Reproduction Flashcards
Simons 1
what is reproduction?
The production of gametes to from new offspring either sexually or asexually.
What is asexual reproduction?
Budding or fission. (plathelminthes)
Fragmentation - splitting of individuals into more than one. (Hydrozoans)
Parthenogenesis - parent produces diploid eggs with no meiosis involved. (Daphnia)
What is sexual reproduction?
Gonochorisom or dimorphic - separate male and female.
Hermaphroditic - male and female organs in one individual.
Produces male and female gametes that fuse and develop into embryos.
How does reproduction in the sea occur?
A-dense and viscous = larvae won’t sink
A-high humidity = gametes won’t dry out
A-high [dissolved nutrients] = larvae can feed passively
D-low [dissolved O2] = eggs or larvae risk suffocation.
sedentary adults and sessile juveniles. = small broods.
What are the marine invertebrates life cycles?
Broadcast spawning - fertilization occurs in the water column and develops into free-swimming larvae ( feeding = planktotrophic, non-feeding = lecithotrophic) that eventually settle and metamorphose.
What are the advantages of broadcast spawning?
- no parental care
- larvea can take advantage of short term food sources.
- dispersing larvae = increases the # habitats where the larvae can settle and increases the # of populations and species.
What are the disadvantages of broadcast spawning?
- high mortality
- lots of energy input into reproduction
What is sperm casting and brood protection?
females lay eggs in tubes and males cast sperm into the water column.
What are the advantages of sperm casting?
- population does not need to be synchronized.
- when laying eggs the individual has stored sperm to use for eggs.
- increase fertilisation success (each egg is fertilised as it is laid)
WHat is the disadvantage sof sperm casting?
- sperm dilution (if not close to a female), decreased fertilization.
What is mixed development?
sexually dimorphic, feamle lays capsules within a tube, males release sperm to the female.
Eggs are fertilised as she lays them, eggs develop in capsules and hatch then settle enand metamorphose into juveniles.
Advantages of mixed development?
- protection from dessication
- protection form predators
What is internal fertilisation and direct development?
insemination occurs when males transfer sperm into the female. then internal fertilization occurs in the female. and a small version of the adult is born.
Advantages of internal fertilisation?
- direct transfer of sperm to the egg
- increased change of survival of the embryo
Disadvantages of internal fertilisation?
- high parental care
Which species employ which strategies and where?
- No clear phylogenetic constraints.
- Body size
– Need enough space in body to produce enough eggs to compensate for high mortality of larvae. - Environment
– Conditions that delay larval development are expected to be selected against planktonic/planktotrophic larval phases.
– Latitude (~temperature) - food and temperature
What are the main advantages and disadvantages to reproducing on land and in freshwater?
How could/did terrestrial and freshwater taxa overcame the limitations of reproducing under these conditions?
What do you think the predominant fertilisation strategy is?
Which phylum is/phyla are most represented in these environments? (fresh and terrestrial)
How have their life history strategies pre-adapted them to
these alternative/stressful environments?
What are the consequences of internal fertilization?
- Complex copulatory behavior leading to sexual selection
- Adults rarely hermaphroditic - Embryos all lecithotrophic
- Eggs must include enough nutrients to enable
development
Non-marine, non-arthropod
invertebrates reproduction:
- Eggs are not freely discharged
- sperm storgae
- internal, intracapsular fertilisation, complex mating behaviors
- large egg yolk concentration
- Absent care of young, guarding/brooding, food provisioning
- often hermaphoroditic
- multiple reproductive events
Small marine invertebrate reproduction:
- eggs not freely discharged
- sperm storage
- internal/intratubular fertilisation
- large egg yolk concentration
- usually brooded care of young
- hermaphoroditic or gonochoristic
- multiple breeding events.
LHS for freshwater & terrestrial invertebrates that are
NOT arthropods
Selection pressures differ:
Environment vs small body size
arthropod reproduction
- Why are Arachnida (spiders, scorpions, ticks & mites), Myriapoda (millipedes & centipedes) & Insecta (insects) so successful?
– Adults AND eggs have waterproof external covering
– Development may be internal - Very strong phylogenetic signal – closely related taxa reproduce in similar/the same way.
Development and metamorphosis in terrestrial arthropods?
- Arachnida & Myriapoda
– Live birth (scorpions)
– Eggs - hatchlings that look like small adults (spiders)
– Eggs - hatchlings look like adults, but - fewer pairs of legs (mites and ticks) or legs and segments (millipedes and centipedes)
- Hexapoda/Insecta
– Various levels of metamorphosis.
Development in crustaceans:
one taxa is fully terrestrial - woodlice [isopod]
Incomplete metamorphosis
insect development
Ametabolous - no metamorphosis, just gets bigger
Hemimetabolous - incomplete metamorphosis
Holometabolous - complete metamorphosis
Insect life history strategies:
- 3 modes of parental care
– Non-carers (e.g., Ephemeroptera, locusts)
– Guarders look after eggs but don’t provide extra food - Protect against predators, keep eggs clean of fungi etc.
– Provisioners provide offspring with food (e.g., certain
wasps, dung beetles) - Life history traits expected to differ among these
groups towards optimising reproductive success
– Egg size, life-time fecundity
Parental care trade-offs in insects:
- No trade-off between egg size and number
- Mean egg size ALWAYS increases with body size regardless of degree of parental care.
- Within adult size classes, egg size does not increase with increased levels of parental care.
parental care trade-offs in marine and fresh water insects:
- In marine and freshwater invertebrates, egg size (usually) increases with
– increased parental care, and
– decreased adult size - Why insects showing parental care may lay large eggs (guarders AND provisioners)
– Increased developmental time increases the period of protection
– Decreased mortality of eggs
– Fewer larger eggs decrease sibling conflict after hatching.
parental care trade-offs in non-cares/guarders/provisioners
- For non-carers and guarders
– There was no significant trade-off between lifetime fecundity (clutch size) and egg size.
– Lifetime fecundity increases slightly with adult body size - Guarders find it equally easy to look after big and small broods
-
For provisioners
– Lifetime fecundity (clutch size) decrease with an increase in adult body size and egg size - Larger provisioners laid fewer eggs
- Limit to how much it can increase foraging rate as adults get bigger,
– If clutch size increases too much, she won’t be able to collect enough food to feed whole brood.
– Better to keep clutches smaller.
Why do animals reproduce when they
do?
- Reproduction can only happen when multiple coordinated sequences of cellular activity have been completed
- Timing of reproduction is coordinated by
– Ultimate forces - Evolutionary forces that control timing of reproduction
– Reason for coordination
– Proximate forces - Environmental events that regulate the progression of gamete production & therefore timing of reproduction
– Process of coordination
Control of reproduction in marine
invertebrates
Temperature effects in reproduction in marine invertebrates
- Timing of spawning
- only when all sequences are synchronized, specific ques
- when it is dark there are less predators
Synchronous reproduction in marine invertebrates
Multispecies spawning on the Great Barrier Reef
- hard and soft coral mass spawning in Panama.
These spawning events usually occur in early summer, after a specific period of darkness, and at low tide after the full or new moon. - when there are less predators.
These are the proximate forces. What are the ultimate forces? That is, WHY would spawning occur at these times?
Endocrine control of reproduction in
marine invertebrates
Hormones that stimulate gonad function & development
Reproduction in Nereidid polychaetes
- Female (summary)
– High brain hormone → growth of body tissue, mitotic division of oogonia (cells that develop into oocytes)
– Low Brain Hormone, low temperature, short days → vitellogenesis
– Lower Brain Hormone, warm temperature, longer days → oocyte maturation - Male:
– High Brain Hormone → mitotic division of spermatogonia (i.e., cells that develop into sperm)
– Low Brain Hormone → meiosis and spermatogenesis (development of sperm) continues - Lunar cue→ spawning
Semi-continuous breeder Cirratulus cirratus
Environmental conditions don’t exert
control over oogenesis
Control of reproduction in terrestrial
and freshwater invertebrates
Environmental conditions that may influence reproductive cycles in terrestrial & freshwater invertebrates:
Very high seasonal variability
– Food availability
– Temperature
Reproductive activity
vs.
Reproductive inactivity
Environmental cues:
Photoperiod - perception
Photoperiod info
Endocrine system
Reproduction (long days)
Reproductive inactivity (short days)
Reproductive inactivity?
- Quiescence - adult stages of molluscs, earthworms, some insects
- Diapause
– Physiological resting phase
– Facultative - adult stages of molluscs, earthworms, some insects
– Obligatory - early stages: eggs, larvea, pupae
Survive drought/ polar winter:
* Cold winters
* Extreme heat
* Low / no food
Insect larval or pupal diapause
Shut down of brain – Prothoracic Gland axis
– Most common system
Adult insect diapause
Shut down of JH (Juvenile Hormone) synthesis by corpora allata in the brain
