2. What are the 3 major groups of lake zooplankton? How are they similar/different? 3. What do...

2. What are the 3 major groups of lake zooplankton? How are they similar/different?

3. What do zooplankton eat? How do they feed?

1. Which groups of aquatic invertebrates dominate in lakes? ponds? rivers?

4. What 4 things influence feeding rate in zooplankton?

Chapter 3The Organisms

Invertebrates

• Represent the majority of animal diversity

• Zooplankton

• Insects

• Annelids

• Mollusks

• Other crustaceans

Most zooplankton belong to one of four major groups

Cladocerans Copepods

www.uv.es/~ciros/zoopl_en.html

http://www.eeb.cornell.edu/hairston/hairston.html

Diaptomus (< 2 mm)Daphnia(2-3 mm)

Brachionus (300 m)

Protists

Rotifers

www.ac-rennes.fr/pedagogie/svt/ photo/microalg/ceratium.htm

Ceratium

Amphipods

Other groups include:

Jellyfish (Craspedacusta)

Water mites Ostracods

Flatwormswww.biologie.uni-ulm.de/ bio3/gmaier/project.htm ebiomedia.com/gall/classics/ Plan/planaria.html

www.ittiofauna.org/webmuseum/ invertebrati/

www.marksimmons.org/closeup/ microimg/pages/ostracod.htm www.microscopy-uk.org.uk/ mag/artdec99/mite3.html

Fairy Shrimp Tadpole shrimp

Clam shrimp Chaoborus—phantom midge—Insectwww.zi.biologie.uni-muenchen.de/ .../feinstruktur/em.htm

www.microscopy-uk.org.uk/mag/ artjul00/dwtriops.html nature.org/.../states/oregon/ science/art1587.html

mailbox.univie.ac.at/ ~edere6/UZK/

Protists (Kingdom Protista)

Flagellates

Ciliates

Eukaryotes, but unicellular

Many can both photosynthesize and feed on bacteria and other organisms

Have a major role in the cycling of organic carbon and other nutrients in the plankton

Small animals, typically <100-1000 um long, easily confused with ciliates

Rotifers (Phylum Rotifera)

Very common and diverse in freshwater

Probably the only phylum that evolved in freshwater

www.sams.ac.uk/dml/ projects/microeco/

Ciliatewww.sacsplash.org/critters/ rotifer.htm

Rotifer

Two Main Groups of Rotifers

Monogononta

Bdelloidea http://www.mcb.harvard.edu/meselson/Proseola.jpg

http://fresc.fsl.orst.edu/graphics/zooplankton/kcochlearis.jpg

Foot and toes

General body plan

corona (crown) of cilia that draws a vortex of water into the mouth.

trophi (jaws) grind the food. Diagnostic for species ID

The body has semi-flexible, extendible, transparent cuticle covering. With or without lorica

Various forms of rotifer trophi

Bdelloid rotifers reproduce by obligate parthenogenesis

Can also undergo cryptobiosis —females can dry out and be rehydrated.

Philodina roseola (~ 400 m) 

no males

Cyclical Parthenogenesis: combination of sexual and asexual reproduction

Monogonant Rotifers have a slightly more complicated life-history

home-4.tiscali.nl/~t936927/ folio/1/galleryframe4.html

Most of the time, females reproduce asexually and produce genetically identical daughters

Both mother and daughter are diploid (2N)

Cyclical Parthenogenesis:

home-4.tiscali.nl/~t936927/ folio/1/galleryframe4.html

When conditions begin to decline, the so-called “amictic” females produce “mictic” females

Amictic female (2N) Mictic female (2N)

Cyclical Parthenogenesis:

home-4.tiscali.nl/~t936927/ folio/1/galleryframe4.html

Mictic females produce haploid (N) eggs

Mictic female

Unfertiliz

ed eggsMale rotifer (N)

Fertilized eggsResting eggs (2N)

Thick walledDormant

Laboratory conditions suggest:Low food resources

CrowdingShort day length

Rotifers are a haplo-diploid system

Unclear what triggers the induction and termination of dormancy in the field.

John Gilbert has shown that inSynchaeta pectinata, dormant eggs can be produced by parthenogenesis—but short term dormancy

: ebiomedia.com/gall/rotifers/ rotifer3.html

Rotifers can be herbivorousBrachionus Keratella

LecaneKelicottia

Other rotifers are predatory

Asplanchna

http://www.microscopy-uk.org.uk/mag/wimsmall/extra/rotif2.html

Synchaeta

What are some advantages and disadvantages to parthenogenesis?

Phylum ArthopodaSubphylum Crustacea

Class BranchiopodaOrder CladoceraOrder Anostraca (Fairy Shrimp)Order Notostraca (tadpole shrimp)Order Conchostraca (clam shrimp)

Class MaxillopodaOrder CalanoidaOrder CyclopoidaOrder Harpacticoida

Subphylum UniramiaClass Insecta

Cladocera—“water fleas”

Taxonomy not well resolved

Very common in freshwater, not so in marine systems

Major grazers and major food item for fish in many freshwater systems

Both “large” and “small” cladocera but in general, larger than rotifers. 1-3 mm is typical, but can be up to 4-6 mm (predators are even bigger).

General body plan of suspension feeding Cladocera

Single compound eye as adult

Bi-valved carapace

Filtering appendages

Swimming antenna

Some are herbivoreswww.uv.es/~ciros/ zoopl_en.html

ourworld.compuserve.com/homepages/ gpmatthews/chydorus.jpg

http://www.cnas.smsu.edu/zooplankton/images/dbir1.jpg

Chydorus

Bosmina

Diaphanosoma

http://www.cnn.com/NATURE/9910/01/pollution.eaters.enn/daphnia.jpg

Daphnia

Some are predatorshttp://www.potomacriver.org/images/biology/Leptodorabig.jpg

http://www.foodwebdisruption.org/images/cercopagis.gif

Cercopagis

BythotrephesLeptodora

Polyphemus

From: Mort 1991

Ephippium with

2 diapausing eggs

Asexually produced male

Asexually produced daughter

Eggs

Sperm

Cladocerans also reproduce by cyclical parthenogenesis, but not as complicated as with the rotifers

Almost always hatch into females. Hatching cue is also not well resolved

For both Rotifers and Cladocera:

Dormant eggs can float, and possibly be dispersed to other systems by wind, ducks, frogs etc.

Dormant eggs can sink and stay dormant for over 100 years

Dormant eggs are sexual reproduction, so allow for recombination

Timing of sexual reproduction is synchronous—some species do it in the fall, some species do it in the spring.

www.biologie.uni-ulm.de/ bio3/gmaier/project.htm

Copepods

Three Orders:

Calanoida Cyclopoida Herpacticoidahttp://www.sci.sdsu.edu/salton/sscletocam3_250sm.gif

Note general body shape, placement of eggs, antenna length

Can be herbivorous

Or predatory

dnr.metrokc.gov/wlr/waterres/ lakes/biolake.htm

Epischura

www.cnas.smsu.edu/zooplankton/ diaptomus.htm

Diaptomus

All copepods reproduce sexually. Have instars:

Cyclopoids have 11 life-history stages5 naupliar6 copepodite

Sexual dimorphism, males have geniculate antenna, and an asymmetrical 5th leg used for capturing and attaching the spermatophore

Diaptomus reighardi

Diaptomus siciloides

www.cnas.smsu.edu/zooplankton/ diaptomus.htm www.vvm.com/~jevans/ cope01.html

Cyclopoids do not make dormant eggs, instead diapause as subadults.

Some freshwater calanoids produce dormant eggs

Hairston et al. (1995) recorded eggs at 300+ years for Diaptomus sanguinious

Not all calanoids produce dormant eggs

What are the main similarities and difference between the life – cycles of:

RotifersCladoceraCopepods (cyclopoid vs. calanoid)?

How will sexual vs. asexual reproduction influence population dynamics?

The time to maturity, clutch size, switch to dormancy will be governed by the selection pressures of the particular systems.

For example, zooplankton in temporary ponds need dormancy, whereas its role in permanent systems is not as obvious.

How will variation in life-history traits among species influence population dynamics and community structure?

Before zooplankton can grow or reproduce, they have to eat

Grazing is more precisely called “suspension feeding” because the “grazers” eat other things besides algae.

3 Step process (three different rates):

Assimilation

Capture (selection)

Ingestion (selection, loss by sloppy feeding)

I (cells/hour) = F (cells/ml) x C (ml/hour)

Clearance rate (filtering/grazing rate) (C) = # of ml of water/hour that the animal can filter.

C is influenced by how fast is the animal moving its filtering appendages.

Ingestion rate (I) = # of cells/hour into the animal

Food concentration (F) (cells/ml)

We will not talk in detail about assimilation

4. food concentration—but more food does not always mean a higher rate (saturation).

These rates vary with:

1. body size—original hypothesis (Brooks and Dodson 1965) was that grazing rate always increased with body length—not necessarily true.

2. Food type—for example, blue-greens can slow down filtering rates of big Daphnia because they spend time cleaning and rejecting (coupled to body size).

3. temperature—everything moves faster when it is warmer

How do grazers capture and ingest food?

Rotifers set up feeding currents to draw food into their mouth by the action of the corona.

Trophi then grind the algal cells, detritus, bacteria etc.

Can choose which particles get ingested by both screening particles out, or rejecting particles.

Instead, individual cilia likely removing cells from feeding current.

Peter Starkweather measured clearance rates for many species of rotifer and found they varied.

So did the rejection rate.

Not really filtering, because rotifers experience low Reynold’s number, which means viscous forces dominate.

Rotifers are small animals, relatively low clearance rate.

Most work on feeding ecology for cladocerans (Daphnia in particular) because they are the ones that have the biggest impact on the algae

Cladocera also set up feeding currents, by moving their thoracic legs

“Big” grazer

“Little” grazer

The very smallest phytoplankton can escape grazing by most cladocera, but are vulnerable to rotifers.

particles are retained on the “filtering combs” of their legs…

….which get collected in a ventral groove and pushed up to the mouth.

The width of these filtering combs vary and determine the range of particles eaten.

Cladocerans can’t select what they will capture, but they reject a bolus of food by “kicking” it out with their post abdominal claw.

Bern fed polystyrene beads to Daphnia cucullata

Calculated Selectivity Index (sometimes called electivity index), general way of measuring preference for an item in the diet, relative to its frequency in the environment

0 means not selective+ means actively selects for- means actively selects against

-1

-0.5

0

0.5

1

0 10 20 30 40

FileringCombs

Gut

Bead diameter (um)

Ind

ex

They then pull cells out of the current.

Copepods set up a feeding current with their antennae.

Much more selective than the other two groups.

From R. Strickler

Again, not really filtering because low Reynold’s number

Strickler’s work suggested that based on rejection rates of certain kinds of algae, copepods were tasting their food.

DeMott used polystyrene beads

Can zooplankton taste their food?

Copepods (Eudiaptomus) when offered a mixture of beads and algae will taste each particle and reject the beads

www.lfu.baden-wuerttemberg.de/ .../zooplankton.htm

But, when he “flavored” the bead by incubating them with algae, the copepods ate the beads

Given the different feeding mechanisms, which group of zooplankton likely has the

biggest impact on the dynamics of the phytoplankton?

Is this true for all phytoplankton, or are there some types of algae that are more or less

vulnerable to grazing?

Class Insecta

Class InsectaOrder Ephemeroptera (Mayflies)

scrapers, collectors (predators)

Class InsectaOrder Odonata

(Damselflies and Dragonflies)

predators

Class InsectaOrder Plecoptera (Stoneflies)

shredders, collectors, predators)

Class InsectaOrder Trichoptera (Caddisflies)predators, scrapers, collectors

Class InsectaO. Megaloptera (Dobson flies) Neuroptera (lacewings)

predators

Class InsectaOrder Hemiptera (“bugs”)

predators

Class InsectaOrder Lepidoptera (“caterpillars”)

shredders, scrapers

Class InsectaOrder Coleoptera (water beetles)

predators, scrapers, collectors shredders

Class InsectaOrder Diptera (flies and midges)

predators, scrapers, collectors, shredders

Mollusks (Phylum Mollusca)

Class Bivalvia Class Gastropoda

Clams and Mussels Snails

http://www.inhs.uiuc.edu/cbd/musselmanual/page128_9.html

Potamilus capax

fat pocketbook pearly mussel Pomatiopsis lapidaria

http://images.google.com/imgres?imgurl=http://members.aol.com/Martinkcl/Shells/Bithytentac300.jpg&imgrefurl=http://members.aol.com/mkohl1/Rissoacea.html&h=138&w=191&sz=6&tbnid=ACQu1TinaNAJ:&tbnh=70&tbnw=96&start=17&prev=/images%3Fq%3D%2BBithynia%2Btentaculata%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DG

Can be small and inconspicuous or as large as a fist

Have either 2 shells (bivalves) or 1, coiled shell (snails)

Need CaCO3 for their shells, so not found in very soft water

Freshwater species are herbivorous, either scrape or filter feed.

Currently, more than 70% of native mussel species are listed as recently extinct, endangered, threatened, or of special concern

Concepts to know

• Compare relative body-sizes of different species of zooplankton and understand how this influences ecological interactions.

• Compare the life-cycles of the different types of zooplankton.

• Understand how the life-cycle will influence the potential for population growth and long-term persistence.

• Compare the diets and feeding strategies of the different types of zooplankon.