Chapter 11

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University of Toronto Scarborough
Biological Sciences
Maydianne Andrade

Chapter 11 • Mating System: specifies way animal societies are structured in relation to sexual behaviour – who mates with who under what circumstances • Monogamy: 1:1, Polygyny: 1 male: many female, Polyandry: 1 female: many male, promiscuity: > 1 male + female • Social mating system: based on observed interactions between individuals – mating, parental care, pair bonds – inaccurate • Genetic Mating system – paternity and maternity patterning • Polygyny most common – excess of male sperm • 3% males social monogamous, 90% birds – genetic polygamous • Study of drosophila: more females inseminated – more eggs fertilized, greater reproductive success of the male • Male posthumous mate guarding gains exceed cost – if mate is potentially receptive after 1 mating, and finding a second female is low • Monogamy in nature o Clown shrimp: guard receptive male o Sea horse: male can only clutch 1 pouch of eggs  If a female can keep pouch supplied, no need to seek new mate o Prairie voles: social and genetic lifelong bonds o Penguins: social and genetic monogamy o Marmosets: social and genetic monogamy • Mate assistance hypothesis: males remain with a single female because parental care and protection of offspring is advantageous o Surviving offspring compensate for monogamy o California mice: increases # of surviving offspring  Explains why birds use this most –make significant difference • Bird males can incubate and feed young • Only female mammals can gestate and lactate • Female enforced monogamy: females attack the males o Burying beetle releases pheromone scent, but mate attacks to stop o Emerald coral goby: dominant female suppresses reproduction – accepts fate because will die if chased off o Razorbills: attack rivals with beak • Mate guarding: payoff for guarding is high, few other opportunities exist o Marie fish defend territories against each other o Guarding a mate of high quality – eg. Fecund female  Last male fertilizes most eggs , unguarded females remate  Females widely distributed hard to locate • Extra Pair copulation: socially monogamous might not be genetically monogamous – young sired may be raised by others Male monogamy in Mammals • Males may protect infanticidal male intruders which destroy infants o Offspring will also tend to travel with offspring if parents were bonded • Some examples of anti-infanticide hypothesis: some primates have a bigger female than male so males would not dominate her o Rather it is the ecological factors that tilt the cost benefit towards mate guarding which leads to monogamy • Monogamy in birds o Yellow eyed junco: male cares for the first brood while the female nd incubates a 2 clutch – parent help is good for survival o Starling: both parents incubating, eggs stay warmer, develop more rapid o Widowed snow buntings – produce 3 or fewer young, control = 4+ o Give male spotless starling more testosterone and less willing to feed, while blocking testosterone = more likely to feed • Birds sire all offspring of their monogamous mates o Loons and scrub jays are exceptional – engage in extra pair copulation  Females mate with other males other than social partner and use the sperm to fertilize some/all eggs  Males may be taking advantage of this to mate with more females • Polygynous males prevent primary mate from other males while inseminating other females - display ornaments  Monogamous males may just be strangled by their female who get a say in who mates with them • When male life expectancy is short – leave more offspring by other tactics • Most breeding females have several monogamous males, rather than one social partner and few extra pair mates • Galapogos hawk: monogamy to polyandry o Polyandry: scarcity of suitable territories – high male operational ratio  Favour males who can hold a breeding site – harem of males • Purple swamphen: males all have the same chance – equal opportunity • Some species, mates of females receive a clutch of eggs to share responsibility o Wattled jacana: fight for territories to accommodate multiple males  Monogamous male to polyandrous female is disadvantaged for male as he may be clutching other male offspring • Reck neck phalarope: care for own brood o Female produces 2 clutch and draw mate from a male who lost a first clutch – males are more likely to receive a familiar female to reduce egg fertilized elsewhere • Spotted sandpiper: female take the role in courtship o Secure males and gives him a clutch to rear and so on o 5 egg clutches cannot be incubated properly – 4 is optimal  so instead of more eggs, supply more clutches o forced into monogamous males by several factors  ratio biased towards male  nest in areas with mayfly hatches that are food for females/young  single parenting is as effective as double parent o First sperm may be stored for later use What do females gain from polyandry • Usually sufficient sperm, and output does not increase with more males • Can be costly – less parental care, STD, time/energy cost • Galapogos hawk: recruit multiple males to protect her terrirtory • Kentish plover: take advantage of male ratios • STD threat may suggest highly polyandrous species have stronger immune system o Nunn: study macaque and gibbon – higher wbc in female • Benefits to polyandrous female can be categorized as genetic (indirect) or material (direct) o Genetic example: reduce risk of infertile mate  Fertility insurance hypothesis o Coercive mating has no benefit (maladaptive) o Good genes, sexy sons, genetic compatibility – indirect benefits  Good genes hypothesis: lower quality partner will provide less benefit than an attractive  Genetic compatibility: increase genetic variety for good match o Resources, protection, infanticide reduction – direct benefits
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