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 9 8 • Male, biparental 7 6 care is rare 5 = 4 3 2 How do we account for 1 Number of broods of Number 0 the general female bias golden-lion tamarin in parental care? 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 Proportion of extra-pair young (EPY) 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? Mode of fertilization Extra-pair paternity Provider sex Internal External may select for decreased guppy tree male care Male Few Many piranha swallow 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 8 .