Thermoregulation

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Thermoregulation

• Peter B. McEvoy
• Insect Ecology
• Ent 420/520

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Classifying Thermal Relationships
Homeotherm
Body Temperature Tb
Poikilotherm
Ambient Temperature Ta
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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

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Caterpillars Maintain Body Temperatures Above
Ambient
Tb Ta
Tb Ta is greater for low T than for high
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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

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Shifts in Location and Posture With Changing T on
Hot and Cold Days
? Location
? Posture
Ground
Vertical
Hot
Cold
Time
Ground
on ground decreases, vertical increases,
with increasing T
Vertical
Temp
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Larvae of Australian sawfly Perga dorsaliscool
evaporatively from back using rectal fluid
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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

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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).
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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

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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

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Orange Sulphur (Colias eurytheme)
http//www.dallasbutterflies.com/Butterflies/html/
eurytheme.html
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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

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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
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Predicting Thermal Regimes From Photoperiod Cycles
Thermoperiod and photoperiod out of phase
Slope (signal strength) and scatter (precision in
prediction)
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Warming up by Basking
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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)

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Thoracic and Abdominal Temperatures of Bombus
vosnesenskii Queen
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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

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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
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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