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Thermoregulation

Thermoregulation. Peter B. McEvoy Insect Ecology Ent 420/520. Classifying Thermal Relationships. Homeotherm. Body Temperature Tb. Poikilotherm. Ambient Temperature Ta. Homeothermy in Ectotherms Hyles lineata (Lepidoptera: Sphingidae). Occurs in Mojave desert of SW USA

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Thermoregulation

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  1. Thermoregulation Peter B. McEvoy Insect Ecology Ent 420/520

  2. Classifying Thermal Relationships Homeotherm Body Temperature Tb Poikilotherm Ambient Temperature Ta

  3. Homeothermy in EctothermsHyles lineata (Lepidoptera: Sphingidae) • Occurs in Mojave desert of SW USA • Polyphagous on desert annuals • Abundant in April and May, dormant rest of year • Population size varies drastically yr to yr • Caterpillars regulate Tb through position and postural changes

  4. Caterpillars Maintain Body Temperatures Above Ambient Tb = Ta Tb – Ta is greater for low T than for high

  5. sun wind How Do Caterpillars Maintain Steady Tb Above Ta? • By exploiting thermal heterogeneity of it microhabitat through position and postural changes • As Ta increase mid-day, spend less time on ground and more on plant (can feed either on ground or plant) • On warm days, as temperature increases, spends more time in vertical position on stem

  6. Shifts in Location and Posture With Changing T on Hot and Cold Days  Location  Posture Ground Vertical Hot Cold Time % on ground decreases, % vertical increases, with increasing T Ground Vertical Temp

  7. Larvae of Australian sawfly Perga dorsaliscool evaporatively from back using rectal fluid

  8. Apache cicada Sonoran desert Dicerooproctoa apache • Among the loudest insects on record • Sings when TA 40oC in shade • Keeps cool by evaporative cooling from fluid shed from dorsal pores • Extravagant water loss for desert insect made possible by xylem feeding

  9. Stilts and ParasolsTenebrionidae of the Namib Desert The head-standing beetle (Onymacris unguicularis) creeps to the crest of a dune when fog is present, faces into the wind and stretches its back legs so that its body tilts forward, head down. As fog precipitates onto its body and runs down into its mouth the beetle drinks (Armstrong 1990).

  10. Morphology and Thermoregulation • Insulation – air sacs, scales, setae • Color – dark wing undersides • Stilts add Parasols – ground dwelling beetles on host sands of Namib Desert • Countercurrent and Alternating-Current Heat Exchanges

  11. Environmental Uncertainty and Evolution of Physiological Adaptations in Colias Butterflies • Variation in melanin on the underside of the hind wing, seasonal polyphenism • Allows insect to absorb solar energy and warm more quickly to 35-38oC required for flight • Intraspecific and interspecific variation

  12. MALE (DORSAL) SUMMER FORM MALE (DORSAL) WINTER FORM Orange Sulphur (Colias eurytheme) http://www.dallasbutterflies.com/Butterflies/html/eurytheme.html

  13. Adjusting Phenotype to Environmental Regime • If cues to thermal regime, two factors contribute to uncertainty • Noise in the signal • Magnitude (or strength) of the signal • If cues to photoperiod • Signal noise free • Free to respond to lack of accuracy with which signal predicts temperature

  14. Seasonal Variation in hindwing Underside Coloration in Colias eurytheme in relation to photoperiod Short day, low reflectance, high melanin Long day, high reflectance, low melanin

  15. Predicting Thermal Regimes From Photoperiod Cycles Thermoperiod and photoperiod out of phase Slope (signal strength) and scatter (precision in prediction)

  16. Warming up by Basking

  17. Warming Up by Shivering • Who does it?Found among large, active flyers across the insects • dragonflies (Odonata) • moths and butterflies (Lepidoptera) • katydids (Orthoptera) • cicadas (Clypeorrhyncha or Homoptera) • flies (Diptera) • beetles (Coleoptera) • wasps and bees (Hymenoptera) • How do they do it?Involves disengaging flight muscles form wings and synchronous contractions of muscles that normally alternate in flight • Who does it best?Honey bees and bumble bees represent the zenith of shivering response among any host-blooded animal (invertebrate and vertebrate)

  18. Thoracic and Abdominal Temperatures of Bombus vosnesenskii Queen

  19. Countercurrent and Alternating Current • Countercurrent flow recovers heat from thorax by passing cold, incoming flow from abdomen by the warm, outgoing flow from the thorax • Alternating current removes heat from thorax by alternating warm outgoing and cool incoming flow

  20. High artic bumblebeeBombus polaris By incubating brood with abdomen, queen can produce a batch of workers in ~2 weeks http://pick4.pick.uga.edu/mp/20q

  21. Summary • Insect performance depends on temperature • Thermoregulation allows some insects a measure of independence from variation in the thermal environment • Biochemical, physiological, behavioral, morphological mechanisms involved • Consequences from individuals to populations and communities

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