Lecture 6 - sexual selection Flashcards
describe darwins theory of natural selection
- the fittest individuals will survive and reproduce
- succeeding generations will become adapted to their environment
what was darwins problem with the theory of natural selection?
The problem with the theory of natural selection is that it can’t explain costly traits that lower an individual’s survival
e.g. peacocks tail - costly to clean, carry and attracts attention of predators
what is darwins theory of sexual selection
“a struggle between the individuals of one sex, usually the males, for possession of the other sex”
what is male- male competition?
intrasexual selection-
Competition between members of the same sex - can be in obvious forms such as males fighting or less obvious e.g. impressive characters
what is female choice?
intersexual selection-
Choice, by one sex, of mates of the other sex
why did it take a while for female choice to be accepted?
many old male scientists doubted that the course of evolution could be determined by females
what are secondary sexual characters?
characters not obviously used for reproduction e.g. size, fighting ability, courtship behaviour
what are primary sexual characters?
- directly linked to reproduction e.g. genitalia size
what caused the evolution of sexual dimorphism?
- competition of mates - only the ones competing have over the top, garish traits
how can you understand the basis of sexual selection?
to understand you must look at the fundamental differences between the sexes i.e. anisogamy = non identical gametes - females produce few costly eggs and males have small mobile sperm - males can generally fertilise eggs at a faster rate than females can produce them
describe bateman (1948) experiment with drosophila on potential reproductive rates
the number of offspring produced by the male drosophila increased linearly with the number of copulations
- Males have a higher potential reproductive rate than females
- So males compete and females choose (leads to sexual dimorphism) - females arent going to waste their costly eggs
- female= quality male = quantity
what is the most basic form of male-male competition?
direct physical contests among the members of one sex, over access to mates
describe male-male competition in elephant seals
- Male elephant seals can weigh 2000kg and they fight vigorously
- The winner (beachmaster) has a harem of dozens of females
- Other males get few or no matings
- in this case size makes a male dominant/successful as increased dominant rank results in increased copulations
- DNA analysis shows mating success is directly linked to paternity
what does mating in male elephant seals select for?
extreme selection to grow large - however some males dont both growing large and sneak copulations in the sea
when does large sizes in elephant seals only occur?
only occur when they can monopolise a large area of females otherwise its not worth it - e.g. a beach - cant monopolise an area in the sea