Polygyny

How it’s accomplished Diverse strategies have evolved Factors Female defense polygyny Resource defense polygyny Lek polygyny Scramble competition polygyny Factors Female distribution Food availability Territory size

Female Defense Females in groups are easy for a male to dominate and monopolize, relative to many dispersed females Mammals where females live in groups are always polygynous Lions Bighorn sheep Gorillas Key element is following females, not nests or territories

A female defense strategy

Passive female defense

Resource defense Females don’t live together, but visit a resource on a regular basis Male controls the resource, gets access to many visiting females Floating vegetation Rotting bark Rotting fruit

Resource defense Any safe place to lay eggs is a defensible resource

Female Perspective Polygyny threshold model Resource level at which she has more to gain by mating with a polygynist on a good territory than a monogamous male on a poor territory Predict: female should have same fitness with either type of male if territory is constant Test: count fledged hatchlings of a songbird that has males that can attract one or two females per season Result: 1.3 vs 1.6 fledged young (poly vs mono) Test 2: manipulate habitat so polygynous male is preferable to monogamous male Result 2: red winged blackbird females pick the male with the best territory, even if she becomes part of a harem (she has almost 2x better reproductive success) Males may provide good nesting areas apart from each other in his territory so the second female is unaware that she is second. But note song frequency data—reduced when mated once.

Scramble Competition When females are widely distributed (or resources), male territory defense doesn’t make sense Searching becomes the primary method Fireflies Squirrels Requires different set of abilities—perceptual, endurance, etc.

Hippocampal dependence Hippocampal dependence? Spatial memory for where male had interacted with soon-to-be fertile females

Hippocampus and spatial memory Polygynous voles have sexually dimorphic hippocampal volume Reproductively active males outperform females on mazes Males have larger home ranges than females or immature males Polygynous males expand their home range during the breeding season

Size of home range correlates with spatial ability

Lekking species Males gather in groups to display for females, with each male defending a small area of the lek Searching vs. lek formation? Not understood, maybe predator defense? Hypotheses for congregation in leks Hotspot: males go to territory where females go Hotshot: males go where the dominant male goes Female preference for sites with multiple males

Hotshot hypothesis Male decoys attract both male and females Especially very elaborate, attractive male decoys Lek sites change over time Removal of popular male (hotshot) leads to lek dispersal

Success at the lek In some species, 6% of males sire 80% of progeny (bats) In manakins, one male sired 75% of the progeny, a second 13%, and the rest 12% Males at the center of the lek enjoy more mating success

DQ Benefits to females of lek mating is choosing mates of high genetic quality. Few males tend to dominate the lek. What are the consequences for genetic variability in lekking species? What does this mean for the first idea, that females go to leks to choose good genes? How can we reconcile these findings?

A common draw These tree frogs both respond to the same cues to come to the pond at night