Chapter 11
Chapter 11 • • • • • • • • •
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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
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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 incubates a 2nd 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 • • • • • •
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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 More resources, caregivers, protectors, and confusion amongst more offspring and multiple mates Longer the mate is away, more likely to wander Lower social mate attractiveness, more visits to neighbour o Good looking mate, females less likely to cheat Blue tit: females are polyandrous o Nests contain extra-pair young – unrelated to father o Good gene hypothesis: attractive males should have less Few EPY = high survivorship of male (attractive) Several partners increase odds of receiving sperm of exceptional quality o Offspring more fertile and survival Seek male of high quality that could meet demands o Extra pair copulation enable female to acquire good genes o Older males in song birds have demonstrated an ability to stay alive By inheriting traits that made their father sexually appealing, sexy sons increase the odds their mother will have many grand offspring Genetic compatibility – heterozygous enjoy advantages o Prefer dissimilar heterozygous mates - certain combinations result in death Oldryoyd/Fewel: honey bee queen stacking sperm from multiple males o Antidisease: parasite resistence o Variable workers = strong workforce
Polyandry and material benefits • • • •
Material benefits in form of food or nutritious spermatorphores – bribe females to mate with them o Hypothesis: more polyandrous a female, greater reproductive output Multiple mates – more help in raising the young Mating with several males may cause partners to leave infants alone Convenience polyandry: females do not benefit from mating with several males, except that it cost them less to mate with unwanted than fight them
Mating system evolution • • •
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Differential parental investment: role of polygamy increases reproductive success Amount of Care: required for the raising of surviving offspring Ecological factors and reproductive biology: mate cost/benefit o Ecological factors: environmental potential for polygamy o Biology: ability to capitalize on environment Together: ability to monopolize on mates • Promiscuious/one mate/monopolize multiple mates o Mating system Environmental potential for polygamy o Defensible territory size + resources Mates tend to clump – high EPP, widely distributed – low EPP o Group living – clump is high EPP, distributed is low Reproductive Biology o Period of receptivity – synchronous (brief), asynchronous (prolonged) Synchronous – low EPP, insufficient time Asynchronous – ample time, high EPP o Humans: higher pheromone exposure = more ovulatory pheromone, low = more follicular pheromone v control Males are more likely to be emancipated from parental care - capitalize on EPP
Diversity of the Polygynous Mating system • • • •
Polygyny – high EPP, low benefit of male parental care Female defense polygyny: males fight with others to monopolize females o Advantages of group living (protection) and males get controlled access Resource defense polygyny: defend territory that is good for egg laying o Access females indirectly by controlling critical resources Lek polygyny: defend bowers to attract females not resources o Leads to skewed mating systems – 1 male may claim most o Lekking evolves when other tactics do not pay off Do not live in permanent groups – travel great distances – food is random – staying at one tree might be bad
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o Hotspot hypothesis: routes frequently traveled by females o Hotshot hypothesis: subordinate male cluster around attractive mates to get a chance at females o Female preference hypothesis: males cluster because female prefer large group of males – quick safe and quality comparison Hotshot hypothesis seems likely in some cases Hotspot hypothesis cannot apply to females who forage to compare male – density is not correlated with lek • No one hypothesis holds true – general idea is to enable individual to demonstrate superior condition Scramble competition polygyny: outrace rivals to receptive females o Search for females without contest o Mate with as many female as possible – best strategy o Spatial memory development can help relocate potential mates o Explosive breeding assemblage: formation of large groups of maters Larger home range = polygyny, small home range = monogamy o As a home range is contracted, a male can monitor closer In mammals, polygyny most common where females are in groups, rare otherwise o Regardless of parental care Polygny Threshold Model: more advantageous to mate with a polygynist on a good territory than monogamy in a resource poor area o Polygyny: join an already mated with good territory o Monogamy: unmated with poor territory o Females prefer monogamy if territory is equal o Choose polygyny when polygyny territory is high quality o Mate choice by territory o Polygyny more common in patchy variable environments Anolis lizard: fertilize as many eggs as possible o High density = high EPP (high females) – fitness good for defense Select for male body size to win territory and females o Low density = fewer females, low EPP – fitness for scramble No selection in size Meadow vs. Pine vole o Promiscuous vs. socially monogamous o Home range size male > female vs. male and female same Spatial learning ability meadow >vole, hippocampus bigger Polyandry – 1 female, many male o Female reproductive limited Frequent clutch failure, variable food sources, success decreases with eggs per clutch Produce more clutches but can’t care for all by herself Abandon broods, male cares (emancipation) - Capitalizing on EPP o Male defense (sandpipers, phalarope)
Unpredictable egg mortality due to starving Female fight for males – male care of eggs o Resource defense (jacana) High predation on eggs, flooding of nests • Parental care can’t do much, energy for eggs • Defense of eggs by multiple males – male care
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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
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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 incubates a 2nd 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 • • • • • •
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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 More resources, caregivers, protectors, and confusion amongst more offspring and multiple mates Longer the mate is away, more likely to wander Lower social mate attractiveness, more visits to neighbour o Good looking mate, females less likely to cheat Blue tit: females are polyandrous o Nests contain extra-pair young – unrelated to father o Good gene hypothesis: attractive males should have less Few EPY = high survivorship of male (attractive) Several partners increase odds of receiving sperm of exceptional quality o Offspring more fertile and survival Seek male of high quality that could meet demands o Extra pair copulation enable female to acquire good genes o Older males in song birds have demonstrated an ability to stay alive By inheriting traits that made their father sexually appealing, sexy sons increase the odds their mother will have many grand offspring Genetic compatibility – heterozygous enjoy advantages o Prefer dissimilar heterozygous mates - certain combinations result in death Oldryoyd/Fewel: honey bee queen stacking sperm from multiple males o Antidisease: parasite resistence o Variable workers = strong workforce
Polyandry and material benefits • • • •
Material benefits in form of food or nutritious spermatorphores – bribe females to mate with them o Hypothesis: more polyandrous a female, greater reproductive output Multiple mates – more help in raising the young Mating with several males may cause partners to leave infants alone Convenience polyandry: females do not benefit from mating with several males, except that it cost them less to mate with unwanted than fight them
Mating system evolution • • •
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•
•
Differential parental investment: role of polygamy increases reproductive success Amount of Care: required for the raising of surviving offspring Ecological factors and reproductive biology: mate cost/benefit o Ecological factors: environmental potential for polygamy o Biology: ability to capitalize on environment Together: ability to monopolize on mates • Promiscuious/one mate/monopolize multiple mates o Mating system Environmental potential for polygamy o Defensible territory size + resources Mates tend to clump – high EPP, widely distributed – low EPP o Group living – clump is high EPP, distributed is low Reproductive Biology o Period of receptivity – synchronous (brief), asynchronous (prolonged) Synchronous – low EPP, insufficient time Asynchronous – ample time, high EPP o Humans: higher pheromone exposure = more ovulatory pheromone, low = more follicular pheromone v control Males are more likely to be emancipated from parental care - capitalize on EPP
Diversity of the Polygynous Mating system • • • •
Polygyny – high EPP, low benefit of male parental care Female defense polygyny: males fight with others to monopolize females o Advantages of group living (protection) and males get controlled access Resource defense polygyny: defend territory that is good for egg laying o Access females indirectly by controlling critical resources Lek polygyny: defend bowers to attract females not resources o Leads to skewed mating systems – 1 male may claim most o Lekking evolves when other tactics do not pay off Do not live in permanent groups – travel great distances – food is random – staying at one tree might be bad
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o Hotspot hypothesis: routes frequently traveled by females o Hotshot hypothesis: subordinate male cluster around attractive mates to get a chance at females o Female preference hypothesis: males cluster because female prefer large group of males – quick safe and quality comparison Hotshot hypothesis seems likely in some cases Hotspot hypothesis cannot apply to females who forage to compare male – density is not correlated with lek • No one hypothesis holds true – general idea is to enable individual to demonstrate superior condition Scramble competition polygyny: outrace rivals to receptive females o Search for females without contest o Mate with as many female as possible – best strategy o Spatial memory development can help relocate potential mates o Explosive breeding assemblage: formation of large groups of maters Larger home range = polygyny, small home range = monogamy o As a home range is contracted, a male can monitor closer In mammals, polygyny most common where females are in groups, rare otherwise o Regardless of parental care Polygny Threshold Model: more advantageous to mate with a polygynist on a good territory than monogamy in a resource poor area o Polygyny: join an already mated with good territory o Monogamy: unmated with poor territory o Females prefer monogamy if territory is equal o Choose polygyny when polygyny territory is high quality o Mate choice by territory o Polygyny more common in patchy variable environments Anolis lizard: fertilize as many eggs as possible o High density = high EPP (high females) – fitness good for defense Select for male body size to win territory and females o Low density = fewer females, low EPP – fitness for scramble No selection in size Meadow vs. Pine vole o Promiscuous vs. socially monogamous o Home range size male > female vs. male and female same Spatial learning ability meadow >vole, hippocampus bigger Polyandry – 1 female, many male o Female reproductive limited Frequent clutch failure, variable food sources, success decreases with eggs per clutch Produce more clutches but can’t care for all by herself Abandon broods, male cares (emancipation) - Capitalizing on EPP o Male defense (sandpipers, phalarope)
Unpredictable egg mortality due to starving Female fight for males – male care of eggs o Resource defense (jacana) High predation on eggs, flooding of nests • Parental care can’t do much, energy for eggs • Defense of eggs by multiple males – male care
