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Lecture 20

BGYB51H3 Lecture 20 Notes Nov 17

Biological Sciences
Course Code
Maydianne Andrade

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BGYB51H3 Lecture 20 Notes
-sexual dimorphism is where males and females in a species have different features and
-males are more affectionate in that they seek out more mates to copulate
-sexual dichromatism is differences in colour
-structural dimorphism is differences in structure
-sexual size dimorphism is differences in behaviours
-many traits that are dimorphic reduce survival
-selection for survival unlikely explains differences between sexes
-differences in selective pressures are due to females investing more in offspring than males
-parental investment is anything that increases the chances of survival of current offspring
while decreasing the ability to produce future offspring
-females are defined as producing large and relatively few eggs while males have inexpensive
-usually maternal care is more than paternal care
-in any given species, sperm are present in excess compared to eggs
-male reproductive output is limited by access to eggs
-female reproductive output is limited by access to resources
-males can increase fitness by increasing mating fitness
-males have higher maximum reproductive output than females
-increasing the amount of mates a female acquires has little effect on reproductive output
-females have the same fitness as males although some males have variation in mating success
-sexual selection is a subset of natural selection that focuses on traits that have higher mating
-sexual selection has its strongest effects on the sex (male or female) whose reproductive
output is limited to access to mates
-intrasexual selection has success in competition for females being the agent of selection
-]vƵoo]}v]vÀ}oÀZu[ choosiness being the agent of selection
-members of the sex with more variable reproductive success will compete
-traits favoured in intrasexual selection are
x large body size
x armour
x weapons
-alternate tactics involve strategies that would normally be advantageous in competition but
are ways in which sneaky males can increase reproductive success
-sperm competition involves competition between sperm of different males that occurs
inside the body of the female
-different adaptations for sperm competition
-in intersexual selection, females are usually choosy and males try to convince them to mate
-traits favoured in intersexual selection are
x displays
x ornamentation
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