Sex behaviour Sexual Investment Cf E Advanced Higher

Sex & behaviour: Sexual Investment Cf. E Advanced Higher Biology Unit 2: Organisms and Evolution

Key area 2. 4 ØParental investment ØCourtship

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

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.

Darwin’s Puzzle: Why are males and females different? Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex. 1 st ed. , Murray, London. Think, pair, share… What are your thoughts on the above statement?

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?

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)

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

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

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

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

Sperm vs Egg • In sexuallyreproducing 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

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’.

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

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.

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.

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

Answer the following questions on these key areas: 1. Compare sperm and egg production in relation to the number and energy store. 2. Which sex has the greater investment? 3. List the problems and solutions for sessile organisms. 4. What are the costs and benefits of external and internal fertilisation? 5. If parental investment is so costly, why do animals dedicate so much energy to it?

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

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

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.

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.

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.

How many, and how often? r Selection K selection (aka. Quick-and-many) (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

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

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

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).

Key area 2. 4 ØParental investment ØCourtship

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.

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.

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.

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).

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

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 speciesspecific sign stimuli and fixed action responses.

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

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

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.

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 speciesspecific 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.

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?

Describe the characteristics of rrelated species. 5

1. (relatively) small 2. Many offspring OR High fecundity 3. Early maturation OR short generation time 4. Low parental investment 5. Low probability of surviving to adulthood 6. Opportunistic 7. Exploit less crowded/ unstable ecological niches OR poor competitors in stable niches

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

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.

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.

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.

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

Sexual Investment & Courtship Task Information Your Task… In small groups you are to produce an A 3 summary sheet to cover the key areas below and create your own summary notes for this key area. You will explain your A 3 summary sheet to another group and assess them on their understanding of this area. You may choose how you assess them.

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 speciesspecific 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.