Reproduction and Recruitment

Reproduction Sexual –Hermaphroditism (simultaneous) (inverts) –Dioecious (mammals, fish, inverts) –External fertilization (invertebrates, fish) –Internal fertilization (mammals, inverts, sharks) Asexual –Fragmenting (corals) –Rhizomal (Sea grasses) –Budding (hydroids) –Division (anemones)

To have sex or not? Asexual reproduction good in stable habitats –Easily propagate, spread, compete, waste no time or energy on sex, local distribution Sexual reproduction good in unstable habitats –Allows for genetic variability, plasticity

Dispersal and Recruitment: Production of Larvae Many marine animals release huge numbers of eggs. –Even so, rates of fertilizations are thought to be <20% for a wide range of invertebrates Sperm are short-lived (a few hours at most) In most cases, sperm concentrations are rapidly diluted by currents and waves Donors are sparse

Dispersal and Recruitment: Production of Larvae (cont) Behavioral modifications can overcome sperm limitation –Mollusks can form spawning aggregations –Barnacles use internal fertilization

Fertilisation Internal fertilisation –Requires males and females to meet –Rare in sessile organisms (but does occur: for example barnacles) External fertilisation –Release of eggs and sperm into sea –Requires eggs and sperm to meet Most marine invertebrates spawn eggs and sperm into the sea Mobile taxa may aggregate to spawn

Broadcasters vs Brooders Broadcast spawning –shed eggs and sperm into water column most fish, echinoderms and algae Internal fertilization –females collect sperm from water column and fertilize eggs internally Sponges, cnidarians mollusks, ascidians –copulation with male placing sperm inside female reproductive tract gastropods, crust., sharks, mammals

Sexual Reproduction- Hermaphroditism A single individual has gonads that can produce gametes of both sexes A single individual can produce gametes of either sex at different times in it life (sequential hermaphrodites) –protandry male to female –protogony female to male

Protoandry Function as Males first Found amongst species in which males are able to spawn with large female Ex. Clown fish –Males are small, Females large and territorial –Removal of female causes male to switch –A juvenile then becomes male

Protogyny Often Male maintains territory with harem of females; size of males matters If male is removed, one female changes to male –Behavior (immediately) –Gonads (a few days) Major rearrangement of anatomy, physiology, hormones, and behavior (Need not be a pure strategy - gonochoristic males and females can exist within population)

Synchronous hermaphrodite Gonad has sperm and eggs Often a monogamous pair takes turns playing male and female role - Ensures no cheating ex. Hamlets (coral reef)

WHY? Size Advantage Hypothesis Lifetime fitness and size Size Eggs produced or fertilized Size Eggs produced or fertilized Female Male ProtogynousProtoandrous

Strange reproductive practices of fish Hermaphrodites Sex change (born one sex, become the other) Large fish in harems are often sex-change males (protogony) Large fish in non-harem species are often sex-change females (protandry) Parasitic males “Sneaker” males that look like females Sex-role reversal (male pregnancy in seahorses) Males often do parental care in fish

Rainbow wrasse Thalassoma lucasanum Two types of males Two types of reproduction. 1) Females (yellow/red lateral stripes) 2) Primary males (look like females) 3) Terminal males (blueheads) - born female, turn into males

Rainbow wrasse T. lucasanum Two types of reproduction 1)Broadcast spawning - Many males and females rush to surface and release gametes 2) Harems: one terminal male guards group of females and mates with them individually. Death of secondary male- large female turns into new terminal male

Mass spawning of the rainbow wrasse Thalassoma lucasanum

Barred serrano Serranus psitticinus Sea of Cortez Simultaneous hermaphrodite (can act as male or female at any time) -dominant male in harem mates with “females”. Serranus annularis Caribbean Orange back basslet

Parental care Preparation of nests or burrows Egg guarding Production of large yolky eggs Care of young (inside or outside body Provisioning of young (before or after birth) Care of offspring after independence

Seasonality Seasonal Reproduction –Short reproductive phases where high percentage of individuals are reproductively active –Small eggs, high fecundity and synchronized gamete development within individuals and within the population.

Seasonality cont’d Year-round reproduction (1) Asynchronous Individuals have discrete gamete production Not synchronized within the population (2) Continuous Most adults within population contain gametes year round

Dispersal and Recruitment The importance of recruitment has been recognized by marine ecologist for nearly a century, but only in the past yrs have marine ecologists incorporated recruitment as a centerpiece of population and community models. –It is a common sense notion that an empty patch of habitat will be uninhabited by a given species if its propagules are unable to reach it. –If true then the intensity of density dependent interactions will be determined by the degree to which settlement is successful

Definitions Recruitment is the addition of new individuals to a populations or to successive life stages within a population

Pre- and Post Settlement Processes Immigration Emigration Population Size Recruitment Mortality

Dispersal and Recruitment: Processes causing variation in recruitment Production of larvae Dispersal of larvae in the plankton Risk of mortality while dispersing Larval settlement Growth and survival of settlers until they get counted as new recruits

Many marine species have ‘bipartite’ life histories 1.Planktonic dispersive early stage 2. Benthic or site attached adult stage BENTHIC ADULTS REPRODUCTION SETTLEMENT PLANKTONIC LARVAE * Larva: an independent, often free- living, developmental stage that undergoes changes in form and size to mature into the adult. Common in insects and aquatic organisms.

More marine-terrestrial differences: you don’t see the bipartite lifestyle often on land

Dispersal and Recruitment: Complex Life Cycles

Marine organisms: complex life cycles

Recruitment is a multi-step process Four major accomplishments of recruitment: 1)Dispersal & survival in water column 2)Settlement in an appropriate site 3)Successful metamorphosis into adult body form 4)Post-settlement survival and growth until detected by an observer 1 cm

Three basic modes of larval development Lecithotrophic -- “yolk feeding” Nonfeeding larval stage. Larvae do not require food to complete development. Planktonic lifespan is typically short (minutes to days) Planktotrophic -- “plankton feeding” Feeding larval stage. Larvae are incapable of completing development without feeding Planktonic lifespan typically long (days to months) Direct -- essentially no larval stage Larval stage encapsulated, internally brooded or bypassed entirely

Thorson’s rule: a latitudinal cline in pelagic larvae in gastropods Thorson’s data for gastropods, interpreted by Mileikovsky, reveals a clear latitudinal cline in the proportion of species reproducing via a pelagic larva Red data: northern hemisphere White data: southern hemisphere

For most marine species, we have NO idea where larvae go

Vertical migration can result in retention of larvae within estuary: larvae rise on flood tide, and sink on ebb Larval behavior can allow for retention Tidal Flow – Ebb tide Tidal Flow – Flood tide

Typical life cycle of marine organisms Pelagic larvae Cue detection & metamorphosis Sedentary Benthic adults Planktonic dispersal Roughly 80% of all marine organisms (> 90,000 currently described species of vertebrates, invertebrates & algae) have a biphasic life cycle and produce planktonic propagules

Typical life cycle of marine organisms Pelagic larvae Cue detection & metamorphosis Sedentary Benthic adults Planktonic dispersal Problem with swimming larvae: water motion often carries them away from appropriate habitat Water flow in the ocean is complex -- internal waves, longshore drift, wind- driven currents and eddies can all affect where larvae end up

Typical life cycle of marine organisms Pelagic larvae Cue detection & metamorphosis Sedentary Benthic adults Planktonic dispersal Cues used to assess habitats can be chemical or physical, and larvae often respond to some combination of multiple cues Cues can be positive or negative

Ecological consequences: egg size, larval type and dispersal Larval type is related to egg size –Feeding (planktotrophic) larvae hatch from small eggs –Non-feeding (lecithotrophic) larvae hatch from larger eggs Egg size dictates fecundity –Females produce more small eggs than large ones (fecundity/egg size trade-off) Feeding larvae tend to spend longer in plankton, and hence have the potential to disperse further

Dispersal potential is related to gene flow and hence speciation Data from Siegel et al., MEPS, 260: (2003)

How does an aggregation begin? Someone had to be the first one to settle, and they didn’t respond to other adults! Desperate Larva Hypothesis: larvae search for suitable site until they run out of energy and then take whatever they can find rather than die in the water column Founders & Aggregators: Some species produce two distinct types of larvae: one type seeks out adults of their own species, the other is specifically a ‘pioneer’ larva that seeks new uninhabited, bare surfaces to colonize. If the ‘pioneer’ larva survives and grows into an adult, it can form the nucleus of a new aggregation.

Gregarious settlement

Larvae settle on (or very near) adults of the same species Identifying settlement cues is difficult and not many larval inducers have been conclusively identified Many species cannot move after settlement & even those that can need to feed soon Larvae settling with adults can obviously tell that site will be able to support them after they settle

Settlement choice Bacteria probably play an important role, but exact effects are unknown for all but a couple of species Physical cues associated with flow conditions at site of settlement are frequently important Chemical cues (e.g., from food source or conspecifics) frequently play a role, also

Do numbers of settlers reflect number that eventually recruit to the assemblage? Barnacles (Bertness et al., 1996) –Yearly differences in number and distribution of larval settlers, reflecting wind effect on larval populations Scallops (Peterson & Summerson, 1992) –Variability in spat explained 71% variability in recruitment in 1988, but only 4% in 1989 Lobsters (Hernkind & Butler, 1994) –No relation between settlers and subsequent recruits over 3 years in Florida The answer is sometimes

Post-settlement mortality Organisms only recruit to population (establish) if they survive after settlement Little suggestion that mortality higher in polar regions

Causes of post-settlement mortality Delay of metamorphosis Biological disturbance Physical disturbance Physiological stress Predation Competition for space or food

Physical and chemical defenses of larvae Other -- larvae may have behavioral or physical adaptations to avoid detection larvae may be transparent, or only active at night when it is difficult to see them Physical -- spines & bristles make it difficult for small fish & invertebrate predators to swallow them Chemical -- chemical defenses make larvae distasteful some chemical defenses simply taste bad others have more dramatic effects – e.g., some coral and tunicate larvae make fish vomit immediately after ingesting a larva

So 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? Life history theory predicts species in marine environments do best when they ‘hedge their bets’ –some larvae recruit to adult habitats and others disperse to try new habitats

Dispersal: Metapopulations

What is the optimal network design? How do we Design an Effective Network? We need a much better understanding of larval dispersal

Migratory patterns Anadromous - breed in freshwater and living in seawater –salmon, shad, sea lamprey Catadromous - Adults live in in freshwater then migrate to seawater to spawn –eels Anguilla Oceanodromous- live totally in seawater –herring cod and plaice

Catadromous - breed at sea, migrate into rivers to grow (16 spp freshwater eels) adults spawn and die in Sargasso Sea / larvae in plankton 1 yr+/ metamorphose into juveniles / grow and mature in rivers

Figure 8.22 Skipjack tuna (Oceanodromous) Tropical species that travels to temperate water to feed. Halfway across globe each year. Salmon (Anadromous) Spend lives at sea feeding, return to rivers to breed: Magnetic field and smell of home rivers

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