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