Chapter # 8 Life History Patterns (pg )

Transcription

1 Chapter # 8 Life History Patterns (pg )

2 8.1 Reproduction May Be Sexual or Asexual What are the goals for living organisms?

3 8.2 Sexual Reproduction Takes Many Forms Parthenogenesis born w/o fertilization Dioecious Separate Males and Females Hermaphroditic Individual organisms with both male and female organs. Monoecious separate male and female flowers on the same plant.

4 8.3 Mating Systems Describe the Pairing of Males and Females Mating Systems Range from Monogamy to Promiscuity

5 8.3 Mating Systems Describe the Pairing of Males and Females Polygamy the acquisition by another individual of two or more mates, none of which is mated to other individuals. A pair bond exists between the individuals and the individual having multiple mates is generally not involved in caring for the young. - Size of group depends upon synchrony of fertility and receptivity. - Small time period fewer individuals. - Longer time period more individuals.

6 8.3 Mating Systems Describe the Pairing of Males and Females Polygyny Where an individual male pairs with two or more females. Polyandry Where an individual female pairs with two or more males (exception rather than the rule) Access to resources Parental Investment

7 8.3 Mating Systems Describe the Pairing of Males and Females Relevance to Population Ecology Life-history characteristics determine Organization of individuals in space and time Examples How the population perpetuates itself discretely vs. continuously; rapidly vs. slowly, etc Which characteristics will be selected for and persist within the population (due to sexual selection) Conversely, selective pressures (abiotic factors, distribution of resources, etc..) will affect the lifehistory patterns observed.

8 8.4 Acquisition of a Mate Involves Sexual Selection What is the advantage to the individual and species by this display?

9 8.4 Acquisition of a Mate Involves Sexual Selection Sexual Selection involves: -Intrasexual selection: male:male competition or female:female competition for access to potential mates. The maintenance of traits that assist in competition within the gender successful mating. - Intersexual selection: differential attractiveness of males to females and vice versa. The maintenance of traits that are attractive to the opposite gender. Which gender determines the winner?

10 Intersexual Selection: A Focus on Female Choice Material benefits: Nutrition Ex: hangflies) Length of mating time depends on quality and size of courtship gift

11 Intersexual Selection: A Focus on Female Choice Material benefits: Anti-predator substances Defensive compounds in arctiid moths Photo: butterfly-conservation.org

12 Intersexual Selection: A Focus on Female Choice Ability of males to provide sufficient sperm Female fruit flies (some species) choose virgin males. Photo: San Francisco Exploratorium

13 Intersexual Selection: A Focus on Female Choice Parental Ability Cannot assess directly May be correlated with other features of the male Example 1: Redwing blackbirds Epaulettes correlated with nest defense Courtship effort correlated with feeding effort Photo: Vancouverislandbirds.com

14 Intersexual Selection: A Focus on Female Choice Parental Ability (Ex: sedge warbler) Size of song repertoire correlates with chick weight at fledging

15 The Sedge Warbler (cont.) Female sedge warblers choose on the basis of repertoire size. Thus they choose the most fit males.

16 Intersexual Selection: A Focus on Female Choice Health/Genetic Quality Example: song repertoire in great reed warbler where: Females chose males with larger repertoires. This was correlated with greater offspring survival (unrelated to parental care).

17 Intersexual Selection: A Focus on Female Choice Health/Genetic Quality Example: Bright coloration of sticklebacks negatively correlated with low parasite loads

18 Intersexual Selection: A Focus on Female Choice Health/Genetic quality (bright color negatively correlated with parasite load) Advantages to females choosing these males Avoid getting parasites while mating Avoid transferring parasites to young Are choosing healthier males; their health status may be related to genetic quality

19 Origin/maintenance of Mate Choice for Exaggerated Characteristics In some species, why do males develop what appear to be extreme traits that actually can hamper their survival? Example: Peacock s tail

20 Origin/maintenance of Mate Choice for Exaggerated Characteristics Hypothesis 1: Runaway selection (R.A. Fisher - early 20 th Century) Directional that takes on a life of its own Starts as an honest signal more extreme. Mechanism: Females choose males with large tails, multiple eyespots. the next generation has a higher proportion of these males. Will work even if his traits are not honest signals of quality. Why? Evidence of arbitrary choices by females (bird band example)

21 Origin/maintenance of Mate Choice for Exaggerated Characteristics Hypothesis 2: Handicap or good genes hypothesis (R.A. Fisher) Exaggerated trait might decrease chance of survival, only males with superior genes can survive despite the handicap. Example: peacock tail as a handicap. In this case, a female choosing a male with these traits would be improving her fitness. (His signal is an honest signal of fitness.)

22 Distinguishing Between Runaway Selection and Good Genes (Petrie) Methods Males of different ornamentation/tail length randomly bred with females Why random? Young raised under identical conditions and then released Results Offspring of the attractive males weighed more at day 84. Offspring of the attractive males were more likely to be alive after two years Which hypothesis is supported by this data?

23 Marion Petrie s Peacock Data Source:

24 Origin/maintenance of Mate Choice for Exaggerated Characteristics How extreme can a characteristic become? Under what conditions will directional selection stop? (Think about costs vs. benefits )

25 Intrasexual Selection - Adaptations to Gain Access to Females Dominance behavior & characteristics Example 1: sexual dimorphism in elephant seals

26 Male-male competition and sexual dimorphism (seals) NOTE: Each point represents a species

27 Intrasexual Selection - Adaptations to Gain Access to Females Weaponry for fighting with other males. Example: dung beetle! Male dung beetle, Phanaeus vindex (Rattlebox photography)

28 Intrasexual Selection - Adaptations to Gain Access to Females Sneaker strategies Example: Plainfin midshipmen Dominant male features and behavior Nest building, singing, guarding Sneaker male features and behavior No nest, no singing, just sex Small fish, big balls!

29 Dung Beetles - Two Morphs Behavioral and morphological differences similar to midshipmen Large, dominant males with horns defend burrows Small, hornless males with big balls sneak Midshipmen Genetically-based differences Dung beetles Nutritionally-based differences

30 Intrasexual Selection - Adaptations Favoring Use of Sperm - Displacing or inactivating rival sperm Damselfly scooper penis

31 Intrasexual Selection - Adaptations Favoring Use of Sperm - Displacing or inactivating rival sperm Example: Chemical sperm inactivation in fruit flies Photo: San Francisco Exploratorium

32 Mechanisms to avoid sperm displacement Intrasexual Selection - Adaptations Favoring Use of Sperm - Mate guarding (Example: many crab species)

33 Intrasexual Selection - Adaptations Favoring Use of Sperm - Mechanisms to avoid sperm displacement Prolonged mating and cannibalism (example: redback spider) Female less likely to mate with another if she eats him He has low likelihood of finding a new mate (high predation) Andrade, 1996

34 Intrasexual Selection - Adaptations Favoring Use of Sperm - Mechanisms to avoid sperm displacement Anti-aphrodisiac (Example: Heliconius erato)

35 8.5 Females May Acquire Mates Based on Resources In sexual Selection, the female will select mate(s) based on their physical characteristics, because this is an indirect measure of their health OR their (their mate s) ability to acquire and defend resources (e.g., food and space). Territoriality - Monogamy

36 Sexual Selection Defined: Selection for characteristics/behaviors that maximize chances of mating and producing the most, and highest quality, offspring. A category within natural selection General pattern: Male-male competition and female choice Common pattern with many exceptions!

37 Example: Satin bowerbird mating Each male builds an elaborate bower where he conducts his courtship display Bowers located near each other Each female visits several times, finally chooses a mate behavior

38 Bowerbird Males: # of Mates Some males are much more successful than others.

39 Bowerbird Females: # of Mates Only ~1/3 of females have >1 mate.

40 Why Do Males Usually Compete, While Females Choose? Hypothesis 1, A.J. Bateman: Eggs are expensive, sperm is cheap! Amount of energy invested in a single gamete is much greater for females (eggs) than for males (sperm) Female bird may invest up to 30% of body weight in eggs.

41 Eggs Are Expensive, Sperm is Cheap. Difference in investment per gamete Example: Fairy wrens Males have 8 billion sperm in testes at once Females lay six eggs maximum per clutch Female limited by egg production, Male limited by number of mates only (presumably unlimited sperm) Operational sex ratio skewed toward males

42 But, Is Sperm Really Cheap? It often takes a large number of sperm to fertilize a single egg, due to Hostile environment within female Acid Attacks by the immune system

43 But, Is Sperm Really Cheap? Sperm competition among males Occurs when females have multiple mates Possibly the predominant situation Fitness advantages for female (will explore in next lecture) Some males may actually run out of sperm Garter snakes, zebra finch, blue crabs, rams

44 What if there is No Sperm Competition? In sea horses, eggs are deposited into pouches, and there is not sperm competition. Why not? Male sea horses have relatively low sperm counts!

45 But, Is Sperm Really Cheap? Drosophila bifurca: one sperm with long tail Sperm tail is 20x length of his body. His testes make up 11% of his body mass.

46 Why Do Males Usually Compete, While Females Choose? Hypothesis 2 (R. Trivers): Competition vs. choice is based on individual with the most total parental investment Often the female (example: mammals) But in some species, male makes a greater total investment.

47 Gulf Pipefish While male cares for a single brood, a female can produce two clutches of eggs male has greater total parental investment Operational sex ratio skewed toward females. Males choose large, ornamented females over small, drab ones. Female Male

48 Overview A mating system includes how members of a particular species (or population) choose and bond with mates how many mates per individual how parental care (if it occurs) takes place. Types of mating systems Monogamy: One male mates with one female Polygyny: One male mates with several females Polyandry: One female mates with several males Social vs. genetic monogamy

49 Key Principles The system that evolves depends upon the individual interests of each gender. Male and female interests are often in conflict. Why? Differences in gamete investment and/or total parental investment Male default system =. Why? Is there a female default system? Why? Interests/behavior of one gender serve to constrain options available to the other gender.

50 Polygyny Resource defense polygyny Example: African cichlid fish, Lamprologus callipterus Defended resource = shells in which females lay eggs

51 Polygyny Female defense polygyny Example: Elephant seals (females aggregate) Photo:

52 Polygyny Female defense polygyny Example: Elephant seals (males compete for beachmaster status) Photo:

53 Polygyny Lek polygyny Males clump, but not due to another resource Males become the clumped resource! Example 1: satin bowerbirds

54 Satin Bowerbirds: multiple signals of health and fitness (and good genes?)

55 Polygyny Lek polygyny Males clump, but not due to another resource Males become the clumped resource! Example 2: sage grouse (filoplumes and sound in central area of lek determines mate preference)

56 Polygyny Lek polygyny Example 3: bullfrogs Females choose males with longest, loudest and deepest calls But don t forget the sneaky f--kers

57 Polygyny: benefits/costs Male: number of offspring (+) Female: gets a high-quality male (+) gets less of the male s time and attention for raising young being defended against predators

58 Monogamy Common or rare? In which group of animals is it most common? What hypotheses would account for it?

59 Monogamy: alternate hypotheses Mate assistance: it takes two parents to raise the offspring Example: Adelie penguins Both parents needed for chick survival Photo: Karen Haberman

60 Monogamy: alternate hypotheses Mate guarding: guarding assures paternity; not guarding jeopardizes it. Especially critical if females are rare or receptive for a limited time Example: many crab species

61 Monogamy: alternate hypotheses Female-enforced monogamy Similar to mate-guarding, but done by female. Example: Burying beetles A female would lose resources, and possibly her offspring if she allows her male to mate again.

62 Monogamy: alternate hypotheses Danger theory Leaving increases chance of dying if predation rates are high. Example: The mantis shrimp Lysiosquilla sulcata Lysiosquilla sp. Opencage.info

63 Mantis shrimp (another type)

64 Monogamy: alternate hypotheses Pop em out theory Highly fertile mate Not worth time/energy to seek another. Example: Djungarian hamsters bbs.petsky.com.cn

65 Social Monogamy and extra-pair copulations Extra-pair copulations can increase fitness of participants. Males: More mates more offspring possible. Females: Historical (not current) ideas: no advantage for females Observational/experimental evidence: clear fitness benefits documented for some species Example: Yellow-toothed cavy

66 Yellow-toothed cavy: Offspring survival as a function of multiple mates for females

67 Social Monogamy and extra-pair copulations Direct fitness benefits: genetically based Good genes What does this mean? Genetic compatibility What does this mean? Genetic variability among offspring Why important?

68 Social Monogamy and extra-pair copulations Other benefits that may improve fitness for females: More resources hypothesis Example: Orange-rumped honeyguides swap food for sex. Better protection/care hypothesis Example: Dunnocks (European song bird) Mate with two males both care for young Infanticide reduction hypothesis Example: chimpanzees (who s dad?)

69 Polyandry (w/o polygyny) Spotted sandpipers: near-complete sex-role reversal Females arrive on breeding grounds; compete with other females for territories. Initial male arrives, mates, cares for her first clutch. Second male arrives later, mates, and cares for her second clutch.

70 What Circumstances Promote Polyandry? Female: only lays 4 eggs at once Add eggs (experimentally) decrease the total young successfully raised Related to incubation effort and protection Female can reproductive success by laying a second brood Needs second mate Reproductive success limited by mates rather than gametes in this case

71 What Circumstances Promote Polyandry? Why would males comply? Operational sex ratio biased toward males (related to absolute ratio for this species) She abandons He stays offspring survive He leaves offspring die Male 1: Certain of paternity for clutch 1; possibility of paternity for clutch 2 How is this possible? Male 2: Later arrivals less dominant, but still have a chance of paternity if they stay.

72 What Circumstances Promote Polyandry? Food fluctuation hypothesis In food-poor years, females put all energy into eggs and have no energy left for care of eggs/young. Mate assistance (by male) essential monogamy In food-rich years (i.e. many mayflies), the female recovers her body mass and can lay another batch Monogamy Polyandry

73 What Circumstances Promote Polyandry? Heavy predation pressure on nests Multiple nests assure that at least some young will survive. Male is needed to prevent predation Young will all be lost if he doesn t stay.

74 Patterns of Reproductive Effort Variations Numbers of young produced at a time More young = less parental investment/individual high mortality among young Care of eggs/larvae Variability in parental investment Type of young produced Precocial vs. altricial offspring (What is the difference?)

75 Patterns of Reproductive Effort Variations Number of reproductive events in a lifetime Semelparous: one big reproductive event in lifetime/many offspring Many are relatively short-lived (squid, annual plants) But some are long-lived (periodical cicadas) Itoparous: many reproductive events in lifetime/ fewer offspring per event. Common especially birds and mammals Timing is an issue: begin early materials/energy into reproduction, Begin later materials/energy into survival and growth

76 r vs. K strategists r -strategists Semelparous Many offspring Little/no parental investment per individual offspring Relatively short lifespan Begin to reproduce relatively early in life Good colonizers of newly available habitat, but often not effective competitors K -strategists Itoparous Few offspring High levels of investment per individual offspring Relatively long lifespan Begin to reproduce relatively later in life Not usually colonizers, but arrive later in succession, compete successfully