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