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

Oviparity Bony fish and frogs Birds and reptiles Known as Shell - 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

Viviparity Egg yolk viviparity Placental viviparity Types 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