Digestive, Excretory, & Endocrine Systems

Main Points: General morphology: mouthparts, esophagus, crop, proventriculus, midgut, gastric cecae, hindgut, rectum Adaptations for digestion depend on type of food eaten. Salivary glands aid ingestion/digestion in various ways. Special adaptations include filter chamber (water shunt), symbiotic microorganisms. DIGESTION

Digestive and excretory organs of a typical terrestrial vegetarian insect. from Gullen & Cranston 2000 pyloris

Digestive system & functions. from Evans 1984

Main Points: Excretory adaptations driven interactively by: 1) nitrogenous waste elimination & 2) water conservation. Waste elimination relies on active ion transport and osmosis. Most important organs of elimination are Malpighian tubules & rectum. Main molecule of nitrogenous excretion = uric acid (but exceptions). EXCRETION

Trade-offs in energy vs. water required in synthesis in different nitrogenous waste molecules. most insects vertebrates aquatic insects uric acid ammonia urea more energy more water

Excretory organs & functions. As in nutrient absorption, the complex process utilizes diffusion gradients, osmosis, active ion transport, and pH changes. from Evans 1984 Malpighian tubule

from Gullen & Cranston 2000 Major organs and primary functions of typical terrestrial insect excretory system. Malpighian tubule X-sec.

Malpighian tubule X-sec. Showing nuclei (outlined) of 2 adjacent cells. Single layer structure of Malpighian tubule. from Evans 1984

Structure of rectum. from Gullen & Cranston 2000

Aquatic species May excrete ammonia May have “chloride cells” (osmoregulation) Blood feeders food: high-N, high water Plant Vascular Feeders May have a “filter chamber” shunt Nonterrestrial & Atypical Systems dragonfly nymph aphid horse fly

Diagram of the filter chamber, a modification of the digestive system that functions to shunt excess water around the midgut. (water & sugars) (proteins, etc.) from Gullen & Cranston 2000 Adult female mosquitoes also face an excess water waste problem after taking a blood meal but do not have a filter chamber. Why would a filter chamber not be necessary?

Fat tissue, oenocytes, and nephrocytes from Snodgrass 1935 Fat body, a diffuse organ with multiple functions : 1)Carbohydrate & lipid metabolism 2)Storage of glycogen, fat, & protein 3)Synthesis of blood proteins 4)Regulation of blood sugars Cell types: 1)Urocytes, waste storage 2)Trophocytes, many functions 3)Mycetocytes, symbionts 4)Oenocytes 5)Nephrocytes

Main Points: Hormonal control is vital to many aspects of insect physiology & behavior, including: development, molting, & reproduction. Major hormonal centers include the brain, corpora allata, corpora cardiaca, prothoracic gland. There are dozens of known insect hormones. Best known system = “the Triumvirate” of 1) neurohormones, 2) ecdysteroids, & 3) juvenile hormones. Some insect hormone analogs are used as pesticides. Legacy insect hormone research at UW Endocrine System

Important aspects of the typical insect endocrine system. from Gulen & Cranston 2000 => PTTH pro-thoracico-tropic-hormone PTTH (storage) => JH juvenile hormone => Ecdysone (ecdysteroids)

Juvenile Hormones (sesquiterpenes) Several forms, sometimes >1 produced by same species Functions: Control of metamorphosis Retention of larval characteristics Inhibition of metamorphosis Regulation of reproduction Stimulation of egg yolk deposition in ovary of mother Controls accessory gland activity Controls production of pheromones Neurohormones (peptides) Most diverse class Regulate various developmental and metabolic processes Modes of action: Along nerve axons Through haemolymph (carrier proteins) Indirect: through effects on other glands Ecdysteroids (sterols, from diet) Primarily ß-ecdysone. Molt-promoting but many other functions. Major Insect Hormone Types ß-ecdysone

Kopec’s simple ligation & debraining experiments (ca. 1919). Demonstrated involvement of hormone from anterior body & timing of release. Confirmed location of hormone in brain. from Evans 1984 Historical Perspective

Insect Hormone Research Legacy Edwards (emeritus at UW, insect glia, other neurobiological aspects) Riddiford [& Truman] (recently active at UW, JH functions in molting, development; other aspects) Williams (Harvard, conditioning via environment, prothoracic gland target) Wigglesworth (Oxford, confirmed Kopec’s work, connection with molting, timing of release) Kope ć (Poland, demonstrated PTTH) Gilbert (UNC, neurosecretory cells) Fukuda (U. Tokyo, importance of prothoracic gland)

COLORCOLOR

Sources of Color in Insects 1)Incidental e.g. internal organs, haemolymph, transparent cuticle. 2)Pigments endogenous metabolic sources, sequestered from plant host, microbial endosymbionts. 3)Physical (cuticular surface quality) interference, scattering.

Microstructure of a butterfly wing scale.

In many species: a teneral or callow state occurs immediately after molting, before cuticle tans and pigments are deposited.

X-sec Insect Wings Identical basic veination pattern in all winged insects indicates a single origin

APTERYGOTA Predominance of wings in insects. PTERYGOTA

a firebrat (THYSANURA), a primitive apterygote

“PALEOPTERA” NEOPTERA Modern vs. ancient wings

ODONATA

“EXOPTERYGOTA” ENDOPTERYGOTA (~85% of species) Prevalence of holometaboly and highly advanced wings

THYSANOPTERA

HEMIPTERAHEMIPTERA

LEPIDOPTERA

LEPIDOPTERALEPIDOPTERA

HYMENOPTERA

COLEOPTERA

DIPTERA

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