BIOL 286: Lecture #6 Review (Life History Strategies, r- vs. K-Selection)

Species can vary drastically with their . . .

life cycles

Examples of life cycle variation: (4)

(1) have changes to body plan; (2) have direct development (e.g. orcas); (3) alternate between asexual and sexual reproduction (e.g. Daphnia); (4) switch their habitats during development (e.g. salmon)

life history

The pattern of development and growth of a given species

Life history characteristics have . . . over time

evolved

Variation in life history strategies among different species derives from the fact that individuals . . . and . . .

have limited energy; may allocate their energy any number of ways

Investment in each life trait has . . . and . . . to the organism. That is

for a given trait

For each life stage

there is an optimal investment into a certain life history trait

Life cycles comprise three key developmental features: (3)

(1) the process by which an embryo becomes an adult; (2) the presence of dormant stages during development; (3) the development and constancy of the organism's sex

Two general types of life cycles: (2)

(1) simple life cycle; (2) complex life cycle

simple life cycle

A type of life cycle wherein juveniles develop from a fertilized egg

A key characteristic of a simple life cycle is . . . of juveniles to adults

direct development

complex life cycle

A type of life cycle in which there are at least two distinct stages that differ in their habitat

A complex life cycle may include changes in . . .

including . . . and/or . . .

Complex life cycle parasites may have . . . stages

alternate between . . .

Purposes of metamorphosis: (6)

(1) exploit resources; (2) resources may be ephemeral; (3) specialized body plan for different life stages; (4) dispersal (e.g. larval fish); (5) reduce competition (e.g. tadpoles may primarily eat algae

Costs of metamorphosis: (2)

(1) significant energy expenditure; (2) vulnerability to predation at certain stages

Advantages of metamorphosis: (3)

(1) specialization on different functions of different life stages; (2) exploitation of different ecological niches; (3) reduced competition among larvae and adults

neoteny

Occurs when an individual reaches sexual mature without undergoing metamorphosis

The selective forces that lead to neoteny are . . .

not fully understood

Neoteny appears to be more common in . . .

extreme environments

Factors associated with neoteny among salamanders: (3)

(1) cooler temperatures; (2) higher altitudes; (3) permanent bodies of water

resting stage

A developmental stage during which an organism is dormant

Provide an example of a resting stage with respect to Daphnia.

Daphnia produce ephippia--specialized

sequential hermaphroditism

A complex life cycle phenomenon in which the sex of an individual organism changes over the course of its lifetime: the organism is male at one age or developmental stage and female at a different age or stage.

Types of sequential hermaphroditism: (2)

(1) protandry; (2) protogyny

protandry

A form of sequential hermaphroditism in which the individual matures first as a male

protogyny

A form of sequential hermaphroditism in which the individual matures first as a female

When is sequential hermaphroditism beneficial?

(1) If the social system limits reproduction to a few larger

Types of asexual reproduction: (4)

(1) budding; (2) vegetative reproduction; (3) parthenogenesis; (4) fragmentation

Types of asexual reproduction: Budding

A form of asexual reproduction that occurs when a parent cell forms a bubble-liked bud. This bud stays attached to the parent cell while it grows and develops.

Types of asexual reproduction: Vegetative reproduction

A form of asexual reproduction whereby portions of plants may be used to produce offspring (e.g. runners)

Types of asexual reproduction: Parthenogenesis

A form of asexual reproduction in which an embryo may develop from an unfertilized egg (e.g. Daphnia)

Types of asexual reproduction: Fragmentation

A form of asexual reproduction whereby an offspring may be produced from a fragment of the parent (e.g. starfish)

cost of meiosis

The reduction in the genetic contribution of a parent to offspring as compared to asexual reproduction (~50% vs. 100%)

Genetic diversity can produce . . . for selection to act upon

phenotypic differences

Genetic diversity among asexually reproducing species emerges from . . .

mutations alone

Asexual reproduction can allow . . . to produce many offspring at once

a beneficial genotype

Some species alternate between . . . and . . . reproduction

sexual; asexual

Discuss alternation between sexual and asexual reproduction as a complex life cycle trait of Daphnia.

Most of the time

cyclical parthenogenesis

A life cycle typical of aphids

Simultaneous hermaphrodites contain . . .

both male and female reproductive structures

Because simultaneous hermaphrodites contain both male and female reproductive structures

they may undergo both . . . and . . .

self-fertilization

A reproductive strategy involving the fusion of male and female gametes produced by the same individual

For which types of lifestyles might simultaneous hermaphroditism be beneficial? (3)

(1) sessile or low mobility species; (2) species often at low densities; (3) "weedy" species that colonize new areas

. . .

. . .

There may be . . . between self-fertilization and out-crossing

trade-offs

iteroparity

A reproductive strategy whereby species reproduce multiple times throughout their lives; also known as repeated reproduction.

Many . . .

. . .

semelparity

A reproductive strategy whereby individuals of a species reproduce only once and then die; characterized by a large investment into a single reproductive event (a.k.a. "big bang" reproduction)

Semelparity is characterized by . . .

a large investment into a single reproductive event

Some . . .

. . .

life span

The maximum length of life of a species

Life span . . . among species

varies greatly

senescence

Degenerative changes that increase mortality rates as an individual ages

Life span is partly under . . .

genetic control

Theories why species are not under selection to live forever: (3)

(1) Deleterious alleles that affect individuals after reproductive age will not be under the same selective pressures as those that affect individuals by or before reproductive age; (2) Pleiotropy: one gene may affect multiple phenotypic traits. Genes that benefit younger individuals will be selected for even if they have some pleiotropic negative effects in old age; (3) Limiting soma theory: Resources devoted to reproduction means there is decreased somatic maintenance

limiting soma theory

The hypothesis that senescence is caused because resources devoted to reproduction are not available to maintain somatic tissues

There are trade-offs between . . .

. . . .

r

K selected species

A species with a low intrinsic growth rate such that the population increases slowly until it reaches carrying capacity; characteristic of species normally near carrying capacity and facing intense competition

K selection is characteristic of species normally . . . and . . .

near carrying capacity; facing intense competition

K selection represents a reproductive strategy to increase . . .

offspring quality

Typical characteristics of K selected species: (4)

(1) parental care; (2) iteroparity; (3) late age at maturity; (3) small clutches; (4) large offspring

r selected species

A species that has a high intrinsic growth rate

r selected species are usually . . .

below carrying capacity (fluctuating but often low density)

r selected species are typically encountered . . .

in fluctuating environments

r selection represents a reproductive strategy to increase . . .

offspring quantity

Typical characteristics of r selected species: (4)

(1) semelparity; (2) large clutches; (3) early age at maturity; (4) small offspring

r-selection is geared towards . . .

whereas K-selection optimizes for . . .; that is