reproduction Flashcards
what’s Gonochoristic (dioecious)
Separate sexes (all chondrichthyans, most actinopterygians)
what’s Hermaphroditic
have both male + female reproductive parts
- Synchronous: can be both sexes at the same time - Useful in low abundances
- Sequential: one sex after another
-Protandrous - male becomes female
-Protogynous - female becomes male
Advantages of sequential protandrous hermaphroditism
- Small male can produce a lot of sperm – small cells, cheap to make
- Larger females will have more energy reserves – able to make lots of eggs
- More chance of getting your genes into the environment
reproductive strategies of Most actinopteryginians
- Large numbers of eggs with little provision (little yolk) and no aftercare e.g. cod
- Most fish
- High Fecundity - maybe millions of eggs per individual (related to body size - older, larger females produce more eggs)
- Gametogenesis (produces egg) and vitellogenesis (produces yolk) both require large amounts of energy - Eggs therefore small (<1mm) + have little yolk
reproductive strategies of chondrichthyans
Very few offspring with lots of provision (lots of yolk) and aftercare e.g. most sharks
what is Broadcast spawning
- Unique to aquatic animals
- High fecundity of small eggs - gametes released into water column for external fertilisation without mate selection
- Not a random process - There are both temporal and spatial requirements
temporal and spatial requirements needed for broadcast spawning
- Eggs and larvae are usually planktonic so released into offshore currents to take away from land
- Strong currents to mix gametes for fertilisation
- Synchronization of timing:
availability of food for larvae
greatest chance of fertilisation
predator saturation
what is Attrition
far more zygotes produced than will ever reach maturity - mortality rates of over 99.99%
what is batch spawners and its advantage
spawning multiple batches of eggs
- spread the energy cost
- allowing higher fecundity and reducing the risk of mortality caused by freak conditions
what are Ichthyoplankton
eggs and larvae of fish – most teleosts spend a lot of time in plankton stage to feed and become juvinilles
how does Spawning synchronization occur
Timing tied to maturation cycle within adult which is cued to environment:
- Photoperiod (most reliable) and temperature are the most common cues
- Location important as juvenile stages need appropriate food and protection
Spawning sites characteristics
- If larvae come from single spawning site they will end up in the same nursery area
- Spawning sites tend to be consistent between generations, producing a hydrographic containment of that population
- This generates reproductive isolation from other populations of the same species which spawn at different locations or different times
- Such independent populations are known as a stocks
what is parity and its 2 different types
How many times you reproduce
- Semelparity (semelparous) = Once in a lifetime (monocyclic) - Usual in stable environments
- Iteroparity (iteroparous) = More than once in a lifetime (polycyclic) - Unpredictable environment
when do Fish start reproducing
at first maturity – generally, slow growing fish start later in life
how does fishing affect populations
Fishing reduces average size/age of first maturity in population
- Fishing removes fish from population
- With less competition for food, the remaining fish grow quicker and mature earlier
- Fishing targets older/larger individuals
- This selects against later maturing fish, allowing earlier maturing fish (genes) to predominate
3 strategies for parental care
- Oviparous - no parental care
- Oviparous - some parental care
- Internal incubation/gestation
what is Oviparous with no parental care
no parental care
- The most common style of reproduction in fish + essential for broadcast spawners
- Production of demersal eggs without parental care (herring, some capelin) is uncommon and may be the start of evolution to parental care
what is Oviparous with some parental care
some parental care
- Spawning site selection
- Territorial behaviour
- Nest building
- Courtship
- Investment activities usually short-lived
what is Internal incubation/gestation
Viviparity is rare in teleosts
More common in elasmobranchs
what kind of fertilisation do Chondrichthyans show
internal fertilisation
- Intromittent organs (transfer sperm): claspers formed from the posterior portions of pelvic fins
explain oviparity in Elasmobranch reproduction
egg laying
- Few large eggs are laid individually with large yolk reserves and tough egg case.
- Development time is considerable (5-12 months, typically)
- Newly hatched juveniles are totally independent e.g. skates, dogfishes
explain Ovoviviparity (aplacental) in Elasmobranch reproduction
live birth
- Many elasmobranchs
- Eggs retained in body after internal fertilisation
- If eggs hatch substantially before birth, the young will require further nutrition:
- Uterine oophagy: consuming unfertilised eggs produced for this purpose - sandtiger sharks show uterine cannibalism: the largest foetuses consume the smaller ones until only a single pup is present in both of the uteruses
- Some rays produce a fat and protein-rich uterine “milk”
explain Viviparity (placental) in Elasmobranch reproduction
live birth
CARCHARHINIFORMES
- Developing embryo is nourished via a placenta
- The empty yolk sac attached to the uterine wall to form a yolk- sac placenta
- Nutrients and oxygen pass from mother to foetus through an umbilical cord derived from the yolk sac stalk, waste passes the other way
e.g. In smoothounds the embryo is nourished from a yolk sac for 3 months then via a placenta for 7-8 months
what are Permanent intertidal residents
Occupy region most of time
- most are herbivorous
what’re Non-resident intertidal visitors
Use intertidal on seasonal and tidal basis
- most are carnivorous - have to adjust their behaviour patterns to coincide with the presence of their prey
- Most visiting fish use the intertidal for many of the same reasons that they use estuaries:
Predator avoidance
Increased food supply
Increased water temperature
what do Most visiting fish use the intertidal for
many of the same reasons that they use estuaries:
Predator avoidance
Increased food supply
Increased water temperature
what are intertidal areas common for and why
nursery areas for juvenile fish because..
- Small fish have:
Bigger range of predators – small in size
Smaller range of food items – smaller mouths
- First year of life is period of maximum mortality, especially the first winter
- Bigger fish with more food reserves survive winter better
- Adult fish that use such areas do so for the primary reason that they are full of young fish for lunch
Intertidal environmental challenges
Wave effects
Temperature effects
Desiccation
Respiration in air
Salinity effects
**Permanent residents show adaptations for these
adaptations of intertidal residents for Wave effects
- Fish are dense and negatively buoyant (small or no swim bladder)
- Some possess suckers (clingfish, lumpsucker and gobies use modified pelvic fins) - allow to attach to something
- Thickened epidermis
- Body shape often depressed to reduce drag and generate downward pressure
adaptations of intertidal residents for Temperature / Desiccation effects
- Must be eurythermic
- Behavioural adaptation to stay under cover or rockpools
- Physiological adaptations such as slow permeability skin, tolerance to water loss (can be up to 20% of body weight)
- Temperature and desiccation often control upper limit of distribution
adaptations of intertidal residents for Salinity / respiration effects
- fish need to be euryhaline
- Can fluctuate from high levels (>90) in rockpools in summer to almost freshwater in winter storms
- Modifications to aerial respiration through modified gills or accessory organs
main additional adaptation of intertidal fish
- camouflage - Morphological coloration is usually mottled brown/green
- size - need to hide from predators, minimize wave drag and dislodgement means most are small sized
what do many intertidal fish show a high degree of
territoriality
what is reproductive territoriality
Common in intertidal fish as many show parental
care, such as egg guarding
- Requires choice of appropriate location: avoiding desiccation, predation and temperature fluctuations
- Eggs require aerating, defence from predators, prevention of algal overgrowth
- Mudskippers make a burrow nest within their territory - Another reason to defend it with walls
what is non-reproductive territoriality
Usually associated with partitioning environment to ensure efficient use of resources (such as food and shelter) and regulating population size
- Access to shelter is very important : Poor swimmers, so need holes and crevices to hide in and the ability to find them quickly when threatened
- Aquatic gardening common in tropical blennies, significant energy investment so it is important to defend them from neighbours
- Some mudskipper species build mud walls to demarcate their territory
what does Territoriality require
- Fish does not move far (common in intertidal fish)
- Ability to recognise and remember surroundings, and use this memory to relocate to territory - This is homing (return to a place formerly occupied instead of going to equally probable places)
- Vision and olfaction thought to be important
- Hierarchical behaviour also common in territorial fish (dominating male or female) - Common blenny show a dominance hierarchy which controls their behaviour patterns
what are Biological rhythms and what are they initiated by
Provide synchronisation of activity within the predictably changing conditions of the intertidal
- Can be initiated by exogenous cues such as:
Flooding
Light
Temperature
Salinity
- Many species also have endogenous rhythms (rhythms within the fish itself) - more important in non-resident intertidal fish
