Reproduction and Development in the Animal Kingdom
Chapter 36: Reproduction and Development in Animals
Introduction
Lecture Presentations by Kathleen Fitzpatrick (Simon Fraser University) and Nicole Tunbridge (Kwantlen Polytechnic University)
Copyright © 2025, 2020, 2016 Pearson Education, Inc.
Concept 36.1: Asexual and Sexual Reproduction in Animals
Sexual Reproduction: The creation of offspring by the fusion of male gametes (sperm) and female gametes (egg) to form a zygote.
Asexual Reproduction: The creation of offspring without the fusion of egg and sperm.
Mechanisms of Asexual Reproduction (1 of 2)
Budding: New individuals arise from outgrowths of existing ones, commonly observed in invertebrates.
Fission: Separation of a parent organism into two approximately equal-sized individuals, also common in invertebrates.
Example - Hydra Budding
Observation of a Hydra undergoing budding, showcasing a common mode of asexual reproduction.
Example - Sea Anemone Fission
Visual representation of a sea anemone undergoing fission.
Mechanisms of Asexual Reproduction (2 of 2)
Fragmentation: The breaking of the body into pieces, where some or all can develop into adults, requiring regeneration.
Parthenogenesis: Development of a new individual from an unfertilized egg, occurring in some vertebrates under low population density conditions.
Sexual Reproduction
Involves fertilization where an egg of one parent is fertilized by sperm of another parent.
Fertilization Types:
External Fertilization: Eggs are fertilized outside the female body (e.g., fish, amphibians).
Internal Fertilization: Sperm deposited in or near the female reproductive tract results in fertilization within the tract.
Animals typically produce gametes in specialized organs called gonads:
Testes: Produce sperm.
Ovaries: Produce eggs.
Copulation: Sexual union that facilitates the reception of sperm.
Sexual Reproduction: Evolutionary Enigma
Sexual reproduction results in varied genotypes among offspring, potentially enhancing reproductive success in changing environments.
Asexual reproduction may be more advantageous in stable, favorable environments.
Variation in Patterns of Sexual Reproduction (1 of 2)
Finding a partner for sexual reproduction can be challenging for many animals.
Hermaphroditism: Each individual has male and female reproductive systems, enabling mating compatibility between any two hermaphrodites. Some can self-fertilize.
Variation in Patterns of Sexual Reproduction (2 of 2)
Some species undergo sex reversals:
Example: Bluehead wrasse, a coral reef fish, can transform the largest female into a male if the defending male dies, able to produce sperm within a week.
External and Internal Fertilization (1 of 3)
Fertilization is essential for sexual reproduction and occurs via:
External Fertilization: Requires a moist habitat to prevent drying out gametes, applicable to many aquatic invertebrates that release gametes into water.
External and Internal Fertilization (2 of 3)
Timing is crucial for gamete release to ensure sperm and egg encounter each other.
Internal Fertilization: Enables efficient sperm transport to eggs, even in dry environments.
Concept 36.2: Reproductive Organs Produce and Transport Gametes
Sexual reproduction relies on designated cells that produce eggs and sperm.
Many animals possess gonads for gamete production, with more elaborate systems including accessory tubes and glands for nourishment and protection of gametes and embryos.
Human Male Reproductive Anatomy
External reproductive organs: Scrotum and penis.
Internal structures:
Gonads: Produce sperm and hormones.
Accessory Glands: Secrete essential products for sperm movement.
Ducts: Carry sperm and glandular secretions.
Testes
Male gonads, or testes, produce sperm in coiled tubes called seminiferous tubules; require cooler temperatures than core body temperature.
The scrotum maintains testis temperature for optimal sperm production.
Ducts
Sperm from seminiferous tubules pass into the epididymis for maturation.
Upon ejaculation, sperm travel through the vas deferens and ejaculatory duct to exit the body via the urethra.
Accessory Glands
Semen Composition: Includes sperm and secretions from:
Seminal Vasicles: Contribute about 60% of semen volume.
Prostate Gland: Secretes products into the urethra.
Bulbourethral Glands: Secrete a clear mucus to neutralize urine acidity in the urethra.
Penis Structure
Comprised of three cylinders of spongy erectile tissue and urethra; during arousal, blood fills erectile tissue, causing erection.
Human Female Reproductive Anatomy
External reproductive structures: Clitoris, labia majora, labia minora.
Internal structures: A pair of gonads (ovaries) and a duct system for carrying gametes and supporting embryonic development.
Ovaries
Female gonads located in the abdominal cavity, packed with follicles comprising oocytes and support cells that protect and nourish the developing egg.
Oviducts and Uterus
Mature egg moves from the ovary to the uterus via th oviduct.
Cilia in the oviduct aid in egg transport; the uterus has a richly vascularized lining called the endometrium.
Vagina and Vulva
Vagina: Elastic chamber hosting sperm and serving as birth canal.
Vulva: External female genitalia including labia, hymen, and clitoris.
Gametogenesis (1 of 3)
Gametogenesis is the production of gametes, closely linked to gonad structure and function.
Gametogenesis (2 of 3)
Spermatogenesis: Development of sperm, costs about 7 weeks, continuous, and prolific—millions produced daily; all four meiotic products develop into mature gametes.
Human Spermatogenesis Overview
Primordial Germ Cells develop to Spermatogonial Stem Cells via mitosis.
Spermatogonia divide to produce Primary Spermatocytes.
Meiosis I produces Secondary Spermatocytes followed by Meiosis II producing Spermatids.
Maturation yields Sperm Cells with a distinct structure (head, midpiece, tail).
Gametogenesis (3 of 3)
Oogenesis: Development of mature eggs, a lengthy process with immature eggs in embryos that don’t mature until years later. Only one meiotic product becomes the egg, unlike spermatogenesis.
Concept 36.3: Hormonal Control in Mammals (1 of 3)
Reproduction is regulated by hormones from the hypothalamus, anterior pituitary, and gonads, primarily Gonadotropin-Releasing Hormone (GnRH), which stimulates release of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
Concept 36.3: Hormonal Control in Mammals (2 of 3)
FSH & LH: Act on gonads regulating production of sex hormones like…
Androgens: e.g., Testosterone.
Estrogens: e.g., Estradiol, Progesterone.
Both genders produce androgens and estrogens but at differing concentrations.
Concept 36.3: Hormonal Control in Mammals (3 of 3)
Hormones directly and indirectly regulate gamete production along with influencing sexual behavior and development of sex characteristics.
Androgens stimulate male sexual behaviors while estrogens do so in females.
Biological Sex, Gender Identity, and Sexual Orientation in Humans (1 of 4)
Biological Sex: Assigned at birth based on genitalia and chromosomes; influenced by the SRY gene for gonadal development into testes.
Biological Sex, Gender Identity, and Sexual Orientation in Humans (2 of 4)
Intersex individuals (1 in 100) may have both male and female characteristics and atypical chromosome configurations.
Biological Sex, Gender Identity, and Sexual Orientation in Humans (3 of 4)
Gender Identity: Internal sense of being male, female, both, or neither; distinctions:
Cisgender: Identity aligns with assigned sex.
Transgender: Identity does not match assigned sex.
Biological Sex, Gender Identity, and Sexual Orientation in Humans (4 of 4)
Sexual Orientation: Defines romantic, emotional, or sexual attraction, encompassing:
Heterosexual, Homosexual, Bisexual, Asexual.
Human sexuality exhibits considerable variation.
Hormonal Control in Male Reproductive System (1 of 2)
FSH & LH direct spermatogenesis in testes:
Sertoli Cells: Nourish developing sperm in response to FSH.
Leydig Cells: Secrete testosterone under LH influence to promote spermatogenesis.