Ch. 10 Life History Flashcards
Life histories involve _______
tradeoffs
Reproduction can be _____ or ______
sexual; asexual
Major advantage of sexual reproduction
- immediate gene mixing between two individuals
- duplicate copies of genes available
Major disadvantage of sexual reproduction?
immediate loss of beneficial gene combinations
Asexual reproduction advantages
- rapid reproduction
- no required minimum population size
- inbreeding is not an issue
Parthenogenesis
natural form of asexual reproduction in which growth and development of an embryo occurs without fertilization
Facultative parthenogenesis
a sexually reproducing species that can also reproduce asexually
Simultaneous hermaphrodites
both sexes at one time; possess both male and female sex organs
sequential hermaphrodites
male or female depending on the life cycle stage
protandrous
all born male
Genetic sex-determination
- XX/XY
- XX/X0
- X0/X0
- ZW/ZZ
Most mammals (including humans) and many insects use which sex chromosomes?
XX/XY
In the XX/XY system, which sex is more prone to sex-linked disorders?
males; they’re heterogametic (XY)
In the XX/X0, which one is female?
XX
XX/X0 is found in
several rodent lineages and many insects
ZW/ZZ is found in
birds, some reptiles, and insects
in the ZW/ZZ system, females are
ZW; and more prone to linked diseases
Bipotential
develop into testes or ovaries
Genetic sex determination
one sex has a different chromosome
temperature dependent sex determination
nest temperature determines offspring of sex
temperature dependent sex determination is occurs in
- most turtles
- most/all crocodilians
- many lepidosaurs
Three patterns of TSD
- males from cooler nests (1a)
- females from cooler nests (1b)
- females from coolest and warmest nests, males from intermediate nest temps
primary sexual differentiation
gonads become ovaries unless gene product from Y chromosome
secondary sexual differentiation
follows primary sexual differentiation; copulatory organs, display structures
Hypothesized mechanism of TSD
testosterone in egg (from mother) affected by temperature-dependent enzyme called aromatase
In temps that produce females, aromatase:
converts testosterone to estradiol; makes gonads become ovaries; produces more estrogens, creates a positive feedback
In temps that produce males aromatase:
converts testosterone into dihydrotestosterone; makes gonads become testes
Some consequences of TSD
- affects sex ratio at hatching
- may affect some species ranges due to climate change
Reproduction involves both costs and benefits. The overarching, evolutionary dilemma is:
how to reproduce with the maximum possible fitness
Common problems of trying to reproduce with the maximum possible fitness
- early reproduction typically results in a reduced lifespan
- early reproduction typically results in reduced future offspring potential
- producing too many offspring results in lower average competitive ability of each individual
- producing few offspring results in too few individuals
Age at maturity is a key aspect of an organism’s
life history
Age at maturity is often seen as:
age at first reproduction
Reproductive effort is governed by
tradeoffs
fecundity
the number of offspring produced per unit time
reproductive effort
the total energetic costs of reproduction per unit time
Tradeoffs that govern reproductive effort
- energy demands
- nutrient demands
- physiological demands
- movement
- competition for mates
- parental care
An optimized life history is one where conflicts between demands for survival and reproduction are resolved to be the most advantageous for the
individual’s fitness
each set of offspring is seen as an
economic choice
offspring as an economic choice
- all are created equal
- no wasting of resources
Parent-offspring conflict
offspring will always want more resources for themselves compared to what the parents are willing to offer
Robert Trivers’ theory
- each offspring should demand more than its fair share from the parent’s point of view
- offspring are demanding more, at the expense of their siblings and the parent’s future offspring
parents want to maximize their benefit
per unit effort
offspring want the parents to maximize their benefit (to offspring)
per unit effort; this is why offspring will ALWAYS beg for food more than what the parents ever give
There is a trade-off between the ____ and _____ of offspring produced
number; size
altricial
offspring are born/hatched helpless and are cared for
precocial
offspring are born/hatched capable of moving and foraging
When organisms spend less time and energy on gestation, this results in _____ offspring
altricial
When organisms spend more time and energy on gestation, offspring are ______
precocial
Species differ in the ______ of reproduction
timing
Iteroparous
organisms that produce offspring more than once over their lifetime
Semelparous
invest all energy to growth, development, and acquiring energy early in life
_______ systems describe the pairing of males and females
mating
mating system
the pattern of mating between the males and females of the system; highly variable
Monogamy
the formation of a lasting pair bond between one male and female
Social monogamy
role in parenting a particular set of offspring
genetic monogamy
an iteroparous species that mates with only one individual after sexual maturity
promiscuity
no mating in long-term pairs, no pair bonds, many mates
Polygamy
pair bonds with one sex and multiple individuals of the opposite sex
polyandry
least common; one female, keeping multiple male partners
polygyny
one male, keeping multiple female partners; most common
Two situations in which polyandry would benefit a male?
- scarcity of food
- intense competition for territories/resources
acquisition of a mate involves
sexual selection
sexual selection is ultimately driven by conflict meaning:
- females produce large gametes (high energy and time, limited number)
- male sperm is cheap and always available
anisogamy
sexual reproduction by the fusion of dissimilar gametes
Intersexual selection
reproductive selection based on male dominance/territoriality
Infanticide
new male lion coalitions will kill preexisting cubs left in the pride to increase their fitness
Intrasexual selection
reproductive selection of one sex from the other
Why are females selecting males with different traits?
- good gene hypothesis
- handicap hypothesis
- sexy son hypothesis
good gene hypothesis
females are selecting mates based on external signals that correlate with the genes they are carrying
handicap hypothesis
females select males that are able to live with an obvious handicap
sexy son hypothesis
females choose a mate whose genes will produce male offspring with best chance of reproduction
Patterns of life-history characters reflect
external selective forces
Fast-slow continuum hypothesis
- some animals are burst producers that die young
- others take decades to mature and have a few offspring
r-strategists
typically small, short lived organisms
- rapid development
- little/no parental care
- high reproductive rates at low population sizes
- high mortality
k-strategists
typically large, long lived organisms
- competitive species
- slow development
- parental care
- low reproductive rates
