Life in Freshwater

Life in Freshwater

Lecture 1

Life in Freshwater

Freshwater is a small percentage of all water on earth and occupies a small percentage of earth’s surface area
Fairly rapid turnover of water in lakes, rivers, and streams
Water has unique physical properties
Freshwater bodies are ephemeral on a geological time scale

10-15K yrs since the last ice age, not a lot of time for evolution in glacial lake basins
Likely will be another glaciation in a few 10K yrs

Freshwater bodies are physically discontinuous

Small waterbodies separated by land with incomplete interconnections

In really old, deep lakes some endemic species have evolved (Baikal, Tanganyika, Malawi)

Origins of Freshwater Life

Animals

Originally evolved in the sea, some such as crustacea, invaded freshwater directly from the sea
Some, such as insects, moved to land and then invaded freshwater from land

Plants

Vascular plants evolved on land, invaded freshwaters thus presence of stomata and problems with root anaerobiosis

Microbes

Most evolved originally in the sea and invaded fw from there

Life History Patterns

Nutrition: Needed for Energy and Essential Elements/Compounds

Autotroph (primary producer): manufactures its own biomass from inorganic materials (CO₂, minerals)

Photoautotroph: utilizes sunlight as an energy source and CO₂ as the C source H₂0 + CO₂ + sunlight à (CH₂O) + O₂
Chemoautotroph: utilizes reduced inorganic compounds as energy source and CO₂ as C source.

Heterotroph (consumer): requires C in form of complex organic molecules for both energy and essential elements/compounds

Herbivores: consumers which feed on living plant material
Carnivores: consumers which feed on living animal material\
Detritivores: consumers which feed on detritus (saprophytes)

H₂0 + CO₂ à (CH₂O) + O₂

Reproduction

Asexual:

offspring are genetically identical to parent
usually allows for rapid growth of population
low metabolic cost per offspring

Sexual:

Normally involves two parents of different genotype
Allows formation of new genotypes
Facilitates evolutionary adaptations
May also be used to produce resting stages

Sexual Life History Patterns

Usually involve alternation between haploid (1 chromosome set per cell) and diploid (2 chromosome sets per cell) forms
Meiosis and fertilization allow switching between the two forms
Types of Sexual Life History Patterns

Gametic Meiosis: Meiosis produces gametes – eg. Humans
Sporic Meiosis: Meiosis produces spores – eg. Ulva (sea lettuce)
Zygotic Meiosis: Zygote undergoes meiosis, is only diploid cell

Other definitions

Isomorphic: Haploid and Diploid individuals are the same

Kingdom Monera (The Bacteria)

Characteristics:

Bacterial cell wall containing murein
Bacterial ribosome 70S
Reserve material is poly-$-hydoxybutyric acid, glycogen
No organelles or membrane-bound bodies with the cell
May possess flagella
No membrane-bound nucleus, nuclear material is single circular loop of DNA
May from endospores – small bacterial cell within multiple membranes and wall structures, resistant to high temperatures, drying, etc.

Classification:

Based on

Morphology (rod/bacillus, coccus/sphere, spirillum/spiral)
Gram stain reaction
Specific structures/behavior
Metabolic features (this will be the focus of our discussion)

Phototrophic Bacteria (energy obtained from photosynthesis/primary producers)

Cyanobacteria (“blue-green” algae)

Conduct traditional photosynthesis
Produce O₂
Electron donor is H₂O
Ecologically similar to true “algae”
Reproduction by fragmentation or thick-walled resting cells (akinetes)
N₂ fixation by species with heterocysts & by other species in dense colonies
Gas vacuoles: allow regulation of buoyancy
Some toxic strains
Most abundant in polluted or nutrient enriched systems
Examples of morphological diversity

Rhodospirilliaceae (purple non-sulfur bacteria)

No O₂ production
Found only in anaerobic conditions
Electron donor is H₂, thiosulfate, organic S

Chromatiaceae (purple sulfur bacteria) & Chlorobiaceae (green sulfur bacteria)

No O₂ production
Found only in anaerobic conditions
Analogous to regular photosynthesis with H₂S as electron donor and elemental sulfur is deposited

Gram-negative chemolithotrophic bacteria (energy from inorganic molecules)

Nitrobacteriaceae (used nitrogen & sulfur-oxidizing bacteria)

Nitrobacter: oxidize nitrite to nitrate
Nitrosomonas: oxidize ammonia to nitrite
Thiobacillus: oxidize hydrogen sulfide to sulfate

Siderocasaceae

Derive energy from Iron or Manganese oxidation

Methane-producing bacteria

Restricted to anaerobic habitats such as sediments
Strip oxygen from organic compounds for respiration and leave methane behind

Gram-negative aerobic rods and cocci

Pseudomonadaceae

Common inhabitants of sediment and freshwater
Generalized heterotrophs
Wide temperature tolerances

Azotobacteraceae

Inhabitants of sediment and water
Heterotrophs which fix N2

Rhizobaceae

Restricted to nodules of legumes
Heterotrophs which fix N2

Methylmonadaceae

Similar to Pseudomonadaceae, but only use 1-C organic molecules

Halobacteriaceae

Similar to Pseudomonadaceae, but require high salt concentrations

Gram-negative facultatively anaerobic rods

Vibrionaceae

Facultative anaerobes
Generalized heterotrophs
Found in fresh and salt water

Gram-negative cocci and coccobacilli

Acinetobacter

Ubiquitous decomposer
Generalized chemoorganotroph (hetrotrophs)

Gram-positive cocci (most are associated with plants or animals)

Micrococcus

Generalized chemoorganotrophs (hetrotrophs)
Found in soil and fresh water

Endosport-forming rods and cocci

Bacillus

Aerobic and chemoorganotrophic
Found in decaying plant and animal matter

Gliding bacteria

Aerobic chemoorganotrophs
Found on decomposing plant matter and animal feces
Some have been isolated from freshwater (eg. Beggiatoa)

Sheathed bacteria

Heterogeneous group
Sphaerotilis: heterotroph found in slow-running polluted waters (“sewage fungus”)

Kingdom Myceteae (Fungi)

Characteristics

Eukaryotic cells
Organelles
Organized nucleus with membrane
80S ribosomes in cytoplasm
most have a cell wall of cellulose and chitin
most produce filaments known as hyphae
hyphae may be septate or coenocytic
fungi produce a wide variety of spores involved in reproduction and dissemination

Division Mastigomycota (produce flagellated cells, zoospores)

Class Chytridiomycetes

Produce motile cells each with a single posterior whiplash flagellum
Prevalent in aquatic habitats/soil
Microscopic
Some parasitize algae
Some are unicellular with no mycelia
Some have rhizoids (short delicate filaments, no nuclei, for anchorage and nutrient absorption)
Some have rhizomycelia (hypha-like filaments)
Example: Rhizophidium

Class Oomycetes

Biflagellate zoospores with 1 tinsel flagellum (directed forward) and 1 whiplash flagellum (trailing)
Cell walls contain no chitin
Sexual reproduction is oogamous by contact
Meiosis is gametangial (=~gametic)
Free-living (saprobic) or ectoparasitic on algae, water molds, small animals
Easy to culture on hempseed
Example: Saprolegnia

Division Amastigomykota (no flagellated cells known)

SubClass Hyphomycetes

Septate hyphae
Reproduce only asexually (conidia) making classification difficult
Many are plant or human pathogens or industrial fungi
Some prey on nematodes
Very important in the breakdown of leaves of terrestrial origin in streams

Hyphae help in invasion of tissue
Fungi are better able to attach structural polyments like cellulose and pectin than bacteria

Kingdom Protista

-unicellular, colonial or filamentous eukaryotes without specialized cells or tissues

Subkingdom Algae (photosynthetic protests)

Characteristics

Ecologically similar, but taxonomically diverse group
Divided into groups (divisions/classes) based on:

Pigments
Storage compounds
Motility
Wall Material

Class Chlorophyceae

Chlorophyll a, b
", $ -carotene
Starch as storage material
Flagellated cells common
Cellulose as wall material
Taxa of Interest

Order Volvocales

Flagellated cells and colonies
Cup-like chloroplast
Progression of genera:

Chlamydomonas (unicell)
Gonium (flat plate colony, 4-32 cells)
Pandorina (sphere, 4-32 cells)
Eudorina (sphere, 16-64 cells)
Volvox (hollow sphere, 500-50,000 cells)

Asexual reproduction

Autocolonies
Palmella resting stage

Sexual reproduction

Zygotic meiosis
Isogamous

Order Chlorococcales

Nonflagellated cells, aggregations, and colonies
Representative genera:

Pediastrum
Scenedesmus
Ankistrodesmus

Asexual reproduction: autocolony formation
Sexual reproduction: isogamy

Order Ulotricales

Filaments with uninucleate cells, band-shaped chloroplast
Asexual reproduction:

Binary fission & fragmentation
Zoospores

Sexual reproduction

Flagellated isogametes
Meiosis inferred to be zygotic

Representative Taxa

Ulothrix

Order Oedogoniales

Filaments with uninucleate cells & reticulate chloroplast
Wall thickenings (rings) created during mitosis
Asexual reproduction

binary fission and fragmentation
zoospores (multiflagellate)

Sexual reproduction

Ooganous
Zygotic meiosis

Representative Genera

Oedogonium
Bulbochaete

Order Cladophorales

Filaments with multinucleate cells
Chloroplasts reticulate or discoid
Asexual reproduction

Binary fission and fragmentation
Zoospores

Sexual reproduction

Some documented with gametic or sporic meiosis, more work needed.

Representative genera

Cladophora
Rhizoclonium

Class Charophyceae

Generally similar to the chlorophytes, but in cellular ultrastructure are distinctly different
Chlorophyll a, b
", $ -carotene
Starch as storage material
Flagellated cells common
Cellulose as wall material
Taxa of Interest

Order Charales (stoneworts)

Macrophytic
Branching filaments with apical growth and complex reproductive structures
Representative genera:

Chara
Nitella

Order Zygnematales

No flagellated stages
Asexual reproduction: binary fission and fragmentation
Sexual reproduction: conjugation
Representative genera:

Spirogyra (filament with spiral chloroplast)
Zygnema (filament with starlike chloroplast)\
Mougeotia (filament with band chloroplast)
Cosmarium (desmid with twin spheres)
Closterium (desmid with two curving cones)

Division Euglenophyta

Basic Characteristics

Chl a, b
b-carotene
paramylon as storage
protein pellicle as outer covering
all cells flagellated

Only a few genera, all are flagellated unicells

Euglena, Phacus (naked, only pellicle)
Trachelomonas (also has outer shell or test)

Only asexual reproduction by binary fission has been observed

Division Chrysophyta

Basic Characteristics

Chl a, c
Fucoxanthin as carotinoid
Chrysolaminarin, oils as storage
Some are naked, some have silica walls or scales
Flagellated cells are heterokontous

2 flagella: 1 whiplash, 1 tinsel

Class Chrysophyceae

Cells naked or covered with silica scales or shell (lorica)
Some cells are phagocytic in addition to photosynthetic
Limited number of genera, single cells or colonies of cells

Ochromonas (unicell, naked)
Mallomonas (unicell, siliceous scales)
Dinobryon (colony of cells in siliceous wineglasses)
Synura (spherical colony of unicells)

Reproduction

Asexual

Binary fission
Cyst (statospore) formation

Sexual

Isogamous or anisogamous
Zygotic meiosis

Class Tribophyceae

Non-flagellated cells and filaments
Reproduction

Asexual

Binary fission, fragmentation
Zoospores

Sexual

Isogamy or anisogamy or oogamy
Resting zygotes
Zygotic meiosis

Representative genera

Tribonema (fine filament)
Vaucheria (large bore coenocytic (no crosswalls) tube)

Class Bacillariophyceae (diatoms)

Silica wall (frustule) like a “petri plate”
Taxonomy based on wall structure
Two main groups

Pinnate: bilaterally symmetric
Centric: radially symmetric

Very important freshwater primary producers

Abundant, particularly in spring and fall
Desirable food for small invertebrate grazers

Reproduction

Asexual

Binary fission
Decreasing size

Sexual

Oogamy (centric) or isogamy (pinnate)
Zygote is resting cell (auxospore)
Gametic meiosis

Representative genera

Synedra (unicellular pinnate)
Fragilaria (filamentous (side-by-side) pinnate)
Asterionella (“wagon-wheel” pinnate colony)
Cyclotella (unicellar discoid centric)
Melosira (barrel-shaped filamentous centric)

Division Pyrrhophyta (dinoflagellates)

Properties

Chlorophyll a, c
Peridinin as xanthophylls
Starch as storage
Naked or cellulose shell (theca)
Distinctive cell structure

All unicells
2 flagella: 1 girdle whiplash, 1 trailing whiplash

Analogous non-photosynthetic cells in Subkingdom Protozoa
Some may secrete toxins and form “red tides”

Reproduction

Asexual

Binary fission

Sexual

Cells function as gametes
Zygotic meiosis

Representative taxa

Ceratium (very large “Eifel tower” form)
Peridinium (spherical unicell with plates)
Gymnodinium (naked unicell, “gymno-” means naked)

Division Cryptophyta

Properties

Chlorophyll a, c
Phycobilins
Starch as pigment
All are naked flagellated unicells
Reproduce by cell division, no sexual reproduction

Representative taxon (very few genera)

Cryptomonas