Development: Flashcards
What is direct development in marine invertebrates?
A strategy where offspring bypass the free-living stage, and directly develop into juvenile forms resembling adults
What are the characteristics of eggs in direct debelopment?
Large, yolky eggs that provide the nutrients needed for the developing embryo
What are the trade-offs of direct development?
High parental investment, low fecundity, reduced dispersal capabilities, potentially higher offspring survival
What is indirect development in marine invertebrates?
A strategy characterised by a free-Iiving larvae stage
What are the two types of indirect development?
Planktotrophic and lecithotrophic
What eggs are found in lecithotrophic development?
Telolithical eggs
What type of eggs are found in planktotrophic development?
Isolithical eggs
What are the characteristics of lecithotrophic larvae?
Develop from large, yolky eggs, non-feeding, fast development, moderate dispersal, increases survival compared to planktotrophic larvae
What are the characteristics of planktotrophic larvae?
Develop from small eggs with little yolk, feeding larvae, long planktonic stage, large dispersal range, high mortality rate.
What percentage of marine invertebrates use planktotrophic development?
90-95% of all marine invertebrates.
What is mixed development in marine invertebrates?
Combines features from both direct and indirect development, where there can be brooding (internally or externally), and a larval stage that can be either lecithotrophic or planktotrophic
What are the characteristics of eggs in mixed development?
- Moderately telothical eggs
- egg size is moderate
- parental investment: mod-high
- fecundity please low to moderate (depending on external or internal brooding)
- dispersal = low to moderate (depends on time in larval form)
What are the advantages of mixed development?
Offers a compromise in terms of fecundity, dispersal potential, offspring survival, and parental investment cost
Give examples of mixed development in marine invertebrates:
Some nudibranch species deposit eggs in protective ribbons with chemical defenses against predation. Barnacles reproduce internally until reaching the Nauplius 1 stage, then release larvae into the water column.
