physiologically
fit and costly (exertion in
flight) as well as being
more expensive to
develop
Revealing Handicap:
Bright color honestly signals
immunocompetence and
parasite/disease resistance

18. Asymmetry is indicative
of developmental
instability and possibly
“bad genes”. Symmetry
is chosen in some species

19. Bateman’s
Principle
Fisher’s
Runaway
Model
Fisher’s
Sexy Son
Hypothesis
Zahavi’s
Handicap
Hypothesis
What we have
learnt……