Mating systems and parental investment Mating systems Pattern of matings 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 dunnock Polygyny threshold ??? Polygyny threshold Male with no other females (monogamy) 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 display arenas hammerhead bat Uganda kob Leks Classical lek: males display in sight of each other Exploded lek: males rely on vocal communication, 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? Polyandry • Usually characterized by sex-role reversals • Factors favoring polyandry include – Male-biased sex ratio Wilson’s – Precocial offspring jacana phalarope – Superabundant food Polyandry spotted sandpiper x Clutch manipulations Selects for production reveal incubation of two clutches constrained at four eggs Monogamy Given sex differences in gamete production, why monogamy? Monogamy Duration may be variable Rare in mammals (<5%) common in birds (>90%) Monogamy Occurs in species 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 sexes 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 red-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 genetic diversity 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 humans 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 Nutrition in egg fitness of offspring at cost to parent 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 parental care? 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 Extra-pair 9 8 paternity 7 6 may select for 5 4 decreased tree 3 male care 2 swallow 1 Number of broods of Number 0 If costs to male and female to rear young 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 Proportionare the of same, extra-pair but young only (EPY) 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 dunnocks 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 fish 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 .