Cost/benefit approach

Transcription

1 Cost/benefit approach Care FEMALE Abandon MALE Care F: wp 2 WP 1 M: wp 2 WP 1 Abandon F: wp 1 WP 0 M: wp 1 (1+p M ) WP 0 (1+p M ) P 0,1,2 = probability eggs survive given 0, 1, or 2 parents W, w = eggs laid by deserting or caring female, respectively P M = probability deserting male mates again If female cares then male should abandon if: wp 2 < wp 1 (1+pm)

2 Birds Care FEMALE Abandon MALE Care F: wp 2 WP 1 M: wp 2 WP 1 Abandon F: wp 1 WP 0 M: wp 1 (1+p M ) WP 0 (1+p M ) - caring/abandonment by parents is a game between 2 players: M & F - the best decision by one player depends on the decision of the other. - we can understand caring/abandonmentin terms of the probability of remating (M), eggs laid (F) or loss of offspring when raised by a single parent (M and F) - Environmental conditions that abruptly alter these costs and benefits may also abruptly alter parental care and mating strategy e.g., facultative polygamy

3 Social Monogamy - 90% of all birds - primitive/original mating system - monogamy and biparental care go hand-in-hand (not w/o exceptions) Why? What factors that promote monogamy and biparental care in birds? Facultative Monogamy: individuals fail to acquire additional mates b/c of shortage of members of the opposite sex (e.g., synchronous breeding and unbalanced sex ratio) Obligate Monogamy: Selection for monogamy per se both sexes gain e.g., males are less successful with 2 mates than 1 e.g., in females, pairing with an unmated male better than with a mated male

4 Pair bonds may last for life (e.g., parrots, albatrosses, eagles, geese, pigeons), but separation is quite common, and usually after failed breeding attempts. Mute Swans: 5% of breeding pairs and 10% of non-breeding pairs separate each year In Adelie Penguins: 16% of old pairs and 44% of young pairs stay together more than 1 breeding season. Lastly, if one considers passerines have 60-70% survivorship rates, there is a only a 36-49% chance both members survive til the next year so why delay breeding waiting for a mate to show up or not.

5 What do males do? Nest construction by males is the prevailing mode among non-passerines E.g., Male Hairy Woodpeckers conduct 95% cavity construction (Lawrence 1967) Courtship feeding Rifleman First and 2nd clutches of are 84% and 72%, respectively, of the females body mass. Males contributes 42% of the food they gather to females before first clutch and care entirely for the young as 2nd is laid

6 Are males necessary? (1) Shared incubation - 67% of Families of Neognathous birds Western sandpipers removal of either parent led to 100% failure (2) Female provisioning common in raptors, hornbills, and other groups 7 of 8 male kestrel removals resulted in nest abandonment (the exception was a female who lost her mate on day 24 of a 27 day incubation period)

7 Are males necessary? (3) Post-hatching care - Effects of male-removal on nesting productivity Song sparrows decrease by 51% Seaside sparrows decrease by 66% Dark-eyed juncos decrease by 38% Also in kestrels, rock doves, tree swallows and other passerines. (4) Post-fledging care 3 passerine studies show loss of male leads to 37-66% reduction of young to independence # Nests...conclude that in monogamy, both mates are necessary for raising young, and/or it is the strategy that yields the greatest # offspring for both male and females # chicks fledged

8 Avian Reproduction Finding/attracting Mates Nest construction Egg laying incubation (1) Shared incubation (2) Female provisioning Caring for young Precocial young leave the nest after hatching Altricial young Nestlings Fledglings (2) Female provisioning (3) Post-hatching care (4) Post-fledging care

9 EPCs Extra-pair copulations copulations outside the pair-bond - Once thought to be very rare until DNA-fingerprinting become common, now it appears everyone is doing it. EPCs broods with extra- offspring fathered observed pair paternity by extra-pair matings Black Vulture 0 Common Loon 0 Ea. Screech Owl 0 Willow Warbler Fulmar Wood Warbler Eu. Bee-eater Zebra Finch Pied Flycatcher Blue Tit Shag Red-winged Blackbird Purple Martin Indigo Bunting Superb fairy-wren 76

10 EPCs in the Red-winged blackbird

11 Benefits to EPCs Males sire more offspring so long as it doesn t comprise the benefit from its social mate in value of paternal care # opportunities (density of females) in the ability to guard mate (from the female s perspective of soliciting EPCs)

12 Benefits to EPCs Males sire more offspring so long as it doesn t comprise the benefit from its social mate in value of paternal care # opportunities (density of females) in the ability to guard mate (from the female s perspective of soliciting EPCs) } Will the prevalence of EPCs Females No gain in the # offspring, so why engage in EPCs? (1) It is forced Mallards (2) Insurance against infertile males (3) Sperm competition may the best sperm win or.

13 (4) Good Genes Most females cannot mate with the best male (constraint) so they seek out EPCs to increase their overall fitness Predicts: Females will seek EPCs with better males: Test: Zebra finch (Houtman 1992) Zebra finch # males = EPCs -4-2 Down-grading Improvement Difference in rank between social mate and EPC-mate

14 This begs the question of why not have more EPCs with the best/better males? Probably risk of mate-abandonment if confidence of paternity is compromise

15 This begs the question of why not have more EPCs with the best/better males? Probably risk of mate-abandonment if confidence of paternity is compromise

16 FEMALE Care Desert MALE Care Desert F: wp 2 WP 1 (1+p F ) M: wp 2 WP 1 F: wp 1 WP 0 (1+p F ) M: wp 1 (1+p M ) WP 0 (1+p M ) P 0,1,2 = probability eggs survive given 0, 1, or 2 parents W, w = eggs laid by deserting or caring female, respectively P M, p F = probability deserting mal/female mates again If female cares then male should desert if: wp 2 < wp 1 (1+p M )

17 Polygyny polygymous mating system in which males have multiple mates - 2% of all birds Paleognathous spp multiple females lay in the male s nest who then gives almost exclusive paternal care Neognathous spp New world wrens and blackbirds (marsh-nesters) Old world Cavity nesters, e.g., some owls, pied flycatcher

18 Two models (1) Polygyny threshold model (Orians 1969) (2) Deception model (von Haartman 1969) (3) no other choice best of a bad situation In Picman s (1987) study of the marsh wren females settle with mated males only after all bachelor males had paired

19 Polygyny threshold model posits that there is an uneven distribution of important resources that males control access to through territoriality

20 Thus, females must decide whether to (i) mate with an already mated male on a high quality territory or (ii) an unmated males on a poor territory. The threshold is the point at which a female will do as good or better with option i Female Reproductive success 1 2 #1 e d c b a Territory Quality

21 #2 e d c b a

22 #2? #3 e d c b a e d c b a

23 #2 #3 e d c b a e d c b a #6 #5 #4 e d c b a

24 Deception model posits that the female pays a cost of polygyny b/c the male conceals its bigamous relationship from the females Male and female Pied Flycatchers Once males attract one female they fly off to another nest site some distance away (200m, on average, but up to 3.5 km) to attract a second female. B/c of the distance, secondary females cannot assess whether they male as another mate 10-15% of males are successful at having 2 mates

25 Male Female #1 Female #2 Some distance away No male assistance

26 In conclusion, there are 3 scenarios that may lead to Polygyny: (1) Females have no other choice but to mate with a mated male (2) Females may be deceived (3) Females may actively assess the consequences of their decision and make an adaptive choice

27 FEMALE Care Desert MALE Care Desert F: wp 2 WP 1 (1+p F ) M: wp 2 WP 1 F: wp 1 WP 0 (1+p F ) M: wp 1 (1+p M ) WP 0 (1+p M ) What if p F >> p M?

28 Polyandry polygynous mating system in which females have multiple mates - 1% of all birds - involves sex role-reversal, such that females defend territories, compete for mates, take the lead in courtship Occurs largely in shorebirds: - Painted snipes - Jacanas - Phalaropes - Plains wanderers These birds often have abundant resources, require only a single parent to care for their precocial young, thus enabling the female to desert after laying eggs to find another mate.

29 = 5.0 = 5.0 = 6.7 = 3.7 β = 3.0 = 3.8 β = 3.8 = 7.6 Dunnock Prunella modularis

30 Leks Promiscuous mating system - 1% of birds - males provide no parental care - males congregate at sites not used for other purposes - no resources (territory) are on display for females - females chose among males a selected sperm donor Manakins: Exploded Leks - solitary individuals that may interact vocally Cock-of-the-Rock: Classical Leks conspicuously clumped communal mating/display grounds often with extreme fidelity from year to year hummingbirds, scolopacids, birds-of-paradise, grouse, and a parrot