1. CHAPTER 46 ANIMAL REPRODUCTION Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: Overview of Animal Reproduction 1. Both asexual and sexual reproduction occur in the animal kingdom 2. Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly 3. Reproductive cycles and patterns vary extensively among mammals

2.  Asexual reproduction involves the formation of individuals whose genes all come from one parent.  There is no fusion of sperm and egg.  Sexual reproduction is the formation of offspring by the fusion of haploid gametes.  Ovum: female gamete - usually large and nonmotile.  Spermatozooan: male gamete - usually small and motile.  Sexual reproduction increases genetic variation among offspring.  Oogenesis in female and spermagenesis in males both involve meiosis but differ in three significant ways Both asexual and sexual reproduction occur in the animal kingdom Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

3.  Invertebrates:  Fission: asexual reproduction in which a parent separates into two or more approximately equal sized individuals.  Budding: asexual reproduction in which new individuals split off from existing ones.  Gemmules of sponges are an example of a type of asexual reproduction that involves the release of specialized cells that can grow into new individuals. Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

4.  Fragmentation: the breaking of the body into several pieces, some or all of which develop into complete adults.  Requires regeneration of lost body parts.  Advantages of asexual reproduction:  Can reproduce without needing to find a mate  Can have numerous offspring in a short period of time  In stable environments, allows for the perpetuation of successful genotypes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

5.  Reproductive cycles are controlled by both environmental and hormonal cues to ensure both sexes are sexually mature at same time and are both in the same location so mating can occur.  Animals may be solely asexual or sexual.  Or they may alternate between the two modes depending on environmental conditions.  Daphnia reproduce by parthenogenesis under favorable conditions and sexually during times of environmental stress. Reproductive cycles and patterns vary extensively among animals Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

6.  Sexual reproduction in sessile or burrowing animals or parasites who may have difficulty encountering a member of the opposite sex. –Hermaphroditism: one individual is functional as both a male and a female.  Some self-fertilize.  Most mate with another member of the same species.  Each individual receives and donates sperm.  Results in twice as many offspring as would occur if only one set of eggs were fertilized. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

7.  Sequential hermaphroditism: an individual reverses its sex during its lifetime.  Protogynous: female first sequential hermaphroditism. Protandrous: male first sequential hermaphroditism. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8.  Parthenogenesis is the process by which an unfertilized egg develops into (often) haploid adult.  Parthenogenesis plays a role in the social organization of species of bees, wasps, and ants.  Male honeybees are haploid and female honeybees are diploid.  Several genera of fishes, amphibians, and lizards produce by a form of parthenogenesis that produces diploid zygotes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. Section B: Mechanisms of Sexual Reproduction 1. Internal and external fertilization both depend on mechanisms ensuring that mature sperm encounter fertile eggs of the same species 2. Species with internal fertilization usually produce fewer zygotes but provide more parental protection than species with external fertilization 3. Complex reproductive systems have evolved in many animal phyla

10. Fig. 33.7, A hydrozoan, Obelia, Cnidaria Hydras, among the few freshwater cnidarians, are unusual members of the class Hydrozoa in that they exist only in the polyp form. –When environmental conditions are favorable, a hydra reproduces asexually by budding, the formation of outgrowths that pinch off from the parent to live independently. –When environmental conditions deteriorate, hydras form resistant zygotes that remain dormant until conditions improve. Hydra

11.  Internal fertilization usually results in the production of fewer zygotes than does internal fertilization.  However, the survival rate is lower for external fertilization than it is for internal fertilization.  There are many examples of both internal and external fertilization among the taxa of several Phyla Species with internal fertilization usually produce fewer zygotes but provide more parental protection than species with external fertilization Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. http://sps.k12.ar.us/massengale/earthworm_dissection.htm Earthworms are hermaphroditic meaning each worm has organs of both sexes. The male gonopores are usually within the first 12-15 segments, and the female gonopores are further back, close to the clitellum (the swollen area in adult worms). One worm has to find another worm and they mate juxtaposing opposite gonadal openings exchanging packets of sperm, called spermatophores. Some species also appear to be either parthenogenetic (females producing all females, "virgin birth") or may be able to self-fertilize.

13. The clitellum produces a mucous sheath and nutritive material, and as the sheath slides forward, it picks up ova from the earthworm's ovaries then packets of sperm that had been transferred to the worm from another worm during mating. As the sheath slides off the worm’s head, the ends are sealed to form the cocoon. Initially, the cocoon is quite soft but soon after it is deposited in the soil it becomes slightly amber in color, leather-like and very resistant to drying and damage. http://sps.k12.ar.us/massengale/earthworm_dissection.htm

14. Most Insects have internal fertilization, with complex reproductive systems, and generally with separate sexes  In many species the female reproductive system includes a spermatheca, a sac in which sperm may be stored for a year or more. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 46.7

16.  The basic plan of all vertebrate reproductive systems are very similar.  However, there are variations.  In many non-mammalian vertebrates the digestive, excretory, and reproductive systems share a common opening to the outside, the cloaca.  Mammals have separate opening for the digestive and reproductive systems.  Female mammals also have separate openings for the excretory and reproductive systems. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

17.  External fertilization requires a moist habitat that will protect a developing egg from desiccation and heat stress. –Specific mating behaviors assure that sperm and egg will be in the same place at the same time. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 46.4

18. Most fish have separate sexes but some can switch from male to female. The vast majority of fish have external fertilization and most have no parental care but some have quite a high degree of parental care, e.g., sea horses.

19. Terrestrial reproduction in vertebrates requires them to have internal fertilization. Also the resulting zygote must be retained internally or encapsulated in an egg that can protect the zygote and developing embryo. The embryo retained internally receives nutrients, and oxygen from the mother who in turn removes carbon dioxide and waste products from embryo. The embryo developing in an egg must have all nutrients encapsulated with it, be able to exchange gases through the shell, not loose or gain excess water, and produce a non-toxic waste product of metabolism that is retain inside the egg.

20. Fig. 46.14  Secondary sex characteristics:  Deepening of the voice.  Distribution pattern of facial and pubic hair.  Muscle growth.  Androgens are also responsible for sexual behavior and general aggressiveness. Spermatogenesis in male and oogenesis in female both involve meiosis A complex interplay of hormones regulates reproduction Fig. 46.15

21. Fig. 46.11 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Overview of development of spermatogenesis in human male

22. Fig. 46.13 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The overview of the development of the ovum in the human female ovary The process of Oogenesis is the production of ova from oogonia.

23. Fig. 46.8 Male reproductive organs

24. Fig. 46.9 Fem ale reproductive organs

25. Sexual behaviour in humans differs from many animals in that it can occur at any time of the year and not always for the purpose of fertilization of eggs. This in part may relate to pair bonding where the young have a long maturation period under parental care where both parents would have been required. Thus unlike many other vertebrates there is not a defined reproductive period that is controlled by environmental factors, such as light and etc.

26. Fig. 46.16 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Embryonic and fetal development occur during pregnancy in humans and other eutherian (placental) mammals In placental mammals, pregnancy is the condition of carrying one or more embryos. Pregnancy is preceded by conception and continues until birth. A human pregnancy averages 266 days. Fertilization occurs in the oviduct. 24 hours latter the zygote begins cleavage. 3- 4 days after fertilization the zygote that reaches the uterus the embryo is a ball of cells.It takes about 1 week past fertilization for the blastocyst to form. After 5 more days it implants in the endometrium.

27. The placenta provides for the diffusion of material between maternal and embryonic circulations. Placenta secretes progesterone, which maintains the pregnancy.

28.  Hormonal regulation of birth. Fig. 46.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

29. Fig. 46.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Control measures used to prevent pregnancy in humans and in other animals as well