lec 23- the evolution of life history Flashcards
what does life history traits involve?
energy trade-offs
what is the energy invested in?
growth, maintenance, and reproduction
what optimizes trade-offs in a specific environment?
natural selection, it maximizes the number of offspring surviving to maturity
what are species life spans, age of sexual maturity, number of offspring, and sex ratios largely determined by?
genes
what are some examples of short and long life spans?
short- aquatic nymphs live for one to several years and adult mayflies live for hours to days and reproduce a lot before dying
long- elephants live for 48-70 years but have fewer offspring
what is senescence?
deterioration of cells with age
what happens to the body with age?
-altered DNA and proteins
-repair mechanisms for DNA and immune system decline in effectiveness
-noninfectious diseases become more common and contribute to increasing senescence
-pleiotropic genes with benefits to youth may shut down
what causes aging or senescence?
telomeres on chromosomes shorten with each cell replication
what do tumor-suppressor proteins do?
kill or prevent abnormal cells from dividing, but can also damage cells if too active
what does calorie restriction do in mice?
slows the aging of mice making them live longer, but potentially lowers their growth and reproduction
what is the opossum life history in the wild?
-average life span is 2 years
-aging starts at 18 months
-most die by predation rather than old age
why do the opossums on sapelo island live longer?
-lack of predators meaning longer life and slower aging
-longer survival means females can have more offspring than those with short life, which would favour mutations that allocate more resources to maintenance later in life, leading to healthier conditions in old age
what is the difference between island and mainland opossums?
-mainland: short life span, more offspring, less investment, high senescence
-island: long lifespan, less offspring, more investment, low senescence
why do humans live longer after their last birth than other primates?
-because human babies need extensive care and eggs become damaged with age so menopause is helpful at preventing mutated children from occuring
-mother and grandmother hypothesis, help take care of children and grandchildren who share genes to increase future generation’s fitness
what is menopause?
when a female cant get pregnant
what does natural selection favor in humans?
early reproduction, and high parental care
how does predation drive life history traits in guppies located in Trinidad according to David Resnick?
-high predation: females reproduce early and produce more offspring but are smaller
-low predation: females reproduce later and produce less offspring but are larger and more fit for survival
-high predation males: males are dull in color to camouflage (even when females prefer bright) and sexually mature early to reproduce earlier, are also smaller in size
when do trade-offs arise?
when investment in one trait results in lower investment in another trait
what trade off does reproduction have?
-investment in reproduction results in less energy towards growth or maintenance
why do females do more parental care then males?
-they invest less energy (cheap sperm) into offspring and are uncertain if the offspring is even theirs
what is polyandry?
sex role reversal (more females than males ready to mate and males raise offspring)
-e.g. female jacanas fight for access to males
why does the male sand goby eat some of the eggs it cares for?
-in low oxygen environments, survival of eggs is low, as such eating some reduces competition and increases survival of some
what is the Trivers-Willard hypothesis?
-Mother can alter sex ratio of their offspring depending on the condition
-females in good condition produce more sons in a polygynous species so more offspring are fathered
-females in bad condition produce more daughters because a bad condition son cant compete well in a polygynous species, causing no grandsons or grandaughters
what are the two ways an organism can regulate the number of offspring to maximize fitness?
-miscarriage (if child is abnormal it occurs, reproductive time lost is short and may mate again shortly)
-cannibalism (may occur if conditions do not favour survival of all offspring)
what do some species do when they are able to switch sexes?
start and breed as females when young and small, and then switch to males when large enough for more successful breeding (seen in polygynous species)
what is an example of an animal that can switch sexes in a polygynous environment?
cleaner wrasse
how do Seychelles warblers adjust the sex ratio of offspring?
-in good environment, females produce more daughters which can help raise other offspring
-in bad environment, females produce more males which can disperse away and find better environment to increase fitness
what is parental care conflict?
-strategies to increase offsprings produced over lfietime
-males leave after seeing if the female has laid all their eggs, as such the female may hide some eggs to make the male think she can still lay more resulting in him still providing for the female and help protect the nest
what is genomic imprinting?
-the silencing of a gene by methylation of cytosine
-offspring may express either the maternal or paternal copy of a gene but not both
how can genomic imprinting be biased to favour expression of either maternal or paternal gene over the other?
-fathers may favour more investment by the female in current offspring, future offspring wont be his, so his copy of the gene is favored for larger offspring
-mothers may favor less investment than the current father to save resources for the future reproduction, silencing father’s genes for smaller offspring to save energy
