BIO2242 Lecture Notes - Lecture 18: Life History Theory, Resource Allocation, Hermaphrodite
Lecture 18 – Invertebrate Life History I
The Ideal Animal
• Long lifespan – live forever → maximise reproductive output
• Lots of offspring
• Reach sexual maturity as early as possible
• Mature at birth and reproduces immediately
• Continually produce large numbers of high-quality offspring
• Live indefinitely
• No animals exist like this
o Environment impact this
o Decrease amount of resources → competing with other animals
o Constraints
o Limitations
o Trade offs: only certain amount of resources allocate resources
• Darwinian Demon
o A hypothetical organism that could maximise all aspects of fitness
simultaneously, if the evolution of a species was entirely unconstrained
Life History
What is Life History?
• An individual’s pattern of allocation, throughout life, of time and energy to
various fundamental activities such as growth, maintenance and reproduction
o The amount of energy an organism can harvest and used is finite
o Biological processes take time
o Energy and time devoted to one activity cannot be devoted to another
activity
• Specimen
o Look at body size, morphology and structure
▪ Large body size: late maturing
▪ Penis: internally fertilising → decreasing amount of offspring it
can have because fertilises in mother → more investment in
each of offspring
▪ Family grouping: late maturing → lives longer
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• Life History Traits
o Clutch/litter size
o Incubation/gestation length
o Offsrping size
o Sex ratio
o Presence, degree and length of parental care
o Growth rate
o Age and size at maturity
o Adult body size
o Frequency of reproduction
o Deviation
▪ Long lift
▪ Large body size, produces lots of young but relatively low
survival
▪ E.g. turtle
• Life History Evolution
o Different species address questions in different ways
▪ Diverse range of life history strategies in invertebrates
o Different in body size and number of eggs → different allocation of
resources
▪ Life history differences reflect different resource allocation
strategies
▪ Life history theory attempts to make sense of diversity
o No ‘correct’ life history strategy
▪ Variation within and among species
▪ Make shifts in strategies in response to prevailing environment
o Aims to maximise lifetime reproductive success
Constraints and Trade-offs
• Constraints
o Not possible to do everything
o Genetic architecture
o Phylogenetic history
▪ Limited spectrum of evolutional pathways it can follow
▪ Once lost wings, hard to revolve them unless gene just needs to
be switched on
o Biophysical and mechanical factors
o Life style
o Limits the spectrum of opportunities
▪ Limit the course of evolution and shape it
▪ Similare responses to same environment
• Trade-offs
o Finite resources
o Resource allocation
▪ Growth
▪ Body maintenance
▪ Reproduction
o Constrain the simultaneous evolution of two or more traits
o Within individuals or evolutionary timescale
▪ Not fixed within species
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Document Summary
Marine invertebrates: 3 main life history patterns: external fertilisation and planktonic larvae, majority of marine invertebrates, e. g. Internal fertilisation and direct development: e. g. advanced gastropods, crustaceans (e. g. amphipods, isopods), Cephalopods (octopus, squid), chaetognathes (arrow worms: copulation and often sperm storage after internal fertilization, egg deposited within capsules or brooded by adult, few, well provisioned embryos, lower amount of young, females put more investment. Provide more resource and nutrients to offspring: no planktonic stage, rare in marine invertebrates, high adult dispersal patchy/unpredictable environments. Internal fertilisation widespread: most terrestrial invertesbrates, sperm storage, more likely to have k selection, younger developing internally, loss of planktonic larvae, tendency towards hermaphroditism, flying insects with aquatic life stages, internal fertilisation, large eggs, aquatic larval stages, e. g. Odonates (dragonflies), ephemerotypera (mayflies), plecoptera (stoneflies: two main lineages of terrestrial invertebrates, insects, arachnids, gonochoristic. Internal fertilisation: spermatophores or intromission, parental care, brooding, vividparity. Insect life cycles: two modes of insect development, hemimetabolous (gradual metamorphosis)
