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Behavioural Ecology

Sperm competition

QuestionAnswer
Selection arising from sperm competition is a product of: Polyandry - (how many males might enter the competition) (female has more than one male mate)
Overt examples of male:male competition ultimately function to: - avoid sperm competition - enhance the success of self’s sperm
Sperm competition: internal fertilisation Sequential males or sperm Replicate crosses and mating order, then genotype offspring to compare N males with I males success
Sperm competition: simultaneous males or sperm Replicate crosses, then genotype offspring to compare F males with R males success
Behaviour Genitalia Gonads Ejaculates Spermatozoa Vary in: 1. Number 2. Size 3. Motility 4. Polymorphism 5. Cooperation 6. Gigantism
Behaviour: mate guarding Natural soapberry bug populations show plasticity in male mating/guarding duration depending on risk of sperm competition from OSR (Carroll 1993)
Behaviour – Female mate manipulation and rival sperm removal Interrupted mating experiments show the different stages of copula involved with sperm removal (Stage I) and sperm transfer (Stage III) in Mnais pruinose (Siva-Jothy & Tsubaki 1989)
Physiology: testes size Multi male primate testes bigger than single living males
Sperm number and size Copula duration = number of sperm transferred More sperm transferred = more fertilisations = relative sperm number important
Sperm size Experimental approach reveals that sperm competition intensity selects for longer, more costly sperm - sperm becomes larger and more competitive
Sperm polymorphism All butterflies and moths produce two distinct sperm types: eupyrene (fertile, 10%) and apyrene (NON-fertile, 90%)
Sperm cooperation Heads are hooked Sperm trains allow for greater velocity
Sperm gigantism Significant association between sperm length and female sperm storage site size across Drosophila species
A paradox? Anisogamy selects for lots of tiny sperm, but sperm competition selects for larger sperm
Conclusion Sperm competition opportunities widespread Important fundamental mechanism underlying anisogamy and governing gene flow
Conclusion Has profound influence on male reproductive behaviour, morphology, physiology Leads to diverse and unexpected adaptations at the gamete level – many yet to be discovered….?
Created by: rose.coo
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