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Small Invertebrates - EVPP/BIOL 350 Freshwater Ecosystems...

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EVPP/BIOL 350 Freshwater Ecosystems Lecture 10 – Small invertebrates Dr. Kim de Mutsert Fall 2011
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Zooplankton - Characteristics Rotifers Small invertebrates Multicellular, heterotrophic, eukaryotic Suspension feeders ‘Rotating’ cilia near mouth create a feeding current, also moves organism through water Relatively small (0.2- 0.6 mm) Generation time: ~ 1 wk Small filter-feeding rotifers Brachionus Polyarthra Keratella Larger predaceous rotifer Asplanchna 50 μm
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Zooplankton - Characteristics Rotifers Life History Have both sexual and asexual (parthenogenetic) reproduction Asexual during favorable periods Stressful conditions induce sexual reproduction which produces “resting eggs” Resting eggs are resistant to drying, cold, heat, etc. and can hatch when favorable conditions return
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Zooplankton - Characteristics Cladocera Small invertebrate arthropods Multicellular, heterotrophic, eukaryotic Use jointed appendages for swimming and feeding “water fleas” Very characteristic of freshwater Bosmina, a small cladoceran Leptodora, a large predaceous cladoceran Daphnia
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Zooplankton - Characteristics Cladocera Most are herbivorous filter feeders Filter algae from the water as they swim in a rather passive fashion Some are raptorial predators, mainly on other cladocera Adults range from 0.3 mm up to 3 mm except Leptodora up to 10 mm Generation time as low as 2 weeks when asexual
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Zooplankton - Characteristics Cladocera Closeup of filter comb
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Zooplankton - Characteristics Cladocera Like rotifers, have both asexual and sexual reproduction During favorable conditions, there can be many generations of asexual reproduction (eggs that don’t need fertilizing) When stress occurs, males are produced and sexual females, meiosis occurs to produce gametes Male gametes fertilize eggs in brood chamber producing sexual (epphipial) eggs
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Sexual reproduction Diploid fertilized eggs go into diapause (resting stage; delay in development) When the female molts a thickened carapace (ephippium) closes over the resting eggs Within this enclosure, eggs can survive being dried, frozen or eaten
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Sexual reproduction The black coloration of the ephippium in Daphnia attracts visual predators such as fish, and thereby increases the probability of dispersal Diapause lasts until the proper signal is received to resume active metabolism and continue development Example: exposure to light and warm temp after period of darkness and/or freezing
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Zooplankton - Characteristics Copepods Small invertebrate arthropods Multicellular, heterotrophic, eukaryotic Use jointed appendages for swimming and feeding Found in freshwater, estuaries and the ocean Very characteristic of both freshwater and marine habitats
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Zooplankton - Characteristics Copepods Some are passive filter feeders, but most go after individual particles Take algae and small invertebrates Adults range from 0.5 mm to 5 mm Calanoid & Cyclopoid common in plankton Calanoid Cyclopoid
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