1. Mating Reproductive Strategies in Animals
Year 11 Biology Unit 2
Mating
Reproductive Strategies
in Animals

2. Reproductive Strategies
Type of reproduction
Asexual
Sexual
Gender system
Sexes exist as separate males and females
Hermaphrodite
Parthenogenesis
Mode of fertilisation
External
Internal
Mating system
Monogamy: single pair matings
Polygamy: multiple matings of individuals
Promiscuity
Numbers of offspring
r-selection
K-selection
Place of development and source of nutrition for the embryo
Oviparity: egg laying
Viviparity: giving birth to live young (several types)
Investment of parental care into offspring
Nil
Care by one or both parents
Care by extended family

3. Mating Background Three key aspects of sexual reproduction
Sexual reproduction creates variation
Reproduction is biologically expensive
Eggs are expensive
Sperm is cheaper
Organisms will not waste either gamete

4. Don’t need to find a mate?
Hermaphrodites
Have both male and female gonads eg snails, slugs, worms
Parthenogenesis
Growth of an embryo without
fertilisation of an egg
Seen in aphids, bees, wasps,
some fish, amphibians and
vertebrates
Whip lizard – two eggs combine
Snails
Worms
Aphid

5. Sex Determination
The gender of an animal’s offspring is determined by either :
Genetics
Environment

6. Sex Determination - Genetics
Humans have 46 chromosomes in diploid cells:
44 Autosomes
2 Sex Chromosomes
Humans the egg
and sperm carry
23 chromosomes
(Haploid cell)

7. Sex Determination - Genetics
Sex chromosomes in sperm
determine your sex
Males XY
Females XX
Chromosome number
Males 22 pairs + XY
Females 22 pairs + XX

8. Sex Determination - Genetics
Sex Chromosomes
Animal
Male
Female
Human XY XX
Birds ZZ ZW
Drosophila
Grasshopper XO
XO means only one chromosome
Note : In birds the female gametes determine sex

9. Sex Determination - Genetics
Platypus – egg laying mammal
Sex determination by 10 sex chromosomes
Males XXXXXYYYYY
Females XXXXXXXXXX
Footnote :
The X chromosomes in sperm carry genes similar to other mammals and birds. Researchers are looking at the structure of the sperm’s chromosomes to identify links between birds and mammals

10. Sex Determination - Genetics
Black Howler Monkeys
Have four sex chromosomes
Not common amongst mammals

11. Sex Determination - Genetics
Sex Determination in Mammals
On the Y chromosome is a gene called SRY
Six weeks after conception the SRY gene triggers testis formation.
No SRY gene - gonads form into ovaries
How ?
The SRY gene produces a type of protein called a transcription factor
The transcription factor turns on other genes that cause testis formation

12. The Role of Environmental Factors in Sex Determination
The sex of offspring or adults can be determined by a variety of environmental conditions:
Temperature
Population dynamics
Day Length
Food Availability
Bacterial Infection

13. Temperature Sex Determination (TSD)
The temperature of the incubating
eggs determines the sex of the offspring
Affects all crocodiles, most turtles and
some lizards
These animals have no sex chromosomes
Temperature
Type
Low
Middle
High 1
All Males
All females 2
All Females 3
Both Sexes

14. Temperature Sex Determination (TSD)
Temperature ranges in some species may be as little as 1oC or as much as 4oC in turtles
* Minimum temperatures for sex determination
Species
All
Males
Both
Sexes
Females
Spur Tortoise
29oC*
30-31oC
31.5oC
Saltwater Crocodile
32oC
31oC
30oC
Nile Crocodile
31oC to 34.5oC
---
<31oC and >34.5oC
Loggerhead Turtle
28oC
29oC

15. Temperature Sex Determination (TSD)
Environmental influences of incubating eggs
Eggs are laid in nests
Position of the nest
- sunny or shady
Egg position in the nest
High temperatures at the top
Low temperatures at the bottom

16. Day Length Gammarus duebeni – freshwater shrimp
Day length determines sex of offspring
Long days – male dominated hatchings
Short days – female dominated hatchings
In northern colder climates
these trends are reversed
Long days produce females
Short days produce males

17. Food Availability Nematode worm Mermithid lives inside insects
When population densities is high more males are produced
When populations density is low more females are produced
This regulates the population numbers
Mermithid nematode coiled in the thorax of a mosquito
Mermithid nematode emerges from a mosquito larvae

18. Population Changes Clownfish All young are sexually immature
Each can change into a male or
into a male then a female
Live in a hierarchy of
dominant female
smaller male and
sexually immature
If a clownfish dies another takes its place and if
need be changes to the required sex

19. Population Changes Oysters All offspring mature into males
After their first spawning all males
change into female
Some species have :
males that do not change sex
males that can change sex
females that all can change sex
Egg production
Sydney Rock Oyster – up to 20 million a year
Pacific Oyster – million a year

20. Sex Determination – Reproductive Parasites
Meet Nosema granulosis – a protozoan infecting
shrimp of the intertidal pools in Europe
Transmission via egg cytoplasm
Males can not pass on the protozoan
– sperm has too little cytoplasm
Inside a male shrimp egg Nosema changes the
offspring’s sex to female
– it takes over the sex determining mechanism

21. Sex Determination - Bacteria
A genus of bacteria called Wolbachia
Infect insects, spiders, mites, crustaceans, nematodes
the most common parasitic bacteria on earth
Infect 20% of all insects
Members of the genus Wolbachia can:
Change males to females
Alter sex determination mechanism in the fertilised egg
Kill males
Bacteria in males die but males become food for developing females (Only found in insects)
Induce parthenogenesis (producingonly female offspring)
Wolbachia causes egg’s chromosomes to duplicate and develop

22. Sex Determination - Bacteria
White-Barred Acraea (Acraea encedon)
Infected with male killing bacteria
In some populations 95% of
females are infected (rare to be this high)
Highly skewed sex ratios
Females assemble in large
numbers for courting – Leks
Female leks are very rare

23. How Many Partners? Animals reproduce in one of four ways: Monogamy
Mating Systems…
Animals reproduce in one of four ways:
Monogamy
One partner
Polygynandry
Multiple partners
Polygyny
One male, many females
Polyandry
One female, many males

24. Monogamy One male one female Both parents look after offspring
Not common in animals
Biologically all “eggs in one basket”
Pairing may be either:
Only for a season, or
Life long
Usually occurs where the cost of
finding a mate is very high

25. Polygynandry Females mate with several males
Female chimpanzees have been
recorded having sex with 8
males in 15 minutes.
WHY ? (Hint… infanticide)

26. Polygyny One male mates with many females.
Examples : lions, seals, gorillas, birds
Dominant males establish harems
Males fight for the rite to breed
Male Elephant Seals
Alpha Male - Elephant Seal
90% of Australian fairy wrens appear monogamous but offspring were from mates other than the presumed father.
Fairy Wren

27. M F
Polyandry
One female mates with many males but males mate with only one female.
In Birds there are two types:
Simultaneous – eggs fertilised from many males sperm
Sequential – eggs fertilised by one male, female leaves male with the eggs, and mates again e.g. Emu, Rheas, Jacana
Often accompanied with role reversal,
male incubates eggs
Bronze
Wing
Jacana
Simultaneous Acorn woodpecker Sequential – Northern jacanas, Spotted sandpipers& red Phalaropes
Rhaes – female mates with many males and gives each a few eggs to incubate
Bronze wing jacana – 4 males for each female – 4 clutches of eggs

28. Passing on Gametes Fertilisation can be either : External Internal
No direct transfer of gametes
between male and female
Internal
Gametes are transferred into
the female’s body

29. External Fertilisation
Courtship synchronises gamete release
Gametes are released in water.
Why?
Fertilisation is “hit and miss”
Large number of gametes released
Pacific Oyster million eggs per year
Parental care varies with species
Some fish provide no care
Some create “nests”
Mouth brooders

30. External Fertilisation
Mass Spawning
Synchronised release of gametes
Great Barrier Reef coral spawn
5 -6 days after the full moon
in October, November or
December depending
on the species

31. Internal Fertilisation
Sperm is passed from the male into the female’s body
Increases the chance of fertilisation
Less sperm needs to be produced
Means of transfer varies
Mammals – penis, Birds – cloaca,
Shark – clasper (modified fin)

32. Fertilised Eggs – Now What ?
Developing eggs:
Remain inside the female, or
Are laid
Young develop with differing amounts
of parental care

33. Place of Development… Oviparity (‘egg-bearing) Viviparity
Eggs are released by the mother so that embryos develop outside the mother’s body
Nutrients for the embryo come from the from the egg yolk (larger the yolk, larger the young).
Larger the egg size, less eggs produced, and have longer periods of embryonic development, and vice-versa.
Eggs can be a target for predators…
Viviparity
Produce miniature, live-born young
Increased chance of survival as embryo protected within mother
3 types:
Egg yolk viviparity
Eggs retained inside mother eg sharks
Placental viviparity
All nutrients delivered from maternal bloodstream via placenta eg all mammals except WHO?
Other sources
Eg shark placenta, unfertilised eggs, uterine milk.

34. How many? How Often? K-selection r-selection Octopus eggs
Humpback whale
K-selection
‘slower and fewer’ strategy
Mature slowly
Produce fewer and larger offspring
Extensive parental care
Longer life span
Typically longer gestation
r-selection
‘quick and many’ strategy
Reach sexual maturity quickly
Produce large numbers of offspring
Little or no parental care
Have high fecundity (no. of eggs produced annually)
High mortality rates

35. Australian Marsupials
Developed strategies that equip tem for successful reproduction in drought prone environment
Embryos develop in uterus for very short time
Born at very immature stage of development
Newborn attaches to nipple and undergoes further development

36. How often do mating occur?
Breeding season
The period when mature individuals have sperm and eggs ready for release.
Influences by hormones, temperature, day length
Most female mammals will mate only when in oestrus (cycle of egg production)
Once in a lifetime
Breed once then die
Salmon

37. Case Studies Anaconda Scorpions Preying mantis Sharks Penguins
Cichlids
Damselfly
Butterfly
Wolves
Frogs
Seahorses
Blue Throat Wrasse

38. Anaconda – A love triangle?
Case Study 1
Anaconda – A love triangle?
Female leaves a scent trail to attract males.
More than one male follows
the trail leading to her
Males wrap around the female
all trying to mate with her
This “breeding ball” of snakes
may last two weeks.

39. Scorpions – A Careful Union
Case Study 2
Scorpions – A Careful Union
Internal fertilisation but with no
physical mating occurs
Male and female embrace each
other claws and dance back and forth
The male deposits a package of
sperm (spermatophore) on the ground
and drags the female over it
Scorpion spermatophore

40. Preying Mantis – No Head for Sex
Case Study 3
Preying Mantis – No Head for Sex
Fertilisation is internal, large sexual dimorphism
Males carefully mate but female will eat him
His body nourishes the developing eggs
Some males can’t copulate until decapitated

41. Penguins – What a Couple !
Case Study 4
Penguins – What a Couple !
The penguins walk to their
inland rookery and mate
She lays one egg, then
returns to the sea to feed
He incubates the egg at 31oC
for 2 months over winter
She will return when the egg
hatches bringing food
He leaves to feed, both parents feed chick

42. Cichlids – Shells Anyone?
Case Study 5
Cichlids – Shells Anyone?
The cichlid (Lamprologus callipterus)
are fish living in Africa
Show extreme sexual dimorphism
Males can be 13 times larger
than females
Males creates a nest of up to 30 shells
and defends his nest
Females ready to spawn
enter the shells
Male fertilises the eggs

43. Damselfly – Clean First.
Case Study 6
Damselfly – Clean First.
Males have a penis that inflate
like a balloon
The penis has:
two horns at the tip and
bristles along the side
In one species the male scours
sperm from inside the female
before depositing his own
Other species use it for extra stimulation to induce
her to eject sperm from previous lovers

44. Green Veined Butterfly’s Chastity Belt !!
Case Study 7
Green Veined Butterfly’s Chastity Belt !!
Males pass sperm, nutrients and a chemical chastity belt to the female during mating
After mating the female emits a smell that
repels other males. Time for his sperm to fertilise
the eggs
Nutrients increase female’s
fecundity and longevity
Virgin males provide more
nutrients than older males

45. Sharks - Egg Layers to Live Birth
Case Study 8
Sharks - Egg Layers to Live Birth
Some species lay eggs ,others
retain them in their body
Retained eggs develop and young
are born alive
Some species nourished young on unfertilised
eggs the female produces
Some young eat their siblings

46. Wolves – She’s mine ! Case Study 9 Alpha pair rule the wolf pack
Often they are the only breeding
pair
Breed once a year
Copulation ends with the penis
swelling, and locking the male
inside the female for 5-30
minutes.
Why?

47. Frogs – Have the Stomach for it !
Case Study 10
Frogs – Have the Stomach for it !
Gastric Breeding Frog (Rheobatrachus silus)
Fertilised eggs or larvae are
swallowed by the female
Gastric juices are stopped by
hormones the young produce
After 6-7 weeks up to 25
young frogs are born
Her digestive systems starts
working again after 4 days

48. Seahorses – Who does what ?
Case Study 11
Seahorses – Who does what ?
After courtship, eggs are transferred to male
Male fertilises, then carries eggs until hatching
Pot Bellied Seahorse
Has a pouch for eggs
Leafy Sea Dragon
Eggs develop on his tail
Hippocampus abdominalis

49. Blue Throat Wrasse – Bullies
Case Study 12
Blue Throat Wrasse – Bullies
Born female
Live in harem, alpha male bullies females
If he dies he is replaced by largest female
Within a few hours she behaves male
After a few days colouration is changing
After 14 days she has changed sex
Hippocampus abdominalis
Male
Female

50. Where do new cars come from?
Any similarities?
Where do new cars come from?