Mating systems and systems

Pattern of in a population

green anole

Antithesis = promiscuity Polygyny

Scramble: no attempts to defend females, resources horseshoe crabs

Northern barred frog Female defense: must be clustered elk

Dulichiella spp. Polygyny

Montezuma’s oropendola Polygyny

Resource defense: males defend food, nest sites

Red-winged blackbird Lamprologus cichlid Resource distribution

Distribution of females affects males’ ability to guard them

Males cannot monopolize wide-ranging females

Polygyny threshold

??? Polygyny threshold

Male with no other females () Male with other female(s)

polygyny threshold

Quality of male’s territory Polygyny threshold

Polygyny threshold = point at which it’s better to be polygynous on a good territory Male dominance polygyny

When females and sage grouse resources too dispersed, males compete

Leks = communal arenas

hammerhead bat Uganda kob Leks

Classical lek: males display in sight of each other

Exploded lek: males rely on vocal , e.g. kakapo Leks

High variance in male mating success – 10-20% males achieve >50% copulations – one male got 75% copulations

wire-tailed manakin Leks

• Hotshots – Females attracted to lek by dominant male Leks

• Hotshots – Females attracted to lek by dominant male • Hotspots – Leks located in high-use areas Leks

• Hotshots – Females attracted to lek by dominant male • Hotspots – Leks located in high-use areas • Female preferences – Females prefer large groups of males Leks

Position of most successful male territory shifts (hot shot?) black grouse

Removal of dominant male may cause lek to shift, disband Leks

Lek placement varies with respect to female density (hot spot??) Paradox of the lek

How is genetic variation maintained?

Hamilton Rowe and Zuk and Houle Paradox of the lek

If females mate once, why do leks form?

• Usually characterized by -role reversals • Factors favoring polyandry include – Male-biased sex ratio Wilson’s – Precocial jacana phalarope – Superabundant food

Polyandry

spotted sandpiper

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Clutch manipulations Selects for production reveal incubation of two clutches constrained at four eggs Monogamy

Given sex differences in production, why monogamy? Monogamy

Duration may be variable

Rare in mammals (<5%) common in birds (>90%) Monogamy

Occurs in where females are widely distributed, rarely encountered

mantis shrimp Mate assistance

Important when young are Important where habitat is energetically demanding harsh or offspring survival is low

cotton-top tamarins emperor penguins Mate assistance

Female + male Female only Female enforcement

Conflict of interests between the regarding care of offspring, opportunities for additional matings

Female untethered Female tethered

burying beetle < 6 min > 6 min Duration of male pheromone emission Extra-pair copulations

In some species, >50% offspring are extra-pair young

tree swallow 9 8 7 6 5 4 3 2 1 Number of broods of Number 0

0.0 - 0.10 0.91 - 1.0 0.11 - 0.20 0.21 - 0.30 0.31 - 0.40 0.41 - 0.50 0.51 - 0.60 0.61 - 0.70 0.71 - 0.80 0.81 - 0.90 superb fairy wren Proportion of extra-pair young (EPY)

50-90% EPY (avg. 78%) Why do females solicit EPCs?

Material benefits?

Adelie penguins get rocks from EPC partners Why do females solicit EPCs?

Material benefits?

scorpionfly • EPCs are less “institutionalized” version of polyandry

• Many of the same benefits apply Why do females solicit EPCs?

Male defense

…against nest predators …against infanticidal males

-winged blackbird Hanuman langur 32% predation on females with EPY 54% predation on females with no EPY Females may mate often to confuse paternity Why do females solicit EPCs?

Genetic benefits – Guard against poor sperm quality of mate

pseudoscorpion Why do females solicit EPCs?

Genetic benefits – Guard against poor sperm quality of mate – Increase of offspring

blue tit Why do females solicit EPCs?

Genetic benefits – Guard against poor sperm quality of mate – Increase genetic diversity of offspring – Mate with genetically superior male

bluethroat EPCs in

Population % nonpaternity southern Africa (!Kung) 2 rural Michigan, USA ~10 Munich and Copenhagen >10 Italy 13.2 India 15.3 urban Michigan, USA 20.1 Liverpool, UK 20-30 Parental investment Parental investment

Behavior that increases in egg fitness of offspring at cost to Pre-hatching (nest site, protecting eggs)

Post-hatching (provisioning, lowland gorilla protecting young) Parental investment

Post-hatching investment is rare Patterns of parental investment

mallee fowl • Female-only care predominates • Male, biparental care is rare

How do we account for the general female bias golden-lion tamarin in ? Patterns of parental investment

=

Richard Dawkins Logic suffers from “sunk cost” or What about the abrupt “Concorde” fallacy termination of investment in polyandrous species? Patterns of parental investment

Explained by order of gamete release? Mode of fertilization

Provider sex Internal External guppy Male Few Many piranha

Female Many Few

How to explain the predominance of male care in frogs where males deposit sperm first? Importance of paternity

9 8 7 6 Extra-pair 5 4 paternity 3 2 1 may select for Number of broods of Number 0 decreased

0.0 - 0.10 0.91 - 1.0 tree 0.11 - 0.20 0.21 - 0.30 0.31 - 0.40 0.41 - 0.50 0.51 - 0.60 0.61 - 0.70 0.71 - 0.80 0.81 - 0.90 male care swallow Proportion of extra-pair young (EPY) If costs to male and female to rear young are the same, but only 3 of 4 chicks are his…

He should reduce his dark-eyed level of investment junco Recognition of unrelated young?

No apparent discrimination against EPY

male female

Male tree swallows show Male yellow warblers do no feeding bias to own not adjust feeding rate chicks, feed those closest in response to cuckoldry or most in need Recognition of unrelated young?

Alpha, beta male care for young in proportion to time spent with female

Females may use mating solicitations to manipulate male parental investment Experimental = male Control = male bluegill on nest with bluegill on nest “sneaker” in a jar

Tested defensive responses to nest predator Recognition of unrelated young?

Why the difference between care of eggs and care of fry? Sex differences in costs of investment

St. Peter’s Male care persists where costs to females exceed costs to males?

Male care depends on costs/benefits to male ~11 days ~7 days Sex differences in costs of investment

giant water bug

Large eggs require high level of care