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Evolution Notes

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Biology 3466B
Yolanda Morbey

Evolution NotesNov 2011 Sexual dimorphism is the difference between males and females Males tend to be larger and more brightly coloured Sexual selection Definitiondifferential reproductive success due to variation among individuals in mating success Postulates of sexual selection 1 phenotypic variation 2 variation is heritable 3 variation in mating success 4 mating success is nonrandom Sexual selection in males vs females The strength of sexual selection differs in males than in females Female eggs are nutrient rich takes more to make egg and they provide substantial parental care takes more time and energy huge investment Male sperm is cheap and they provide little parental care There is more investment in egg than sperm Limits on reproductive success Sexes differ In the sex with greater parental investment time and resources limit reproductive success Resources not the availability of sperm limit it There is weak sexual selection This is usually seen in females A females potential reproductive success will be small In the sex with lower parental investment mating success number of available mates limits reproductive success There is strong sexual selection This is usually seen in males A males potential reproductive success will be large Sexual selection variation in mating success will be a more potent force in the evolution of males than in the evolution of females Sexrole reversed species are exceptions to the general pattern of stronger sexual selection among males In phalaropes females now have strong sexual selection and mating success ability to find mates is limited Limits on reproductive success in newts Mating systemMales arrive at breeding ponds early and stay long Females visit ponds to mate with males Females lay 300 eggs over several weeks or months There is no parental care Male investment spermfemale investment eggs Mating success and reproductive success in males was highly skewed Most males were not successful at finding mates and most males had very few offspring But some males can achieve most of the reproductive success some males are able to find lots of mates and have lots of offspring This creates strong sexual selection Mating success and reproductive success in females showed a normal distribution All females were successful at mating and all had offspring As the number of mates goes up the reproductive success goes up but only in males This is because female reproductive success doesnt depend on mating success An increased on the graph equals an increased potential for sexual selection Consequences of limiting factors Number of mates strong sexual selectioncompete for access to mates ex malemale competition for females Time and resources to make eggs and provide parental care weak sexual selectionchoosy about mates Limits on reproductive success in pipefish Mating systemFemale lays eggs in brood pouch of males Males provide all parental care until eggs hatch Male investment sperm and parental carefemale investment eggs The reproductive success and mating success of males shows a more normal distribution The mating success and reproductive success of females is more skewed Many females werent successful at transferring eggs to males There is strong sexual selection on females Sexual selection is stronger in females have increased slope The stronger the skew the stronger the sexual selection The steeper the slope the stronger the relationship between mating and reproductive success Intrasexual vs intersexual selection Intrasexual selection involves competition combat among members of one sex fordirect control of mates direct control of resources top rank in dominance
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