A full compilation of all 15 lectures of the University of Bristol course 'Optimisation of Behaviour: Sex, Behaviour and Life Histories'. Independent reading is included (highlighted in yellow). The module focuses on the evolution and maintenance of sex.
What is sex?
Sex: “the recombination of genes from separate sources into a single organism”
For most eukaryotes it involves alternation between diploid and haploid life stages
Dominant diploid phase: e.g. animals and flowering plants (haploid phase = gametes)
Dominant haploid phase: e.g. fungi, moss and algae (diploid phase = haploid mating
types (gametophytes) join to form a sporophyte, which immediately undergoes
meiosis to form 4 spores)
(could look at fungi lectures from 1st year)
Haploid and diploid phases can look very similar (e.g. Ulva)
Dioecy (gonochorism) = reproductively subdivided into two sexes (sexual dimorphism)
Reported in close to half of all angiosperm families (Heilbuth, 2000)
Rumex nivalis (flowering plant): heavier and earlier germinating male seeds (Barrett
& Hough, 2013)
Silene latifolia (short-lived flowering plant): females grow larger and live longer
(Barrett & Hough, 2013)
Mating types = incompatibility systems, but not the same as ‘sexes’
Can have multiple mating types, each of which can mate with any others but not its
own type
: e.g. Stylonychia Mytilus (a ciliate) has ~100 mating types
In many species of microorganisms (fungi, protozoans)
Main factors of sex in eukaryotes:
Alternation between diploid and haploid life stages
Reduction division via meiosis (chromosome number halved – haploid phase)
Crossing-over (prior to separation of homologous chromosome pairs)
fusion of haploid gametes with those of the opposite sex (syngamy)
Costs of sex
meiosis is energetically costly (consumes more ATP than mitosis) and error prone (high
error rate)
finding a mate is energetically costly
males spend time and energy fighting with males and trying to impress females
females spend time and energy finding the ideal mate
recombination: separation of linked, co-adapted genes
crossing-over and mixing with other organisms genes disrupts adapted gene
combinations
heterozygote advantage
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