5 Reproduction, Dispersal, and Migration Notes for Marine Biology: Function, Biodiversity, Ecology By 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 - clone Colonial 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 employed for display to attract females and for combat with 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 larger Therefore, there is a threshold size when female function begets more offspring.Smaller individuals do better as males.

Male at advantage Female at advantage Number of offspring produced Male Body size 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)

Pandalus jordani fishery Changes in Body Size Changes in Size of Change from Male to Female

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 Spawning Area Nursery/Juvenile Feeding 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

Norway Migration of the herring in the North Sea Adult feeding area Spawning areas

N. America Europe Africa

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 Pluteus larva of an urchin Planktotrophic larva of snail Cymatium parthenopetum

Loss to offshore waters Wind-driven recruitment onshore Internal waves, tidal bores Self-seeding eddies Longshore drift Shore Population

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 the ebbing 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 Recruitment of juvenile corals Distance from reef perimeter Newly settled coral

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 Abundant diatoms 1950 Normal phytoplankton 1000 500 Cyprids settling Early Larval stages Later Larval Stages Number of larvae 1951 Failure of phytoplankton Diatom failure March April Semibalanus balanoides settlement in a Scottish Sea Loch

Postsettling problems Energetic cost of metamorphosis Predation Crowding --> mortality Initial 6 months 12 months Expectation of life (months) 18 months 2 Interindividual contacts per cm Expectation of life of Semibalanus balanoides as function of crowding

Stages in the selection of substratum by planktonic larvae Free-swimming larva Selection Behavior Alternating Photo+ and Photo- stages Block in behavior, contact with inappropriate surface Releasor Random contact With a surface Selection behavior- crawling and test surfaces Releasor Releasor Releasor Block in behavior, e.g., contact with crowded surfaces Contact w. Substance on Sfc. Of another species Contact w. pits and grooves Contact w. adults of same sp. Selection behavior- frequent turning and flexing ATTACHMENT Stages in the selection of substratum by planktonic larvae

The End