Life History Diversity. All organisms produce offspring, but the number and size of offspring vary greatly.

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1 Reproduction

2 Life History Diversity All organisms produce offspring, but the number and size of offspring vary greatly.

3 Life History Diversity An organism s life history is a record of events relating to its growth, development, reproduction, and survival. Life history characteristics include: Age and size at sexual maturity Amount and timing of reproduction Survival and mortality rates

4 Life History Diversity The life history strategy of a species is the overall pattern in average timing and nature of life history events. It is shaped by the way the organism divides its time and energy between growth, reproduction, and survival.

5 Life History Strategy

6 Life History Diversity Phenotypic plasticity: One genotype produces different phenotypes under different environmental conditions. For example, growth and development may be faster in higher temperatures.

7 Life History Diversity Changes in life history traits can cause change in adult morphology. Ponderosa pines in cool, moist climates allocate more biomass to leaves relative to sapwood than pines in warmer desert climates, resulting in different tree shapes.

8 Plasticity of Growth Form in Ponderosa Pines

9 Life History Diversity Phenotypic plasticity may result in a continuous range of sizes; or discrete types called morphs. Spadefoot toad tadpoles have small omnivore morphs and larger carnivore morphs.

10 Life History Diversity Carnivore tadpoles grow faster and metamorphose earlier. They are favored in ephemeral ponds that dry up quickly. Omnivores grow more slowly and are favored in ponds that last longer; they metamorphose in more favorable conditions and have more chance of survival.

11 Methods of Reproduction Sexual reproduction Meiosis, gamete formation, and fertilization Offspring show genetic variation Asexual reproduction Single parent produces offspring Offspring are genetically identical

12 Life History Diversity Modes of Reproduction Asexual reproduction: Simple cell division (binary fission) all prokaryotes and many protists. Some multicellular organisms reproduce both sexually and asexually (e.g., corals).

13 Life Cycle of a Coral Asexual Reproduction Sexual Reproduction

14 Asexual Reproduction Spontaneous fission Animals split or cut in two can regenerate new tissues to become two clones

15 Asexual Reproduction Propagation Plant cuttings or broken-off segments (vegetative propagules) propagate new clones

16 Asexual Reproduction Parthenogenesis Ovum develops without fertilization by male Environmentally controlled/ induced

17 Asexual Reproduction Budding Individuals bud off clones Rare in animals (e.g sea anemones, sponges) Common in plants (rhizomes or runners )

18 Life History Diversity Sexual reproduction has disadvantages: An individual transmits only half of its genome to the next generation. Population growth rate is only half that of asexually reproducing species. Recombination and chromosome assortment during meiosis can break up favorable gene combinations.

19 Life History Diversity Most plants and animals and many fungi and protists reproduce sexually. Isogamy: Gametes are equal in size. Organisms such as the green alga Chlamydomonas reinhardii have two mating types that produce isogametes.

20 Isogamy and Anisogamy

21 Life History Diversity Anisogamy: Gametes of different sizes. Usually the egg is much larger and contains nutritional material. Most multicellular organism produce anisogametes.

22 Types of Sexual Reproduction Separate male and female individuals Most animals Dioecious plant species have male and female flowers on separate individuals e.g. holly trees, stinging nettle

23 Types of Sexual Reproduction Simultaneous Hermaphrodites Animals with both male and female organs (e.g. earthworms and snails) Plants with bisexual flowers containing both stamen and pistil. e.g lilies Monoecious plants have male and female flowers on the same individual;

24 Sequential Hermaphroditism: Changes in sex during the course of the life cycle. Common in fish and invertebrates. The timing should take advantage of high reproductive potential of different sexes at different sizes.

25 Types of Sexual Reproduction Sequential Hermaphrodites Animals and plants that change sex due to age or environmental cues such as population sex ratio Protogynous- start as females Protandrous start as males

26 Types of Sexual Reproduction Sequential Hermaphrodites Animals and plants that change sex due to age or environmental cues such as population sex ratio Protogynous- start as females Protandrous start as males

27 Sequential Hermaphroditism

28 Life History Continua Number of reproductive events during the organism s lifetime: Semelparous species reproduce only once. Iteroparous species can reproduce multiple times.

29 Concept 7.2 Life History Continua Semelparous species include annual plants. Agave vegetative growth can last up to 25 years; also produces clones asexually. Giant Pacific octopus female lays one clutch of eggs and broods them for six months, dying after they hatch.

30 A Semelparous Plant?

31 Life History Continua Iteroparous species include: Trees such as pines and spruces Most large mammals

32 Life History Continua r-selection and K-selection describe two ends of a reproductive strategy continuum. r is the intrinsic rate of increase of a population. r-selection: Selection for high population growth rates; an advantage in newly disturbed habitats and uncrowded condition.

33 Life History Continua K is the carrying capacity for a population. K-selection: Selection for lower growth rates in populations that are at or near K; an advantage in crowded conditions; efficient reproduction is favored.

34 Life History Continua r-selected ( live fast, die young ): Short life spans, rapid development, early maturation, low parental investment, high reproduction rates Most insects, small vertebrates such as mice, weedy plant species

35 Life History Continua K-selected ( slow and steady ): Long-lived, develop slowly, late maturation, invest heavily in each offspring, low reproduction rates Large mammals, reptiles such as tortoises and crocodiles, and long-lived plants such as oak and maple trees

36 Plant Life Cycles mitosis multicelled sporophyte (2n) zygote (2n) fertilization Diploid Haploid meiosis gametes (2n) mitosis multicelled gametophytes (n) mitosis spores (2n) Fig. 15-2, p.245

37 Plant Life Cycle Origins Terrestrial plants evolved from green algae Ancestral plant life cycle is similar to that of green algae Other similarities: Same pigments, chemical make-up, genetics

38 Evolutionary Trend zygote GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

39 Evolution of Plants Nonvascular plants Bryophytes (mosses, hornwarts) Vascular plants Seedless (ferns, horsetails) Seed-bearing (conifers, flowering plants)

40 Bryophytes

41 Moss Life Cycle zygote fertilization Zygote grows, develops into a sporophyte while still attached to gametophyte. mature sporophyte Diploid Stage Haploid Stage meiosis Spores germinate. spermproducing structure eggproducing structure male gametophyte female gametophyte

42 Fern Life Cycle Sporophyte still attached to gametophyte. zygote fertilization egg rhizome Diploid Stage Haploid Stage meiosis Spores develop. sorus Spores are released. sperm mature gametophyte Spore germinates.

43 Seed-Bearing Vascular Plants Gymnosperms arose first Cycads Ginkgos Gnetophytes Conifers Angiosperms arose later Monocots Dicots

44 Two Types of Spores Microspores Develop into pollen grains Immature male gametophyte Megaspores Develop on sporophyte in ovule Female gametophyte Pollination pine pollen grains

45 Gymnosperms Plants with naked seeds Seeds don t form inside an ovary Four groups Conifers Cycads Ginkgos Gnetophytes

46 Gymnosperms

47 Pine cones Pine Cones Clusters of woody scales bearing ovules Megaspores develop into female gametophyte Male cones microspores become pollen grains are not woody

Pine Life Cycle one cone scale (houses two ovules) section through one ovule ovule one cone scale (houses a pollen-producing sac) mature sporophyte seedling pollen tube

49 Pine Life Cycle one cone scale (houses two ovules) section through one ovule ovule one cone scale (houses a pollen-producing sac) mature sporophyte seedling pollen tube spermproducing cell seed coat embryo seed section through a pollen-producing sac zygote Diploid fertilization meiosis Haploid microspores eggs form megaspores pollination form female gametophyte

Flower Structure STAMEN (male reproductive part) CARPEL (female reproductive part) filament anther stigma style ovary Nonfertile parts Sepals Receptacle Fertile parts Male

50 Flower Structure STAMEN (male reproductive part) CARPEL (female reproductive part) filament anther stigma style ovary Nonfertile parts Sepals Receptacle Fertile parts Male stamens Female carpel (ovary) petal (all petals combined are the flower s corolla) OVULE (forms within ovary) sepal (all sepals combined are the flower s calyx) receptacle

51 sporophyte Flowering Plant Life Cycle (monocot) Diploid double fertilization Haploid meiosis meiosis pollination microspores mitosis without cytoplasmic division two sperm enter ovule female gametophyte

Flowering Plant Life Cycles Dominant form is diploid sporophyte In flowers, haploid spores formed by meiosis develop into gametophytes seed fertilization gametes (sperm)

52 Flowering Plant Life Cycles Dominant form is diploid sporophyte In flowers, haploid spores formed by meiosis develop into gametophytes seed fertilization gametes (sperm) (mitosis) gametes (eggs) mature sporophyte DIPLOID HAPLOID male gametophyte meiosis (within anther) microspores meiosis (within ovary) megaspores (mitosis) female gametophyte

53 Life Cycles Senescence: Phase from maturity to death of plant or parts of plant Dormancy: Seasonal response to environmental change Growth stops, metabolism idles Ends with return to favorable conditions Vernalization: Low temperature stimulation of flowering

54 Animal Life Cycle multicelled body zygote fertilization diploid haploid meiosis gametes Fig. 7-12b, p.106

55 Animal Reproduction and Dispersal External Fertilization Sessile aquatic organisms release gametes into water (broadcast spawning) No energy spent on finding and competing for partner Energy spent on copious gamete production High number of offspring, low survival rate

56 Animal Reproduction and Dispersal Internal Fertilization Common to many types of animals (aquatic, terrestrial, invertebrates and vertebrates) More effective fertilization Fewer offspring, higher survival rate

57 Bearing Offspring

58 Bearing Offspring: Oviparity (Egg laying) Ovuliparity : fertilization is external (arthropods, fishes, most frogs)

59 Bearing Offspring: Oviparity (Egg laying) Oviparity : fertilization is internal, the female lays zygotes as eggs (reptiles)

60 Bearing Offspring: Oviparity (Egg laying) Ovo-viviparity : or oviparity with retention of zygotes in the female s body or in the male s body, but there are no trophic interactions between zygote and parents. In sea horse, zygotes are retained in the male s ventral "marsupium".

61 Bearing Offspring: Viviparity (Live Bearing) Histotrophic viviparity : the zygotes develop in the female s oviducts, but find their nutrients by oophagy or adelphophagy (intrauturine cannibalism in some sharks) Hemotrophic viviparity : nutrients are provided by the female, often through some form of placenta as in most mammals

62 Life History Diversity Complex life cycles have at least two stages. The stages have different body forms and live in different habitats and eat different foods. Metamorphosis: Abrupt transition in form between the larval and juvenile stages.

63 Life History Diversity Most vertebrates have simple life cycles without abrupt transitions. But complex life cycles are common in insects, marine invertebrates, amphibians, and some fishes.

64 The Pervasiveness of Complex Life Cycles

65 Embryonic Development Direct development Individuals develop into adult-like juveniles Indirect development Individuals go through several larval stages before attaining adult form

66 The Life Cycle of Ribeiroia

67 Life Cycle Evolution If the larval habitat is very favorable, metamorphosis may be delayed or eliminated. Some salamanders mature sexually while retaining larval morphology and habitat (paedomorphic).

68 Life Cycle Evolution Mole salamanders have both aquatic paedomorphic adults and terrestrial metamorphic adults in the same population. Frequency of paedomorphosis in these mixed populations depends on factors that influence survival and growth in the aquatic habitat.

69 Paedomorphosis in Salamanders

70 Cost of Sexual Reproduction Specialized cells and structures must be formed Special courtship and parental behaviors can be costly Nurturing developing offspring, either in egg or body, requires resources (usually from mother)

71 Intrasexual selection Intersexual selection Reproductive Costs

72 Sexual Selection Males and females of the same species are often sexually dimorphic and differ greatly in body size, ornamentation, and color Darwin proposed a theory of sexual selection to explain this dimorphism between the sexes Intrasexual selection involves male-to-male competition for the opportunity to mate Large size, aggressiveness, antlers, horns

73 Sexual Selection Males and females of the same species are often sexually dimorphic and differ greatly in body size, ornamentation, and color Darwin proposed a theory of sexual selection to explain this dimorphism between the sexes Intrasexual selection involves male-to-male competition for the opportunity to mate Large size, aggressiveness, antlers, horns

74 (a) Intersexual selection: Sexual dimorphism in a finch species (b) Intrasexual selection: Competing for mates Figure 13.29

76 Sexual Selection Darwin proposed a theory of sexual selection to explain this dimorphism between the sexes Intersexual selection involves the differential attractiveness of individuals of one sex (usually the male) to another Bright/elaborate plumage, horns, antlers

78 Sexual Selection The driving force behind the evolution of exaggerated secondary sexual characteristics in males is selection by females

79 Male investment in elaborate physical traits reduces the amount of energy available for other activities related to individual fitness (e.g., foraging, defense) There is a trade-off faced by species that exhibit sexual dimorphism between the sexes

80 Organisms Budget Time and Energy to Reproduction Reproductive effort - time and energy allocated to reproduction The more energy an organism allocates to reproduction, the less it can allocate for growth and maintenance Terrestrial isopod Douglas-fir tree

82 Organisms Budget Time and Energy to Reproduction The amount of energy invested in reproduction varies for different individuals Investment in reproduction includes production, care, and nourishment of offspring An individual s fitness is determined by the number of offspring that survive to reproduce

84 Trade-offs Number and size of offspring Seed size and number of seeds produced per plant

85 Trade-offs Number and size of offspring Seed size and probability of seedling survival

86 Number and size of offspring Expected reproductive success in wet versus dry environments Dry environments favor large seeds Wet environments favor small seeds Trade-offs

87 Parental Investment Depends on the Number and Size of Young There is an inverse relationship between the number of offspring produced and the parental investment that each receives Large numbers of offspring Are produced by organisms that inhabit disturbed sites, unpredictable environments, or environments where parental care is impossible (r-selected species) Increase the chances that some young will survive

88 Parental Investment Depends on the Number and Size of Young There is an inverse relationship between the number of offspring produced and the parental investment that each receives Parents that produce few young can expend more energy on each Altricial young are born or hatched in a helpless condition and require considerable parental care (e.g., mice) Precocial young emerge from the womb ready to move about and forage for themselves (e.g., ungulate mammals)

89 Parental Investment Depends on the Number and Size of Young The degree of parental care varies widely Parental care is best developed among social insects (e.g., bees)

90 Fecundity Depends on Age and Size The number of offspring produced varies with the age and size of the parent Many plants and ectothermic (coldblooded) animals exhibit indeterminate growth and do not have a characteristic adult size These continue to grow throughout their adult life

91 Fecundity Depends on Age and Size Perennial plants delay flowering until they reach a sufficiently large size Many biennial plants delay flowering until environmental conditions become more favorable The difference in annual plant size is related to the number of seeds produced

92 Fecundity Depends on Age and Size Production of offspring increases with fish size (which increases with age) The number of eggs produced by loggerhead sea turtles is constrained by body size There is a positive relationship between body size and number of young produced by female big-handed crabs

94 Fecundity Depends on Age and Size There is a relationship between body size and fecundity for some endotherms The body weight of red squires is correlated with lifetime reproductive success

96 Food Supply Affects the Production of Young Food availability directly influences reproductive effort in species with indeterminate growth In environments in which resource availability varies, more offspring may be produced than can survive In asynchronous hatching, young are of several ages and the older ones are more likely to be fed when resources are limited Older or more vigorous young may kill their weaker siblings (siblicide)

98 Reproductive Effort May Vary with Latitude Birds in temperate regions have larger clutch sizes than those in lower latitudes Mammals at high latitudes have larger litters than those at lower latitudes Lizards, insects, and plants follow a similar pattern

100 Reproductive Effort May Vary with Latitude Why is there geographic variation in reproductive allocation? Three proposed hypotheses are offered to explain this pattern

101 Reproductive Effort May Vary with Latitude Clutch size is related to food supply more food is available in spring in temperate zones Periodic local climatic catastrophes (common in temperate regions) can restrict population size even when resources are plentiful organisms respond with larger clutches and a higher rate of population increase Clutch size is directly proportional to resource variation (food) and is inversely related to winter food supply

102 Habitat Selection Influences Reproductive Success Habitat selection is the process by which organisms actively choose a specific location to inhabit Habitat selection has a strong influence on reproductive success

103 Habitat Selection Influences Reproductive Success A wide variety of studies have been conducted for bird species that defend breeding territories These studies have demonstrated that: The selection of habitat is related to the vegetation structure Habitat selection involves a hierarchical approach that begins with a general landscape assessment Niche gestalt Birds select habitat on other factors Plant species that produce preferred items Cover, nesting, and perching sites

104 Habitat Selection Influences Reproductive Success Habitat selection is common to a wide variety of other animals Garter snakes select rocks of a certain size Aphids select the largest leaves Even if a given habitat is suitable, it still may not be selected Presence or absence of individuals of the species Presence of predators and human activity Available habitats range in quality from optimal to marginal First-come, first-served!

105 Habitat Selection Influences Reproductive Success Habitat selection by plants is limited (because of their sessile nature) to seed dispersal strategies

106 Environmental Conditions Influence the Evolution of Life History Characteristics Life history characteristics are the product of evolution and reflect adaptations to the prevailing environmental conditions Do species inhabiting similar environments exhibit similar life history patterns? Are life history characteristics related to the habitats that species occupy?

107 Environmental Conditions Influence the Evolution of Life History Characteristics The use of r- and K-strategies for comparing species across a wide range of sizes is limited The concept of r and K is most useful in comparing taxonomic or functionally similar organisms The spotted and redback salamanders

The Land Plants. Chapter 23 Part 2

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