Life cycles, larvae, and reproductive strategies

what is external fertilisation

the union of male and female gametes outside the bodies of the individuals from which they originated, also called spawining

how does external fertilisation occur in the sea

both gametes are released directly into the sea, fertilisation occurs as the gametes mix in sea water, nearly all fish spawn, as do crustaceans, molluscs, squid, and echinoderms

what are the advantages of external fertilisation

allows sessile and widely dispersed, slow-moving species to sexually reproduce, requires little investment of parent time or energy beyond producing gametes

what are the disadvantages of external fertilisation in the ocean

low fertilisation success, gamete wastage, predation, environmental sensitivity, no parental protection (usually)

how can success of external fertilisation be increased

produce huge numbers of small gametes (overwhelm/satiate predators), synchronised spawning, spawn in close contact (success highest when individuals are less than one cm apart, spawn in calm conditions

what are the characteristics of eggs produced for external fertilisation

small with minimal food reserves, eggs typically hatch into planktotrophic larvae, survival rate of eggs produced by broadcast spawning is low, but compensated for by the high number

what is broadcast spawning

a form of external fertilisation where organisms release eggs and sperm into the water column, and fertilisation occurs outside the body

what is internal fertilisation

the union of male and female gametes inside the bodies of the individuals from which they originated, avoids planktonic eggs and larval stages, fertilisation usually occurs in the female and is rare among sessile species (found in some such as barnacles)

what is internal fertilisation associated with

the evolution of copulatory structures and limited mating behaviour

what are the advantages of internal fertilisation

allows mate choice to develop, greater success in fertilisation (fewer gametes necessary and production of larger eggs), planktonic egg stage can be avoided as this often involves brooding the eggs internally or depositing them in a favourable site, planktonic larval stage can be avoided because juveniles can be directly hatched from internally brooded or deposited eggs, non-developing nurse eggs can be provided as food for juveniles

what are the disadvantages of internal fertilisation

have to find a mate, can limit the number of offspring as large, yolk-filled eggs are expensive and brooding young can be expensive, can have a greater predation risk while carrying or caring for offspring

what kind of fertilisation do corals have

broadcast spawning

what challenges do corals face using broadcast spawning

gamete dilution, need for precise synchronisation, low population density (sometimes), predation, environmental sensitivity, high larval mortality

what advantages do corals gain from broadcast spawning

wide dispersal of offspring, increased genetic diversity, no need to physically find a mate, energetically efficient for sessile organisms, resilience after disturbance

what strategies do corals used to maximise reproductive success

precise spawning synchrony, mass spawning events, high gamete production, buoyant gamete bundles, chemical signalling, timing with favourable currents, genetic compatibility mechanisms

what are some key benthic groups that have planktonic larvae

crustacea, echinodermata, annelida, mollusca

what species have trochophore larvae

annelids, mollluscs (in molluscs the trochophore often develops into a veliger larva)

what are the key features of trochophore larvae

free-swimming, ciliated bands for locomotion and feeding, bilaterally symmetrical, often planktonic

what species often have nauplius larvae

most crustaceans (first larval stage)

what are the key features of a nauplius larva

unsegmented body, single median eye, three pairs of appendages (antennules, antennae, mandibles), usually planktonic

what species typically have pluteus larvae

echinoderms, especially sea urchins and brittle stars

what are the key features of a pluteus larva

bilaterally symmetrical, planktonic, equipped with long ciliated arms supported by skeletal rods, used for swimming and feeding

what are the three paths of larval development in benthic animals with limited amounts of energy to invest in reproduction

planktotrophic development, lecithotrophic development, non-pelagic development

outline planktotrophic development

larval stage is spent feeding in the plankton - grow, disperse, many small eggs that hatch quickly: larvae, substrate selection and settlement, bottom dwelling invertebrate

outline lecithotrophic development

non-feeding larval stage is passed in the plankton, disperse only, fewer eggs with more energy: larvae, substrate selection, bottom dwelling invertebrate

outline non-pelagic development

larval stage is passed in the egg and the hatchling is a juvenile: egg capsule, juvenile hatches, bottom dwelling invertebrate

what are the advantages of planktotrophic development

small eggs, so many can be produced, have access to food in plankton, larvae disperse widely

what are the disadvantages of planktotrophic development

variable food supply and conditions in plankton, vulnerable to predations in plankton

what are the advantages of lecithotrophic development

less exposed to predation, less influenced by variable food supply in plankton, still some dispersal

what are the disadvantages of lecithotrophic devleopment

yolky eggs are expensive so fewer are produced

what is the main advantage of non-pelagic development

avoids predation in plankton

what are the disadvantages of non-pelagic development

yolky eggs are expensive so fewer produced, limited dispersal increasing competition with relatives

why is dispersal an advantage

reduction in intra-specific competition, exploitation of new areas, promotes out-breeding

why is survival so poor in pelagic larvae

they often drift away and settle out in unsuitable environments

how do larvae know where to settle

when they encounter: other members of the same species, suitable substrates, food supply, environmental cues such as light or humidity

give a brief overview of the barnacle life cycle

small eggs hatch into planktotrophic larvae, planktonic nauplii, develops into non-feeding stage, cyprid larva seeks site for attachment and metamorphosis, hermaphroditic adult barnacles with cross fertilisation

how do barnacles decide where to settle

cyprids that land where there are no barnacles move on and try again, cyprids which locate adult barnacles settle out and metamorphose

what is reproductive strategy

the way in which species budget energy to produce viable offspring

what defines an individuals sex

the size of gametes, females have few, large, immobile gametes, males have numerous, small, mobile gametes

what does gonochoristic mean

single sex fixed over entire life

what does simultaneous hermaphrodite mean

both sexes occur in the same individual at once

what does sequential hermaphrodite mean

both sexes occur in the same individual sequentially

what does protandrous mean

fish that change from male to female

what does protogynous mean

fish that change from female to male

why does the tilapia industry care about global warming

masculinisation could become uncontrolled, sex ratios in populations may shift