5 Reproduction, Dispersal, and Migration

Notes for Marine Biology: Function, Biodiversity,

EcologyBy Jeffrey S. Levinton

©Jeffrey S. Levinton 2001

Sex and Reproduction

• IS SEX NECESSARY?

• WE MUST SEPARATE SEX AND REPRODUCTION?

• SPECIES CAN REPRODUCE WITHOUT SEX (CLONAL GROWTH INVOLVING FISSION OR BUDDING OF INDIVIDUALS)

Sex and Reproduction

• Non-sexual reproduction:Descendants are genetically identical

- cloneColonial species produce a set of

individuals that are genetically identical, known as a module; each module may have arisen from a sexually formed zygote

Cost of Sex

• FEMALE gives up half her possible genes in progeny

• Sex involves expenditure of energy and time to find mates, combat among males

Benefits of Sex?

• genetic diversity - sex increases combinations of genes - resistance against disease

• Alternative to sex: clones, must wait for mutations to occur

• Sex - recombination produces variable gene combinations, meiosis enhances crossing over of chromosomes: new gene combinations and intragenic variants

Sexual Selection

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

• Can involve selection for display coloration, enhanced combat structures

• Female choice often involved; selection for fit males (good genes hypothesis)

Sexual Selection

The major claw of fiddler crabs is employedfor display to attract females and for combatwith other males

Types of Sexuality

• Separate sexes -gonochoristic

• Hermaphroditism -individual can have male or female function

Hermaphroditism

• Simultaneous • Sequential

Protandrous - first male,then female

Protogynous - first female then male

Sequential Hermaphroditism

• Protandry - size advantage model• Eggs costly in terms of resources, so more offspring

produced when individual functions as female when large• Male function does not produce great increases in

offspring when it gets largerTherefore, there is a threshold size when female function

begets more offspring.Smaller individuals do better as males.

Male at advantage Female at advantage

Female

Male

Body size

Num

ber

of o

ffsp

ring

pro

duce

d

The size advantage model for Protrandry

Protogyny

• Male function must result in more offspring when male is older and larger

• Important when aggression is important in mating success, e.g., some fishes where males fight to maintain group of female mates

Male polymorphism

• Males may occur as aggressive fighting morphs, or less aggressive morphs

• Found in a number of groups, e.g., some fishes and some amphipod or isopod crustaceans

• Determination of morphs can be environmental, genetic

• Less aggressive morphs can obtain mates by “sneaky” tactics, which are often successful

Factors in Reproductive Success• Percent investment in reproduction -

reproductive effort

• Age of first reproduction (generation time)

• Predictability of reproductive success

• Juvenile versus adult mortality rate

Life History Theory

• Tactics that maximize population growth

• Evolutionary “tactics”:Variation in reproductive effort, age of reproduction, whether to reproduce more than once

• Presume that earlier investment in reproduction reduces resources available to invest in later growth and survival

Examples of Life History Tactics• Strong variability in success of

reproduction:reproduce more than once

• High adult mortality: earlier age of first reproduction,perhaps reproduce only once

• Low adult mortality: later age of first reproduction, reproduce more than once

Example: Selection in a Fishery• Shrimp Pandalus jordani,protandrous

• Danish, Swedish catch (Skagerak)

1930-1956 – stable, increased slowly

1956- 1960 – catch tripled (2000 6300 ton/y)

Period % over 80 mm Somaticgrowthchange

1949-1950 44% 01954-1957 25% 01961-1962 14% 0

Period % females < 75 mmlong

Before 1954 01954 7% (65-74 mm)1955-1962 14 % (55-74 mm)

Changes in Body Size

Changes in Size of Change from Male to Female

Pandalus jordani fishery

Sex - factors in fertilization

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

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

Planktonic sperm and eggs

• Specialized binding/fertilization proteins in sperm and receptors in eggs (bindin in sea urchin sperm, lysin in abalone sperm)

• Sperm attractors in eggs

• Binding proteins are species-specific, proteins with high rates of evolution

Gamete matching important in plankton

Timing of sperm and egg release

• Epidemic spawning - known in mussels, stimulus of one spawner causes other individuals to shed gametes

• Mass spawning - known in coral species, many species spawn on single nights

• Timing of spawning (also production of spores by seaweeds) at times of quiet water (slack high or low tide) to maximize fertilization rates

Movement of Marine Organisms

Dispersal versus migration

DISPERSAL: UNDIRECTED

MIGRATION: DIRECTED, RETURN SPECIFIC

Migration scheme

Adult Stock

SpawningArea

Nursery/JuvenileFeeding Area

Migration Types

• ANADROMOUS - fish live as adults in salt 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

Migration

Geographic Specificity ofmigration - non-specific insome, very specific in others(green turtle, oceanic salmon)

Migration ofthe herringin the North

Sea

Norway

Adultfeedingarea

Spawningareas

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

Africa

Europe

N. America

Larval Dispersal

Dispersal Types in Benthic Species

• 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

Lecithotrophic larva: tadpole larva of the colonial ascidian Botryllus schlosseri

Planktotrophic larva ofsnail Cymatium parthenopetum

Pluteus larva of an urchin

PROBLEM OF SWIMMING LARVAE:water motion carries them away fromappropriate habitats

Shore Population

Longshore drift

Loss to offshore waters

Self-seedingeddies

Wind-drivenrecruitment

onshore

Internal waves, tidal bores

Some helping hands in dispersal• Winds that wash larvae to shore

• Internal waves - bring material and larvae to shore

• Eddies that concentrate larvae in spots

• Behavior - in estuaries can allow retention (rise on the flood tide, descend on the ebb tide)

Estuarine larval adaptations - retention

Larvae rise on the flooding tide, sink to bottom on theebbing tide: results in retention of larvae within estuary

Estuarine larval adaptations - movement of larvae to coastal waters, return of later stage larvae

Blue crab, Callinectes sapidus

Effect of local eddies on larval retention in a patch reef on the Great Barrier Reef, Australia

Planula larva

Newly settled coralDistance from reef perimeter

Rec

ruit

men

t of

juve

nile

cor

als

Why disperse?

• High probability of local extinction; best to export juveniles

• Spread your young (siblings) over a variety of habitats; evens out the probability of mortality

• Maybe it has nothing to do with dispersal at all; just a feeding ground in the plankton for larvae

Settling problems of planktonic larvae

• Presettling problems:

Starvation

Predation in plankton

Loss to inappropriate habitats

Example of Effect of Starvation:Phytoplankton variation and barnacle larval success

Semibalanus balanoides settlement in a Scottish Sea Loch

1950Normalphytoplankton

1951 Failure ofphytoplanktonN

umbe

r of

larv

ae1000

500

0

1000

500

0March April

EarlyLarvalstages

Cypridssettling

Abundant diatoms

Diatom

failure

LaterLarval Stages

Postsettling problems• Energetic cost of metamorphosis

• Predation

• Crowding --> mortality

Expectation of life of Semibalanus balanoides as function of crowdingInterindividual contacts per cm2

Exp

ecta

tion

of

life

(mon

ths)

Initial6 months12 months18 months

Free-swimming larva

Random contactWith asurface

Contact w.pits andgrooves

Contact w.Substance on

Sfc. Of anotherspecies

Contact w.adults ofsame sp.

ATTACHMENT

Releasor ReleasorReleasor

Releasor

SelectionBehaviorAlternatingPhoto+ and Photo- stages

Selection behavior-crawling and testsurfaces

Selection behavior-frequent turningand flexing

Block inbehavior,contact withinappropriatesurface

Block inbehavior,e.g., contact withcrowded surfaces

Stages in the selection of substratum by planktonic larvae

The End