6: Sexual selection Flashcards
what is Darwin’s theory of NS? (2)
- the fittest individuals will survive and reproduce
- succeeding generations will become adapted to their environment
what is the problem with NS, also known as the peacocks tail?
it cant explain costly traits that lower an individual’s survival
what is SS and what are the 2 main types?
a struggle between the individuals of one sex, usually males, for possession of the other sex, resulting in differential reproductive success
- male male competition (intrasexual) same sex
- female choice (inter) one sex chooses mate of another sex
what are secondary sexual characters?
distinguishes between the sexes but is not directly linked to reproduction
- size, colouration , courtship displays
give 3 examples of secondary sexual characters
- salmon: males have hooked jaw and red colouration in spawning season
- moose: antlers for display
- wilson’s bird of paradise: bright plumage
what is the basis for SS, causing it to arise?
Anisogamy
allows SS to act differently on the 2 sexes
what is anisogamy?
different sized gametes
what can it lead to if the male competes and the female chooses?
sexual dimorphism
what did Bateman 1948 discover about the potential reproductive rate in Drosophila? (5)
- after first copulation little change in number of offspring produced by females
- male reproductive success increased linearly with copulations
- males have higher potential reproductive rate than females
- female success limited by number of eggs can produce
- leads to female choosing the best male
what is the sexual dimorphism in mallard ducks?
females plain and males have bright plumage
males show courtship behaviour
what is the most basic form of male-male competition?
direct physical contests among members of one sex over access to mates
what did Le Boeuf 1974 fins when studying elephant seals in California? (5)
- males can weigh 2000kg
- fight vigorously
- winner/beachmaster has harem of dozens of females
- other males get few/no mating
- males compete for harems with violent fights
what did McCann discover when studying competition and dominance in elephant seals on south Georgia? (5)
- males fight to become dominant
- dominance correlated with mating success
- higher dominance rank = more copulations
- DNA analysis shows mating success linked to paternity
- location important as large males selected for on the beach but smaller males when in the sea as can sneak up on females
what did Davies and Halliday 1978 discover about male-male competition in Bufo bufo toads that grab passing females to mate with them? (5)
- 10/23 small males were displaced by a larger male
- 13/23 small males successfully mated with female
- 18/18 large males successfully mated
- evolutionary pressure on males to get larger to increase reproductive success
- but no pressure on females so is sexual size dimorphism
what is the relationship between body size and harem size in pinnipeds?
as body size dimorphism increases harem size increases
where is there more male-male competition and more sexual dimorphism, using pinnipeds as an example?
mono systems- little male-male competition
poly- more sexual dimorphism
what was discovered for anter length as a weapon in deer mating systems?
- polygynous males have larger and longer antlers than would expect for body size
- mono has smaller than would expect
what does SS NOT have to lead to and how else can it arise?
sexual dimorphism
can arise from processes other than SS
give an example of how sexual dimorphism can arise from a process other than SS
Huias birds
- males have shorter bills compared to long probing beaks of females
- both occupying 2 different niches
- reduces food competition between the partners
what is female choice hard to distinguish from and how can we show female choice with certainty?
male-male competition
carry out experimental manipulations
what is the Widowbird example by Andersson 1982 to determine if female choice is the underlying mechanism? (5)
- 4 groups of test males: 1 group tail elongated, 1 cut short, 1 left alone, 1 tail cut and restuck
- males with long tails tended to mate with more females than those with short
- females with long tails prefer males with long tails
- female choice
- female female competition may occur
what is the general outcome for each of these:
a) low investment in offspring
b) high investment in offspring
c) equal investment
a) competition
b) choice
c) both sexes compete and both sexes choose- mutual and often monogamous
give 3 points about crested auklets that were studied by Jones and Hunter 1993?
- what was compared?
- both sexes invest in the offspring
- both sexes have crests
- evolved by sensory exploitation
- compared attractiveness of models with short crests to those with long
what were the results on the study of crested auklets by Jones and Hunter 1993? (2)
- M + F performed more courtship displays to long crested males which indicates mutual mate choice
- in both sexes ling crested individuals are dominant which indicates mutual competition
in the study by Jones and Hunter 1993 what % of these interactions were won by long crested birds: male-male and female-female?
M-M: 86%
F-F: 83%
what is the general observation and prediction with sex role reversal?
- observe: in some species males invest more into reproduction than females
- predict: more sex role reversal in these species with the female competing and the male being choosy
give 7 points about the sex role reversal in pipefish
- males get pregnant
- males provide O2 and nutrients to egg clutches in an egg pouch
- females can produce eggs to fill 2 male pouches
- females larger and more competitive
- even sex ratio so pouch space limited
- males choose larger females that produce more eggs
- female biased operational sex ratio
what 2 things may be provided by males often in sex role reversal?
- nutritious spermatophores
- nuptial gifts such as in cricket pairs where the female feeds as the male copulates
give 3 important points about SS
- any pattern of choice and competition can occur
- each sex can play both roles
- the environment can influence the pattern of SS
what is another name for Australian Katydids?
Kawanaphila
what was found in a study on sex role reversal in katydids given that food supply varies greatly through the breeding season? (3)
- when pollen food limited spermatophores hard to produce so produced slower, males are choosy in mating and the females compete more
- when food is abundant males are not choosy
- M + F change behaviour based on environment
what are mormon crickets and what noise do males make?
large, flightless orthoptera
chirping
what do male mormon crickets transfer?
huge edible spermatophore, 25% its body mass, to females so only mate once
how does female investment compare to males in mormon crickets? (4)
- females put fewer resource into mating
- female biased operational sex ratio
- females compete for males
- male choosy and prefers heavier females that can produce more eggs
for mormon crickets what forms in areas where females compete and males are choosy?
high density mating aggregations
what does SS and NS favour?
- which is faster?
SS: mate acquisition and fertilisation
NS: survival and fecundity
- SS as focused on 1 gen
what are the 4 ecological interactions with SS?
- food resources
- predation
- parasitism
- sensory bias
what is a cost to sexual ornaments?
mortality
what can explain traits that go against NS?
SS
give 3 examples of direct benefits from mate choice
- fertile or fecund mates
- good parenting ability
- resources
what often makes an individual compatible as a mate?
complementary and dissimilar MHCs
what does male-male competition often lead to?
sexual dimorphism
what is an example of a case where a group of males will cooperate?
low ranking baboon males work together to gain copulations with females guarded by dominant males
what is an example of where a male and a female is cooperating?
female insect releases sex pheromone that males are attracted to
how do female crickets mating promiscuously with non siblings as well as siblings benefit according to Wedell?
higher hatching success and avoids low egg viability
