Prelim 2 - WhatuseisSex? 16:18

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What use is Sex? 16:18 Sexuality = reproduction that involves creating new genetic combinations Asexuality = reproduction without creating new genetic combinations Cost of sex The cost of making males – population view o Asexual reproductive populations increase much more rapidly than sexual The cost of meiosis – genetic view o ½ chance of gene being passed in sexual, in an asexual, every gene has  100% chance of being passed on. STD’s –in every species Breaking up of co-adapted gene complexes o Perfectly adapted genes get changed (bristle-cone pines) Competitions for mates o Injuries to male squirrels But sexual reproduction must be advantageous over evolutionary and ecological  time  Over evolutionary time because o Sex is nearly ubiquitous o Ancient asexual lineages are rare exception in ecological time (today) because o some species that can reproduce sexually and asexually maintain both  modes of reproduction Some organisms alternate between sexual and asexual reproduction Advantage of sex:
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Variety Viability more flexible than asexual populations Lottery Hypothesis o Creating diverse offspring to cope with unpredictable physical environment Temporal unpredictability – weather Spatial unpredictability – seeds disperse to sand, forest, etc. Red Queen Hypothesis o Creating diverse offspring to cope with unpredictable biotic (living)  environment Parasites/diseases Competitors Predators Unpredictability Sexual – biotic > physical o Marine o Large Lakes o Low latitutes o Low altitudes o Wet o Parasitic o Mainland Asexual – physical > biotic o Fresh water o Small streams o High latitudes o High altitudes o Dry o Free living o Islands ^| bodes well for red queen hypothesis
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Sexual Selection – female choice 16:18 Natural selection
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Sexual Selection – female choice 16:18 Depends on the success of both sexes in relation to general conditions of life Selection for traits that increase survival and reproductive success of both  sexes Sexual selection Depends on success of certain individuals over others of same sex Selection for traits that increase the mating success of some individuals over  others of same sex Female choice of mates Male vs. male competition Both these qualities arise from the fundamental asymmetry in gamete size Females produce small numbers of relatively large gametes Males produce large numbers of relatively small gametes Females also typically invest more in than the male in parental care Difference in investment – evolutionary basis of sexual selection o Males can fertilize eggs at a faster rate than females can produce them
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This note was uploaded on 09/14/2010 for the course BIONB 2210 taught by Professor Seeley during the Fall '10 term at Cornell.

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Prelim 2 - WhatuseisSex? 16:18

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