Reproductive strategies for Survival

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 birds

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 mammals

OviparityBony 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, crocodiles

ViviparityTypes of viviparity are recognised by the nutrient source for the developing embryo

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”)

Activities

Glossary: r selection, K selection, fecundity, oviparity, viviparity, amniote, placenta, mortality, monotreme

Quick check questions: pg 383, 387.

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, emus

Case studies – 1. Australian Mallee Fowl

Male invests energy into nest building – incubation mound made of rotting plant matter

Female invests energy into laying 12 to 24 eggs at once

Male incubates Chicks hatch, do not

require further care

Case studies – 2. Emu

Polyandrous Male is caregiver He builds nest,

incubates eggs, guards young

Female lays eggs and leaves to mate again

Case studies – 3. Australian Marsupials

Australian Marsupials

Placental mammals (not marsupials) have a long period of uterine development

In contrast, marsupials have a short period within the uterus, and a long period developing in the pouch

TURN TO PAGE 391 IN YOUR TEXT BOOK

Australian Marsupials – arrested development Kangaroos and wallabies can suspend

development within the uterus If kangaroo conceives while young is in

pouch, she stops uterine development until pouch young is off the nipple in the pouch.

Activities

Glossary: cephalopod, marsupial, placental mammal

Quick check pg 393