Lecture 20: Reproduction II Flashcards
(52 cards)
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