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13.1Parental care varies among species and reflects life history trade-offs • Parental care – Activities of an adult that enhance the survivorship of offspring • Life history traits – Traits involved with growth, reproduction, and survivorship that are the result of natural selection From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Life history trade-offs • Natural selection will favor the evolution of behaviors that maximize an individual’s lifetime reproductive success • Energy (effort) is limited: effort allocated to reproduction reduces effort that can be allocated to an individual’s growth and survivorship From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Life history trade-offs • Across species, we often see the evolution of life history traits From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Life history variation in fish • Research question: How do life history traits vary among fish? (Vila-Gispert, MorenoAmich, & García-Berthou 2002) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Life history variation in fish • Methods: – Obtained life history data for 300 species, including age at maturity, maximum body size, length of breeding season, number of reproductive events per year, average egg size, fecundity, and level of parental care From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Life history variation in fish • Results: – Species with larger body size tended to have later maturation, larger eggs, fewer reproductive events per year, and higher levels of parental care – Small species showed the opposite trends • Conclusion: – These patterns reflect basic life history trade-offs From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Variation in parental care • Species vary in parental care provided • In some species: – Only females provide care (maternal care) – Only males provide care (paternal care) – Both species provide care (biparental care) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 13.2 Sexual conflict is the basis for sexbiased parental care • In many species, females provide more parental care than males. Why? • Sexual conflict: each sex has different benefits and costs of providing care • Males tend to be less certain of offspring paternity so they have a higher cost of providing care (care for unrelated individuals) – This favors the evolution of reduced care by males From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity uncertainty and parental care in boobies • Research question: Do males vary the level of care within a clutch of offspring? (OsorioBeristain & Drummond 2001) • Hypothesis: Certainty of paternity affects a male’s level of care • Prediction: Males will provide low care when certainty of paternity is low From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity uncertainty and parental care in boobies • Methods: – Blue-footed booby (Sula nebouxii) – Manipulated certainty of paternity by removing pair-bonded males for 11 hours when their mate was fertile – Control males were removed for 11 hours when their mate was not fertile – Observed behavior of males when they returned to their mate From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity uncertainty and parental care in boobies • Results: – 7 of 16 experimental males removed the first egg laid by their mate from the nest – No control males removed eggs from the nest • Conclusion: – Certainty of paternity affects level of paternal care From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press The evolution of male-only care • Birds and mammals have internal fertilization and determinate growth, while many fishes have external fertilization and indeterminate growth • Larger females can produce more eggs, so parental care is now more costly to females; providing care limits growth and future fecundity • External fertilization increases certainty of paternity for males: this lowers the cost of care • For fishes, the higher costs of care for females and lower costs of care for males can favor the evolution of male-only care From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity assurance and male care in water bugs • Research question: Why do water bugs have maleonly care despite having internal fertilization and sperm storage by females? (Smith 1979) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity assurance and male care in water bugs • Methods: – Giant water bug (Abedus herberti) – Observed mating behavior – Experiment 1: Female mated with one male but was not allowed to oviposit. After several weeks she mated with the second male and oviposited eggs on his back – Experiment 2: On day 1, the female mated with one male and oviposited eggs on his back; on day 2, she mated with the second male and oviposited on his back. This was repeated for several days – Recorded the paternity of the offspring on the second male’s back From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Paternity assurance and male care in water bugs • Results: – Experiment 1: For 20 of 25 males, the second male fertilized 100% of the eggs on his back – Experiment 2: 245 of 250 offspring were sired by the male who carried the eggs • Conclusion: – Male water bugs have a high degree of certainty of parentage despite having internal fertilization From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 13.3 Hormones regulate parental care • Many animals undergo a radical change in behavior during the breeding season • Early on, they concentrate on finding and attracting mates • Later, they concentrate on providing care to offspring • Prolactin levels in vertebrates vary over the reproductive season From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and maternal care in rats • Research question: Does prolactin affect parental care? (Bridges et al. 1990) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and maternal care in rats • Methods: – Manipulated prolactin levels in female rats – All females were “primed” with progesterone and estradiol to mimic changes in these steroid hormones during pregnancy – Compared behavior of females treated with either prolactin or control (sodium chloride–sodium bicarbonate) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and maternal care in rats • Results: – Females injected with prolactin exhibited higher levels of care than controls – Females not primed with steroid hormones exhibited little care • Conclusion: – Prolactin strongly affects parental care behavior From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and incubation in penguins • Research question: In birds, what causes prolactin levels to increase during egg laying? (Massaro, Setiawan, & Davis 2007) • Hypothesis 1: The sight of eggs stimulates prolactin production • Hypothesis 2: Tactile stimulation (brood patch contact with eggs) stimulates prolactin production From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and incubation in penguins • Methods: – Yellow-eyed penguins (Megadyptes antipodes) – Sampled prolactin levels – Group 1: Sampled before an artificial egg was added to the nest – Group 2: Sampled three to four days after artificial egg added to their nest (visual and tactile cues) or next to the nest (visual cues only) – Group 3: Sampled at the same time as Group 2, but no egg was added to their nest (control) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Prolactin and incubation in penguins • Results: – Birds that could only see eggs did not have elevated prolactin levels – Birds that had eggs added to the nest had higher prolactin levels than controls • Conclusion: – Visual cues and tactile stimulation result in increased prolactin production in these birds From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Juvenile hormones and parental care in earwigs • In insects, juvenile hormone (JH) affects development and molting and also varies over the reproductive cycle and with levels of parental care • Research question: Does JH affect parental care? (Rankin, Fox, & Stotsky 1995) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Juvenile hormones and parental care in earwigs • Methods: – Ring-legged earwigs (Euborellia annulipes) – Topically added JH in acetone to female – Controls were either untreated or treated only with acetone – Measured duration of egg care From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Juvenile hormones and parental care in earwigs • Results: – Females with JH added showed the least amount of egg care • Conclusion: – JH affects parental care: high levels of JH result in low care and vice versa From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press 13.4 Parental care involves fitness tradeoffs between current and future reproduction • The benefit of parental care is enhanced survivorship of young • The costs of providing parental care involve reductions in both current and future reproduction From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Research question: How does parental care affect an adult’s predation risk? (Reguera & Gomendio 1999) • Hypothesis: Providing care for eggs can increase predation risk • Prediction: Males caring for eggs will experience higher mortality from predators than males not caring for eggs From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Methods: – Golden egg bugs (Phyllomorpha laciniata) – Placed four adult males in an aviary with two bird predators – Two males carried eggs on their backs (parental care); two males did not carry eggs – Recorded the last bug alive in the aviary From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Results: – In 10 of 11 trials, the last bug alive was one that did not carry eggs • Conclusion: – Providing care for eggs by carrying them enhances the risk of predation for an adult From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Research question: Given the cost, why do golden egg bug males carry eggs? (Reguera & Gomendio 2002) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Methods: – Characterized survivorship of eggs laid on plants and eggs carried by adults – Examined variation in egg carrying across populations From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Predation risk and parental care in golden egg bugs • Results: – Eggs laid on plants had a 3% survival rate (high predation on eggs via egg parasitism) – Eggs carried by adults (mostly males) had 25% survival rate – Egg carrying was most common in populations with high rates of egg parasitism • Conclusion: – Providing care for eggs by carrying them enhances offspring survivorship From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Egg guarding and opportunity costs of parental care in frogs • Research question: If egg-guarding parental care increases offspring success, why don’t all males attend eggs at a high level? (Cheng & Kam 2010) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Egg guarding and opportunity costs of parental care in frogs • Methods: – Big-thumbed frogs (Kurixalus eiffingeri) – Uniquely marked males as they tended eggs – Egg masses were quantified and egg mortality noted – Male attendance was recorded each night over six days From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Egg guarding and opportunity costs of parental care in frogs • Results: – Egg mortality was negatively correlated with male attendance – Male attendance was positively correlated with egg mass clutch size • Conclusion: – Males with small clutches may be searching for additional mating opportunities From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Parent-offspring conflict theory • Parent-offspring conflict theory – parents and their dependent offspring are under different selection pressures: – Parents should maximize their lifetime reproductive success – Offspring should maximize the energy and protection they receive from parents to survive to reproductive age • Parental investment – Any investment by parents in an offspring that increases offspring survival at the cost of the parent’s ability to invest in other offspring From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Parent-offspring conflict theory • The optimal level of parental investment is always higher for offspring than for a parent From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Parental care trade-off in treehoppers • Research question: Within a species, why is there much variation in parental care such as egg guarding? (Zink 2003) • Hypothesis: There is a trade-off between current and future reproduction • Prediction 1: Egg guarding will increase egg survival (current reproduction) • Prediction 2: Increased egg guarding will decrease future reproduction From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Parental care trade-off in treehoppers • Methods: – Tree hoppers (Publilia concava) – Marked individual females that had deposited an egg mass – Noted number of days they guarded the eggs From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Parental care trade-off in treehoppers • Results: – Egg hatching success was positively correlated with female egg-guarding duration From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Parental care trade-off in treehoppers • Results: – Females that guarded a clutch for more than ten days had fewer and smaller future broods than females that spent less time egg guarding • Conclusion: – Parental care (egg guarding) enhances current reproductive success but at a cost of future reproduction From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Applying the Concepts Applying the Concepts 13.1 Smallmouth bass defend their nest from exotic predators • Exotic predators can reduce population size of native species • Exotic egg predators in Lake Erie increase the cost of parental care (egg guarding) for smallmouth bass (Micropterus dolomieu) • This increased energy demand of care will likely reduce the lifetime fitness of bass and could lead to population decline From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Brood reduction and parent-offspring conflict • Brood reduction – Differential offspring mortality, often within a single clutch • Theory predicts that brood reduction can be adaptive for a parent by reducing its cost of current reproduction and so enhancing survivorship and future reproduction From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Brood reduction in fur seals • Research question: Why do females give birth in consecutive years? (Trillmich & Wolf 2008) – Some marine mammals give birth in consecutive years, but pups are not weaned for two years. Lactation costs are high for a female with two pups, and the younger pup rarely survives (brood reduction occurs) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Brood reduction in fur seals • Hypothesis: The survivorship of young with an older sibling is related to resource availability • Prediction: The second offspring will suffer high mortality in years of scarce resources and have high survivorship in years of abundant resources From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Brood reduction in fur seals • Methods: – Galápagos fur seals (Arctocephalus galapagoensis) – Marked both unweaned older pups and their younger siblings – Recorded the survivorship of younger siblings – Estimated food availability using sea surface temperature (cold-water years have high food abundance while warm-water years have low food abundance) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Brood reduction in fur seals • Results: – Survival of younger pups was related to water temperature (food availability) • Conclusion: – Brood reduction (pup death) is a function of food availability. Parents can raise pups in consecutive years when food availability is high, but this cannot be predicted in advance From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Applying the Concepts Applying the Concepts 13.2 Food supplementation reduces food reduction in endangered eagles • Brood reduction is common in birds of prey • Conservation biologists are trying to increase the population of the endangered Spanish imperial eagle (Aquila adalberti) • Food supplementation has increased survivorship of second offspring (reduced brood reduction) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Brood parasitism • Brood parasitism – Female lays an egg in the nest of another female • Reduces the cost of parental care (another female raises the young) • Brood parasites can lay all (pure parasite) or some eggs (nesting parasites) in the nest of another female From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Conspecific brood parasitism in ducks • Research question: What reproductive strategy leads to the highest fitness (pure parasite, nesting parasite [mixed strategy], or nonparasites)? (Åhlund & Andersson 2001) From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Conspecific brood parasitism in ducks • Methods: – Goldeneye ducks (Bucephala clangula) – Identified eggs in nests to a specific female in the population using egg protein polymorphisms – Monitored nests to determine egg laying – Quantified the number of eggs or young produced by each female and her reproductive strategy From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press Featured Research Conspecific brood parasitism in ducks • Results: – Nesting parasites (who laid eggs in their own and another female’s nest) had the highest reproductive success • Conclusion: – Brood parasitism can enhance fitness in part by reducing the cost of parental care From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press