Reproduction Flashcards
What is direct development?
Internal fertilisation - Protected - no free living larval stage
* Embryos brooded internally or on
the body of the female to
juveniles
* Large yolky eggs
* Small number of offspring
* High maternal investment
Direct development in marine invertebrates refers to a reproductive strategy where the offspring emerge from eggs as miniature versions of adults, without going through distinct larval stages.
Some species of snails, like Crepidula atrasolea
Certain marine worms
What is indirect development?
90-95% of Marine Invertebrates
* External fertilization
* Embryos and larvae develop in the
environment
- free living larval stage
* Variable maternal investment
– Eggs may be small or large
– Small or large number of offspring produced
Indirect development involves one or more distinct larval stages before the organism metamorphoses into its adult form.
Many marine invertebrates, including most mollusks, echinoderms, and crustaceans
Specific larval forms include trochophore larvae (in mollusks and annelids) and pluteus larvae (in sea urchins)
What is mixed development?
Mixed development combines elements of both direct and indirect development strategies.
Key features:
May involve abbreviated larval stages
Can include brooding of embryos followed by release of larvae
Intermediate dispersal potential
May have characteristics of both feeding and non-feeding larvae
Draw a table comparing egg size, egg yolk content, fecundity, offspring survival, dispersal potential, and cost of reproduction for adult.
Look at drawing.
Explain life-history strategies. (First paragraph of essay)
- The location, pace, and support of
embryonic and larval development varies
among species - Also the size and number of offspring, and
how often they are produced also varies - This leads to the huge range in embryonic
post-embryonic developmental modes and
larval forms - The differences are referred to as life-
history strategies and life-history trade-offs
What are 5 different cues that might be important to planktonic invertebrate larvae when choosing a suitable habitat for settlement at the end of pelagic larval stage?
-depth
-water flow
-temperature
-food
-predator free
-composition of a surface biofilm
-conspecifics
Describe the slow block to polyspermy.
This is a chemical and mechanical block that is active 1 minute after fusion of egg and sperm.
Contact of the sperm acrosomal tubule triggers a series of events called the cortical reaction of the egg. Cortical granules fuse with the egg membrane and release their contents.This causes the vitelline membrane to separate from the egg membrane at the point of sperm contacts the egg forming a cavity the perivitelline space
This gap spreads around the entire egg as the
membrane peels off.
The material released from the cortical granules comprises protease enzymes as well as material that modifies (hardens) the fertilization membrane or fertilization envelope.
One of the proteases (Serine protease) breaks the
bonds attaching the vitelline membrane to the egg pm
allowing the fertilization envelope to elevate.
Mucopolysaccarides cause water to move into the Perivitelline spaces through osmotic pressure – inflating the membrane.
Serine protease also destroy the glycoprotein sperm receptor sites on the egg surface - assist in the slow block to polyspermy.
Upon elevation the fertilization envelope is hardened
by peroxidases and resistant to sperm entry while destruction of
the receptor sites prevents binding of additional sperm.
The hyaline protein attach to the egg surface forming
a layer called the hyaline layer
What is polyspermy?
Polyspermy is the fertilization of an egg by more than one sperm. In most cases, this results in an embryo with an abnormal number of chromosomes, which is usually not viable. Genetic material causes abnormal
development so it is important for the egg to have
mechanisms to prevent it.
Describe the fast block to polyspermy.
The first (the fast block) is transient and occurs within
seconds of sperm-egg contact. The surface of the egg changes polarity from negative to positive. This stops it because sperm only attaches to negatively charged surface of the egg. The ionic imbalance of the surface that is maintained by membrane pumps creates electrical potential across the membrane before fertilised and the membrane is -70 mV. Sperm binding cause NA+ influx and within 1-3 second of the sperm binding the membrane changes to +20mV. The membrane repolarises over time.
What is serine protease?
It dissolves protein connections between the envelope and membrane and clips off binding receptors and connected sperm
What are mucopolysaccarides?
Sticky compounds and produce osmotic pressure. Water rushed in and vitelline envelope raises (fertilisation envelope)
What do peroxides do?
Oxidises and crosslinks tyrosines - hardens fertilisation envelope.
What does the Hyaline do?
Forms coating around the egg called the Hyaline Layer.
