Exam Tuesday
• x pages, x questions– Natural flow regime:– Hydrology of streams: – RCC; FPC; RES– Arthropod taxonomy / evolution: – Insect physiology:
• Lab quiz: – x general invert ID– x insects to order– Label a diagram
Assigned readings• Natural flow regime
• Poff et al. 1997 Natural flow regime
• River management not working
• New paradigm is importance of natural flow = five components
•
Human alterations of flow
• Dams
• Urbanization, tiling, drainage
• Levees
• Groundwater pumping
Ecological functions of flow regime
• High flows, low flows
• Duration, timing
Ecological responses to altered flow regime
• Mortality of fishes below dams
• Loss of habitat
• Loss of flooded habitat
Solution to hydrologic alteration?
• Manage toward natural flow regime
• Controlled releases by dams
• Dam removal
• Alternative ag practices
Riverine Ecosystem Synthesis
Thorp, Thoms, Delong
Review of River Ecosystem Concepts
• RCC
• Flood Pulse Concept
• FPZs
Creates new predictions about river functions
• Stochastic processes different in different patches?
• Communities distributed among FPZs.
• S highest at transition zones.
• % Autochthonous productivity varies among FPZs.
Internal structure and life systems
Exoskeleton
• Arthropods are supported by exoskeletons– Skeleton on outside– Muscles attach to inside
• Exoskeleton is like medieval suit of Armor– Articulating plates = sclerites– Membranes connect sclerites
Respiration
• Terrestrial animals must supply O2 to cells without drying out
• Insect solution relies on waterproof cuticle that allows air to enter at only a few places = spiracles
Respiration
• Spiracles are invaginations of the epidermis
• Cuticle lined air conducting tubes = tracheae
• Tracheae branch and end close to tissues as tracheoles
Breathe air or water?
• Atmospheric breathers:
• Spiracles covered with hairs to prevent water from entering.
Breathe air or water?
• Plant breathers:
• Spiracles modified to pierce plant air channels– Some dipteran larvae, beetle larvae.
Breathe air or water?
• Temporary air stores– Bring bubble underwater
• Belostoma spp.
• Dytiscus spp.
• Permanent air stores– Hairs or meshworks hold gas film = plastron– E.g., riffle beetles (Elmidae)
Breathe air or water?
• Closed tracheal systems
• = no spiracles
• Tracheal gills = outgrowths– In every aquatic insect order, in some species
Circulatory System• Open circulatory system• Blood leaves dorsal blood vessel; percolates
through body cavity (hemocoel)• Thoracic portion of dorsal blood vessel
conducts hemolymph to head• Small pumps move hemolymph into legs,
wings and antennae
The Alimentary Canal
• Gut of an insect is tube that runs from mouth to anus
• Gut functions include:– Digestion of food– Absorption of nutrients across gut wall to hemocoel
• Gut = integumental invaginations from mouth and anus (foregut and hindgut)
• Midgut = nonintegumental connection between foregut and hindgut
The Alimentary Canal
• As food moves through gut it will travel from:
• Mouth->Pharynx->Crop->Proventriculus & Gastric caeca->midgut->Ileum->Rectum
Excretion
• Excretion is removal of waste products of cellular metabolism
• Malpighian tubules = principle excretory organs of insects
• At junction of Midgut and Hindgut• Absorb waste from hemocoel and deposit in hind
gut
Exoskeleton
Exoskeleton = series of tubes
– Hollow tubes stronger then rods
– Size limited, mammal-sized arthropods require prohibitively thick exoskeleton
– larger animals subject to stress related injuries; endoskeleton protected by surrounding tissue
Hydrostatic Skeleton• Relaxed membranous areas can be extended
when muscles compress blood-filled body
• Hydrostatic skeleton maintains shape of soft-bodied larvae, and freshly-molted insect
Integument
• Exoskeleton = noncellular covering– Cuticle – noncellular outermost layer– Epidermis – single layer, secretes cuticle– Epidermis and cuticle separated by subcuticular
space
• Cuticle + Epidermis = Integument
Integument: The cuticle
• Insect cuticles are diverse:– Permeability– Transparency– Rigidity
• Cuticle is laminate – Two major portions:
• Epicuticle • Procuticle
Integument: The Epicuticle
• May be smooth or sculpted
• Rich in lipid and protein– High wax production
• If epicuticle is intact, insects lose little moisture
Integument: The Procuticle
• Divided into layers– Exocuticle – hard dark outer portion– Endocuticle – softer and lighter in color– Made of chitin, protein and lipid
• Chitin is:– colorless polysaccharide– clumped into microfibrils– microfibril orientation compensates for stress
forces
Epidermis
• Epidermis = continuous layer that seals hemocoel from subcuticular space
• Secretes cuticle
Molting
• Arthropods periodically shed exoskeleton to allow for growth and/or metamorphosis
• 7 steps during each molt cycle
1. Apolysis
• Retraction of epidermal cells from endocuticle
• Formation of subcuticular space
• Molting gel secreted
• New cuticle laid down
2. Epicuticle formation
• Epicuticle laid down
• It is extensively wrinkled
3. Procuticle deposition
• Formation of chitin microfibrils
• Endocuticular layers of old cuticle digested
• Enzymes in molting gel initially inactive
4. Ecdysis
• Old cuticle splits along middorsal suture
• Cast skin = epicuticle and exocuticle
• Endocuticle recovered and recycled into new procuticle
5. Expansion• Insect swallows air
• Insect swells, removes wrinkles in epicuticle
6. Hardening and darkening
• New procuticle
stabilized
• Exocuticle formed
7. Endocuticle deposition
• Depositing chitin and protein takes time
• Some insects deposit one lamina of endocuticle every 24 hours
Note: Ecdysis under hormonal control
Dichotomous Key