SEX AND REPRODUCTION

MAIN FEATURES

SEX

REPRODUCTION

COMPLEX LIFE CYCLES

LONG DISTANCE DISPERSAL, MIGRATION

1. IS SEX NECESSARY?

2. ARE SEX AND REPRODUCTION LINKED?

COST OF SEX

-FEMALE gives up half her possible genes in progeny

- finding a mate, fighting off other mates

BENEFIT

-genetic diversity - sex increases combinations

of genes - resistance against disease

Sexual Selection - selection for extreme forms that breed more successfully - major claw of fiddler crabs, deer antlers, colors of male birds

TYPES OF SEXUALITY

Separate sexes (gonochoristic)

Hermaphroditism

Simultaneous (bryozoa, some corals)

Sequential

male --> female or protandrous (oyster)

female --> male or protogynous (many

reef fish

WHEN TO CHANGE SEX?

WHICH WAY TO GO?

SIZE-ADVANTAGE MODEL

SIMULTANEOUS HERMAPHRODITES? question of relative male and female functionFACTORS IN REPRODUCTIVE SUCCESS

1. % investment in reproduction

2. age of first reproduction

3. predictability of reproductive success

low predictability: reprod. more than once

4. juvenile/adult mortality rate

High overall mortality or high adult mortality:

early age of 1st reprod., reproduce once

High juvenile or fluctuating juv. mortality/low adult mortality:

reproduce more than once

SPERM TRANSFER

1. Planktonic sperm (and eggs in many cases). Problem of timing, specificity.

2. Direct sperm transfer (spermatophores, copulation). Problem of finding mates (e.g., barnacles, timing of reproductive cycle)

SEX DETERMINATION - usually genetic, but occasionally environmental (some fish, turtles)

ASEXUAL REPRODUCTION

1. Whole body division (e.g., ciliates, anemones,

diatoms, annelids)

2. Body division into connected colony (e.g.,

corals, bryozoa)

3. Body fragmentation (many seaweeds, corals)

4. Reproduction without fertilization -

uncommon in marine habitats

Mixed strategies (e.g., sperm transfer plus whole

body division - anemones)

MOVEMENTS OF MARINE ORGANISMS

DISPERSAL VS. MIGRATION

DISPERSAL: UNDIRECTED

MIGRATION: DIRECTED, RETURN SPECIFIC

MIGRATION: Common in marine mammals, many fishes, some invertebrates (crustacea, cephalopods)

MIGRATION TYPES

ANADROMOUS - fish live as adults insalt water, spawn in fresh water (shad, striped bass), more common in higher latitudes

CATADROMOUS - fish live as adults in fresh water, spawn in salt water (eel) more common in lower latitudes

FULLY OCEANIC - herring, green turtle

Specificity of migration - non-specific in some, very specific in others (green turtle, oceanic salmon)

Herring - spawning on grounds nearshore, juveniles drift in currents to wintering feeding grounds, adults swim back to spawning grounds

EEL MIGRATION - adults live in marshes, creeks (European, American), migrate to Sargasso Sea, spawn, die, juveniles drift in currents and American eels swim to shore, European eels drift across Atlantic

LARVAL DISPERSAL

PLANKTOTROPHIC DISPERSAL -

female produces many (103 - 106) small

eggs, larvae feed on plankton, long dispersal

time (weeks), some are very long distance

(teleplanic) larvae - cross oceans

LECITHOTROPHIC LARVAE - female

produces fewer eggs (102 - 103), larger,

larvae live on yolk, short dispersal time

(hrs-days usually)

DIRECT RELEASE - female lays eggs, or

broods young, juveniles released and crawl

away

PROBLEM OF SWIMMING LARVAE:

water motion carries them away from

appropriate habitats

Some helping hands in dispersal

1. Winds that wash larvae to shore

2. Internal waves - bring material and larvae to shore

3. Eddies that concentrate larvae in spots

4. Behavior - in estuaries can allow retention

Effect of eddies:

Use of estuarine currents to migrate to shelf

Blue crab, fiddler crab:

Use of estuarine currents to stay in estuary (oysters, mud crab): concentrates larvae upstream

WHY DISPERSE?

important: planktotrophs cannot settle immediately, they have an obigatory period in plankton

- High probability of local extinction; best to

export juveniles

- Spread your young (siblings) over a variety of

habitats; even out probability of mortality

- Maybe it has nothing to do with dispersal at

all; just a feeding ground in the plankton for

larvae

SETTLING PROBLEMS

PRESETTLING PROBLEMS

TIMING OF RELEASE OF LARVAE

STARVATION

PREDATION IN PLANKTON

LOSS TO INAPROPRIATE HABITATS

Example: Starvation

POSTSETTLING PROBLEMS

FINDING EXACT MICROSITE

FIRST MEAL

METAMORPHOSIS

COMPETITION WITH RESIDENTS, OTHER

SETTLERS

BENTHIC PREDATORS

CUES TO SETTLEMENT