Mode of Reproduction

Reproduction can be asexual

-offspring inherit DNA from a single parents

-often produces genetically identical descendants (clones)

-common in plants, unicellular animals, some aquatic animals

Vegetative Reproduction

-produces offspring from non-sexual tissues (egg, sperm, etc)

-budding

Parthenogenesis

produces offspring from a non-fertilized embryo

Asexual vs. Sexual Reproduction

Both strategies are successful

Costs and Benefits of Sex

1- Asexually reproducing lineages repeatdely arise within many groups of organisms

• suggests that asexuality is beneficial

2-Yet they are usually very young

• suggests asexual groups don’t last very long

Sexual Reproduction

-offspring inherit DNA from male (sperm) and female (egg) gametes

• one haploid cell (n) from each parent

-produces genetically unique descendants via genetic recombination

-common in plants and animals

Benefits of Sexual Reproduction

-Genetic Recombination= Increased Genetic variation

-purging of deleterious mutations

-increased ability to deal with variable conditions (plasticity)

-increased ability to respond to pathogens

Benefits of Sex

1. sex is better at eliminating deleterious mutations

   • recombination repairs the genome

   • makes purifying selection more efficient

-parents can produce offspring thathave higher fitness genotypes than themselves

If sexual reproduction purges deleterious mutations,

then sexually reproducing species should persist for longer than asexually reproducing species

There are many costs to sex

-meiosis takes longer than mitosis

-breaks up adpative combinations of alleles at multilocus genotypes

-time/energy spent competing for opportunity to mate and to attract members of the opposite sex

-ime/energy spent searching for mates

-increased risk of predation

-increased risk of disease

Benefits of asexual

-no need to find mate

-no need for males at all

-faster/cheaper reproduction

-pass down 100% genes

Costs of Asexual

no genetic recombination

Pathogens

evolve rapidly

Red Queen hypothesis

-host species evolve new genetic defenses (through sexual reproduction) against parasites, and vice versa

Evidence to support red queen hypothesis

-when parasites are present, asexual reproduction (solid black line) is incredibly costly

Monogamous

-individuals mate with one partner for life

-least common (common in birds?, humans?)

-strong, lasting social bond

-shared parental care (both sexes)

-evolves when male parental care is beneficial

Extra Pair copulations

can select for mate guarding and mating plugs

Polygamous

individuals mate and bond with multiple partners

-polygyny

-polyandry

Polygyny

-one male mates with (and defends) multplie females

-male dominance hierarchies

-guards territory, nesting sites

-high variation in male mating success

Polyandry

-one female mates with multplie males

-rare in vertebrates

-fairly common in insects (female sperm storage)

Promiscuous

individuals mate with multplie partners and form no bonds

-most common by far (all plants, most animals)

-female generally raises young (if any parental care at all)

Every individual has 3 goals in life

1. Consume resources and grow to maturity

2. avoid being killed

3. reproduce- successful offspring

The Darwinian demon

-for maximum fitness an individual should:

• begin reproducing immediately

• produce many large offspring

• never age or die

Why hasn’t natural selection produced such an organism?

-constraints on what is physically possible

-trade offs-

• allocation to one fitness component reduces resources available for other fitness components

Trade-offs

-energy, material, time used for a structure/ function/behavior can’t be allocated to another

Principle of Allocation

natural selection will favor individuals that allocate resources optimally (maximum fitness)

Resources Allocation and Short term trade offs

-number and size of offspring

-clutch size of offspring and survival

• parental care

Life history components

-age of maturity

-parity

• number of reproductive epsiodes

-fecundity

• number/size offspring

-parental care investment

-longevity (lifespan)

Trade off between offspring quanity and quality

clutch size can even affect future reproduction of offspring

Parents work harder to feed more young

-decreased parental survival

Long-Term life history trade-offs

-growth v. reproduction

-age of maturity

-number of reproductive episodes

-lifespan and aging (senescence)

Age of maturity (first reproduction)

-same resources for reproduction and growth

-long-lived organisms reproduce at older age (elephants)

-short-lived organisms reproduce more quickly (bugs)

Cost v. benefits of breeding at a particular age and body size

Hypothetical Example

-number of eggs produced as function of lifespan and age at first reproductio

-older at maturity= bigger body size= higher fecundity/ event

Semelparous

-breed once in lifetime

-store resources for one reproduction

-programmed death after reproduction

Adpative if:

-reproductive cost is extreme

-difficult to survive after reproduction

Iteroparous

breed multiple times

more common

Environmental influences on life histories

-predation risk

-resource availability

Predation Risk

significantly affects life history strategies

Low predation

higher adult size, higher embryo weight, fewer offspring

Higher Predation

lower adult size, lower embryo weight, more offspring

Shortwing morph

-incapable of flight

-early investment in ovaries

Longwing morph

-capable of flight

-late investment in ovaries

Weaponized

-capable of fighting for mates

-produce less sperm

Weaponless

-incapable of fighting for mates

-produces more sperm