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Biology 3300- Sexual Selection

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BIOL 3300
Theresa Burg

Biology 3300 rd March.3 , 2014 Sexual Selection Dimorphisms  where males and females look different - Why are conspicuous traits restricted to one sex? - How could evolution by natural selection account for such traits? - Why do traits that appear to be energetically costly and make individuals more vulnerable to predation exist? o More surface area on the tail for predators to grab onto o Males will have bright coloration which goes against natural selection - Widow Birds o Females are brown and quiet o Males are more colorful and have a long tail - Collared lizards o Male are more brightly colored and have higher predation rates o Females are able to blend nicely into the rocks Natural Selection - Ecological selection: caused by the environment; differential reproductive success due to individual variation in survival and reproductive output (excluding mating success) - Sexual selection: differential reproductive success due to individual variation in mating success o Does one phenotype have higher mating success than another? - Sexual selection, like other forms of selection, involves non-random reproductive success o Choices are being made o How much parental care is being given to offspring? - Acts on individuals and gametes o Motility of sperm. If an individual sperm is able to move faster than the others it will be able to get to the egg first and fertilize it Intrasexual selection: competition between two males or two females - Ex: big horn sheep fighting for the females Intersexual: selection via mate choice, usually non-random mate choice by females Asymmetries in Sexual Selection - Parental investment o Gamete production o Parental care  Caring for young, feeding the young, protecting them, incubating eggs - Limits on reproductive success o Limit as to how many eggs or sperm an individual can produce o May be tradeoffs as to how big - Mating systems o Monogamous, polygamous - Operation sex ratio o How many males and females are present in the population? Is there a certain ratio for reproductive success to be successful? - Different costs and benefits for males and females Anisogamy - Unequal gametes - Females produce few, well-provisioned gametes - Males produce many “cheap” gametes Rates of Reproduction - Study on Drosophila - The more females the male mates with, the more offspring he has o The number of offspring is limited to the number of mates - Females do not have a correlation o Mating with more males doesn’t produce more offspring o Limited by resources (number of eggs she could reproduce) Bateman’s Principle “sperm is cheap” - Male reproductive success is limited by access to females - Female reproductive success is limited by access to resources - Can lead to a conflict between the sexes, with females being the choosy sex o She will want to mate with the best male o Males will want to mate with as many females as possible - Parental investment o Increases offspring survival, but at a cost to parents’ future reproductive success o Tradeoff between next breeding season and taking care of present offspring Parental care  Mating system Birds biparental monogamous Mammals Uniparental female polygynous Fish Uniparental male promiscuous **generally no parental care in fish, but when there is it is usually from the males EPY & Parental Care - The amount of care a male will give depends on how many offspring in the nest is his - If the males can’t tell which offspring are his and he provisions car
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