Sexual Selection Flashcards
Definition of Sexual Dimorphism
phenomenon in which individuals of different sexes of the same species have different genotypes and/or phenotypes
differences in gametes, reproductive organs,
anisogamy
differences in gametes between sexes
unequal sized gametes
Chromosomes in males and females
Genetic Males and Females
humans and birds
Males: XY and ZZ
Females: XX ZW
Gametic Males
sperm producers
Gametic Females
egg producers
gametic definitions of sex only applies to species with
anisogsmy (unequal sized gametes)
Types of Sexual Dimorphism
size, armaments (anatomical weapons), ornamenets
Sexual Selection
-sexually selected traits function to enhance mating success
- subset of natural selection but can be useful to consider seperately
Darwin: depends on advantage which certain indivduals have over other indivduals of the same sex and species exclusive to reproduction
Factors that contribute to fitness
Natural Selection: reproductive rate, survival
Sexual Selection: Number and Quality of Mates
Two Types of Sexual Selection
Intra and Inter sexual selection
Intrasexual selection
competition
differences between indivudals of the same sex
often but not always male-male
access to other sex
Intersexual Selection
choosiness
interaction between males and females
what determines strength sexual selection
number and quality of mates = variance in mating success
Operational Sex Ratio
anything that alters the receptivity of one sex to mating or their potential for mating
Sex Ratio vs operational sex ratio
3 males and 3 females (2 of three females are not availiable/receptive to mating): equal sex ratio. operational sex ratio is male bias
what drives potential reproductive rates
gamete expenditure
egg resource rich, few and large while sperm in inexpisve and many and small
Parental Investment Theory
- Sexes of some species differ in their reporductive investment
- each offspring is produced from sperm and egg
- members of sex that invest little will compete among themselves to mate with members of the sex that invest more
if the only investment in offpsring is gametes
competition between males and choosiness in females
two forms of intrasexual selection competition
pre-copulatory: # of copulations
post- copulatory: success of copulations
pre-copulatory examples
manifestation of competition
fighting behaviour, social status, territoriality
Post- copulatory
manifestation of competition
mate guarding, copulation duration (more sperm and egg produced), sperm removal, sperm plugs, anti-aphrodisiacs
Alternative reproductive strategies
variation in pehnotypes and behaviour within a sex
Negative Frequency Dependant
fitness of a stretegy highest when that strategy is rare in the population
Mate choice
mating bias, mating preference, and mate choice is the same thing
any trait of one sex that biases the mating success of other sex towards preferred type
trait= behaviour, morphology
mechanisms individuals choosing
visual cues, tacile cues, acoustical cues, olfactory cues
females prefer complex calls
- traits are common and preferred by mates and there is a selection for *
- elaborate
- eloboration
Hypothesis for Choice
indirect and direct benefits
direct benefits
- involve direct natural selection on the individual making the choice.
- chooser produces more offspring
female choosiness based on resources rather than male attributes
male trait is indicator of these resources
indirect benefits
- involve genetic benefits to offpsring of the individual making the choice
- choosers offspring are of higher genetic quality and more fit
females prefer males traits that indicate high genetic quality.
large peacock display size preferred
males traits that are indicators of resource provisioning or other direct benefits
- territory quality
- defense
- parental care
- lack of parasites (STIs)
indirect benefits
parental investment theory
- sexes differ in their reproductive investment
- members of the sex that invest little in offspring will compete among themselves to mate with members of the sex that invest more in offspring
when males invest a lot relative to females= males choosiness and female competition
environmental effects on relative PI and mate choice
- resource levels decline = male avaliability declines, venefit to female of resources from males increases
Predictions: male choice and female competition
How do alternative reproductive strategies influence female choice
parental males offer direct benefit to females
ex: defend nests and provide care to young
