Reproduction, Dispersal, and Migration

Objectives: Recognize the different forms of reproduction and their benefits, protrandry, protogyny, factors in fertilization. Know what’s involved in larval dispersal, r vs K strategists, meroplankton vs holoplankton. Be able to describe forms of migration and related intricacies.

Reproduction

  • Asexual: clonal offspring, budding and fission

  • Sexual: you know this

  • Ability to switch between both, ex. bryozoans

Cost of Sexual Reproduction

  • Energy is needed for females to produce offspring and harbor young

  • Expenditure of energy and time to find mates

  • Combat costs among males

Sexual selection vs natural selection? Sexual selection involves forms that are attractive to females. Think deer antlers, coloration in birds, etc. Females choose fit males. ex. fiddler crab has a large claw to fight against other males with.

Types of Sexuality

  • Separate sexes is called gonochoristic.

  • Hermaphrodism: individuals can have male or female function, simultaneously (acorn barnacles) or sequentially, during sexual maturity. Protandry - First male, then female. Larger females are more advantageous. Protogyny - first female, then male. Larger males are more advantageous. Ex. aggression, protecting territory.

  • Male polymorphisms: some males are more aggressive morphs and others are less aggressive morphs. Ex. Isopods, Anglerfish

Factors in Reproductive Success

Percent investment in reproduction/effort

  • r-strategist: high fecundity (produce a lot of young), small body size, early maturity, short generation time. ex. Bunny

  • K-strategist: larger body size, fewer offspring, extensive care, long life expectancy ex. Elephant

  • Other factors: Age of first reproduction, predictability of reproductive success (reproduce more than once), juvenile vs adult mortality rate

Weird case: Orange Roughy - First reproductive age at 20 years old (very old)

Fertilization Factors

  • Planktonic sperm/eggs: problem of timing. Binding proteins on the surface of sex cells need to match to fertilize.

  • Direct sperm transfer: problem of finding mates.

Timing of sperm and egg release

  • Epidemic spawning: One spawner causes a mass spawning. ex. mussels

  • Mass spawning: Many species spawn at single periods. ex. coral

  • Timing of spawning at times of quiet water to maximize fertilization rates

Dispersal of Larvae

Meroplankton: Organisms that spend part of their life cycle in plankton.

Holoplankton: Organisms that spend entire like in plankton

Dispersal types in Benthic species (close to seafloor)

  • Planktotrophic larvae (70% of benthic invertebrates): Females produce many small eggs. Larvae feed on plankton, long distance larvae cross oceans.

  • Lecithotropic larvae: females produce fewer larger eggs. Larger larvae live on yolk (lipids and proteins), short dispersal time.

Examples of reproductive strategies: jaw fish incubates his eggs in his mouth

Birth and how young are handled

Direct release: Females lay eggs/brood young, juveniles are released and crawl away. Uncommon in invertebrates

Viviparous - mini-adults released, embryonic development inside (mammals)

Oviparous - egg sacs attached to rocks, little embryonic development (snails)

Benthic larvae: Multiple larval stages (poecilogonic), varying feeding modes, morphological adaptations (spines, transparency)

Dispersal Scales: Microscale (mm to cm), Mesoscale (m to km), Macroscale (100 to 1000s of km). Why disperse? Food sources may be scarce.

Settling problems of planktonic larvae

  • Presettling problems: Starvation, predation, loss to inappropriate habitats

  • Postsettlng problems: Energetic cost of metamorphosis, predation, crowding by other organisms

Migration

Spawning area → nursery area → adult stock

Influential factors

  • Feeding: Sufficient resources while avoiding competition?

  • Spawning conditions: Change between fresh and saltwater (salmon), need land (turtles)

  • Nursing: requires optimal temperature and shelter

Migration types

  • Anadromous - live as adults in seawater, go to freshwater to spawn. Occurs at higher latitudes (lamprey, salmon, trout)

  • Catadromous - live as adults in freshwater, travel to seawater to spawn. Common in lower latitudes.

  • Diadromous - residence time divided between fresh and saltwater environment

  • Fully oceanic (Tuna)