huelsenbeck7-8slides - Whiptail Lizard Sexual Selection...

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Unformatted text preview: Whiptail Lizard Sexual Selection Charles Darwin and Alfred Russell Wallace Noticed that males of many species have highly elaborated traits that seem maladaptive (secondary sexual characters) Antlers Irish Elk (extinct) Hercules Beetle Male Female Horns Bighorn Sheep Elephant Tusks African Lion: Mane is used for protection during male clashes (male-male competition) Pheasant: Elaborate bright red wattle on cheek Pheasant: Elaborate spur used in male-male ghting and by females to choose. (Notice the fake spur on the right. Some males try to trick females, but do not ght.) Two Types of Sexual Selection Male-male competition (intra-sexual selection) Mate (female) choice (inter-sexual selection) Male-male competition Within group dominance Female-defense polygyny Territorial polygyny Lekking (competition for a position in the lek) Within group dominance Grey Wolves Female defense polygyny Northern Elephant Seals Territorial defense polygyny Impala Waterbucks head butting Sperm competition Mate Choice Resource based Non-resource based Two broad categories: In most cases, females are the choosy sex, but not always. Why? Grouse, a lekking species Why are females choosy? Investment cost eggs are expensive relative to sperm internal fertilization and carrying young to term is costly When are males choosy? When their contributions exceed the cost of making eggs The chances of mating with multiple females is small (biased sex ratiomany females and very few males) (sex-role reversal) Example: Sea Horse (males care for the young) Mate choice mate with correct species better fertilization ability or higher fecundity provides more food better parental ability better breeding territory or defended resource lower risks or hazards (e.g., predation) partner offers higher heritable viability or other heritable qualities that are important (Why choose in the Frst place?) Mate choice Direct benefts (proximate benefts) Example: Bush crickets (nuptial giFts) 1. Males provide spermatophores which Females Feed on. OFten consist oF up to 30-40% oF male body weight (i.e., very costly) 2. More spermatophores allow Female to lay more eggs. Mate Choice Indirect benefts (ultimate benefts) Good genes Others (e.g., isherian runaway sexual selection, which will not be discussed) Good Genes emales (or males) choose a mate which oFFers high quality genes inuencing survival Mate quality is indicated by a secondary trait Secondary trait must be heritable Must be heritable variation in mate quality No, low, or high cost to males bearing the trait (e.g., bearing the cost is an indicator oF good (e....
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This note was uploaded on 05/24/2011 for the course BIO 1B taught by Professor Carlson,mischel,power during the Fall '07 term at University of California, Berkeley.

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huelsenbeck7-8slides - Whiptail Lizard Sexual Selection...

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