reproduction & biogeography Flashcards
definition of reproduction
Replication of individuals (required for population maintenance/growth)
definition of dispersal
Geographical spread of progeny
definition of migration
Directed movement to a different location
what’s the reproductive strategies
asexual vs sexual
gonochorism vs hermaphroditism
what’s the fertilisation strategies
broadcast spawning
copulation
what’s the larval strategy
associate energy with number of larvae
name asexual reproduction strategies and what organisms do it
- Asexual reproduction in salps and doliolids
- Fission in polychaetes and echinoderms
- Fragmentation in corals
- Budding in colonial invertebrates (corals, ascidians, etc.)
- Budding in solitary cnidarians (anemones)
- Strobilation in scyphozoans
when is asexual reproduction beneficial
under favourable conditions; where mates are hard to find or (in colonial forms) where size confers an advantage (e.g. stronger feeding currents, resistance to predation)* - requires less energy
what is Hermaphroditism
Both male and female reproductive organs
what are the 2 different types of Hermaphroditism
Sequential hermaphrodites
- Start as one sex, changes to another e.g. slipper limpet
Simultaneous hermaphrodites
- Possesses both reproductive organs at the same time
- Self-fertilisation rare, however but any two organisms of the same species can mate with each other e.g. barnacles
what kind of method does sexual reproduction require
method of sperm transferral - living in seawater allows the simple shedding of sperm and eggs into the water column
- Planktonic gamete production is often synchronous (tied to tidal or lunar cycles)
- Special chemical mechanisms for gamete recognition
what ensures successful sperm transferral
Direct contact or copulation
- Physical factors (distance, turbulence) will affect fertilisation success
what is brooding
Fertilisation from copulation, or inhalation of sperm
- Eggs and sometimes larvae are retained - larvae released are comparatively more developed
- For example, decapod larvae undergo the nauplius stage within the egg, hatching as more developed zoea
3 reasons why the Vast majority of planktonic larvae will die
- swept into inhospitable habitats
- predation
- Starvation
what’s the 3 larval strategies
- Direct release
- Dispersal over a short distance (relatively short- lived, lecithotrophic larvae)
- Dispersal over a long distance (longer-lived, planktotrophic larvae)
explain the direct release larval strategy
- Larvae released next to adults: NO PLANKTONIC STAGE
- Many species viviparous, or brood larvae, producing juveniles as miniature adults
- Littorina saxatilis - broods fertilised eggs and releases fully-formed (but very small) snails
- Nucella lapillus = oviparous – eggs are cemented to the substrate and hatch as miniature adults
what are lecithotrophic larvae
- Larvae that depend upon a yolk for nutrition (relatively large egg)
- Larvae have no feeding or digestive structures
- Capable of limited swimming – few hours to a day in the water column
- Short dispersal – 100s metres at most
e.g. tadpole larvae of tunicates
what are planktotrophic larvae
- Feed whilst they are in the plankton
- Feed on planktonic bacteria, phytoplankton, smaller zooplankton
- Planktonic stage can last several months
- Much greater capacity for dispersal over a long distance
- Often, development progresses through a series of stages (e.g. crustacean zoea and megalops stages)
- Particularly long lived larvae can cover very long distances: Teleplanic larvae
what are the two important risks Planktonic larval stages come with
- Predation
- Finding a suitable settlement site
- Some planktotrophic larvae (e.g. Mytlius edulis) can delay metamorphosis until a suitable site is located
Planktotrophic larvae characteristics
- they are in the plankton for longer, so there is a balance between dispersal, energy investment and survival
- For planktotrophs, timing is everything - In British waters, spawning is often timed to take advantage of the spring phytoplankton bloom
- Planktonic larvae = rare at high latitudes
what’s the Position in water collum of Planktotrophic larvae
- Larvae will go through one or more stages of photopositive and photonegative behaviour
- Larvae can show behavioural (depth) changes to take advantages of local currents and tides
- Water = very hard to move through when small – produce monofilaments to reduce drag
what is photopositive and photonegative behaviour
Photopositive – near surface
Photonegative – close to bottom
how do Planktotrophic larvae settle
- Larvae use chemical and mechanical cues to select an appropriate substrate
- Some show gregarious settlement
- SIPC – Settlement-inducing protein complex
what are the Advantages of planktonic larvae
- Species with planktonic larvae generally occur over greater geographical ranges than those without
- Avoiding over-crowding
- Taking advantage of new habitats
- Marine ecosystems are not stable (even in the deep sea)
- Larval spillover from protected areas
what is The fundamental limit on species’ distribution
physiology (also evolutionary history - shown by invasive species)
- The continental shelf is a significant barrier
- Also: currents, major river outflows, land masses
