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Year 11 Biology Unit 2 Mating Reproductive Strategies in Animals.

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1 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 a)Sexual reproduction creates variation b)Reproduction is biologically expensive –Eggs are expensive –Sperm is cheaper c)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 Aphid WormsSnails

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 AnimalMaleFemale HumanXYXX BirdsZZZW DrosophilaXYXX GrasshopperXOXX 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 TypeLowMiddleHigh 1All MalesAll females 2All FemalesAll Males 3All FemalesBoth SexesAll Females

14 Temperature Sex Determination (TSD) Temperature ranges in some species may be as little as 1 o C or as much as 4 o C in turtles * Minimum temperatures for sex determination SpeciesAll Males Both Sexes All Females Spur Tortoise 29 o C* 30- 31 o C 31.5 o C Saltwater Crocodile 32 o C31 o C30 o C Nile Crocodile 31 o C to 34.5 o C --- 34.5 o C Loggerhead Turtle 28 o C29 o C30 o C

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 emerges from a mosquito larvae Mermithid nematode coiled in the thorax of a mosquito

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 – 30-40 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: 1.Monogamy –One partner 2.Polygynandry –Multiple partners 3.Polygyny –One male, many females 4.Polyandry –One female, many males Mating Systems…

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 MF

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

26 Polygyny One male mates with many females. Examples : lions, seals, gorillas, birds Dominant males establish harems Males fight for the rite to breed M F F F F Alpha Male - Elephant Seal Male Elephant Seals Fairy Wren

27 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 M F M M M Bronze Wing Jacana

28 Passing on Gametes Fertilisation can be either : a)External –No direct transfer of gametes between male and female b)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 30-40 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) 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? 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 K-selection ‘slower and fewer’ strategy Mature slowly Produce fewer and larger offspring Extensive parental care Longer life span Typically longer gestation Octopus eggs Humpback whale

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 1.Anaconda 2.Scorpions 3.Preying mantis 4.Sharks 5.Penguins 6.Cichlids 7.Damselfly 8.Butterfly 9.Wolves 10. Frogs 11. Seahorses 12. Blue Throat Wrasse

38 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. Case Study 1

39 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 Case Study 2 Scorpion spermatophore

40 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 Case Study 3

41 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 31 o C for 2 months over winter She will return when the egg hatches bringing food He leaves to feed, both parents feed chick Case Study 4

42 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 Case Study 5

43 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 Case Study 6

44 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 Case Study 7

45 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 Case Study 8

46 Wolves – She’s mine ! 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? Case Study 9

47 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 Case Study 10

48 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 Case Study 11

49 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 Case Study 12 Female Male

50 Any similarities? Where do new cars come from?


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