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Experiments to:
· Explain sex ratios
· Explain why some species reproduce asexually and others sexually – why sex?
· Explain why there is local population variation in traits
· Explain why there are 2 sexes & what determines
· Investigate sexual selection (male-male, sexually antagonistic coevolution, female choice)
· Explain how MHC influences sex & mate choice
· Explain genomic conflict & sex ratio distorters
· Evidence Fisher’s theory & Hamilton’s
1. Brood manipulation experiments separate genetic effects from non genetic (nest in and
direct transmission of parasites from parent to offspring)
· Investigate effects of maternal condition etc
· Investigate parental care system and extent
· Measure costs of reproduction
· Explain reproductive patterns, menopause, and senescence
· Explain fluctuating asymmetry
Reading week
Lehtonen et al (2016) – Isogamy vs anisogamy – Isogamous organisms have gametes that are morphologically
similar. There was a transition to anisogamy with origin of males and females, which is common in
multicellular eukaryotes. But unicellular eukaryotes are isogamous, as were our ancestors. Means equal
parental investment. Anisogamy stable once it has evolved, but can return to isogamy if either zygote
provisioning requirements decreased or if sperm competition and sperm limitation were absent.
Tilquin & Kokko (2016) – Geography of parthenogenesis – Asexuality most prevalent in marginal habitats as
well as newly colonisable areas, or where abiotic selection pressures are relatively stronger than biotic. Due to
abiotic conditions incurring 2-fold cost of sex and there being low parasitism to necessitate evolution against.
Also get reproductive assurance in newly colonisable areas so asexuals outcompete sexuals.
Ram & Hadany (2016) – Condition-dependent sex – Individuals’ condition affects the likelihood that they will
reproduce sexually rather than asexually. Microbes fungi and plants evidence for negative condition-
dependent sex – poor condition individuals more likely to reproduce sexually – is evolutionarily advantageous
under wide range of settings. For facultative sexual organisms. Could be to adapt better to areas undergoing
significant environmental change. Is about increasing genetic variation under unfavourable conditions.
Beekman et al (2016) – Sexual selection in hermaphrodites, sperm- and broadcast spawners, plants and fungi.
Species often lacking sexual dimorphism and never directly contact while mating. Don’t really get
hermaphrodite stuff. Selection after gamete release is cryptic and favours subtle variations in reproductive
physiology.
Haig (2016) – Bryophytes – Multicellular haploid gametophytes produce gametes by mitosis. They spread by
clonal growth but mate locally, within an area defined by range of sperm movement. Can result in unisexual
populations unable to reproduce sexually. Females outcompete males as they spend less on production of
gametes. Haploid selfing is common in bryophytes with bisexual gametophytes, and results in completely
homozygous sporophytes. Spores from these sporophytes recapitulate the genotype of their single haploid
parent. This process can be considered analogous to 'asexual' reproduction with 'sexual' reproduction
occurring after rare outcrossing between haploid parents. Ferns also produce bisexual haploid gametophytes
but, unlike bryophytes, haploid outcrossing predominates over haploid selfing. This difference is probably
related to clonal growth and vegetative competition occurring in the haploid but not the diploid phase in
bryophytes, but the reverse in ferns. Ferns are thereby subject to stronger inbreeding depression than
bryophytes
Themes
1. Origin of sex: why sex is beneficial
1. Features of sex
1. SCAR
ii. Vicar of bray model
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