Fundamental feature of life.


Each individual organism exists as the result of reproduction.


Types of reproduction: asexual and sexual

DEF: occurs when an organism makes copies of itself, without contribution (or with just a little contribution) from another organism

Types:

• fission
  • binary (e.g. archaea and bacteria)
    
  • multiple (e.g. algae)
    
• budding (e.g. yeast, hydra, taenia)
  
• vegetative propagation (e.g. plants like kalanchoe, strawberries)
  
• sporogenesis (e.g. fungi)
  
• fragmentation (annelids, echinoderms)
  
• agamogenesis
  • parthenogenesis (invertebrates: rotifers, nematodes, aphids, insects; vertebrates: at least fish, frogs, salamanders, lizards, snakes, occasionally birds, NEVER in mammals)
    
  • apomixis (e.g. ferns, dandelion)

Advantages :

1. Rapid population growth; especially useful when most individuals were wiped out by a stochastic event.

2. No mate needed; especially useful in isolated habitats and/or with low population density

3. Lower resource investment; useful when conditions are unpredictable.

Disdvantages :

Low genetic variability -> difficult adaptation to environment -> retard evolution (BUT: horizontal genes transfer!)

Muller ratchet - accumulation of mutations

Hojsgaard et al (2015) Resolving genome evolution patterns in asexual plants. InL Next-Generation Sequencing in Plant Systematics (International Association for Plant Taxonomy), 1–18

DEF: a type of life cycle where generations alternate between cells with a single set of chromosomes (haploid) and cells with a double set of chromosomes (diploid). Occurs in 99.9% eucariotes. In terms of pros and cons, theoretically, a reverse of asexual reprodution

Sex does not always generate more variable offspring

Otto S (2008) Sexual reproduction and the evolution of sex. Nature Education 1(1):182

Lehtonen J, Jennions MD, Kokko H (2012) The many costs of sex. Trends Ecol Evol 27:172–178

• Sex and recombination can improve the fitness of offspring, when a species’ environment changes rapid.
  
  “Red Queen” hypothesis for the evolution of sex.
  
  

• Sex and recombination can be favored when selection varies over space

• Organisms that reproduce both sexually and asexually tend to switch to sex under stressful conditions. [Individuals that are adapted to their environment reproduce asexually and less fit individuals reproduce sexually. In this way, well-adapted genotypes are not broken apart by recombination, but poorly adapted genotypes can be recombined to create new combinations in offspring.]

Sex evolves when populations are finite
[sex and recombination evolve much more readily in finite populations]

Otto, S. (2008) Sexual Reproduction and the Evolution of Sex. Nature Education 1(1):182

Evolution of anisogamy and two sexes by gamete competition, based on disruptive selection on individuals varying in size of gametes they produce

PRS in essense: two fundamental pressures:

• numerical productivity (n gamets in unit of time per parent)
  
• zygote fitness (probability of zygote survival to reach adulthood and reproduce)

Step 1: parasitic cytoplasmic elements readily invade and spread by vertical transmission through host populations.

Step 4: the allele (at B locus) spreads by becoming associated with the other allele at locus A -> population with two gamete types, or sexes, one predominantly transmitting the cytoplasm, and the other eliminating it.

Hutson V, Law R (1993) Four steps to two sexes. Proc R Soc B Biol Sci 253:43–51

“It appears that sex is more likely a way of asynchronous evolution rather than a way of reproduction as it was considered before.” V. Geodakyan (1991)