Family groups – Conflicts and Interests among the Family

1. Family groups – Conflicts and Interests among the Family • Before birth: Optimal sex ratios and adjusting for the • circumstances • Conflicts between parents and offspring • Conflicts among siblings

2. Male Female 50 Elephant seal 100 8 Red deer 24 14 Man 888 69 Percent of copulations 0 1 2 3 4 5 6 7 8.............14 If its true, why not produce a sex ratio of say 20 females for every male? and do most organisms deviate from 1:1? Males produce lots of sperm and a few males monopolize mating

3. Male Female 0 1 Male Female 0 1 If p= frequency of males (b-d) = 1/2 p = (a-b-c+d) Suppose there are 20 females for every male... ...then every male has 20 times the reproductive success of every female (on average) Therefore, a parent whose children are exclusively sons enjoys ~20 times the number of grandchildren  female bias sex ratio is unstable

4. Suppose males are 20 times as common as females... Since one sperm fertilizes an egg only 1 in 20 males contribute genes to any offspring and females have 20 times the reproductive success of males (on average)  male bias sex ratio is unstable The rarer sex has the advantage and only when the ratio is 1:1 will the expected success of males and females be equal and the sex ratio stable

5. However, the argument should really be stated in terms of parental investment and not reproductive success...b/c what if sons are 2x as costly to produce? Why might there be gender differences in the cost of offspring?

6. FL scrub Jay In cooperative breeding birds, it is often males who stay behind to help and sex ratios are male- biased • Metcalf’s study of two wasps, • Polistes merticus and P. variatus. • The former has smaller males than • females and a sex ratio biased • toward males, whereas the latter is 1:1 • Investment ratio is 1:1 in both

7. Local Mate Competition – the “Wasted Son” Suppose 2 sons compete to mate with the same female. An extreme case, but it illustrates that when brothers compete for the same females one male is wasted from the mother’s point of view An extreme example is a totally inbred population because all daughters are fertilized by the sons. What to do? Just enough sons to mate with all females • Acaronphenox mite – male are never born, rather they mate with sisters • while still in the mother and dies. • There broods consist of about 20 females and one male

8. if very few, mainly sons Proportion of sons 2nd Female if many, mainly daughters • Parasitioid wasp, Nasonia vitrispennis • Werren suggested that the sex bias depends on the extent of local mate competition - If one wasp parasitizes a pupae the sex ratio is heavily biased towards females (91.3%) - For the second female it depends on how many eggs she lays Ratio of offspring 2nd/1st female

9. Trivers-Willard Effect An ESS 1:1 sex ratio is at the population level. Individuals may specialize (1:5 sex ratio) if an an equal number of other individuals specialize at 5:1 ratio In more or less monogamous human populations, there is evidence that women tend to marry up the socioeconomic scale. As a consequence, some women on the upper end of the scale would be left w/o men to marry while the same would be true for men at the opposite end of the scale Since there is a strong tendency for the socioeconomic status of the parents to determine the socioeconomic status of the children.... ... women at the upper end should produce sons while women at the lower end should produce daughters

10. Male Female Elephant seal 100 8 Red deer 24 14 Man 888 69 In animals.... • Population sex ratio must be 1:1 so that specialization in sons is cancelled • by reciprocal specialization in daughters • (2) One sex exhibits higher variance in Rep. Success than the other (3) Parents can assess – consciously or not (“inherited”) – whether their offspring are likely to fall at the upper or lower bound of Rep. Success distribution e.g., in the above example, if you know your offspring are likely to succeed as competitive elephant seals, you will have more grandchildren if you have sons

11. sons daughters daughters have higher success sons have higher success

12. Sex ratio of offspring is biased toward males when females are high ranking Sex ratio of offspring is biased toward females when females are low ranking

13. In other species, especially primates, males disperse, whereas females remain at their natal sites and inherit their mother’s status.... How do you expect them to differ from red deer? High ranking females produce more daughters than sons • Trivers-Willard Effect doesn’t predict an unambiguous directional change with regard to female status

14. An experimental test: Virginia Opossum (Austad and Sunquist 1986) Experimental mothers were fed sardines during during the breeding season and gestation period, while controls received no food supplementation

15. young had greater mass and male biased sex-ratio

16. Possible mechanisms leading to biased sex ratios

17. In Humans: 1,014 random males of the US èlite born between 1860-1939 - 1,180 sons and 1064 daughters - ratio 1.11:1 (differs from US mean of 1.06) 1,757 male of the German èlite - 1,473 sons and 1,294 daughters - 1.138:1 (differs from German mean of 1.05) 1,179 males of the British èlite - 1,789 sons to 1,522 daughters - 1.1754 (versus 1.06 mean) Ulrich Mueller (1993)

18. 100 80 Percent of older children breast fed 60 40 1550 < 10K > 60K M 1450 Interval (days) before younger child 1350 1250 F 1150 < 10K > 60K Gaulin and Robbins (1991) Trivers-Willard Effect in contemporary NA Society Data derived from a National questionnaire, N=906 M F

19. Duration of breast-feeding (mo.) Percent of older children breast fed Interval (days) before younger child 10 2400 100 F 8 2000 80 F M 6 1600 M 60 M 4 1200 40 F Absent Present Absent Present Absent Present Male

20. How do they do it- Part II As Trivers has noted,the sex ratio at birth is only one indication of how parents distribute their investment (or alter their sex ratio) among male and female offspring Dickemann (1979) has argued that historical preferential female infanticide among high-status families of Europe and Asia reflects T-W investment bias Similarly, Voland (1988) has shown among 17-19th century German households a male based child mortality among all classes except the land-holding class Boone (1988): 15-16th century Portuguese nobility – highest classes invested more into sons (via estates), whereas the lower classes into daughters (via dowry) And on and on and on.... See Pp. 281-282 of your text for infanticide in humans, with supporting data from Canada

21. Parent-offspring conflict Classically viewed from perspective of parents Parents allocate investment to their young so as to maximize the number of surviving young, (or max LRS) and one imagines the offspring as passive vessels Once we see the offspring as an acting participant wanting to maximize its RS we realize that the offspring will presumably want more investment from the parents than the parents are selected to give Herein lies the conflict....

22. offspring survival rate parent parental investment Fundamental Tradeoff between present and future reproductive effort, such that too much effort to the present compromises a parent’s survivorship leading to early death.... What’s true about future RS if you die early? If the mother has fewer future offspring, is there a fitness cost to the present offspring?

23. Tradeoffs among the offspring and among the parents... Parents – if I give too much PI now I will have fewer young in the future Offspring – if I demand too much PI now I will have fewer siblings in the future The key to seeing the conflict between parents and offspring is The offspring is related to itself by r = 1.0 and to its future siblings by r=0.50 (full sibling) or r = 0.25 (half sibling) • Offspring should be selected to demand PI until the cost to the mother is more than twice the benefit to itself (or 4 times if half-sibs) because the mother’s future offspring are devalued by the current offspring

24. What’s even COOLER Hymenoptera colonies – Queen’s perspective sons and daughters have r=0.5 - Worker sister perspective, brother’s r=0.25, sister’s r =0.75 Queen favors a sex ratio (ratio of PI) of 1:1 in the reproductives, whereas sisters favor 1:3 (M:F) How does POC manifest itself? • Disagreement over the sex ratio – Where males require say 2x PI as females, the mother is • selected to produce a 1:2 (M:F) sex ratio. But males have 2x the RS in this case, so the offspring • would prefer to be males. This reduces the mother’s RS, but that reduction is devalued from the • offspring’s perspective leading to conflict. Triver’s determined that: • Parents “prefer” a 1:2 ratio • Offspring prefer a 1:1.414 (see Trivers 1974 for calculation) Who has control?

25. The Test: • Trivers look at sex ratios in: • Prenolepisimparis – 8:1 (M:F) sex ratio among reproductives, but females mass is 25:1. • Comparing dry weights of the population of each sex produce yielded 1:3 ratio. • (2) Compared dry weights of the population of fresh formed reproductives of the fire ant • Solenopsis invicta. Population sex ratio is 1:1, but when adjusted for PI it is 1:3.5 (3) Lastly, sex ratio of ants enslaved by Slave-maker Ants - since enslaved workers have no self interest in the sex ratio we expect the Queen to wield control. Leptothoraxcurvispinosa enslaved by L.duloticus produce a 1:1 ratio L. curvispinosa by themselves = 1:3 (4) Your book adds one more observation: if a new queen takes over the sex ratio shifts from 1:3 towards 1:1 as workers are no longer producing sisters.

26. Time course of Parent-Offspring Conflict No conflict here, adaptive to provide PI 2 B/C of PI No conflict here, adaptive to cease PI 1 time conflict here; parents selected to stop offspring selected to be demanding (2) Weaning and begging In birds and mammals, young are “weaned” off a diet almost exclusively provided by the parents. There is a decline in food delivered to chicks as begging and contact-seeking behavior increases in many birds and mammals. Often, out-right aggression is use as the last act that dissolves the family.

27. Offspring as psychological manipulators Obviously young can not fling their mother to the ground to nurse at will... Presumably the young have better knowledge of their condition and need to communicate this to the parents. Both parties benefit from the communication, but almost immediately this system is subject to manipulation.

28. In brood parasites, the parasite chick begs the loudest – they have nothing to lose in terms the “mother’s” future reproductive success

29. (3) In-utero conflict in humans and mammals “inside the mother the offspring is expected to employ chemical tactics [to compete effectively with its parent]” (Trivers 1974) In-utero, there is potential conflict if the amount and duration of PI can be influenced by genes expressed in the offspring. In placental mammals, the fusion of fetal and maternal organs or tissue for the basis for physiological exchange Crespi and Semeniuk (2004) proposed that constrained antagonistic coevolution between parents and offspring in traits that influence PI has resulted in extreme diversity of placental mammals... There is no other mammalian organ whose structure and function are so species diverse as those of the placenta. This is curious since the ”purpose” of the placenta, presumably, is the same in all species (Faber et al. 1992)

30. Uterine Tug-of-war: • Increased fetal trophoblast “invasion” with the uterine lining (2) Countered increased invasiveness via at least 3 mechanisms: - maternal secretions to reduce invasion, including stronger maternal immune response - evolution of stronger maternal epithelial barriers - shedding of overly invasive trophoblasts with uterine lining Interestingly, transplanted trophoblasts (in mice and pigs) to nonrecptive regions of the uterus results in enhanced trophoblast invasion, which suggests this process is usually suppressed in normal pregnancy (3) Fetal tissue (in humans; see your text P. 280) and Oestrogens (horses) function to increase utero-placental blood flow (via dilation of vessels), thereby supplying the fetus with more resources. Suppression of these oestrogens in horses leads to smaller foals.

31. Family groups – Conflicts and Interests among the Family • Before birth: Optimal sex ratios and adjusting for the • circumstances • Conflicts between parents and offspring • Conflicts among siblings

32. Parent-offspring Conflict: Parents – if I give too much PI now I will have fewer young in the future Offspring – if I demand too much PI now I will have fewer siblings in the future The key to seeing the conflict between parents and offspring is The offspring is related to itself by r = 1.0 and to its future siblings by r=0.50 (full sibling) or r = 0.25 (half sibling) • Offspring should be selected to demand PI until the cost to the mother is more than twice the benefit to itself (or 4 times if half-sibs) because the mother’s future offspring are devalued by the current offspring Sex Ratios, Weaning and begging, In-utero conflict

33. Fraser and Thompson (1990) explored the function of these teeth as neonatal weaponry thru removal exps. 200 Mass Gain light 100 heavy Am. Robin chicks time spent begging Control Chicks exp con exp con 0-3 days 3-7 days time begging – food deprived chicks Sibling Rivalry Once again, an individual is related to itself by r = 1.0 and to its full siblings by r = 0.50. Thus each sib values itself more than its siblings and conflicts ensue... E.g., for resources, i.e., mother’s milk - pigs have slightly sideways facing eye-teeth that they use to slash each other with milking

34. In birds, sibling rivalry frequently takes the form of Hatching asynchrony