BIOE 109Summer 2009Lecture 10- part IMating systems

Types of Mating Systems

Mating Systems In Nature

PolygynyPolygynyMonogamyMonogamyPolyandryMonogamyMating Systems In Nature

?Mating Systems In Nature

PromiscuousMating Systems In Nature

PromiscuousMating Systems In Nature

Hypothesis for the evolution of mating systemsBased on parental care and ecological constraints

Hypothesis for the evolution of mating systemsBased on parental care and ecological constraints

Who can ditch first?

Hypothesis for the evolution of mating systemsBased on parental care and ecological constraints

Who can ditch first?

Is ditching worth it?

Sex allocation

Sex allocationthe allocation of resources to male versus female production in sexual species (Charnov 1982).

Sex Ratio?

What is sex ratio? sex ratio is defined as the proportion of males to females.

What is sex ratio? sex ratio is defined as the proportion of males to females. two distinct sex ratios exist:

What is sex ratio? sex ratio is defined as the proportion of males to females. two distinct sex ratios exist:1. the population sex ratio

i.e., the proportion of males to females in the population

What is sex ratio? sex ratio is defined as the proportion of males to females. two distinct sex ratios exist:1. the population sex ratio

i.e., the proportion of males to females in the population

2. the individual sex ratio

What is sex ratio? sex ratio is defined as the proportion of males to females. two distinct sex ratios exist:1. the population sex ratio

i.e., the proportion of males to females in the population

2. the individual sex ratio

i.e., the sex ratio of progeny from a female

-In many species sex chromosomes cause 1:1 sex ratio

The evolution of sex ratio

Mammals: females are homogametic (XX)

males are heterogametic (XY)Birds: males are homogametic (ZZ)

females are heterogametic (WZ)The evolution of sex ratio

Mammals: females are homogametic (XX)

males are heterogametic (XY)Birds: males are homogametic (ZZ)

females are heterogametic (WZ)Sex chromosomes do not guarantee a 1:1 sex ratio!

Why equal numbers of males and females?

R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1.

Why equal numbers of males and females?

R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1.

since every individual has one mother and one father, each sex contributes equally, on average, to subsequent generations.

Why equal numbers of males and females?

R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1.

since every individual has one mother and one father, each sex contributes equally, on average, to subsequent generations.

therefore, males and females must have the same average fitness.

Suppose:25% male males will have high fitness75% femalebecause they mate with multiple females

Suppose:75% male females will have high fitness 25% femalebecause they mate with multiple males

Members of the rarer sex will experience increased reproductive success relative to common sex

frequency-dependent selection results in stable equilibrium sex ratio of 1:1.

Exceptions to Fishers theory

NOT ALWAYS 1:1

Exceptions to Fishers theory

Local mate competition (Hamilton 1967)

2. Condition-dependent sex allocation (Trivers and Willard 1973)

Exceptions to Fishers theory

1. Local mate competition (Hamilton 1967) proposed to account for female-biased sex ratios (e.g., parasitoid wasps).

Exceptions to Fishers theory

1. Local mate competition (Hamilton 1967) proposed to account for female-biased sex ratios (e.g. parasitoid wasps).

here, a single foundress produces a small group of closely related individuals that mate among themselves.

Exceptions to Fishers theory

1. Local mate competition (Hamilton 1967) proposed to account for female-biased sex ratios (e.g. parasitoid wasps).

here, a single foundress produces a small group of closely related individuals that mate among themselves.

females invest heavily in daughters and dont waste effort in producing sons.

Exceptions to Fishers theory

1. Local mate competition (Hamilton 1967)

MaleFemalesMotherDust mites (Acarophenox)1 son to 20 daughters

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973)Red deer, Cervus elaphus

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973) occurs in polygynous species when females invest heavily in producing and caring for their young.

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973) occurs in polygynous species when females invest heavily in producing and caring for their young.

a good mother can produce larger, or healthier, individuals when they mature.

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973) occurs in polygynous species when females invest heavily in producing and caring for their young.

a good mother can produce larger, or healthier, individuals when they mature.

theory predicts that females in extremely good condition should produce males.

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973) occurs in polygynous species when females invest heavily in producing and caring for their young.

a good mother can produce larger, or healthier, individuals when they mature.

theory predicts that females in extremely good condition should produce males.

Why?

Exceptions to Fishers theory

2. Condition-dependent sex allocation (Trivers and Willard 1973) occurs in polygynous species when females invest heavily in producing and caring for their young.

a good mother can produce larger, or healthier, individuals when they mature.

theory predicts that females in extremely good condition should produce males.

Why? Because sexual selection (usually) occurs more strongly in males and condition matters!

How is sex ratio adjusted by mother?Not known

Sex Allocation RecapSex ratioWhy we see an unbiased sex ratioSex chromosomesFrequency dependent selection

Exceptions to sex ratio:Local mate competitionCondition-dependent sex allocation

Sex in Plants

Sex in Plants

Sex in PlantsWhy and how do they outbreed?

Why do they inbreed?

The evolution of inbreeding and outbreeding

many plant species have evolved traits to avoid inbreeding.

The evolution of inbreeding and outbreeding

many plant species have evolved traits to avoid inbreeding.1. Asynchronous male and female functions

pollen shed after or before plants stigmas are receptive.

The evolution of inbreeding and outbreeding

many plant species have evolved traits to avoid inbreeding.1. Asynchronous male and female functions

pollen shed after or before plants stigmas are receptive.

The evolution of inbreeding and outbreeding

many plant species have evolved traits to avoid inbreeding.1. Asynchronous male and female functions

pollen shed after or before plants stigmas are receptive.2. Monoecy

male and female flowers separated on same plant.

The evolution of inbreeding and outbreeding

2. Monoecy male and female flowers separated on same plant.

The evolution of inbreeding and outbreeding

many plant species have evolved traits to avoid inbreeding.1. Asynchronous male and female functions

pollen shed after or before plants stigmas are receptive.2. Monoecious

male and female flowers separated on same plant.3. Dieocy

sexes are separated in different individuals.

The evolution of inbreeding and outbreeding

3. Dieocy

sexes are separated in different individuals.

The evolution of inbreeding and outbreeding

4. Self-incompatibility loci

prevent selfing or breeding with close relatives.

The evolution of inbreeding and outbreeding

4. Self-incompatibility loci

prevent selfing or breeding with close relatives.5. Heterostyly

two (distyly) or three (tristyly) forms of flowers exist in a species (on different plants).

The evolution of inbreeding and outbreeding

4. Self-incompatibility loci

prevent selfing or breeding with close relatives.5. Heterostyly

two (distyly) or three (tristyly) forms of flowers exist in a species (on different plants).

pollen is more effectively transferred between, rather than within, morphs.

The evolution of inbreeding and outbreeding

4. Self-incompatibility loci

prevent selfing or breeding with close relatives.5. Heterostyly

two (distyly) or three (tristyly) forms of flowers exist in a species (on different plants).

pollen is more effectively transferred between, rather than within, morphs.

acts to maximize outcrossing.

Thrum flowered Primula polyneura Pin flowered Primula polyneura Heterostyly in Primula polynera

Why inbreed?

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:1. through its ovules

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:1. through its ovules2. through its pollen by selfing

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:1. through its ovules2. through its pollen by selfing3. through its pollen by outcrossing.

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:1. through its ovules2. through its pollen by selfing3. through its pollen by outcrossing. another advantage of selfing is reproductive assurance

Why inbreed? partial selfers have a fitness advantage over exclusive outcrossers because genes can be transmitted:1. through its ovules2. through its pollen by selfing3. through its pollen by outcrossing. another advantage of selfing is reproductive assurance

if pollinators are scarce, then a plant can produce at least some seeds by selfing.

OVERALLMating SystemsSex allocationSex ratiosExceptions to 1:1 sex ratioMating in plants