Sexual Selection Flashcards
Sexual Selection
Form of non-random mating which occurs when individuals within a population differ in their ability to attract
Determines who reproduces
Intersexual Selection
Mating success determined by between-sex interactions
Looks at mate choice (choice exerted by members of the opposite sex)
Female choice of males (males must show themselves to be genetically attractive to females)
Intrasexual Selection
Mating success determined by within-sex interactions
Looks at individuals competing to obtain mates (competition between members of the same sex)
Fundamental Asymmetry of Sex
Results from the fact that in most species females invest more in their offspring than males
Male-Male competition
The ability to win fights and produce offspring is determined by body size, then alleles for a large body size have a fitness advantage
Males that win battles monopolize mating with females in their territory
Dramatic head butting
Tusks on male elephants and walruses
Horns in male sheep and beetles
Enlarged claws of male fiddler crab
Sexual Dimorphism
Any trait that differs between males and females of the same species
Weaponry
Ornamentation and behavior in courtship
Body size
Biological Fitness
Reproductive success and reflects how well an organism is adapted to its environment
Greater fitness means the organism leaves more viable/living offspring
Explain the relationship between Natural Selection and Sexual Selection
Natural selection determines who survives while Sexual selection determines who reproduces
Differentiate between intersexual selection and intrasexual selection
Intersexual - looks at mate choice (choice exerted by opposite sex)
Intrasexual - looks at individuals competing to obtain mates (competition between members of the same sex)
Examples of intersexual selection
ex. Male satin bowerbird decorates its nest with blue materials to attract females
Females red-collared widowbirds prefer mating with males with longer tails
Female hanging fly will not mate with male unless he brings her a large offering of food
Examples of intrasexual selection
Male-Male combat over females or resources vital to mates
Tusks on male elephants and walruses
Horns in male sheep and beetles
Antlers on male moose
Female spotted hyenas are larger and more muscular than males, compete to be the alpha
2 important consequences of the fundamental asymmetry of sex
Female fitness is limited by the ability to gain resources needed to produce more eggs and healthier offspring, so females produce few offspring during lifetime
Male fitness is limited by the number of females he can mate with, he can mate frequently because sperm are so energetically inexpensive
Predictions associated with the Bateman-Trivers hypothesis
Females, not males, should be choosy about mates since they invest a lot in each egg (opposite should be true for males)
Males will compete with each other for mates
Alleles that increase a male’s attractiveness or success in male-male competition should increase in population (sexual selection should act more strongly on males than females)
Ideas on why females tend to be choosy when searching for a mate
Gives rise to “good genes” hypothesis which states that the traits females choose when selecting a mate are indicators of the males ability to pass on genes that will increase the survival of reproductive success of her offspring
Physical characteristics that signal male genetic quality
Behavioral characteristics of the male that indicate their ability to provide parental care
Sexual Dimorphism
examples?
Mandarin ducks - males have a bright red beak and colorful plumage, female’s colors are more muted
Male elephant seals have large proboscises that resemble elephants trunk, females don’t
Size of canines in baboons are more than twice as large as that of female canines
Males lions are larger than female and have an elaborate mane
Monogamy
example?
Pattern of having one mate at a time (one male and female have an exclusive mating relationship)
Parental care involves both parents
ex. bald eagle (only form new bond if partner dies, male barn owls (provide dead mice and screech while interested females respond by croaking)
Polygamy
3 different types?
Pattern of having more than one mate at a time - one or more males are bonded socially with one or more females
Polygyny, Polyandry, Polygynandry
Polygyny
examples?
One male mates with two or more females, most common polygamous mating system, female usually provides most parental care
ex. male walrus grab female attention with loud vocalizations, elephant seals, common pheasants, gorillas, spotted hyenas
Polyandry
examples?
One female mates with two or more males, males usually provide most parental care
ex. spotted sandpiper (females compete for territories in order to attract males), pipefishes (relative of seahorses)
Polygynandry
examples?
2 or more males mate with 2 or more females, advantageous from females perspective allows her to have multiple males care for her blood
ex. red foxes, European badgers, sea spiders, ground squirrels
Promiscuity
examples?
Mating system where there is no pair bonding, females mate with multiple males and males mate with multiple females
Female raises the young alone
ex. bonobos, dolphins, hummingbirds
Pair Bonding
Also known as monogamy
One male and female have an exclusive mating relationship
Differentiate between “good genes” hypothesis “sexy sons” hypothesis
The explain the evolution of female preferences in species where females do not receive direct benefits from mating
“Good Genes” hypothesis - the traits females choose when selecting a mate are indicators of the males ability to pass on genes that will increase the survival or reproductive success of her offspring
“Sexy Sons” hypothesis - a females ideal mate choice among potential mates is one whose genes will produce males with the beat chance of reproductive success, other benefits the father can offer the mother are not important (parental caregiver and resource access)
Differentiate between Polygynandry and Promiscuity
Polygynandry - two or more males mate with two or more females are bonded socially
Promiscuity - any male can mate with any female and vice versa without social ties
Examples of animals that use specified mating systems
Monogamy - bald eagle, barn owls, hammerhead sharks
Polygyny - walruses, elephant seals, gorillas
Polyandry - spotted sandpiper, pipefishes
Polygynandry - red foxes, European badgers, sea spiders
Promiscuity - dolphins, bonobos, hummingbirds
Bateman-Trivers Hypothesis
Pattern - traits that attract members of the opposite sex are more elaborate in males
Process - eggs are more energetically costly to create than sperm
2 crucial variables in a mating system
Male and female dispersion (space between)
Desertion by either sex (giving up parental care)
