BIOL1131 Lecture Notes - Lecture 7: Ascidiacea, Thermoregulation, Global Warming
7 Jun 2018
School
Course
Professor
Animal Life Histories
• Strategies evolve if they represent the best trade-off between the costs
and benefits of a particular way of doing things
• Reproductive strategies
o Asexual reproduction
▪ One parent
▪ Offspring are genetically identical to parent and each other
o Sexual reproduction
▪ Two parents with haploid gametes
▪ Offspring and genetically unique (novel combinations of
genes from both parents)
o Benefits of sexual reproduction
▪ Produces new combinations of genes and alleles
▪ Provides insurance against uncertainty in the environment
o Costs of sexual reproduction
▪ Offspring are less well suited to the existing environment
▪ Expensive to parents – gamete production, predation rick,
mate competition, parental care
• Sexual terminology
o Dioecious (gonochoristic) – one sex only, either male or female
▪ Males have the smaller gamete
o Hermaphrodites – produce male and female gametes
▪ Sponges, some cnidarians, all flatworms, sea slugs, garden
snails, sea squirts, even some fish and amphibians
▪ Two types:
• Sequential – change sex during their lifetime and
therefore avoid self fertilisation
o Protandry: male → female
o Protogyny: female → male
• Simultaneous – maintain two sets of reproductive
organs
o Costs:
▪ Productions and upkeep of two
reproductive systems
o Benefits
▪ Increases mating frequency
▪ Useful when the change of meeting a
con-specific is low
o Strategies to avoid self-fertilisation
▪ Anatomical separation of gonads
▪ Complex courtship behaviour
▪ Eggs fertility delayed until sperm are
non-functional
• Asexual reproduction
o Mitotic division produces diploid daughter cells
o Produces offspring genetically identical to the parent (clones)
o Some animals are colonial e.g. bryozoans, corals, hydroids,
ascidians
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o Benefits
▪ Dont need a partner
▪ Can produce many offspring rapidly
▪ Maximizes exploitation of favourable conditions
o Asexual life stages
▪ Cnidarians and Trematoda
o When not to do the asexual
▪ High risk of local extinction – will only be successful of
conditions remain favourable
▪ No genetic diversity, so cant adapt to new or changing
conditions
• Parthenogenesis
o Haploid gamete is produced by meiosis – nucleus fuses and
becomes diploid
▪ Egg cells develop into embryos without fertilisation
▪ Offspring usually female
o Obligate parthenogenesis
▪ Always parthenogenic, e.g. whiptail lizard
o Cyclical parthenogenesis
▪ Some phases of the life cycle are parthenogenic, e.g. some
species of aphids
• Bet hedging
o Changing your reproductive strategy to get the best of both worlds
o Strawberry-Coral Model
▪ Sex and dispersal is often linked
▪ Organisms often reproduce asexually locally, but
dispersive phases are sexual
• A strategic trade-off
o Low reproductive effort
▪ High functionality
▪ Low survival
▪ r-selected or weedy species
o High parental investment
▪ Low fecundity
▪ High survival
▪ K-selected species
• Costs of reproduction
o Complicated reproductive organs
o Provisioning of eggs
o Mating behaviour/competition
o Protection of offspring
o Nourishment of young
o Parental care
o Costs boil down to fertilisation
▪ External: not assured but a cheap option
• Free-living embryos, many larval stages
• Indirect development
o E.g. caterpillar → butterflies
o Planktotrophic larvae
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