Course Outline. Parental care and sexual conflict. Papers for 22 October. What is sexual conflict? 10/19/2009

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1 Parental and sexual conflict Course Outline 1. Sexual selection * 2. Parent offspring conflict * 3. Sexual conflict over parental René van Dijk R.E.van.Dijk@bath.ac.uk 19 October Genomic conflict 5. Mating systems (2) 6. Sex allocation (2) 7. Sexual size dimorphism (2) 8. Mini-test Paper 1 Papers for 22 October Griggioand Pilastro2007. Sexual conflict over parental in a species with female and male brood desertion. Anim. Behav. 74: Paper 2 Smisethet al Interaction between parental and sibling competition: parents enhance offspring growth and exacerbate sibling competition. Evolution 61: Lecture 3 Sexual conflict over parental Why is there a conflict? Sexual conflict over parental Theories of parental Desertion games Parental effort games Tests of models Summary What is sexual conflict? Sexual conflict occurs if the evolutionary interests of males and females do not coincide Two types of sexual conflict Conflict over mating (pre-zygotic) Mate choice, sperm competition Conflict over (post-zygotic) Parental effort, offspring desertion 1

2 Whyis there a conflict over? The common interest of parents is to raise the young to independence and thus spread their genes If parents together, then their young grow and survive better in many insects, fish, birds and mammals E.g. chicks survive better of both parents feed the young in junco (a small N Am songbird) So biparental looks like a good idea in many vertebrates... % Biparental % Femaleonly Cichlids 182 genera Crocodiles 21 species Birds About 9600 species Primates 203 species % Male-only <1 0 <1 0 % No Terrestrial arthropods (no. of orders)...and in some insects Female-only Male-only Biparental Egg Caring of young Provisioning of young Why is there a conflict? BUT is costly Metabolic costs of laying eggs and caring for the offspring Brood rearing Incubation The metabolic costs may have long-term consequences cost of reproduction e.g. several Cladoceraspecies (water fleas) The caring parent is vulnerable to predators The chances of finding a new mate are limited if the parent s For instance, in burying beetles the male and female cooperate to prepare carcass and feed the young Costs of reproduction Reproduction is costly in terms of survival or reproduction later in life ( cost of reproduction ) Thus reproduction should decrease survival and/or reproduction in future years Costs of reproduction Reproduction is costly in terms of survival or reproduction later in life ( cost of reproduction ) Thus reproduction should decrease survival and/or reproduction in future years These predictions were tested in collared flycatcher by experimentally manipulating their clutch size and then looking at survivaland clutch sizeof parents in their next year 2

3 Why is there a conflict? Thus each parent prefers the other to do the hard work of raising young Tug-of-warbetween male and female over : evolutionary increases in male duration of were associated with decreases in female duration of in shorebirds and vice versa Sexual conflict is manifested by: i. Offspring desertion One (or both) parent(s) abandon the offspring The parents decide for each brood whether they or desert Discrete decision ii. Reduced parental effort The parents decide how much effort they spend on raising their young Continuous decision In both situations the behaviour of one parent may depend on the behaviour of its mate Requires game-theoretic analysis (i) Desertion game (Maynard Smith 1977) G= ; D= desert P n = survival of brood d for by nparents p = probability of remating W, w = number of eggs laid by deserting or caring females Above the diagonal: Payoff for the female Below the diagonal: Payoff for the male Desertion game Solving the game: We are looking for the Evolutionarily Stable Strategy (ESS), i.e. The strategy that cannot be invaded by any mutant strategy For instance, biparental is an ESS if: wp 2 > WP 1 and wp 2 > wp 1 (1+p) (i) (ii) Desertion game (iii) (iv) The conditions of 4 ESSs can be deduced for (i) Biparental (L)RS must be greater than if male OR female deserts (ii) Female-only If deserting male has a good chance of mating again (iii) Male-only No difference in survival of young relative to female presence (iv) No No male or female does better (in terms of surviving young) by providing MALE CARES MALE DESERTS Desertion game Example Parental in Penduline Tits??? FEMALE CARES 5.36 ±3.15 (N = 49)??? 4.33 ±2.66 (N = 52) FEMALE DESERTS 2.59 ±1.57 (N = 19) 1.54 ±2.54 (N = 47) 2.81 ±2.45 (N = 3) 3.52 ±2.92 (N = 6) Parents may play coordination game with two alternative ESSs: Female-only, Male-only Basis for future more complex/realistic model 3

4 There are more sophisticated gametheoretic models of C/D We may want to model the behaviour of all members of a population (males and females) Because in reality the animals interact with each other We may allow the parents to produce several broods in a breeding season We may allow the behaviour of the parents to depend on their state, e.g. body reserves ( state-dependent game ) More sophisticated desertion games The body reserves of male ( ) and female ( ---) parents over a breeding season and the predicted pattern of ( female-only, biparental, male-only ) Early in the season the body reserves of females are high and thus the males can desert them, whereas in the middle of the season the females are in a poor condition and thus the males decide to. The females can then exploit the males decision and desert (see Bartaet al Am Nat) (ii) Parental effort games Each parent makes a decision on a continuous scale: how much effort should they spend on raising the young What is the evolutionarily stable parental effort for the male and for the female? Houston & Davies (1985): (ii) Parental effort games (Houston & Davies 1985) The ESS depends on the slopes and intercepts of the functions If males can work harder than females, then males will end up with doing all (middle) If parents are willing to compensate, but only partially, then biparental is the ESS (left) If parents are overcompensating, then either of them may end up with doing all (right) Testing the parental effort games Prediction: in biparental species, the parents should NOT compensate fully for their handicapped mate Experimental test in starlings by handicapping the male or the female parent during brood-rearing: Testing the desertion game The desertion game is very simplistic, and may thus not be suitable for direct testing Bearing this caveat in mind, we can derive predictions from this model Prediction 1: Biparental occurs if both parents provide much better than a single parent Prediction 2: Males desert if they are likely to find a new mate 4

5 Prediction 1: Biparental occurs if both parents provide much better than a single parent Prediction 2: Parents desert if the probabilities of remating are high Male removal experiments in birds brood survival growth Removal reduced Removal did not influence 5 3 Observational test Female rock sparrows desert more their brood more often when unmated males are available in the population Prediction 2: The probabilities of finding a mate should influence caring/deserting decisions Experimental test St Peter s fish desert their brood more often when the population sex ratio is biased: Male biased sex ratio female deserts Female biased sex ration male deserts Parental manipulations Parents may manipulate the behaviour of their mate Forced baby-sitting : male social voles drag females back to the nest to force the females to Parents may withhold e.g. in magnificent frigatebird Males always desert the chick Male desertion time varies among broods After male desertion, the female fully compensates Manipulation and resistance sexually antagonistic coevolution of traits (Holland & Rice 1998) Summary Sexual conflict occurs if the evolutionary interests of males and females do not coincide Care is costly, so each parent prefers the other to do the hard work To solve the conflicting interests of male and female parent, researchers use game theory: i. Desertion games ii. Parental effort games Experimental and observational studies are partially consistent with the predictions of the game theoretic models There is growing evidence that parents DO manipulate their mate s behaviour (see also lecture 5) 5