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18. Paternal Care Parental Care • Includes all behavior directed towards offspring – Feeding – Protecting • Predators • Elements – Teaching 2 Parental care • Very costly behavior – Time – Energy – Vulnerable to predation emperor penguin red shouldered hawk earwig tarantula hawk 3 Evolution of parental care • Bigger gametes – Increase zygote size – Increased survival • More gametes – Increase potential number of offspring • Females initial investment more than males – (larger gamete size, internal development in some animals) 4 Parental Investment • Lots of zygotes – Little care provided • Clutch of Offspring – Some care provided – Greater (longer) parental investment 5 Parental Investment • The fewer the offspring the greater the postnatal care provided; per offspring 6 Parental Investment • The fewer the offspring the greater the postnatal care provided; per offspring 7 Parental Investment • However, the smaller the embryo the greater the number that can be produced. 8 Evolution of parental care • Females have a greater incentive to make sure their gametic investment is not wasted. • There females often provide the majority of parental care. 9 Evolution of parental care • Investment on current offspring • Increased investment = increased probability of young surviving – AND increased fitness for parents • Trade off between current and future reproduction – Time, energy, risks spent by parent on current offspring (parental investment) – influence possibility of having future offspring 10 Evolution of parental care Potential tradeoff: • More energy invested now, less energy available for future reproductive efforts. • Increased parental investment can affect survival of adults. – Potentially decreasing fitness Parental care investment is subject to selection. 11 Life History • Life history traits – characteristics of an individual that influence survival and reproduction Age at maturity House Mouse 2 months African elephant 11 - 20 years Atlantic Salmon 3-6 years 12 Life History • Life history traits – characteristics of an individual that influence survival and reproduction Number of offspring House Mouse African elephant Atlantic Salmon 5-8 young every month 1 calf every 3-8 years 1,500 to 8,000 eggs once 13 Life History • Life history traits – characteristics of an individual that influence survival and reproduction Number of reproductive events House Mouse ~6-12 African elephant Atlantic Salmon ~3-10 1 (semelparous = 1) (interoparous > 1) 14 Life History • Life history traits – characteristics of an individual that influence survival and reproduction Lifespan House Mouse 2 Years African elephant 60-70 Years Atlantic Salmon 3-6 Years 15 Remember EPCs… • Parental care should be proportional to probability offspring are yours. • Females can be quite confident of maternity – Males (when females mate multiply) are less confident of paternity. 16 Opportunity for Polygyny • Variance in reproductive success usually greater for males than females – For example in polygynous, lekking species • Times spent caring for offspring = less time getting more mates. 17 Opportunity for Polygyny • The potential reproductive rate is greater for males than females – Cost / benefit ratio for parenting different between sexes – Cost of parental care is greater for males. 18 Predicting Male care • In male bias systems care is more common – Females limited by number of eggs, gestation – so males increase success by providing care • Female bias more opportunities to reproduce – Males likelihood to desert increases 19 Bi-parental care • Bi-parental care is common (particularly in birds). • In many species, males provide more care than females. Australian mallee fowl Greater rhea Seahorses African cichlids 20 Male uniparental care • Females lay eggs, then provide no care • Males provide care Mouth Brooding Nest Guarding 21 Male uniparental care • A female (left) and male (right) Solenosteira macrospira . – The male's shell is covered with numerous egg cases • After mating, females deposit egg cases on their mate's shell – The males carry this burden (which can exceed 50% of the male's wet mass) until eggs hatch 22 Male uniparental care • Giant water bugs (Belostomatidae) • Large bugs, eggs also larger than typical aquatic insect. • Need to exchange gases (CO2 out, O2 in) – which is easier out of water. 23 Males carry eggs glued to back Males moisten eggs laid out of water No parental care Giant water bugs 24 Caring for the right offspring • Offspring recognition in colonial species – Discriminating parental care Mexican free tailed bat 25 Caring for the right offspring • Offspring recognition in colonial species • Cliff swallows can recognize own young, rough winged swallows cannot cliff swallows colonial barn swallows solitary 26 Caring for the right offspring • Offspring recognition in colonial species 27 Caring for the wrong offspring • It is not worth making a mistake and not caring for your own offspring! – recognition systems are not perfect • Communal care of offspring common in some species that live in groups. Dwarf mongoose 28 Optimal Threshold Model signals you want to accept signals you want to reject acceptance errors rejection errors adapted from Reeve 1989, Starks 2003 29 Adoption • Intra- and Interspecific • Parents will often care for offspring that are not their own • Not resource limited • Decrease risk to own offspring 30 Adoption • Adoption increases survival – If the abandoned offspring can find a foster parent 31 Caring for the wrong offspring • Brood parasites - cowbirds, cuckoos 32 Caring for the wrong offspring • Brood parasites - cowbirds, cuckoos 33 shiny cowbird bronzed cowbird screaming cowbird brownheaded cowbird 34 3 species of cowbirds in northern Argentina bay-winged cowbird screaming cowbird colonial, builds own lays eggs in nests of nests. Egg 1 species - the bay dumping? winged cowbird shiny cowbird lays eggs in nests of 176 different species 35 Brood parasitism • Parasitism success dependent on being able to convince host eggs are their own 36 Brood parasitism • Parasites can also remove hosts eggs to increase care given to their own – And ultimately survival/success. 37 Brood parasitism • Parasite can also remove competition 38 Key to brood parasite success • Size disparity important in success of brood parasites – Since parasite parents do not always know when hosts eggs were laid – Parasite young have to be larger at hatching, and grow faster 39 Nest/Den Construction • Habitat Choice – Territorial – Safety • Dens (or roosts) consist of preexisting structures – Not labor intensive • Nests are constructed – Energetic and time costs – Burrows & Mounds 40 Sibling Conflict • Sibling aggression and siblicide • Occurs when resources are variable or in short supply? • Offspring compete for resources (they only share 50% of genes) 41 Sibling Conflict • Scramble Competition – Every mouth for themselves • Preferential feeding – Largest/Healthiest eat first (Competition) – Hungriest eat first 42 43 Adaptive parental strategies masked booby blue-footed booby have two eggs, first hatched chick always kills second chick have two eggs, often raise two young 44 Parent-offspring conflict • Selection may act on parents and offspring differently. • Some actions that increase fitness of offspring may reduce fitness of parents. 45 Begging • From offspring perspective: – Way of attracting food – Reflect actual needs of the young (Honest) – Greed (dishonest) • From parent perspective: – Way of identifying hungry offspring – Ensure offspring are being fed enough 46 Asynchronous Hatching • Birth order can promote or reduce sibling conflict and parental favoritism – Synchronous hatching, all offspring born at same time – Greater food demand – Can reduce parental efficiency/success 47 Offspring size disparity • Typically first young will be largest and most likely to succeed – Fledge • Females can adjust by increasing investment (larger eggs) for later eggs produced – Enough so that later hatchinglings are born larger, and are able to compete for food 48 Parental favoritism • Likely occurs when resources are variable and adults have more young than they can raise (bet hedging) • Females can invest in eggs differently (even choose sex in some species). • Young can be fed preferentially. Seychelles warbler 49 Can parents control sex of offspring? Seychelles Warbler 50 Control of offspring sex • Haplo/diploid organisms (like ants, bees and wasps) – Fertilized egg = female ; un-fertilized egg = male • Temperature Dependent Sex Determination (TSD) – many reptiles 51 Nest Help • In some animals, juveniles stay to help second nesting effort. – More often female juveniles. • Both direct and indirect benefits. • Direct (learning about maternal care) • Indirect (inclusive fitness by helping rear related offspring voles magpie jays 52 Nest Help • Leads to overlapping generations • Key step in the evolution of sociality? 53 Genetics basis for mating systems / parental care. prairie voles Monogamous male parental care meadow voles polygymous no male parental care 54 Genetics basis for mating systems / parental care. • In male prairie voles, vasopressin and dopamine in the forebrain regulate affiliation between mates (bond formation). • Vasopressin receptor is expressed at higher levels in monogamous species than polygynous species. • Lim and colleagues, used a viral vector to transfer the vasopressin receptor gene from the monogamous species into the polygynous species. • With this change in a single gene, the polygynous species essentially becoming monogamous. 55