MARB 215 Exam 2 (excluding unicellular eukaryotes)

What are the different types of asexual reproduction?

budding, fission, gemmulation, fragmentation/strobilation

Define Budding

A type of asexual reproduction in which the cells divide. When the bud becomes large enough it breaks away and lives on its own (The offspring branches off from the parent)

Define Fission

The parent splits in half creating two genetically identical offspring.

Define Gemmulation

Packets of embryonic cells with a thick protective coating are formed internally.

Define Fragmentation/Strobilation

Segments become mature and are released

What does asexual reproduction produce?

offspring that are genetically identical to the parent

What are the advantages of asexual reproduction?

- rapid population growth

- only one parent needed

- requires less time/energy

- faster than sexual

What are the disadvantages of asexual reproduction?

- no genetic variation

- clones may all be susceptible to the same issues

(only adapted to one habitat; react same way to disease)

Asexual reproduction can be found mostly in

inverts (and parthenogenesis in verts)

What happens during sexual reproduction?

haploid gametes fuse together to form a diploid gamete

What does sexual reproduction produce?

offspring that are genetically varied from the parent

What are the advantages of sexual reproduction?

- genetic variation

- can adapt to environment --> survival advantage

- disease is less likely to affect a population

What are the disadvantages of sexual reproduction?

- lots of time/energy needed to find a mate and make gametes

- isolated individuals cannot reproduce

What is a hermaphrodite?

an organism which has both male and female reproductive elements (monoecious)

Hermaphroditism can be either

simultaneous or sequential

Simultaneous hermaphrodites

individuals that possess male and female reproductive functions at the same time

sequential hermaphrodites

individuals that possess male or female reproductive function and then switch to the other at a different time when needed

- protandrous

- protogynous

Protandrous hermaphrodites

first male (then FM)

Protogynous hermaphrodites

first female (then M)

What are the advantages of hermaphroditism?

- can always self-fertilize

or

- find a mate with anyone in their species

_____________________ arose independently in many lineages

hermaphroditism

Parthenogenesis is a type of

asexual reproduction

What is parthenogenesis?

It is a form of reproduction that happens without a male... an unfertilized egg forms embryo (due to lack of division during meiosis (meiotic) or absorption of polar body (ameiotic))

Sometimes parthenogenesis

requires sperm to be nearby for it to take place, however the sperm are not used in the embryo

Define external fertilization

gametes are fused outside of the parental body

What are the characteristics of external fertilization?

- generally in aquatic environments

- desiccation of gametes not an issue

- water currents help sessile animals colonize new environments

Two types of external fertilization are

1. Broadcast spawning

2. Demersal spawning

Define broadcast spawning

gametes are shed directly into water: gametes are small; fertilization happens by chance; no parental care

Define demersal spawning

females lay eggs in "nest" and male fertilizes: eggs generally bigger; some animals provide parental care

External fertilization can be found in

inverts (porifera, cnidarians, crustaceans, bivalves, echinoderms) and verts (most bony fish, frogs)

Define internal fertilization

fusion of the gametes happens inside the parent organism

Characteristics of internal fertilization

- usually inside the female

- exceptions: some members of class sygnathidae

- copulatory organs required

Internal fertilization males

require sperm, seminal fluids, and structures to transfer sperm to females

Internal fertilization females

require ova, accessory glands (shell/yolk production in some), ducts to connect seminal receptacle to oviducts

Internal fertilization can be found in

inverts (rotifers, acanthocephala, nematodes, gastropods, cephalopods) and verts (chondrichtyes, reptiles, birds, mammals)

Internal fertilization produces young in three ways

- oviparous

- ovoviviparous

- viviparous

Define oviparous

- egg laying; offspring hatches from egg

- all nutrition & gas exchange in egg

Define ovoviviparous

- internal eggs

- nutrition inside egg

- gas exchange through mother/father

- eggs hatch internally; live birth from parent

Define viviparous

- internal development of embryo with nutrition directly from mother

- live birth

What are the three different mating systems?

- monogamy

- polygamy

- promiscuous

Define monogamy

- 1:1 mater per breeding season

- 3-5% of mammals; 90% of birds

- common when offspring need biparental care

Define polygamy

- 1:many

- either polygyny

- or polyandry (less common)

Define polygyny

1 male, mult. female --> mother only care of young

Define polyandry

1 female, mult. males --> father only care of young

Define promiscuous

- many:many

- more common in social groups

- Individual cannot hold territory and monopolize a group of mates

-Social groups where all females become sexually receptive simultaneously

-Paternity often uncertain; selects for males to avoid infanticide

-Environment very unpredictable; high predation

Reproductive strategies are

structural, functional, & behavioral adaptations to improve chances of fertilization and offspring survival

What are the different reproductive strategies?

sexual/asexual reproduction, semelparous/iteroparous, sexual selection, male-male aggression with sneaky males, mate guarding, parental care

helps make sure next generation has their gametes

Define semelparous

reproduce one time in life

Characteristics of semelparous organisms

- put all energy into creating offspring; adult survivorship is not an issue

- litter may have a million+ eggs

- shorter generation times

Define iteroparous

reproduce multiple times over life

Characteristics of iteroparous organisms

- each batch offspring smaller than semelparous

- adult survivorship imperative; conserve energy for next litter

- longer generation times with overlapping generations

examples of semelparous organisms

some bony fish, insects, cephalopods, arachnids

Examples of iteroparous organisms

mammals, birds, reptiles, most fish, mosquitoes, roaches

Sexual selection

- most often by choosy females since females put more energy into creating gametes

- leads to sexual dimorphism

sexual dimorphism

Differences in physical characteristics between males and females of the same species.

Define male-male aggression with sneaky males

- Satellite/sneaky males

- Smaller, look more like female

- No chance of obtaining harem

- Sneak in to mate with females while large male preoccupied

- Is best chance to have their genes passed on

- Seen in many different animals: insects, frogs, birds

ex: elephant seals

Define mate guarding

- male remains close to the female after mating until eggs are fertilized to be sure no others mate with her

- copulatory plugs

What are copulatory plugs?/What do they do?

- sticky mass of ejaculate or portion of the copulatory organ

- can have chemicals in it to stimulate egg production or reduce FM attraction to M

- reduced risk of sperm competition from other males

- physically obstructs the seminal receptacle of female

- in some squids, nematodes, many mammals

What are the different types of parental care?

- biparental care

- paternal care

- maternal care

- allopatric care

Biparental care

- monogamous mating systems

- sexual selection not intense

- adult male: female ratio not skewed

Paternal care

- single parent

- polyandrous mating system

- more common in fish than other animals

Maternal care

- single parent

- polygynous and promiscuous mating systems

- females invest more in fewer/larger gametes --> may have favored maternal care

-prevalent in mammals due to location

Alloparental

- Seemingly altruistic

- Often in social species

- Caring for non-descendent offspring

- Why? Parental experience, reciprocal altruism,exploitation of young

- Mostly found in mammals, birds, and insects

What is r/K selection theory?

the tradeoff of quantity vs quality in offspring and best way to pass genes into next generation

- some animals can change selection strategy based on environmental conditions

r-selected

- Small investment goes into each offspring

- Often spawn/fertilize/disperse

- Each young has high probability of mortality

- Even if resources limited, some will survive

- Common in:

Lower quality environments and Animals with shorter lifespans

- Young are precocial

- more genetic diversity

Define precocial

mature rapidly with early independence

K-selected

- Young enter competitive world in a population at/near carrying capacity

- Few offspring with heavy parental investment (before & after birth)

- Higher probability of offspring survival

- More common in longer lived organisms in stable environments

- Young are altricial

Define altricial

- Born in an immature state and requiring care and feeding by parents

- Slower to mature and later to reach independence

C-selected

birth and death rates are relatively equal (birds and lizards)

Define preformation

- miniature adult in sperm/egg waiting to "unfold"

- used to explain development in 17th-18th century

Who came up with the theory of epigenesis and what does it mean?

- Kaspar Wolff

- "origin upon or after"

- building materials in fertilized egg are directed by "unknown forces"

What were the "unknown forces" Kaspar Wolff observed in the development of the chicks?

cytoplasmic specification and induction

What are the morphogenic determinants in oogenesis? (epigenesis)

- supports nutrition of the embryo

- directs development through cleavage

To aid in fertilization, eggs release species-specific _____________________ molecules to attract sperm (esp. in broadcast spawners).

chemotactic

Sperm have egg-recognition proteins on ____________ recognized by species-specific sperm receptors on egg

acrosomes

All animals have methods to allow penetration by only one sperm. What are some methods of reducing polyspermy?

- Chemical and/or physical change in vitelline layer

- Fertilization membrane (not in mammals) then formed to keep other sperm from entering

What is cleavage influenced by?

yolk amount and location

Holoblastic cleavage is

complete

Meroblastic cleavage is

incomplete

The different divisions of cleavage are

radial, spiral, rotational, and discoidal

What are the different types of eggs that affect cleavage?

telolecithal, centrolecithal, mesolecithal, and isolecithal

Isolecithal eggs

- little yolk throughout egg

- holoblastic cleavage

- direction of divisions can be radial, spiral, or rotational

- found in echinoderms, tunicates, mollusks, cephalochordates, and mammals (humans)

Mesolecithal eggs

- moderate yolk concentrated at vegetal pole

- holoblastic cleavage

- cleavage slower at yolk-rich pole (micromeres and macromeres)

- radial cleavage

- amphibians

Centrolecithal eggs

- much yolk concentrated in center

- meroblastic cleavage (superficial cleavage restricts cleavage to cytoplasm at rim of egg)

- arthropods (insects)

Telolecithal eggs

- much yolk concentrated at vegetal pole

- meroblastic cleavage (cleavage confined to narrow area on top of yolk)

- birds, reptiles, most fish, and some amphibians

Development of the egg depends on

the amount of yolk in the egg

Direct development

- high amounts of nourishing yolk in egg

- mini adult comes out of egg

- telolecithal

Indirect development

- lower amounts of yolk present in egg --> less nourishment

- newborn has a diff body than adult

- isoloecithal, mesolecithal

(mammals inc humans still have direct development due to placenta)

Continuous cleavage creates cluster of cells called the

blastula

Blastula

- all metazoans: single germ layer of cells in blastula

- most animals have fluid-filled cavity -- bastocoel

- no larger than zygote

- DNA has increased immensely

What happens during gastrulation?

the bastopore, 2 germ layers, and archenteron are formed

How is the mesoderm formed? (in triploblasts)

- schizocoely

- enterocoely

What happens in enterocoely?

the mesoderm is formed when the wall of archenteron pushes into space between endoderm and ectoderm; out-pocketing creates coelom

What is schizocoely?

the mesoderm is formed through the proliferation of cells near lip of blastopore; cells in center undergo programmed cell death & mesoderm splits open

Roux-Weismann Hypothesis (1800s)

genome from egg broken into smaller and smaller units with cell division; only information for individual cell types remain

Hans Driesch (late 1800s)

- proved R-W wrong

- shook apart 2-cell stage of sea urchins

- 1 cell died, but the other half-embryo developed into normal larvae

- all cells contain entire genome

Hans Spemann (early 1900s)

- separated salamander zygotes about to divide

- realized grey crescent was required for normal development

- Spemann organizer needed for induction

- Somatic Cell Nuclear Transport (SCNT) - cloning

Cytoplasmic specification

molecules in cytoplasm specify fate of cell

Induction

developmental response due to interactions with neighboring cells

What are the characteristics of cytoplasmic specification?

- cytoplasm is not homogenous

- morphogenetic components partitioned unequally throughout cytoplasm

- causes mosaic development of embryo

- many independently developing cells

- fate of the cell is not fixed until it receives positional info from neighbor cells

- differential spread of maternal mRNA in zygote

- all cells need to properly develop