ANIMAL REPRODUCTION STRATEGIES BIO ST STITHIANS GR11/12

SAGS AIM 1: KNOWING LIFE SCIENCES

Candidates should know how reproductive strategies maximise reproductive success in different environments. [Link to population dynamics]

Study appropriate South African examples to illustrate each of the following;

Courtship (one example)

• External fertilisation vs internal fertilisation (one example of each)

• Ovipary, ovovivipary and vivipary (one example of each)

• Amniotic egg (one example - no details of structures)

• Parental care (one example)

SAGS AIM 2: INVESTIGATING PHENOMENA IN LIFE SCIENCES

Compare the reproductive strategies and analyse how effective these are to the survival of an r-strategy,

(e.g. turtle and a k-strategy, e.g. lion, elephant.)

Candidates should be familiar with a variety of survivorship curves.

SAGs AIM 3: APPRECIATION AND UNDERSTANDING THE HISTORY, IMPORTANCENCE AND APPLICATIONS OF LIFE SCIENCES IN SOCIETY

Reproductive Strategy

Any behaviour that enables a species to breed successfully and produce offspring that survive to reproductive age.

Asexual Reproduction

Production of a new generation that does not involve the fusion of gametes

Sexual reproduction

Production of offspring by bringing together the genetic material of two parents.

Courtship

The signals and behaviour that are designed to attract another animal for mating.

Ovum/Ova (egg cell)

The non-motile gamete

External Fertilisation

The type of fertilisation that occurs in a fluid medium and takes place outside the body of the female

Internal Fertilisation

The type of fertilisation that occurs in terrestrial animals and involves the use of a cloaca/ vagina and a penis.

Ovipary

The reproductive strategy in which the embryo and foetus develop in eggs outside the parent.

Ovovivipary

The reproductive strategy where the embryo and foetus develop in eggs inside the parent, and the offspring are born live.

Vivipary

The reproductive strategy where the embryo and foetus develop inside the parent and derive nutrients from the parent before being born live.

Placenta

The part of the mother that provides continuous nourishment to the developing foetus

Amniotic eggs

Fertilised eggs that develop extra-embryonic fluid-filled membranes and a hard shell that allow the embryo to survive

Yolk Sac

The part of the amniotic egg that holds the nutritious food (yolk) for the embryo.

Allantois

The part of the amniotic egg that acts as a reservoir for nitrogenous waste.

Chorion

The outermost membrane surrounding the embryo, which allows for gaseous exchange

Gaseous Exchange

Gaseous exchange is the biological process where oxygen and carbon dioxide passively diffuse across a membrane.

Albumen

Egg white that provides the embryo with protein and water.

Shell

Calcareous or leathery outer, porous covering that protects the developing embryo

Precocial

Animals that are almost fully developed at birth, requiring little parental care after birth.

Altricial

Animals that are underdeveloped and helpless at birth, needing a lot of parental care.

Parental care

Any behavioural pattern where parents spend time and energy to improve the survival, condition and future reproductive success of the offspring.

Survivorship curves

Type I( Convex Curve):

High survivorship early/high mortality in old age. Represents K-strategy species. Most individuals survive to old age (Humans/Elephants/Dolphins)

Type II (Straight Line): Steady/constant mortality at all ages. Individuals have the same chance of dying at any age. Intermediate strategy.

(Small birds/Squirrels/Coral)

Type III (Concave Curve):

High early mortality/survivors live long. Represents an R-strategy species. Many die young; the few survivors persist.

(Frogs/Plants/Turtles/Fish)

K-Strategy Species

- Few offspring at one time / over a lifetime.

- High parental care. Large body size.

- Late onset of maturity.

- Reproduce multiple times.

- Population size is stable, close to carrying capacity (K).

- Usually climax species.

R-Strategy Species

Many offspring per brood. Low parental care. Small body size. Early maturity. Reproduce once. Many die early (predation). Population size variable. Often pioneer species.

R- Strategy vs. K-Strategy

K-Strategists have a population size close to an environments Carrying Capacity (K).

R-Strategists have a population size that increases exponentially over the carrying capacity (K) of an environment before decreasing at a similarly rapid rate.

Purpose of Courtship Behaviour

- Rituals and actions performed to attract the mate

- Identify partners of the same species

- To choose the right mate (females usually will choose the larger and stronger males with more attractive qualities.)

Visual Stimuli

Brightly coloured displays, elaborate feathers, physical size demonstrations. Example: Male peacock feathers.

Fighting / Strength

Males fight to demonstrate dominance and physical fitness to the watching females. Examples: Lions, elephants.

Performing Intricate Dances/ Touching

Elaborate choreographed movements or physical touching rituals. Examples: Scorpions, eagles, tortoises.

Bringing Food

Male demonstrates ability to provision resources — important for female energy conservation during breeding. Example: Pel's fishing owl.

Building Homes

Males construct elaborate structures to demonstrate skill and resource-holding ability. Example: Weaver birds.

Chemical Stimuli

Pheromones secreted to attract mates - chemical signals that travel through air or water. Example: Moths.

Sound Stimuli

Vocalisations to attract mates and signal fitness. \

Only the healthiest individuals can maintain loud, sustained calls.

Example: Male frogs, birds.

DEFINE: Lek

A lek is an aggregation of males that gather to engage in competitive displays that may entice visiting females surveying prospective partners for copulation.

What is a Lek?

-Leks form before or during the breeding season

- Defined by: male displays + strong female mate choice + conferring of male indirect benefits

- Common in bird species; also found in insects, amphibians, and mammals

-Many males gather, but only dominant males successfully mate

- Example: Blue Crane (National Bird) — courtship involves a "dance" in which the male chases the female with leaps, bows, and bouts of calling

How does Courtship maximise reproduction?

-ENSURES SUITABLE MATES FIND EACH OTHER: The more energetic the calls/dances/rituals, the more likely he will attract females. This is an example of natural selection.

- SEXUAL BEHAVIOUR IS TIMED: Males and females are ready for mating at the same time (often seasonal).

- ENERGY EXPENDITURE BY MALE: the female conserves her energy for breeding, gestation, and caring for young.

External Fertilisation Details

-Occurs in aquatic organisms (fish, frogs) - water provides a medium for sperm to swim and prevents desiccation.

-Egg and sperm cells are released simultaneously into water

-Sessile organisms (coral, anemones, mussels, barnacles, oysters) benefit greatly — they cannot seek out mates

-Disadvantages: eggs and sperm may drift apart; embryos left unprotected; many eggs destroyed by predators; unfavourable temperatures

-Eggs are surrounded by jelly to protect them from desiccation; the yolk provides nutrients

-Frog larvae (tadpoles) do NOT resemble adults - no competition for food. This is a complete metamorphosis

-Advantage: no additional energy spent on parental care or protective shell

Internal Fertilisation Details

- Occurs in insects, reptiles, birds, and mammals

- Male inseminates female by placing sperm into the female's body - eggs are fertilised internally

- Achieved through copulation -penis into vagina (mammals) or cloaca (birds and reptiles)

- Reproductive behaviour is often seasonal - ensures young are born when conditions favour survival

- Advantages: gametes not exposed to drying out; not lost to predation; fertilisation more likely in a contained environment

- Fewer eggs produced - less energy on production; more on quality. Eggs may have a shell and yolk

-Cloaca: common reproductive and urinary opening in birds and reptiles

External vs. Internal Reproduction

DETAILS ON TABLE pg8 notebook

Oviparious Features (Egg Laying)

Many insects, reptiles, all birds, and monotremes (egg-laying mammals) are oviparous. The embryo develops inside the egg outside the parent.

- Egg protected by a shell formed after fertilisation (prevents desiccation)

- Embryo nourished by egg yolk

In aquatic organisms, the embryo is surrounded by jelly

- In land animals (birds, reptiles, monotremes): hard or leathery shell

- Reptiles/birds produce fewer eggs — energy saved goes into: (1) larger yolks

(2) protecting/incubating eggs

(3) parental care of young

- Most reptiles and insects show little parental care, but pythons coil around eggs to protect and regulate temperature; crocodilians protect nests and young

- Almost all birds protect eggs, incubate, and feed young, often with both parents involved

Ovoviviparious (Internal Eggs)

- Egg cells are fertilised internally; membranes form around the embryo

- Eggs are kept inside the mother's body (at constant temperature), but the embryo is nourished by yolk — not from the mother

- Mother provides gaseous exchange and protection, but not food

- Eggs hatch as being laid, or before they are laid; however, they are born live.

- Advantage: young can grow to a fairly large size before birth — better at avoiding predators

- Whale shark - ovoviviparous; gives birth in protected bays and river mouths to protect young and ensure food supplies

- Also: some snakes, cockroaches, Cape dwarf chameleon, Garter snakes

- Fewer eggs produced. The more energy is spent on yolk production

Viviparous Features (Live Birth/ Placental)

- Fertilisation is internal; eggs have no shell

- Embryo develops inside the female and is nourished by the female through a placenta

- Occurs in: placental mammals (NOT marsupials and monotremes), 55% of sharks and rays, some invertebrates (scorpions)

- Advantages: incubation temperature regulated by mother; embryo safe from predation; fitter offspring more likely to survive to adulthood

- Disadvantages: fewer young produced; energetically demanding on the mother

- Mortality rates are lower than in oviparous and ovoviviparous animals

Oviparity vs. Ovoviviparity vs. Viviparity

Table on pg 9

Pre-natal

Parents spend energy on guarding nests, incubating, and nourishing pre-infancy.

Post-natal

Parents spend energy on feeding, protecting, teaching offspring post infancy.

Precocial vs. Altricial

Precocial animals that are born at a higher state of development. (Birds are born in a nest on the ground.)

Altricial animals that are born at a less developed state.

(Birds born in nests in trees.)

TIP:

Pre- Prae- Before

cocial - coquere - to cook/ripen

Therefore, Precocial =

early ripening