Reproductive Animal Strategies Flashcards
define reproduction
the production of a new generation of organisms from an existing generation, it ensures the continued survival of a species
what is the goal of each species and what is it known as
to produce the maximum number of surviving offspring while using the least amount of energy (this is called reproductive effort)
what is the difference between asexual and sexual reproduction
asexual - found in lower and microscopic animals, is energy efficient because it only involves one animal
sexual - happens in all vertebrates, is much more complex which needs higher energy input
what have unique reproductive strategies allowed
maximum reproductive success in different environments enabling the species to breed successfully and then survive to reproductive age
name 6 reproductive strategies
- Courtship
- External versus internal fertilisation
- Ovipary, ovovivipary and vivipary
- Amniotic egg
- Precocial and altricial development
- Parental care
what is courtship
behaviour and/or signals that are designed to attract another animal for mating and breeding
what are examples of simple courtship strategies
chemicals (pheromones), visual (brightly coloured body parts), auditory (mating calls)
- moths produce specific pheromones that guide males towards them
- most frogs have to return to the water for mating and breeding, once the males reach the mating ground they sing (grunt, croak) to attract females, each species have a specific song that only attracts females of that species
what are examples of complex courtship strategies
more elaborate forms of courtship, females are usually attracted to larger males, who have more elaborate physical features and who display more energy during the courtship activity (these characteristics reinforce pair bonding and promise healthier offspring that are more likely to survive)
- The blue cranes courtship display includes a complex and extended series of calls as well as an elaborate dance done by the males
- Springbok have an annual rut (period of sexual excitement) during which the males defend their territories with loud grunts, attack vegetation with their horns and deposit middens of urine and dung in a ritualised display in order to attract females (most young are born 6 months later in spring just before rainy season) so the timing of this ritual also ensures that mothers are in good condition and that there will be enough food for the newborns
- Male Hoopoes feed insects to their mates, allowing the females to save their energy for incubating and breeding
how does courtship maximise reproduction
- it ensure that males and females are suitable mates
- sexual behavior is timed so that males and females are ready for mating at the same time
- energy expenditure is usually by the male so that the female conserves her energy for breeding
define fertilisation
the joining of the nucleus of an egg and a sperm. the sperm are motile as they’re able to swim but eggs don’t move, therefore vertebrates have ways of ensuring that sperm reach the eggs for fertilisation to take place
explain external fertilisation
it takes place in water and occurs in most aquatic vertebrates (fish and frogs)
why is external fertilisation not ideal
- it is wasteful as huge numbers of eggs are produced, most of the eggs are eaten
- fertilisation is not certain
how can external fertilisation maximise reproduction
- huge numbers of of eggs and sperm are released into the water to increase the probability of fertilisation. with the large number of fertilised eggs there are enough to grow into adulthood even though many are lost to predation
- eg. many fish swim side by side when releasing their eggs and sperm which ensure the gametes are close together
(energy expenditure goes almost totally into producing the large number of eggs)
explain internal fertilisation
occurs in terrestrial vertebrates (reptiles, birds and mammals) the sperm is released directly into the body of the female and fertilise the eggs inside the body
examples of internal fertilisation
- most birds and reptiles mate using a cloaca (a single opening in the lower abdomen) during mating the males and females line up their cloaca for the transfer of sperm
- the males of virtually all mammals have a penis to introduce the sperm into the female, this process is known as copulation (the penis ensures that the sperm is transferred successfully without being destroyed by any environmental conditions)
how does internal fertilisation maximise reproduction
fertilisation is more certain as the gametes are plcaed as close together as possible, although it doesn’t ensure fertilisation it makes it much more likely. fewer gametes are therefore needed, so energy saved in production of gametes can be used for other purposes to maximise reproduction, eg. a protective shell and increased yolk can be produced or development can be internal via a placenta
what do ovipary, ovovivipary and vivipary strategies describe and indicate
the terms are used to describe the moment at which the future offspring separates from the parent
and they indicate where the embryo develops and how the embryo and fetus are nourished
what is ovipary
where the eggs develop outside of the parent, they may be fertilised internally or externally, the majority of animals are oviparous, egg yolk is the only food that the developing embryos receive until they have hatched
how does ovipary maximise reproduction in aquatic environments
most fish and amphibians are oviparous, the eggs are released into the water and they’re fertilised externally, lots and lots of eggs are needed as the developing eggs are very vulnerable to predation. the famales have to use high amounts of energy to produce the eggs however they save energy by not needing yolk production and parental care.
give examples of oviparous animals
- catshark females lay eggs that are known as mermaids purses, these egg cases contain the embryo and yolk supply and the young shark eventually hatches out of the case. the egg case negates the need for large numbers of eggs as the developing animal is well protected
how does ovipary maximise reproduction in land environments
these include most reptiles (70%) and birds
- very few eggs are produced particularly by birds therefore saved energy goes into:
- producing eggs with more food (nutrient rich yolk and protein rich albumen) which allows the animal to be more formed at hatching
- protecting and incubating the eggs before hatching
- parental care for the young - a shell protects the developing embryo from predators, pathogens, physical damage and dehydration
what is ovovivipary
animals where the eggs that are fertilised internally are kept inside the females body until they hatch, therefore the offspring are born live
how is the developing embryo nourished
the embryo gets food from the large amount of yolk in the egg and is not dependant on the mother except for physical protection and often gaseous exchange
give an example of an ovoviviparous animal
the ragged tooth shark, whose eggs are fertilised internally, the embryos initially feed on their own supplies of yolk, later they feed on fertilised eggs and other developing embryos (inter-uterine cannibalism) this results in only two pups being born per litter
gestation is 9-12 months depending on water temperature
how does ovovivipary maximise reproduction
it occurs in some fish and reptiles (puff adder)
maximises reproduction because:
- fewer eggs are produced so mothers energy expenditure is less
- the developing embryo is much less vulnerable to predation and cold temperatures
- the young are born fully developed so they’re able to get their own food and escape predators more easily
what is vivipary
animals where fertilisation is internal and the eggs don’t have a shell, the retained egg forms an embryo and then a fetus, which develops inside the mother.
where do these embryos get nourishment
they obtain continuous nourishment from their mother, usually through a placenta and is then born live
where does vivipary occur
- placental animals
- about 55% of sharks and rays
how does vivipary maximise reproduction
the reduced number of eggs means that more energy is available yo:
- nourish and protect the developing embryo and fetus
- provide parental care after the young are born
this results in a higher chance of the offspring surviving and reaching reproductive age
give an example of vivipary
the hammerhead shark, the mother joins with its developing embryo via the yolk sac that forms a connection with the mothers oviduct tissue, it is through this that the developing young receive nourishment until they’re ready for birth, the young are born live and fully functional
explain the difference between early vertebrates and later vertebrates
early vertebrates (fish and amphibians) need to lay their eggs in water and therefore can’t live far from water, they have simple eggs with no shell
later vertebrates (reptiles and birds) known as amniotes can lay their eggs in terrestrial environments as they no longer have to return to water for breeding, mammals are also amniotes but don’t lay eggs (the eggs are retained in their bodies)
what do all amniotes produce
eggs that, after fertilisation, develop extra-embryonic membranes. These are fluid filled membranes (amnion, allantois, yolk sac, chorion) that allow the embryo to survive and develop on land - or in the case of mammals, internally in the uterus. fertilisation is internal and the membranes develop after fertilisation
these eggs are called amniotic eggs
why are amniotic eggs a major evolutionary innovation
they allowed some of the first reptiles to colonize dry land more than 300 million years ago
draw a diagram of a typcial amniotic egg
page 79
how does an amniotic egg maximise reproduction
the amniotic egg maximises the development of the embryo and fetus before hatching/birth enabling the offspring to survive the harsh conditions on land more easily and successfully
- the fluid filled amnion surrounds and protects the embryo against dehydration and mechanical injury
- the allantois acts as a reservoir for nitrogenous waste in birds and reptiles (in aquatic environments waste would pass directly into water)
- the yolk sac in birds and reptiles holds nutritious food for the embryos development
- the chorion surrounds all the other membranes where in birds and reptiles allows for gaseous exchange together with the shell, and in mammals it forms the placenta with the endometrium
what has precocial and altricial development evolved to
- provide nourishment to the developing embryo and young
- protect them from predation
what are precocial species
species that hatch or are born when they are almost fully developed. therefore parental energy expenditure goes into pre-natal developments (the mothers are less involved after birth)
what are some characteristics of precocial species at hatching/birth
- open eyes and hair/down
- have large brains relative to their body size
- are immediately active and mobile (even though they may not be very steady)
- usually not confined to nests (birds have well developed feet and legs)
how does precocial development maximise reproduction
the precocial features help offspring to:
- find and eat food on their own
- look after themselves against predators
therefore the offspring have better chances at survival
what are examples of precocial species
- ground nesting species (penguins, chickens, ducks and ostriches)
- large mammals (elephants, hares, wildebees)
what are altricial species
species that are born/hatch when they are not well developed, so parental care energy expenditure goes into post-natal development of the offspring
what are some characteristics of altricial species at hatching/birth
- often naked, lacking hair/down
- cannot walk or fly
- often have eyes closed
- rely entirely on their parents for warmth, transport and food
- have a coloured mouth-lining or gape-edge (birds)
- require care and protection for a comparatively long time
how does altricial development maximise reproduction
it allows more offspring to reach reproductive maturity because:
- there is parental care, the parents save energy on pre-natal care and therefore have more energy to feed, brood, and protect their young post-natal
- the offspring reach reproductive age quickly because they are easier to feed as they stay in their nests, and grow very rapidly as they are fed large nutrient rich food items
- they are also safer from predation as the nests are inaccessible and the offspring only leave the nest once they’re fully grown and ready to evade predation alobe
what are examples of altricial species
- small mammals (rodents, cats, dogs)
- humans
- tree nesting birds
- marsupials (young are cared for in a pouch)
what is parental care
any type of behaviour in which a parent spends time or energy to improve the survival, condition and future reproductive success of the offspring
draw a diagram to show the result of parental care on a number of eggs…
page 82
give examples of what pre-natal, and post-natal care consists of
pre-natal care - guarding eggs, building nests, carrying broods, incubating eggs, placental nourishment
post-natal care - providing food, protection, teaching offspring
what does parental care in fish consist of
most fish species show no parental care, no fish feed their young. in about 20% of fish species there is little parental care.
this care involves:
- building nests,
- guarding eggs and hatchlings from predators,
- fanning eggs to increase oxygen supply,
- cleaning eggs to eliminate fungus
- having a brood pouch (seahorses)
what does parental care in amphibians consist of
most amphibians return to the water for reproduction,
much of their parental care is directed to minimalise the loss from predators of eggs and embryos by:
- egg guarding (eggs of the midwife toad are kept and carried on the rear end of the male)
- building terrestrial-breeding sites away from water (foam nest frog female secretes a fluid that us churned up with her hind legs into a foam ball to form a nest in trees that hang over water, the fertilised eggs are protected and stay moist inside the ball, once the tadpoles hatch they drop into the water below)
what does parental care in reptiles consist of
they show virtually no parental care besides guarding eggs (lizards and snakes), incubation by body heat (pythons), attacking predators (pythons)
what does parental care in birds consist of
they show extensive parental care (both parents)
including;
- incubation of eggs by using body heat
- nest building (protects eggs from predators, sun, rain)
- brooding (as the offspring can’t thermoregulate) and feeding
- protecting against predators
- teaching young how to get food
what does parental care in mammals consist of
most young mammals are completely helpless at birth, so they require intense parental care
maternal care includes:
- lactation, the composition of each species milk is perfect for the best possible development of that species
- protection against predators and the cold
- teaching to gather food
- licking newborn immediately after birth to establish a unique relationship (no licking will result in the newborn rejecting the mother)
paternal care includes:
- feeding the young
- guarding against predators
some mammals (rodents and carnivores) make special nests (burrows)
what is an example of k-strategy species
Elephants - 70 year life expectancy, begin mating at about 20 years old
- only a few offspring are produced , female elephants have babies about 3 years apart and only have 1 at a time
- high level of parental care so the young have a high chance of surviving, the whole group looks after and protects the young, through childhood and adolescence
- elephants are a climax species as they produce only slightly more offspring than the maximum that the environment can hold (population density)
what is an example of r-strategy species
leatherback and loggerhead turtles - live between 50 and 100 years, become sexually mature late (about 17 years old) this allows the females to put more energy into producing eggs as she doesn’t need energy to grow
- they lay numerous eggs (multiple clutches of 90 and 130 eggs each) every 2-3 years
- no parental care, so only a few offspring will survive (between 2-10 per 1000 eggs laid will reach adulthood)
- low survivorship is due to predation while they are still inside the eggs and when they go into the sea (predation will only decrease when body size increases)
what are survivorship curves
the pattern of mortality of each species expressed as a curve
what do different curves mean on a survivorship curve, give examples of what species would create that curve and why
convex curve:
- most of the offspring become adults
- death occurs mainly amongst older individuals
eg. k -strategy species, elephants, humans
because: these species have high levels of parental care and therefore high survival rate
straight line:
- mortality decreases slowly with time
- a young organism is just as likely to die as an old one
eg. birds and plants
concave curve:
- few offspring become adults
- high mortality rate when they’re young
- once they’re established there is an improvement in life expectancy
eg. r strategy species, turtle
because: these species have no parental care and therefore have a low survival rate when they’re young
