Lecture 20: Reproduction II Flashcards
there are multiple sex determination mechanisms observed in nature
- genetic sex determination
- environmental sex determination
- temperature sex determination
- social sex determination
genetic sex determination
the sex of an organism is determined by its chromosomes (XX for females and XY for males in humans)
environmental sex determination
environmental factors, such as temperature or social conditions, influence whether an organism develops as male or female
temperature dependent sex determination
sex is influences by the temperature during a key developmental period
examples of temperature dependent sex determination
in reptiles and alligators, the incubation temperature of eggs determines the sex of the offspring
social sex determination
an organism’s sex can change based on social interactions, like dominance shifts in groups
examples of social sex determination
- in clownfish, dominant individuals can change sex based on social hierarchies within their group
- some fish, mollusc, and other species
temperature-dependent sex determination in three species of reptiles: American alligator, red-eared slider turtle, and alligator snapping turtle
red-eared turtles
-abrupt change in temperature could affect the sex
- if the eggs are incubated below 28C, all turtles hatching under this temperature will be male
- temperature above 31C, the eggs will be female
- when temperature varies between 28C and 31C, the eggs with hatch to both sexes
Snapping turtles
- abrupt changes in temperature can affect the sex
- eggs incubated below 24C will result in all males
- eggs incubated above 28C will result in all females
- temperatures between 24C and 28C will yield both sexes
American alligator
- temperature plays a critical role in determining the sex
- eggs incubate below 30C will result in all females
- eggs incubated above 34C will result in all males
- temperatures between 30C and 34C will yield both sexes
nest site selection
the process by which an animal, particularly a female, chooses a location to lay eggs or give birth based on environmental factors that maximize the survival and health of their offspring
maternally selected nest
a nest site chosen by the mother based on environmental factors like temperature, which can enhance the chances of survival and success for her offspring
randomly selected nest
a nest site chosen without consideration for optimal conditions, which may result in lower survival rates or compromised offspring health
oviposition
the act of laying eggs
incubation
the period during which eggs are kept warm and protected, allowing embryos inside to develop
maternal and random incubation x proportion surviving
- maternal incubation leads to a higher survival rate of offspring compared to random incubation
- this suggests that when mothers actively choose the nest site, conditions are more favorable for embryo development, leading to better overall success
maternal and random incubation x proportion male
- maternal incubation results in a lower proportion of males compared to random incubation
- nest site selection affects sex ratios – possibly tied to temperature-dependent sex determination (TSD)
external fertilization
- a mode of reproduction in which a male organism’s sperm fertilizes a female organism’s egg outside of the female’s body
examples of external fertilization
- reproductive process of some fish: the female release unfertilized eggs into the water, male releases sperm over the eggs, embryos develop from the fertilized eggs, this leads to the birth of new individual fish
- in frogs: male on females back, both release
internal fertilization
a mode of reproduction in which a male organism’s sperm fertilizes a female organism’s egg inside of the female’s body
examples of internal fertilization
- chickens
eggs are very different among species
fish eggs: small, round, translucent, visible eyes inside the eggs, indicating early development stages
amphibian eggs: clustered in gelatinous masses, also feature visible eyes in developing embryos
reptile eggs: larger, oval shaped with white shells, reptiles hatch breaking egg
amniotic egg
- a type of egg that allows organisms, such as reptiles, birds, and mammals, to reproduce on land
- air breathing egg
- named for amnion, but shell (chorion) was also an important evolutionary development
components of the amniotic egg
amnion, allantois, chorion, yolk sac, yolk, embryo, amniotic cavity with amniotic fluid
amnion
forms a protective fluid filled sac around the embryo, preventing desiccation and providing cushioning
allantois
serves as a storage for waste products and assists in gas exchange
chorion
outermost membrane that allows oxygen and carbon dioxide to diffuse between the egg and the environment
yolk sac
contains the yolk, which provides nutrients to the growing embryo
embryo
- developing organism in egg
- grows through cell division and differentiation, eventually forming into a fully developed animal
- the embryo relies on the surrounding structures for nutrition and protection
yolk
- nutrient rich substance inside the yolk sac
- provides energy and essential nutrients that the embryo needs for growth and development during its time in the egg
amniotic cavity
- the space within the amnion that is filled with amniotic fluid
- the fluid cushions that embryo, providing protection against physical shocks and maintaining a stable environment
- prevents desiccation and allows the embryo to move, aiding its development
oviparous
- egg laying
- reproductive method where eggs are laid outside the body, and the embryo develops externally
examples of oviparous
birds, some reptiles
viviparous
- producing living young and not eggs
- reproductive strategy involving live births, where embryos develop inside the parent’s body
examples of viviparous
some reptiles, humans
ovoviviparous
- producing live young from eggs that hatch within the body
- combines elements of oviparous and viviparous
examples of ovoviviparous
some sharks and reptiles
comparison of oviparity and viviparity
oviparity:
- energetically inexpensive
- variable offspring survival
viviparity:
- energetically expensive
- allows for behavioral thermoregulation (the ability to regulate the temperature of their developing embryos through actions like seeking shade or warmth)
- high offspring survival
precocial young
young animals that are relatively mature and can mostly feed themselves
examples of precocial young
ducklings
altricial young
young animals that are helpless, underdeveloped, and require extensive parental care
examples of altricial young
baby birds
yolk content
- percentage of the yolk in an egg, providing nutrition to the developing embryo
- higher yolk percentages often lead to more independent hatchlings
examples of different yolk content %
20% = bohemian waxwing
30% = arctic tern
40% = ruddy duck
50% = malleefowl
70% = brown kiwi
figure 9.15: gestation and lactation
- highlights the differences between marsupial and placental mammals in gestation and lactation periods
- marsupials (marsupial mouse and wallaroo) have shorter gestation periods but longer lactation periods compared to placental mammals (southern grasshopper mouse and Thomson’s gazelle)
anatomy of an egg
germinal disc (nucleus), calcareous shell, albumen (egg white), yolk
pores of the eggshell
allow gas exchange (O2 and CO2) between the internal environment and the exterior
eggs dry out
there is no way to add moisture, the mom gives the requirements when the egg is formed
adaptations for water loss in avian eggs
- high altitude eggs lose water most rapidly
- sea level eggs show moderate water loss
- red winged blackbird eggs lose the least amount of water
- differences are a result of the structure including the texture and pores of the eggshell
mammalian vs reptilian/avian egg
- smaller
- less yolk
- uterine secretions
- altricial
functions of the placenta
- nutrient exchange
- respiratory exchange
- excretory exchange
- barrier
- anchor
- suppress maternal immune system
- endocrine organ
choriovitelline placenta
- a placenta type connected to the yolk sac, providing initial nourishment to the embryo, commonly found in marsupials
chorioallantoic placenta
a more advanced placenta type associated with the allantois, allowing efficient nutrient and gas exchange, typical of placental mammals
choriovitelline vs chorioallantoic
choriovitelline:
- mammals = marsupials
- gestation time = short
- attachment intensity = low
- chance of immunorejection = low
- nutrient flow = low
- developmental stage/size at birth = small
- risk of hemorrhaging/bleeding = low
chorioallantoic:
- mammals = placental mammals
- gestation time = long
- attachment intensity = high
- chance of immunorejection = high
- nutrient flow = high
- developmental stage/size at birth = more developed/large
- risk of hemorrhaging/bleeding = high
