Transcript Slide 1
Mating Systems and Parental Care Comparative Approach Cost-benefit Approach Mechanism Approach Monogamy – one male and one female Polygyny – one male, multiple females Polyandry – multiple males, one female Promiscuity – multiple, multiple } Polygamy Mating Systems and Parental Care Birds Mammals Fish both male and female female only male only Monogamous Polygynous Polygamy/promiscuity In birds, polygyny often occurs in fruit and seed eaters because these foods can become so abundant that one parent can often care for the young alone... and it is the male who deserts first...why? -- With internal fertilization, the male often has the first opportunity -- With internal fertilization, certainty of paternity is never guaranteed -- The male has more reproductive success to gain – greater selection pressure Families of Teleost fishes Par. care internal external Male Female Neither 2 14 5 61 24 100 Male parental care is commonest with external fertilization, Female parental care with internal fertilization (1) Paternity certainty – still uncertain (2) Order of gamete release – N/A (3) Association – internal fertilization leads to greater female association whereas in fishes, eggs are laid in male’s territory and he is most closely associated with the embryos – territoriality to attract females becomes coupled with nest and offspring defense Cost/benefit approach FEMALE Care Desert Care F: wP2 M: wP2 WP1 WP1 Desert F: wP1 M: wP1 (1+p) WP0 WP0 (1+p) MALE P0,1,2 = probability eggs survive given 0, 1, or 2 parents W, w = eggs laid by deserting or caring female, respectively p = probability deserting male mates again If female cares then male should desert if: wP2 < wP1(1+p) FEMALE Birds Care Desert Care F: wP2 M: wP2 WP1 WP1 Desert F: wP1 M: wP1 (1+p) WP0 WP0 (1+p) MALE - caring/deserting 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/deserting in 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 Social Monogamy - 90% of all birds Factors that promote monogamy and biparental cases are oviparity and endothermy b/c 2 parents often required for successful reproduction 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 What do males do? Are males necessary? (1) Shared incubation 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) (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 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. offspring fathered by extra-pair matings Black Vulture Common Loon Ea. Screech Owl 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 0 0 0 0 0 0 1 2 4 18 18 28 35 35 76 EPCs in the Red-winged blackbird Benefits to EPCs Males – sire more offspring so long as the xtra effort does not compromise parental effort with its social mate in value of paternal care # opportunities (density of females) in the ability to guard mate } 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…. (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 0 +2 +4 +6 Improvement Difference in rank between social mate and EPC-mate 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 from EPCs to polygyny Social/genetic monogamy Male parental care is not essential Females may seek EPC Male response: Increased mating effort Decreased parental care = Polygyny (1) 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 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 10-15% of males are successful at having 2 mates separated by 0.2 – 3.5 km apart thereby concealing the 2 relationships from each other Deception model male conceals its bigamous relationship from the females Male Female #1 Some distance away Female #2 No male assistance Polygyny threshold model posits that there is an uneven distribution of important resources that males control access to through territoriality Females must decide whether to (i) mate with an already mated male on a high quality territory or (ii) an unmated male on a poor territory. The threshold is the point at which a female will do as good or better with option i #1 Female Reproductive success 1 ♀ 2 e ♀ d c Territory Quality b a #2 #3 e d c b a e c d b a #6 #5 e d c b a e d c b #4 a 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) Males control access to resources, but also Females may actively assess the consequences of their decisions and make an adaptive choice ....let’s examine this relationship between resources and females more closely in mammals....