behaviour sexual investment CfE Advanced Higher Biology Unit 2 Organisms and Evolution SQA mandatory key areas Comparison of investment in sperm and egg production number and energy store greater investment by females Problems and solutions of sex for sessile organisms ID: 547364
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Slide1
Sex & behaviour:sexual investment
CfE
Advanced Higher Biology
Unit
2:
Organisms and EvolutionSlide2
SQA mandatory key areasComparison of investment in sperm and egg production – number and energy store; greater investment by females. Problems and solutions of sex for sessile organisms. Parental investment, optimal reproduction and reproductive strategies in terms of the number and quality of current offspring versus potential future offspring. Classification of parental investment into discrete r-selected and K-selected organisms does not reflect continuous range of life history strategies. Slide3
Key conceptsParental investment is costly but increases the probability of production and survival of young. Simplistic various reproductive strategies have evolved ranging from polygamy to monogamy. Slide4
Darwin’s Puzzle:Why are males and females different?Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex. 1st ed., Murray, London.Slide5
Parental investment and sexual selectionTrivers 1972Slide6
AssumptionAssumption: every organism has adaptations that function to facilitate reproductionMembers of a population/species live in the same environment, so why do some animals have different adaptations than others?Morphs: age, sex, othersSEX: male and female adaptations are differentWHY?Slide7
Parental investment“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)Slide8
Sperm vs. egg
In sexually-reproducing species, the relative size of gametes
define
who is male and who is female.Slide9
Sexual dimorphismAmongst 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’.Slide10
Nurturant femalesIn most animals, and almost all mammals, females provide far more parental investment than just the eggInternal fertilization protects, but at a costCod vs. gorillasHumans (mammals):Prolonged internal gestation (pregnancy)
Placentation
LactationSlide11
Female reproductive strategyFemales have much to lose if they mate with the wrong male, they are thus selective about who they mate with. They look for certain criteria:
Physical Features
: size and strength which confer dominance and so preferential access to resources.
Behavioural Features
: may indicate willingness to invest or good parenting skills.
Females will compete with other females for the right to choose the most desirable (alpha) males.
They gain little from multiple
matings
and seek quality not quantity.
Almost every reproductively capable female will be able to find a mate of some sort. Slide12
Male reproductive strategy Males are far less choosy as they as they little to lose and everything to gain if they can have as many mating opportunities as possible. Males are not tied to rearing offspring and so seek
quantity
.
While they would prefer a superior female, they are less choosy.
If presented with a sexual opportunity they will take it.
Males compete vigorously with other males for access to fertile females.
Male reproductive success is however very variable, a small number of males will achieve many
matings
, while many males may never mate. Slide13
Competitive malesMales are fighting with each other to mate with as many females as possibleMore females = more offspring (sharp contrast to females)Slide14
Sexual selection and parental investment theoryFor 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.For members of the sex that invests less in offspring, reproductive success is limited by the number of mates one can acquire.Slide15
Bateman’s GradientBateman (1948) observed that the number of offspring fathered by male fruit flies increased in proportion to the number of females with which the male had mated. Female reproductive success did not increase as her number of partners increased. This is 'Bateman's gradient' - the steeper the gradient the stronger is sexual selection.
males
females
No. of mates
No. of offspring
From Anderson & Iwasa (1996) p 54.Slide16
Sexual selection and parental investment theoryWhat of it?Selection acted on males differently than it acted on femalesSpecifically, differences in parenting strategies cause differences in adaptationsSex that invests more: adaptations to survive and get resources for offspringSex that invests less: adaptations to help them get as many mates as possible
It explains why, in many species, males look and behave differently than femalesSlide17
Sexual selection and parental investment theoryExplains primary sex differences (uteruses vs. testes)Explains secondary sex differencesDifferences in weaponry (intrasexual selection)Differences in ornaments (intersexual selection)When the sexes have different adaptations, they are “sexually dimorphic”Slide18
r & K Selectionr/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality 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.Slide19
How many, and how often?
r Selection
(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 birdsSlide20
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 mammalsSlide21
Oviparity
Bony fish and frogs
Birds and reptiles
Known as
-
Amniote eggs
Shell
None, or leathery membrane
Usually a hard, calcerious shell
Benefits
Wedge into safe crevices
Better protected from desiccation – do not have to reproduce in water
Dangers
Desiccation
Damage
Cannot be hidden in crevices
Examples
Port Jackson shark, amphibians
Hens, monotremes, crocodilesSlide22
Viviparity
Egg yolk viviparity
Placental viviparity
Other source of nutrient
More notes
Cool habitat – kept warmer within body
Largish eggs
Any – nutrient sent via blood stream to embryo
Very small eggs
Feed them unfertilised eggs
Feed them “uterine milk” – secretion from uterus
Examples
Some sharks and snakes. Sea snakes – so that they do not have to return to land to breed
Mammals except monotremes, hammerhead shark
Porbeagle
shark (feeds with eggs), Bat rays (feed with “milk”)
Types of viviparity are recognised by the nutrient source for the developing embryoSlide23
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, emusSlide24
Assessment taskChoose two organisms to compare reproductive strategies (one r and one K selection) including:Comparison of 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.