After Conception: The Evolution of Life History and Parental Care (L20)

Exam 3 Lecture 20

Life history strategies

• Physiological and behavioral features that incorporate reproductive traits, survivorship, length-of-life characteristics, preferred habitat, and competitive ability

• Iteroparity vs. semelparity

• Continuous vs. seasonal iteroparity

• R and K selection

• Grime’s Triangle

Iteroparity vs Semelparity

Iteroparity:

• a pattern of repeated reproduction at intervals throughout an organism’s life

• common in vertebrates and perennial plants

• Tends to happen when the survival of juveniles is poor/unpredictable

Semelparity:

• When offspring are produced at a single event in an organism’s life

• common in insects and invertebrates

• Tends to happen when the environment is stable

Continuous vs. Seasonal Iteroparity

Continuous:

• Individuals that reproduce repeatedly at any time of year

Seasonal:

• Individuals that reproduce during distinct breeding seasons

r and K selection

r selected species:

• maximize growth rates to exploit unstable/temporary environments

• usually small with short lifespans, and with little parental care

K selected species:

• adapted to survive in stable environments near/at carrying capacity

• usually large, with long lifespans, and invest in parental care

Survivorship Curves

Type I:

• Most individuals die later in life

• few offspring

• Ex: Elephants and Humans

Type II:

• uniform death rates over time

• Ex: Birds, reptiles, beavers

Type III:

• Most individuals die early on

• The curve flattens for organisms that avoid death

• Ex: fish and marine invertebrates

Grime’s Triangle

Ruderals:

• Adapted to take advantage of habitat disturbance

• Ex: annual plants

Competitors:

• adapted to live in competitive but gentle environments

• Ex: trees

Stress Tolerators:

• adapted to cope with extreme environmental conditions

• Ex: Cacti

Operational Sex Ratio

Ratio of male to female individuals who are available for reproducing at a given time

Gulf Pipefish

• Males carry eggs in a pouch

• Males choose to mate with a few, high-quality females to maximize egg survival rates

• (role reversal)

Red-winged Blackbirds

• Young females produce more females

• Old females produce more males

• Example of adjusting the sex ratio

Trivers-Willard Hypothesis

• Parents in good condition tend to bias their offspring sex ratio toward the sex with a higher reproductive value (males)

• Parents in bad condition favor the opposite sex (females)

• Some species switch their own sex to fit this hypothesis (start as female when they are small/weak, then turn male when larger/stronger)

Parental-offspring conflict

• When parents benefit from withholding parental care from some offspring and invest in other offspring

• leads to sibling competition

offspring-offspring conflict

• Siblings competing for parental care or resources

• can lead to siblicide

Ex: Skylark chicks, American coots, Nazca boobies

Genomic Imprinting

• When the effects of a genome inherited from one parent are silenced due to methylation

Methylation: when methyl groups are added to certain nucleotides. Associated with altered gene expression

Intralocus sexual conflict

Conflict between the fitness effects of alleles of a locus on males and females

(The mother/father genes are in competition with one another to be expressed)

Senescence

• Deterioration of the biological functions of an organism as it ages

• Actuarial: age related decline in survival

• reproductive: age related decline in reproduction

• Calorie restriction can slow the aging process but reduce fitness (DAF-16 gene)

Mother/Grandmother Hypothesis

Mother Hypothesis:

• It’s advantageous to stop reproduction earlier (menopause) to invest care into offspring

Grandmother hypothesis:

• It’s advantageous to live to old age so grandparents can invest care into grandchildren. This allows daughters to have more offspring.