Mod 4. L27 Flashcards
reproduction in animals
Asexual reproduction
(before sexual reproduction)
genetically similar or identical copies of an individual organism are created Without genetic material from another
ex: binary fission, budding
binary fission
asexual reproduction
in bacteria (ex: E.coli)
DNA replication followed by cell division
Budding (in Hydra)
new organism develops from a bud (outgrowth) due to cell division
Some species of Hydra reproduce sexually under harsh conditions
swellings in body wall develop into ovary or testes -> gametes released into water (external fertilization)
sexual reproduction
2 gametes (sperm + ovum) fuse to form zygote
gametes generally from individuals of different sex
Pros:
- maximize genetic diversity
- better spatial spread of an individual’s genes
Cons:
- transmit fewer genes per offspring
- riskier (requires a mate)
- more costly
external fertilization
fusion of gametes outside the body
(mainly in water environments)
what is an impact on the evolution of sexual reproduction caused by the transition to land?
from external fertilization to internal fertilization
reasons:
- vulnerability of gametes to dehydration
- evolution of internal fertilization
innovations of internal fertilization (2)
1) Structural innovations like intromittent organs (e.g., penes) increase the efficacy of internal sperm transfer
2) behavioral innovations (e.g., courtship, phenotypes increasing access to females)
sex steroid hormones
steriod hormones are synthesized from chloesterol and are lipophlilic (hydrophobic)
involved in gametogenesis
synthesized by the gonads and brain
ex: progesterone, testosterone, estradiol
seminiferous tubules
the site of spermatogenesis
fill the testes of the human male, continuously producing millions of sperm.
as sperm mature, they move from the outer layer of the tubule toward the center, where they are shed into the lumen of the tubule
Leydig cells
testosterone levels
synthesize testosterone (and other androgens)
response to luteinizing hormone (LH)
Sertoli cells
testis size / spermatogenesis
promote and support spermatogenesis in response to follicle-stimulating hormone (FSH) and testosterone
Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH). [spermatogenesis]
LH -> Leidig cells
FSH -> sertoli cells
produces by the anterior pituitary
lead to the synthesis and release of testosterone from testes (males)
NEGATIVE FEEDBACK loop
(testosterone inhibits LH and FSH release)
secondary sex characteristivcs and male-typical sexual behavior (in males)
regulated by testosterone
Large body size and ornaments
aggression for secure resources and access to females
glucocorticoids
steriod hormones
released from the adrenal cortex
mediate stress responses
ex: cortisol (in primates), corticosterone (other animals)
stressors like dominance hierarchies can serve as long term chronic stressors influencie glucocorticoid levels
ex subordinate males in species living in social groups have lower testosterone levels
