Mating systems and parental investment Mating systems
Pattern of matings in a population
green anole
Antithesis = promiscuity
Polygyny Polygyny
Scramble: no attempts to defend females, resources horseshoe crabs
Northern barred frog Female defense: must be clustered elk Montezuma’s oropendola
Dulichiella spp.
Polygyny Resource distribution
Resource defense: males defend food, nest sites Distribution of females affects Red-winged blackbird Lamprologus cichlid males’ ability to guard them
Males cannot monopolize wide-ranging females
dunnock
1 Polygyny threshold Polygyny threshold
Male with no other females (monogamy) Male with other female(s)
polygyny threshold
??? Quality of male’s territory
Polygyny threshold Male dominance polygyny
When females and sage grouse Polygyny threshold = point at which it’s resources too dispersed, better to be polygynous on a good territory males compete
Leks = communal display arenas
hammerhead bat Uganda kob
Leks Leks
High variance in male mating success – 10-20% males achieve >50% copulations – one male got 75% copulations
Classical lek: males display in sight of each other
Exploded lek: males rely wire-tailed manakin on vocal communication, e.g. kakapo
2 Leks Leks
• Hotshots • Hotshots – Females attracted to lek by dominant male – Females attracted to lek by dominant male • Hotspots – Leks located in high-use areas
Leks Leks
• Hotshots Position of most successful – Females attracted to lek by dominant male male territory shifts (hot shot?) • Hotspots black grouse – Leks located in high-use areas • Female preferences – Females prefer large groups of males
Removal of dominant male may cause lek to shift, disband
Leks Paradox of the lek
Lek placement varies with respect to female density (hot spot??) How is genetic variation maintained?
Hamilton Rowe and Zuk and Houle
3 Paradox of the lek Polyandry
• Usually characterized by If females mate once, why do leks form? sex-role reversals • Factors favoring polyandry include – Male-biased sex ratio Wilson’s – Precocial offspring jacana phalarope – Superabundant food
Polyandry Monogamy
Given sex differences in gamete production, why monogamy?
spotted sandpiper
x
Clutch manipulations Selects for production reveal incubation of two clutches constrained at four eggs
Monogamy Monogamy
Occurs in species where females are widely distributed, rarely encountered
Duration may be variable
Rare in mammals (<5%) mantis shrimp common in birds (>90%)
4 Mate assistance Mate assistance
Important when young are Important where habitat is energetically demanding harsh or offspring survival is low
cotton-top tamarins emperor penguins
Female + male Female only
Female enforcement Extra-pair copulations
Conflict of interests between the sexes regarding In some species, >50% offspring are extra-pair young care of offspring, opportunities for additional matings tree swallow 9 8 Female untethered 7 Female tethered 6 5 4 3 2 1 Number of broods of Number 0
0.0 - 0.10 0.91 - 1.0 burying beetle 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 < 6 min > 6 min Proportion of extra-pair young (EPY) Duration of male pheromone emission 50-90% EPY (avg. 78%)
Why do females solicit EPCs? Why do females solicit EPCs?
Material benefits? Material benefits?
scorpionfly • EPCs are less “institutionalized” version of polyandry
• Many of the same benefits apply
Adelie penguins get rocks from EPC partners
5 Why do females solicit EPCs? Why do females solicit EPCs?
Male defense Genetic benefits …against nest predators …against infanticidal males – Guard against poor sperm quality of mate
red-winged blackbird Hanuman langur 32% predation on females with EPY 54% predation on females with no EPY Females may mate often pseudoscorpion to confuse paternity
Why do females solicit EPCs? Why do females solicit EPCs?
Genetic benefits Genetic benefits – Guard against poor sperm quality of mate – Guard against poor sperm quality of mate – Increase genetic diversity of offspring – Increase genetic diversity of offspring – Mate with genetically superior male
bluethroat
blue tit
EPCs in humans Parental investment
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
6 Parental investment Parental investment
Behavior that increases Nutrition in egg fitness of offspring at cost to parent Pre-hatching (nest site, protecting eggs) Post-hatching investment is rare
Post-hatching (provisioning, lowland gorilla protecting young)
Patterns of parental investment 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 parental care?
Richard Dawkins Logic suffers from “sunk cost” or What about the abrupt “Concorde” fallacy termination of investment in polyandrous species?
Patterns of parental investment Importance of paternity
Explained by order of gamete release? 9 8 7 6 Extra-pair Mode of fertilization 5 4 paternity 3 2 1 may select for Provider sex Internal External broods of Number 0 decreased guppy 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 Male Few Many piranha swallow Proportion of extra-pair young (EPY)
Female Many Few If costs to male and female to rear young are the same, but only 3 of 4 chicks are his… How to explain the predominance of male He should reduce his care in frogs where males deposit sperm first? dark-eyed level of investment junco
7 Recognition of unrelated young? Recognition of unrelated young?
No apparent discrimination against EPY Alpha, beta male dunnocks care for young in proportion to time spent with female male female
Male tree swallows show Male yellow warblers do no feeding bias to own Females may use mating not adjust feeding rate chicks, feed those closest solicitations to manipulate male in response to cuckoldry or most in need parental investment
Experimental = male Recognition of unrelated young? Control = male bluegill on nest with bluegill on nest “sneaker” in a jar Why the difference between care of eggs and care of fry?
Tested defensive responses to nest predator
Sex differences in costs of investment Sex differences in costs of investment
St. Peter’s fish giant water bug Male care persists where costs to females exceed costs to males?
Male care depends on costs/benefits to male ~11 days ~7 days
Large eggs require high level of care
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