Chapter 46 Animal Reproduction

Reproduction Asexual (one parent)  fission (ex. Bacteria: parent separates into 2 cells)  budding (ex. Hydra: new splits off from old)  gemmules (ex. Sponges: cells come together and become enclosed in protective coat)  fragmentation & regeneration (ex. Starfish: full body grows from a fragment) Sexual (fusion of haploid gametes)  gametes (sex cells)  zygote (fertilized egg)  ovum (unfertilized egg)  spermatozoon (male gamete)

Reproductive Cycles and Patterns Parthenogenesis  unfertilized egg development; haploid, sterile adults (honeybees) Hermaphroditism  both male & female reproductive systems; sessile & burrowing organisms (earthworms) Sequential hermaphroditism  reversal of gender during lifetime protogynous (female 1st) protandrous (male 1st)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig Mechanisms of sexual reproduction Fertilization  (union of sperm and egg) 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.

Mechanisms of sexual reproduction Internal fertilization requires cooperative behavior 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. Parental care of offspring may occur regardless of whether fertilization is external or internal. Pheromones  chemical signals that influence the behavior of others (mate attractants)

 The least complex reproductive systems lack gonads.  Polychaete worms lack gonads.  Eggs and sperm develop from undifferentiated cells lining the coelom (body cavity). Some reproductive systems, such as that seen in parasitic flatworms, can be very complex. Evolution of reproductive system in animals Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 46.6

 Most insects have separate sexes with complex reproductive systems.  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

 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.

Mammalian reproduction: Male Testes: male gonads Seminiferous tubules: location of sperm formation Leydig cells: hormone production Scrotum  contains the testes, outside of the body  maintain temperature Epididymis  sperm development Vas deferens  sperm propulsion Penis/urethra  semen delivery

Mammalian reproduction- Human Male Seminal vesicles: thick alkaline fluid contains fructose Prostate gland: anticoagulant enzymes and citrate (nutrient) Bulbourethral glands: acid (urine) neutralizer

 The Male Pattern.  Androgens secreted by Leydig cells are responsible for primary and secondary sex characteristics.  Primary sex characteristics:  Development of the vasa deferentia and other ducts.  Development of the external reproductive structures  Sperm production.  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. A complex interplay of hormones regulates reproduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig (Gonadotropic Releasing Hormone) Follicle Stimulating Hormone Luteinizing Hormone

Spermatogenesis Puberty until death! Seminiferous tubules ~ location Primordial germ cell (2N)~ differentiate into…. Spermatogonium (2N) ~ sperm precursor  Repeated mitosis: large numbers, differentiate into…. Primary spermatocyte (2N)  1 st Meiotic division forms.. 2 Secondary spermatocytes (1N)  2 nd meiotic division forms.. 4 Spermatids (1N) differentiate into 4 Sperm cells (1N)

Mammalian reproduction: Female Ovaries: female gonads  Follicle: egg capsule  Corpus luteum: hormone secretion Oviduct: fertilization Uterus/endometrium: womb/lining Cervix/vagina: sperm receptacle

The Female Pattern  A cyclic pattern of hormone secretion and reproductive events.  Humans and many other primates have menstrual cycles.  If pregnancy does not occur the endometrium is shed through the cervix and vagina: menstruation.  Other mammals have estrous cycles.  If pregnancy does not occur the endometrium is reabsorbed by the uterus.  Associated with more pronounced behavioral cycles than are menstrual cycles.  More pronounced seasonal and climatic effects than seen associated with menstrual cycles.  Humans females may be sexually receptive throughout their cycles.  Most mammals will copulate only during the period surrounding ovulation.  This period of sexual activity is called estrus.

A complex interplay of hormones regulates reproduction  Hormonal coordination of the menstrual and ovarian cycles involves five hormones.  Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus.  Follicle-stimulating hormone (FSH) secreted by the anterior pituitary.  Luteinizing hormone (LH) secreted by the anterior pituitary.  Estrogens secreted by the ovaries.  Progesterone secreted by the ovaries.

Female Pattern Ovarian/Menstrual cycles  follicular phase: follicle growth  Ovulation: oocyte release  luteal phase: hormone release

 Estrogens are also responsible for female secondary sex characteristics.  Deposition of fat in the breasts and hips.  Increased water retention.  Affects calcium metabolism.  Stimulates of breast development.  Mediates female sexual behavior. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Secondary Sex Characteristics

Oogenesis In the ovaries of the embryo: Primordial germ cells (2N) Oogonium (2N) Primary oocyte (2N)  Between birth & puberty; remain in prophase I of meiosis  Puberty; FSH; completes meiosis I Secondary oocyte (1N) and 1 st polar body  Continues through menopause  Meiosis II; stimulated by fertilization Ovum (1N); 2 nd polar body

Embryonic & fetal development Gestation ~ length of pregnancy 1st trimester:  organogenesis fetus (week 8; all adult features) HCG hormone (menstruation override; pregnancy test detection) Parturition ~birth Labor ~uterine contractions Lactation ~prolactin & oxytocin

Modern technologies