BIOL 240M Chapter Notes - Chapter 46: Female Reproductive System, Bluehead Wrasse, Vas Deferens

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6 Feb 2017
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Animal Reproduction
I. Both Asexual and Sexual Reproduction Occur in the Animal Kingdom
a. Modes of reproduction
i. Sexual the fusion of haploid gametes forms a diploid cell, the
zygote
1. Female Gamete egg, large and nonmotile
2. Male Gamete sperm, small and motile
ii. Asexual new individuals are generated without fusion of egg and
sperm
1. Relies entirely on mitotic cell division
b. Mechanisms of Asexual Reproduction
i. Invertebrates
1. Budding new individuals arise from outgrowths of
existing ones
a. Stony corals
2. Fission separation of a parent organism into two
identical individuals of equal size
ii. Two-Step Process
1. Fragmentation breaking of body into several pieces
2. Regeneration regrowth of lost body parts
a. Numerous sponges, cnidarians, tunicates
iii. Parthenogenesis egg develops without being fertilized
1. Bees, wasps, ants
2. Among vertebrates, parthenogenesis is extremely rare
a. Komodo dragon and hammerhead shark
b. Females were isolated from males, but still
rarely produced offspring
c. Sexual Reproduction: An evolutionary Enigma
i. Hypotheses focus on unique combination of parental genes
forming during meiotic recombination and fertilization
1. Increasing reproductive success when environmental
factors change
2. Asexual is most beneficial when environmental
conditions remain stagnant
d. Reproductive Cycles
i. Hormones
1. The secretion can be regulated from seasonal changes,
when energy is or is not available
ii. Ovulation the release of mature eggs
iii. Sexual and Asexual Reproduction
1. The water flea (Daphnia) produces eggs of two types
a. Requires fertilization to develop
i. When environment is unfavorable
b. Undergoes parthenogenesis
i. When environment is favorable
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2. Whiptail lizards (Aspidoscelis) undergoes only asexual
reproduction, no males
a. Sometimes, one "acts" like a male
i. Believed to occur because the
parthenogenetic lizards could have
evolved from species with two sexes,
sexual stimuli still required for maximum
reproduction
e. Variation in Patterns of Sexual Reproduction
i. Sometimes finding a sexual partner is challenging; evolution
made hermaphroditism each individual has both male and
female reproductive systems
1. Therefore, any two individuals can mate with each
other
2. Bluehead wrasse (Thalassoma bifasciatum)
a. Live with several females per male
b. When male dies, biggest female becomes male
3. Certain oyster species undergo sex reversal
a. Individuals reproduce as males, then later as
females when size maximized
i. This maximizes gamete production
ii. Result: enhanced reproductive success
because oysters release gametes into
surroundings rather than mating directly
II. Fertilization depends on mechanisms that bring together sperm and eggs of
the same species
f. Fertilization union of sperm and egg
i. External female releases eggs into environment where male
then fertilizes them
1. Always requires moist habitat
2. Spawning individuals clustered in the same area
release gametes into the water at the same time
ii. Internal sperm are deposited in or near the female
reproductive tract (fertilization occurs within tract)
1. Requires cooperative behavior that leads to copulation
2. Requires sophisticated and compatible reproductive
systems
iii. Both release pheromones chemicals released by one
organism that can influence the physiology and behavior of
other individuals of the same species
1. Small, volatile or water-soluble molecules that are
active at very low concentrations
g. Ensuring the survival of offspring
i. Internal fertilization produces fewer gametes than external
fertilization
1. Results in survival of higher fraction of zygotes
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2. Zygotes are protected when fertilized internally from
predation
ii. Some animals retain embryo for a portion of development
1. Marsupial mammals such as kangaroos spend short
period in uterus as embryos
2. Then crawl out and finish development attached to a
mammary gland in mother's pouch
h. Gamete Production and Delivery
i. Gonads organs that produce gametes, found in many but not
animals
1. Cycles of growth and mitosis then amplify number of
cells available for making eggs or sperm
ii. Insect species
1. Female reproductive system includes one or more
spermathecae sacs in which sperm may be stored for
extended periods
iii. Vertebrate reproduction
1. Nonmammalian
a. Digestive, excretory, and reproductive systems
have a common opening to the outside cloaca
structure probably present in all vertebrates in a
common ancestor
III. Reproductive organs produce and transport gametes
i. Human Male Reproductive Anatomy
i. Overview
1. External organs: scrotum and penis
2. Internal organs: gonads that produce sperm and
reproductive hormones, accessory glands that secrete
semen contents, and ducts that carry sperm and
glandular secretions
ii. Testes
1. Male gonads (testes) produce sperm in highly coiled
tubes called seminiferous tubules
2. Scrotum, a fold of the body wall, keeps testes 2 degrees
C below body core body temperature
iii. Ducts
1. Epididymis sperm pass into coiled duct from
seminiferous tubules
a. 3 weeks to travel through 6 meters, undergo
maturation
2. Vas deferens during ejaculation, sperm are propelled
from each epididymis through this muscular duct
3. Ejaculatory duct has both vas deferens join from the
seminal vesicle and open into the urethra outlet tube
for both excretory and reproductive system
iv. Accessory Glands
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