Lecture 6 - sexual selection Flashcards

1
Q

describe darwins theory of natural selection

A
  • the fittest individuals will survive and reproduce

- succeeding generations will become adapted to their environment

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2
Q

what was darwins problem with the theory of natural selection?

A

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

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3
Q

what is darwins theory of sexual selection

A

“a struggle between the individuals of one sex, usually the males, for possession of the other sex”

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4
Q

what is male- male competition?

A

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

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5
Q

what is female choice?

A

intersexual selection-

Choice, by one sex, of mates of the other sex

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6
Q

why did it take a while for female choice to be accepted?

A

many old male scientists doubted that the course of evolution could be determined by females

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7
Q

what are secondary sexual characters?

A

characters not obviously used for reproduction e.g. size, fighting ability, courtship behaviour

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8
Q

what are primary sexual characters?

A
  • directly linked to reproduction e.g. genitalia size
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9
Q

what caused the evolution of sexual dimorphism?

A
  • competition of mates - only the ones competing have over the top, garish traits
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10
Q

how can you understand the basis of sexual selection?

A

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

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11
Q

describe bateman (1948) experiment with drosophila on potential reproductive rates

A

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
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12
Q

what is the most basic form of male-male competition?

A

direct physical contests among the members of one sex, over access to mates

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13
Q

describe male-male competition in elephant seals

A
  • 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
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14
Q

what does mating in male elephant seals select for?

A

extreme selection to grow large - however some males dont both growing large and sneak copulations in the sea

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15
Q

when does large sizes in elephant seals only occur?

A

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

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16
Q

what did the experiment on male-male competition in Bufo Bufo toads demonstrate?

A

there was greater sexual dimorphism in species with alot of competition - the pattern wasnt the same in monogamous species

17
Q

what is the link between body size and harem size in pinnipeds?

A
  • as body size dimorphism increases harem size increases i.e. there is greater dimorphism between the sexes in polygynous species as there is less direct male-male competition in monogamous species
18
Q

describe the link in antler length and mating systems in deer

A
  • polygynous male deer species have larger antlers than expected for their body size and monogamous species have smaller antler than expected by body size
19
Q

what are two important points about sexual selection and dimorphism?

A
  • Sexual Selection doesn’t have to lead to Sexual Dimorphism
  • Sexual Dimorphism can arise from processes other than Sexual Selection e.g. if they occupy different niches ad therefore have different feeding patterns - could lead to different beak shape in a bird for example
20
Q

what is often hard to distinguish between when studying sexual selection?

A
  • Often difficult to distinguish between male-male competition and female choice
  • Need to carry out experimental manipulations to show female choice with any degree of certainty
  • acceptance of partner isnt choice only rejection can be deemed as choice
21
Q

describe one of the first experiments to successfully demonstrate choice

A
  • Female long-tailed widowbirds come to a lekking and choose a dancing male
  • was notices females preferred males with long tails
  • to determine is this was because the long tailed males are better at competing or if its female choice they manipulated the males tail length and observed that females still had a preference for the elongated tails because the males themselves hadnt changed
22
Q

describe how investment in offspring effects competion/choice

A

Low investmentin offspring = competition
high investment in offspring = choice
equal investment in offspring = both sexes compete and both sexes choose

23
Q

describe sexual selection in crested auklets

A
  • Both sexes invest in the offspring
  • Both sexes have crests
  • both sexes compete and both choose
  • the crest ornament only grows in the breeding season
  • experiment displayed both sexes perform more courtship displays to long crested models = mutual mate choice
  • in both sexes long crested individuals are dominant = mutual competition
24
Q

what is sex role reversal

A

In some species males invest more in reproduction than females

25
Q

when is it predicted that sex role reversal will occur

A
  • There will be sex role reversal in species in which males invest a lot in offspring.
  • Females will compete and males will be choosy
26
Q

describe sex role reversal in pipefish

A
  • Males get “pregnant” and provide oxygen and nutrients to a clutch of eggs in an egg pouch
  • During male pregnancy, females can produce eggs to fill 2 male pouches. Given an even sex ratio, male pouch space is limited.
  • Males choose large females that produce more eggs than small ones
27
Q

what is choosiness dependent on in katydids?

A
  • males provide nuptial gift for female
  • choosiness of males is dependent on availability of resources for making the gift
  • when food is scarce males are more choosy and the females compete more
28
Q

describe sex role reversal in mormon crickets

A
  • mormon crickets and large and flightless
  • Males transfer a huge (25% body mass) edible spermatophore to females when they mate so they can only mate once.
  • Females can produce several clutches
  • therefore the males choose larger females that produce more eggs to be fertilised
  • mating aggregations occur where females compete for males - the operational sex ratio is female biased as the females can mate more than the males
29
Q

3 facts about sexual selection

A

1) Any pattern of choice and competition can occur
2) Each sex can play both roles

3) The environment can influence the pattern
of sexual selection