1. Sex & behaviour: Sexual Investment
CfE Advanced Higher Biology
Unit 2: Organisms and Evolution

2. Key area 2.4
Parental investment
Courtship

3. “What am I?” Guess the key word Post-It Note game….
First Task…
“What am I?” Guess the key word Post-It Note game….

4. Key areas
Comparison of sperm and egg production in relation to number and energy store.
Problem and solutions of sex for sessile organisms.
Compare costs and benefits of external and internal fertilisation.
Benefits and drawbacks of parental investment.
Classify r-selected and K-selected organisms.
Various reproductive strategies have evolved ranging from polygamy to monogamy.
Give examples of courtship behaviour.
Describe lekking species and the alternative successful strategies of dominant and satellite males.
Describe how courtship behaviour in birds and fish can be a result of species-specific sign stimuli and fixed action pattern responses.
Describe the effect of imprinting on mate choice later in life.

5. Darwin’s Puzzle: Why are males and females different?
Darwin, C The Descent of Man and Selection in Relation to Sex. 1st ed., Murray, London.
Think, pair, share…
What are your thoughts on the above statement?

6. Assumption
Assumption: every organism has adaptations that function to facilitate reproduction
Members of a population/species live in the same environment, so why do some animals have different adaptations than others?
Morphs: age, sex, others
SEX: male and female adaptations are different
WHY?

7. Parental Investment What is it?
“Any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring” (Trivers 1972)

8. Parental investment
Parental investment is costly but increases the probability of production and survival of young.
Group task:
Split up into groups of 4 and each make notes on one of the case studies in your notes booklet. Choose one of the following and tell the rest of your team about it.
King Penguin
Mole Rats
Kestrels
Cardinal Fish

9. Examples of pre-natal care Examples of post-natal care
Preparing a nest
Providing food for young
Guarding eggs
Protecting young from predators
Carrying young
Positive reinforcement (Eg. Teaching baby birds to fly)
Placental nourishment in mammals

10. Sexual Selection and Parental Investment Theory
For members of the sex that invests more in offspring, reproductive success is limited by the amount of resources an individual can secure for itself and its offspring.- Females
For members of the sex that invests less in offspring, reproductive success is limited by the number of mates one can acquire.- Males

11. Nurturant Females
In most animals, and almost all mammals, females provide far more parental investment than just the egg.
Internal fertilization protects, but at a cost.
Fish vs. mammals
External fertilization, less protection not as physically costly but other cost?
Humans (mammals):
Prolonged internal gestation (pregnancy)
Placentation
Lactation

12. Sperm vs Egg
In sexually-reproducing species, the relative size of gametes define who is male and who is female.
Sperm- 5µm across, tail 50µm long.
Ovum- 0.1 mm (size of a small full stop)
Why?
Twig: Sperm Twig: Ovum

13. Sexual Dimorphism
Amongst vertebrates, the clearest dimorphism is between gamete (sex cell) size. This single physical difference explains why behavioural sex differences exist.
Females gametes: large, nutrient-filled, expensive to produce, limited in number, and produced infrequently. If fertilised this will lead to high costs to the female.
Male gametes: small, have no nutrients, cheap to produce, constantly made throughout life.
Reproductive Capability: females are thus classed as the ‘slow sex’ and males the ‘fast sex’.

14. Costs and benefits of external and internal fertilisation
Internal fertilisation is the process by which the sperm and egg nuclei fuse inside the female. Conversely, external fertilisation is when this fusion occurs outside the female.
Internal External

15. External- costs and benefits
In external fertilisation, large numbers of eggs and sperms are released into the water and fertilisation occurs in the absence of parents.
External water is essential here to prevent gametes from drying out and to provide a medium for sperm to swim to eggs.
Courtship behaviour is important in external fertilisation because timing is crucial to ensure that mature sperm and ripe eggs meet.
Environmental stimuli, such as temperature or day length, may cause all the individuals of a population to release their gametes at the same time, while chemical signals from one individual releasing gametes may trigger gamete release in others.

16. Internal- costs and benefits
Internal fertilisation is necessary where no external moisture is available.
Cooperative behaviour which ultimately leads to copulation is required.
Internal fertilisation requires highly advanced reproductive systems.

17. Sessile Organisms What are they? Organisms that aren't mobile
Reproductive problems?
How do they find mates, swap genetic information, come into contact?
Solutions?
Asexual reproduction, clustering, budding, motile stages of life cycle, reproductive blooms
Coral spawning

18. Answer the following questions on these key areas:
Compare sperm and egg production in relation to the number and energy store.
Which sex has the greater investment?
List the problems and solutions for sessile organisms.
What are the costs and benefits of external and internal fertilisation?
If parental investment is so costly, why do animals dedicate so much energy to it?

19. Compare sperm and egg production in relation to the number and energy store.
Males
Female gametes
Small
Large, nutrient-filled
Have no nutrients
Expensive to produce
Cheap to produce
Limited in number
Constantly made throughout life
Produced infrequently
If fertilised this will lead to high costs to the female

20. Reproductive problems
2. Which sex has the greater investment?
Females
3. List the problems and solutions for sessile organisms.
Reproductive problems
Solutions
How do they find mates?
Asexual reproduction
Swap genetic information?
Clustering
Come into contact?
Budding,
Motile stages of life cycle
Reproductive blooms

21. 4. What are the costs and benefits of external and internal fertilisation?
Internal costs
Internal benefits
External costs
External benefits
High parental cost
Low number of egg and sperm
Large numbers of eggs and sperms
Low parental cost
Requires highly advanced reproductive systems.
Water not required
Water is required
High survival rate of offspring
Low survival rate of offspring
Environmental stimuli, such as temperature, day length, or chemical signals are required for external fertilisation.

22. 5. If parental investment is so costly, why do animals dedicate so much energy to it?
Parental investment is costly but increases the probability of production and survival of young.

23. r & K Selection
r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity (r) and quality (K) of offspring.
The focus upon either increased quantity of offspring at the expense of individual parental investment, or reduced quantity of offspring with a corresponding increased parental investment, varies widely, seemingly to promote success in particular environments.

24. How many, and how often? r Selection K selection Age of maturation
(aka. Quick-and-many)
K selection
(aka. Slower and fewer)
Age of maturation
Young – usually before the next breeding season
Older – usually many seasons after birth
Number of offspring
Many
Few
Frequency of breeding
Usually frequently (many times a season) – high fecundity = many eggs produced per breeding season
Generally once a season. Low fecundity
Size of offspring
Usually small
Generally larger
Mortality rates
High – many offspring do not live to sexual maturity
Low – offspring generally survive
Examples of species
Mice, rabbits, most insects, cane toads, octopus, mass spawning organisms
Humpback whales, elephants, humans, some birds

25. Eggs or liveborn young? Oviparity Viviparity Literally means
Ovum = egg, parus = bearing
Vivus = living, parus = bearing
Description
Eggs released by mother, embryos develop outside mother’s body, nourished by egg yolk
Embryo develops in mother, born as young. Mode of nutrition varies
Benefits
Reduced energy use in care of young
Yolk provides good nutrient source
More likely for offspring to survive to birth
Drawbacks
Eggs may need to be incubated
Less chance of survival to birth due to eg. Eggs desiccating, predators, poor environment
Energy expenditure for female carrying offspring
Examples
Birds, sharks, reptiles, monotremes
Humans, some snake species, most mammals

26. Parental care or not? No parental care Care of laid eggs Care of young
What is it?
No contact with offspring after eggs are laid
Guarding and/or incubating eggs to hatching
Care of young after hatching/birth
Benefits
Free to mate more
No energy expenditure
Eggs have protection from predators/ harsh conditions
High chance of offspring survival
Drawbacks
High levels of mortality
Energy expenditure
Some mortality after hatching
Very high levels of energy expenditure – may not be able to mate for many years after offspring birth
Examples
Reef fish, frogs, turtles
Seahorse, diamond python, cephalopods (eg. Octopus, squid), spiders
Humans, primates. Mammals (milk), emperor penguins, emus

27. Key concepts
Examples of r-selected species are; toads, insects and mice.
Examples of K-selected species are; humans, elephants and deer.
Parental investment can be classified into discrete r-selected and K-selected organisms but it does not reflect continuous range of life history strategies.
Various reproductive strategies have evolved ranging from polygamy (many mates) to monogamy (one mate).

28. Key area 2.4
Parental investment
Courtship

29. Female choice
When females choose a mate they have to make a selection and are therefore assessing each male’s fitness. This could be:
Physical appearance- this indicates good genes
Chemical signals- also indicates good genes
Presence or absence of parasites- the absence of parasites shows that the male is healthy.

30. Male Reproductive Strategy
Male–male rivalry: large size or weaponry increases access to females through conflict.
Alternatively some males are successful by acting as sneakers.

31. Sneakers
Males can be sneaky in order to get an opportunity to mate with a female. This strategy can be seen in smaller male octopuses when they impersonate a female. A large male will proudly display his dark stripes while he guards a female in her den. The smaller male will try to sneak his way to this female by swimming low, camouflaging his stripes, in a similar way to the female. If the large male does not recognise him as a rival then this small male will be able to approach without being attacked and he is able to hide behind a rock and extend a mating arm to the female. This behaviour results in the smaller male being able to mate and pass his genes on to the next generation.

32. Competitive Males
Males are fighting with each other to mate with as many females as possible.
More females = more offspring (sharp contrast to females).
Whilst some males fight, less dominant males can sneak a mating encounter (seen in lekking species also).

33. Courtship displays
Courtship behaviours can take various forms of colouration, displays, ‘dances’ etc
Successful mating can result from these sign stimuli.
Fixed response is to mate.
Lekking Birds

34. Species-specific stimuli and fixed action responses
A species-specific stimuli is a feature of a species that can cause a fixed action response.
A fixed action response is an instinctive behaviour response triggered by a specific stimulus.
This behaviour cannot be stopped ‘midstream’.
Successful courtship behaviour in birds and fish can be a result of species-specific sign stimuli and fixed action responses.

35. Species
Stimuli
Fixed action response
Birds
Presence of opposite sex
Mating dances
Male stickleback
Stickleback with red belly
Aggression and attack
Stickleback with swollen belly
Courting behaviour
Some moths
Ultrasonic signals produced by bats
Fold their wings and drop to the ground
Humans
Seeing another human/animal yawn
To yawn themselves

36. Lekking Species
Read through your notes booklet and make your own notes on lekking.

37. Imprinting
This is an irreversible developmental process that occurs during a critical time period in a young birds life and may influence mate choice in later years.

38. Courtship - Key Concepts
Male–male rivalry: large size or weaponry increases access to females through conflict.
Alternatively some males are successful by acting as sneakers.
Females generally inconspicuous; males have more conspicuous markings, structures and behaviours.
Female choice: involves females assessing honest signals of the fitness of males.
Fitness can be in terms of good genes and low parasite burden.
In lekking species (those that fight for alpha male status - territorial behaviour), alternative successful strategies of dominant and satellite males.
Reversed sexual dimorphism in some species.( eg, owls)
Successful courtship behaviour in birds and fish can be a result of species-specific sign stimuli and fixed action pattern responses.
Imprinting: irreversible developmental processes that occur during a critical time period in young birds may influence mate choice later in life.

39. Homework Tasks
Choose two organisms to compare reproductive strategies (one r and one K selection) including:
Investment in sperm and egg production – number, size, energy store.
Parental Investment – number of offspring produced and by which method (oviparity or vivaparity), degree of parental care.
Explain each organisms chance of survival in light of this information.
And, write a short section comparing the naked mole rats reproductive strategy to other mammals. What are the key differences?

40. Describe the characteristics of r-related species. 5

41. (relatively) small
Many offspring OR High fecundity
Early maturation OR short generation time
Low parental investment
Low probability of surviving to adulthood
Opportunistic
Exploit less crowded/ unstable ecological niches OR poor competitors in stable niches

42. Write an essay on courtship:
Sexual dimorphism 4
Male-male rivalry 1
Sneakers
Lekking
(10)

43. Sexual dimorphism (maximum of 4 marks): 1
Sexual dimorphism (maximum of 4 marks): 1. Sexual dimorphism is the physical difference between males and females of the same species. 2. Usually, males are more conspicuous than females / a suitable description. 3. Being inconspicuous mean that females can better protect their young due to camouflage. 4. Sexual dimorphism is a product of sexual selection. 5. Sexual dimorphism can be reversed in some species.

44. Male-male rivalry (maximum of 1 mark): i Males often use large size to out compete other smaller males for mates. ii Some males use weaponry to win females / suitable description of horns or antlers. Sneakers (1 mark): I Smaller males may still be successful using sneaker / satellite behaviour.

45. Lekking (maximum of 4 marks):
a) Lekking is where males collect in a display area and present to females.
b) The display area is called a lek.
c) A suitable example, e.g. grouse, capercaillie.
d) Females assess male fitness. . .
e) . . .and choose based on 'honest' signals. . .
f) . . .such as low parasite burden.

46. Sex & Behaviour Sexual Investment & Courtship
CfE AH Biology Unit 2 Organisms and Evolution
Sex & Behaviour Sexual Investment & Courtship
Learning Tool Task

47. Sexual Investment & Courtship
Task Information
Your Task…
In small groups you are to produce an A3 summary sheet to cover the key areas below and create your own summary notes for this key area.
You will explain your A3 summary sheet to another group and assess them on their understanding of this area.
You may choose how you assess them.

48. Try to include as many of the key areas below:
compare sexual investment between males and females;
explain the problems faced by sessile organisms in relation to sex, and describe solutions to these problems;
State that parental investment is costly, but greatly increases the chance of successful reproduction;
compare the features of r-selected and K-selected organisms;
state that classification of parental investment into discrete r-selected or K-selected
categories fails to reflect the complex range of life history strategies;
explain the correlation between the reproductive strategy employed, and the number and quality of current offspring versus possible future offspring;
define the term sexual dimorphism; describe male-male rivalry in courtship behaviour, explaining that smaller males may use a variety of techniques such as sneaking;
explain that successful courtship behaviour in birds and fish can be a result of species-specific sign stimuli and fixed action pattern responses;
define the term imprinting and discuss the effect it may have on mate choice later in life;
explain that females use courtship behaviour to make choices based on male fitness, usually related to advantageous genes or low parasite infestation;
using examples, explain what lekking is.