(3) Reproductive strategies

Sept 26 - Oct 8

Sexual reproduction

A reproduction method in which progeny inherit DNA from two parents

Asexual reproduction

Produces:

• clones

• Binary fission

Clones

Individuals that descend asexually from the same parent and bear the same genotype

Binary Fission

reproduction through the duplication of genes followed by division of the cell into two identical cells

Costs of sexual reproduction

requires considerable energy and resources

• genetic cost: 50% reduction in the number of genes passed to the next generation

Hermaphroditism

when an individual produces both male and female gametes

Benefits of sexual reproduction

• genetic purging: can lose deleterious mutations during meiosis

• increased genetic variation (fitness advantage)

Mutational load of an organism

asexual organisms do not have a pay of purging mutations so they can constantly build

Red queen hypothesis

sexual reproduction (recombination) allows hosts to evolve at a rate that counters the rapid evolution of parasites

• e.g. snails in shallow water infected with trematode worms

strategies - Simultaneous hermaphrodites

• problems: self-pollination

• Perfect flower: flowers that contain both male and female organs

sexual strategies - sequential hermaphrodites

individuals that possess female or male reproductive function and then switch to the other

sexual strategies - monoecious

Plants that have both sex functions on the same individual but not necessarily in the same flower

Sexual strategies—dioetic

Plants that contain either only male flowers or female flowers on a single individual

• most animals are dioicous: associated with sexual dimorphism

Selfing vs. outcrossing

sequential hermaphroditism reduces the problem of self-pollination by separating sexual function by time

• limits inbreeding

Mixed mating strategies

Some species can switch between outcrossing and selfing, when mates are available they outcross but when mates are unavailable they self-fertilize

Genetic sex determination

in organisms with separate sexes, the sex ratio of male to female is often 1:1

• sex is often determined by inheritance of sex specific chromosomes the sex that possesses two different chromosomes will produce an approximate number of gametes with each chromosome

Environmental sex determination

a process in which sex is determined largely by the environment

• temperature-dependent sex determination occurs when the sex of an individual is determined by the temperature at which eggs develop

Offspring sex ratio

females can influence the sex ratio of their offspring

e.g. red deer can selectively abort male embryos as make fawns are energetically expensive to produce

Mating systems

the number of mates each individual has and the permanence of the relationships with those mates

• reproductive success depends on the amount of fertilized eggs

Polygamy:

a single individual of one sex forms long-term social bonds with more than one individual of the opposite sex

• 3 varieties

Polygyny

a male mates with multiple females

• may evolve when males compete for females, or when a male can defend territory and resources

Polyandry

A female mates with multiple males

• may evolve when females search for superior gametes or receive material benefits from each mate

Monogamy

when a mating pair form a social bond that persists through the period that is required for them to rear offspring

• favoured when males make important contributions in raising offspring

Extra-pair copulation

when an individual that has a social bond with a mate also breeds with other individuals—cheating in monogamy

• e.g. bluethroat chicks are commonly fathers through extra-pair copulation