16_Life_History.pdf
Transcript
Lecture 16: Evolution and Life History BIO 4083: Evolution Today’s Lecture Evolution of life history traits Parental investment Sex ratios Conflict in life history traits Life history strategies are subject to evolution Life History: pattern of investment an organism makes in growth and reproduction...
Lecture 16: Evolution and Life History BIO 4083: Evolution Today’s Lecture Evolution of life history traits Parental investment Sex ratios Conflict in life history traits Life history strategies are subject to evolution Life History: pattern of investment an organism makes in growth and reproduction. Life history traits include an organism’s age at first reproduction, the duration and schedule of reproduction, the number and size of offspring produced, and life span. Life history traits vary widely among different species Short life, many eggs Reproduce once in a short life Long life, fewer offspring Continually reproduce over a long life Evolution of life history traits Life history traits involve trade-offs Limited amount of energy to invest in survival, maintenance, and reproduction Natural selection optimizes life history in light of trade-offs Maximizes number of offspring surviving to maturity Depends on likelihood of survival to different age classes Data from opossums support predictions from life history theory Sapelo Island, GA: no predators Island opossums live longer, have fewer offspring Data from opossums support predictions from life history theory But what could be a trade-off for living longer? Sapelo Island, GA: no predators Island opossums live longer, have fewer offspring Data from opossums support predictions from life history theory But what could be a trade-off for living longer? Antagonistic pleiotropy Sapelo Island, GA: no predators Island opossums live longer, have fewer offspring Predation risk drives life history evolution in guppies High predation More offspring Lower weight Younger reproductive age Transplant experiments demonstrate rapid evolution of life history traits Green bars: guppies in predator-free streams for 11 years Trade-off between reproduction and growth/survival can be visible during the lifetime of an individual Brown anolis lizards: removing ovaries led to larger females Parental investment Females are more likely than males to provide parental care Males have less investment Males have uncertain paternity These roles are reversed in some species Operational sex ratio (OSR) Sexual selection becomes an important agent when members of one sex compete with each other to mate Sex role reversal in jacanas Jacanas: males incubate eggs and protect chicks; females guard harems of males and are larger Sex role reversal in jacanas Do you predict OSR is male or femalebiased? Jacanas: males incubate eggs and protect chicks; females guard harems of males and are larger Sex role reversal in jacanas Do you predict OSR is male or femalebiased? Up to 2.22 F:1 M (Emlen and Wrege 2004) Jacanas: males incubate eggs and protect chicks; females guard harems of males and are larger Sex role reversal in pipefishes Mate choice is important in male pipefishes Here we have “male choice”? Notice the variation in number of mates in males vs. females Competition between parents: Conflict over parental care Strategies to maximize offspring produced over a lifetime can differ for the sexes Balance between leaving the nest earliest (don’t have to care for the offspring), but too early is risk (offspring can die) Competition among siblings: Siblings may compete for parental investment Barn swallows Color on mouths Adjusting numbers and sex ratios of offspring Organisms may regulate the number of offspring to maximize fitness Miscarriage Cannibalism Organisms may also regulate the sex ratio of offspring to maximize fitness Trivers-Willard hypothesis Mothers alter sex ratios depending on conditions Produce females when in poor condition; daughters will likely have some offspring even if in poor condition Produce males when in good condition; males likely to benefit more from being large and will more readily attract mates Shyu and Caswell (2016) Some organisms cannibalize eggs or offspring Sand gobies Ultimately higher fitness and survival in the offspring Females may alter sex ratios of offspring Fig wasp How are wasps (Hymenoptera) able to do this? What is the mechanism? Females may alter sex ratios of offspring Thrips are haplodiploid too! Fig wasp How are wasps (Hymenoptera) able to do this? What is the mechanism? Haplodiploidy (arrhenotoky) Sex ratio adjustment in Seychelles warblers With high resources, females favored Daughters can help raise more offspring = beneficial With low resources, males favored Disperse away from poor habitat Sex ratio adjustment in Seychelles warblers With high resources, females favored Daughters can help raise more offspring = beneficial With low resources, males favored Disperse away from poor habitat Question: This type of sex ratio adjustment from mothers seems to be rare in mammals (although there is growing evidence it does occur). What is a possible mechanism that is responsible for this difference between birds and mammals? Some species switch sex in a “TriversWillard-predicted” manner Bluestreak cleaner wrasse Why do we predict this? (Think cost-benefits) Start as females and breed as such when young and small, but switch to male when they are large Sex ratio controlled by Wolbachia bacteria Sex ratios controlled by unique genetic elements in some species of booklice Some females only have daughters; only transmit genes from their mothers Paternal genome elimination Pseudo-arrhenotoky Males inherit but do not pass on their father’s genetic material Functionally equivalent to haplodiploidy Why are sex ratios often balanced? Frequency-dependent selection Production of each sex favored when rare Rare sex has more mating opportunities Conflicts between sexes within the genome Genomic imprinting Gene expression silenced by methylation by one parent Offspring express either maternal or paternal copy of gene, but not both Smith et al. 2020 Genomic imprinting and hybrid inviability Male donkey x female horse Male horse x female donkey Mules and hinnies: both hybrids of horses and donkeys, but different species is the father Differences in phenotype linked to genomic imprinting Genomic imprinting and parental conflict Epigenetics: heritable changes in gene expression (perhaps accrued during the individual’s lifetime: behavior and environment) What does this remind you of? Genomic imprinting and parental conflict Epigenetics: heritable changes in gene expression (perhaps accrued during the individual’s lifetime: behavior and environment) What does this remind you of? Lamarck Assignments Activity on Friday Read the Zimmer article (“What is a Species”)
