Sexual Selection Flashcards
Secondary sexual traits
Traits are sex-limited in expression but not directly associated with reproduction
Sexual dimorphism
Morphological (and behavioral) differences between sexes
Sexual selection
A form of natural selection. Differential mating success associated with phenotype/genotype. Mates per year!
Rules of thumb for sexual selection
(Usually) stronger for males, (usually) stronger in polygamous systems, (usually) leads to traits that are costly to other fitness components
Mechanisms for sexual selection
Intrasexual competition and mate choice
Intrasexual competition
(Male-male ; female-female) Compete directly for reproductive access to individuals of opposite sex. Ex: Northern elephant seals
What sort of traits would we see for intrasexual competition?
Bluff displays, weaponry, stamina, fighting ability, large size
Mate Choice
(Usually females) Individuals have mating preferences - indirect competition.
How might choosy females benefit over non-choosy females?
Direct benefits: food resources, good parent, healthy mate
Indirect benefits: good genes, sexy sons
Sensory drive: favors males that are best detected by female’s sensory system
Sexy sons
Females have sexy sons, must have females with preference in population, can “runaway.” Ex of runaway: Male bird with long tail is preferred in population. Mates with females that only prefer long tails, the future could have birds with exaggerated long tails
What are the types of mating systems?
Monogamy (weak sexual selection), polygyny (one male, multiple females) and polyandry (both strong selection and fall under the category of polygamy)
Female-defense polygyny
Males compete for females, occurs when females are “clumped”
Resource-defense polygyny
Males compete for resources, occurs when resources are “clumped.” Ex: Plainfin midshipman fish that uses nest as resource
Alternative mating strategies
Conditional strategy ; Balanced polymorphism of the sneaker, satellite, and parental fish
Alternative mating strategies favor the rarer strategy until strategies are equal
Conditional strategy (alternative mating strategy)
Strategy depends on the “condition” of the individual (“the best of a bad job). Ex: Dung beetle: some males have horns and some don’t. Males without horns have to adopt an alternative strategy in order to mate with females. The beetles live and mate in tunnels guarded by a horned-beetle. The beetle without a horn will dig a side tunnel that intersects below the entrance where the guard is. The beetle will mate with a female and leave.
