Sociality

1. Sociality

2. Sociality: space • Habitats are a mosaic of differing elements (heterogeneity) • Not surprisingly, an individual’s fitness can vary dramatically over such a landscape

3. Sociality:space • Some patches may offer better resources than others • E.g. prey abundance, nesting sites, shelter, hiding places • Thus NS will favor those individuals that choose better habitat/patches (that in turn result in higher fitness)

4. Sociality:space • Resources are distributed throughout the landscape in one of three ways: random, clumped or uniform (variance to mean ratio)

5. Sociality:space • Uniform (dispersed) distributions generally indicate a level of competition and K-selection; random or clumped distributions indicate little about factors influencing the distribution of the organisms concerned

6. Sociality:space • Organisms vary in their mobility • Viscous(low gene flow, large inter-population genetic variation) vs.fluidpopulations • Some are philopatric • Home ranges are the area in which an individual roams during a typical day; it is not necessarily defended • Territories are actively defended (exclusive use)

7. Sociality:space • How do territories evolve? As long as territories are cost-effectively defended, they will be

8. Sociality:space • Are there ways to minimize the costs of territoriality? Yes… • Neighbor recognition by the male Ovenbird

9. Sociality: space • What else can influence territory size?

10. Sex • Most organisms reproduce sexually…why? • Many plants and invertebrates may only use this strategy occasionally • Sexual reproduction has evolved multiple times • Initially, bacteria exchange genetic material (although not reproduction) • Eventually this leads to diploidy (& meiosis)

11. Sex • Diploidy may have evolved as a result of predation • Evidence that the components of prokaryotes, bacteria and blue algae, have been incorporated into eukaryothic higher organisms as cell organelles • It is more efficient to have a division of labor (sedentary, nutritious egg & mobile DNA)

12. Sex • This division is termed ‘anisogamy’ • There is numerous versions of sexual reproduction • E.g. facultative sexuality water fleas • E.g. earthworms • E.g. marine fish switching sex

13. Sex • Some have argued sex is maladaptive in higher vertebrates (evolutionary benefits of genetic recombination must outweigh losing 50% of genetic material) • However with biparental care, usually can raise 2x the young, offsetting the lose of genetic material

14. Sex • Another thought is sex lowers competition between siblings…how?

15. Sex • Humans and parthenogenesis (pg. 206)

16. Sex Ratio • In many species, there is an equal number of males and females • Why are there so many males (or any at all?) • Remember, the reproductive success of all females must equal that of all males • Thus if the numbers are different, the sex with fewer individuals leaves on average, more offspring/individual (which should even out relatively quickly)

17. Sex Ratio • Thus a good strategy would be to invest ½ your energy in males and ½ in females (actually numbers may change on investment)

18. Sex Ratio • Let’s consider the difference between the primary sex ratio and the secondary sex ratio • One of the things that may influence the sex ratio is differential mortality of the sexes during the period of parental care

19. Sex Ratio

20. Sex Ratio • However, in systems where there is already a great deal of variation in reproductive success within a sex, things can change…

21. Sexual Selection • Given an organism mixes it genes with another, it is in both parties interest to select the mostfitindividual • This battle for the sexes is intrasexual selection • While this doesn’t usually lead to direct combat, there is real competition • Wise decision making should be at a premium

22. Sexual Selection • Maynard Smith (1956) demonstrated mating preferences in fruit flies • Females that mated with inbred males laid an average of only 264 fertile eggs (compared to 1134 for outbred males) • Virgins and males (90% vs. 50%)

23. Sexual Selection • Over evolutionary time, natural selection operates to produce a correlation between male genetic quality and female preference (“good genes hypothesis” or “sexy son hypothesis”)

24. Sexual Selection • Animal populations also have mating systems • Most birds are monogamous, most mammals are polygynous…why? • Many other systems also available • Polyandry, promiscuity, sequential monogamy, polygynadry

25. Sexual Selection • Intersexual sexual selection is termed epigamic selection; it is ‘the reproductive advantage accruing to those genotypes that provide the stronger heterosexual stimuli’ • In other words, what is good the male may not be good for the female • Consequently, females exert a much stronger mating preference (more investment as well)

26. Sexual Selection • Female choice can lead to extremes in sexual dimorphism

27. Sexual Selection • However in most systems, monogamy is best for the female and she tries to impose it upon males (and successfully) • Conversely, males need to be assured offspring are going to be his: mate guarding • E.g. birds/people

28. Sexual Selection • What drives mating systems? • Skewed sex ratio… • Of polygyous NA birds, 11 of 14 sp are found in grassland/wetlands…why? In Europe, similarly 5% polygynous, but not same habitat • Can you think when it may not be in her best interest to be monogamous?

29. Sexual Selection • Reproductive success of female RWBL of varying harem sizes… making good choices

30. Sexual Selection • Polygyny threshold

31. Sexual Selection • In these systems, whatever traits that allowed males to be selected can quickly become exaggerated

32. Sexual Selection • In marine mammals (pinnepeds), there is a strong correlation between degree of sexual size dimorphism and harem size

33. Sexual Selection • Leksare associations of males displaying themselves for females • The offspring of such ‘choices’ then become either exaggerated (like father) or daughters tend to make similar decisions as mother (runaway selection)

34. Sexual Selection • An alternative to this is the handicap hypothesis; the males ability to survive despite the handicap • Good health hypothesis

35. Sexual Selection • Alternative mating tacticsexist for both males and females • Females tend to sneak EPCs with superior males • Males could be satellite males, building managers, or bigamists

36. Sexual Selection • Can anyone think of another advantage of sexual dimorphism?

37. Fitness

38. Fitness • An organism’s fitness is determined by the interaction between its phenotype and the totality of its environment • In K-selected species, fitness is almost completely determined by the biotic environment whereas the fitness of r-selected species is frequently determined by the abiotic environment

39. Fitness • Compared with breeding individuals, members of a nonbreeding floating population have very low immediate fitnesses (although their fitness rises if they are able to breed later) • Even within a breeding population, fitness may vary widely (polygynous males vs. females)

40. Group Selection • Many ecological phenomena have been interpreted as having been evolved for the benefit of the population rather than for the benefit of individuals • Clutch size, sex ratio, alarm calls, density-dependent reproduction, and many aspects of sexual selection have all been attributed to group selection

41. Kin Selection • For example, why does the worker honey bee sacrifice her own reproduction for the good of the colony? She will even sacrifice her life if the hive is attacked. • Remember, true altruism does not exist!

42. Kin Selection • Table 10.2

43. Kin Selection • Kin selection occurs when an individual actually gains more helping family than it loses by foregoing its own reproduction (Hamilton) • Usually one may sacrifice for many • Where r is the coefficient of relatedness, n is the number of relatives benefited, b is benefit received and c is the cost to the donor rnb – c > 0

44. Kin Selection • In an extreme example, you should sacrifice yourself for >2 sibling • Close relative are worth more than distant ones • Can you envision when even 1 sibling is worth it?

45. Kin Selection • However, the fact sociality has evolved in so many different groups suggests there is a real evolutionary benefit to social behavior

46. Kin Selection • Fischer (1930) considered the potential influence of kin selection and warning coloration • For each colorful, yet distasteful, individual, it is certainly NOT in their best interest to be colorful and gaudy

47. Kin Selection • How do birds learn what is palatable? • The benefits to siblings would be large, especially if they happen to stay in relatively small social groups…why? • Fischer quantified this difference beyond individual fitness to be inclusive fitness (but cannot spread unless all members share it)

48. Eusociality • Two orders of insects have evolved eusoliatility (hymenoptera and isoptera) • Hymenoptera (bees, wasps, ants, hornets) frequently live in colonies • They have a peculiar haplodiploid system; males are produced asexually and are haploid (thus identical with identical sperm) • Females are diploid, but all share fathers exact genome (thus have a r of 0.75)

49. Kin Selection • What are the implications of a colony having an r of 0.75 for sister` s and 0.50 for brothers? • Some species mate once on the single nuptial flight, others may have several males (sperm is stored with last male siring first offspring) • Can you make any predictions about the timing of colony unrest?

50. Kin Selection • Termites (Isoptera) also have highly organized colonies, king and queen, workers in various castes • They have ‘normal’ diploid genetic breeding system • However, if king and queen are somewhat inbred, then offspring have a very high r