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Thermoregulation. Peter B. McEvoy Oregon State University Corvallis. 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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Peter B. McEvoy

Oregon State University


classifying thermal relationships
Classifying Thermal Relationships


Body Temperature Tb


Ambient Temperature Ta

homeothermy in ectotherms hyles lineata lepidoptera sphingidae
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 body temperature Tb through position and postural changes
caterpillars maintain body temperatures above ambient
Caterpillars Maintain Body Temperatures Above Ambient

Tb = Ta

Tb – Ta is greater for low T than for high

how do caterpillars maintain steady t b above t a



How Do Caterpillars Maintain Steady Tb Above Ta?
  • By exploiting thermal heterogeneity of it microhabitat through position and postural changes
    • As Ta increases mid-day, spends 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
shifts in location and posture with changing t on hot and cold days
Shifts in Location and Posture With Changing T on Hot and Cold Days

 Location

 Posture






% on ground decreases, % vertical increases, with increasing Ta




environmental uncertainty and evolution of physiological adaptations in colias butterflies
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
orange sulphur colias eurytheme



Orange Sulphur (Colias eurytheme)

adjusting phenotype to environmental regime
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
Seasonal, Inter-Generational Variation in Hindwing Underside Coloration in Colias eurytheme in relation to photoperiod

Short day, low reflectance, high melanin

Long day, high reflectance, low melanin

predicting thermal regimes from photoperiod cycles
Predicting Thermal Regimes From Photoperiod Cycles

Thermoperiod and photoperiod out of phase

Slope (signal strength) and scatter (precision in prediction)


polyphenism in butterflies and moths the pipevine swallowtail battus philenor nice and fordyce 2006

Dorsal view, male

Polyphenism in butterflies and moths:the pipevine swallowtail Battus philenor (Nice and Fordyce 2006)

Dorsal view, female

Larvae are red in AZ to western TX

Larvae are black in CA and SE USA

  • In South Texas, both forms occur
  • Each population, CA and Tx, has potential to produce either form
  • Color cued directly to temperature
  • Color can be changed at each larval molt

Ventral view

aristolochia host plants http plants usda gov java profile symbol arist2
Aristolochia host plants

A. recta

thermoregulation by an ectotherm
Thermoregulation by an Ectotherm
  • Larvae of the pipevine swallowtail butterfly, Battus philenor, employ behavioral and phenotypic plasticity as thermoregulatory strategies
  • Two years of field observations in south Texas:
    • Behavior. Larvae were also observed to shift their microhabitats by climbing on non-host vegetation and avoided excessive heat in their feeding microhabitat
    • Phenotypic plasticity. Proportion of red larvae increases with increasing daily temperatures as the growing season progresses
Proportion of red larvae increases with increasing daily temperatures as the growing season progresses

Fig. 2  Proportion of pipevine swallowtail larvae (Battus philenor) at the Freeman Ranch, TX field site observed exhibiting the red phenotype from April to June. Data from field surveys conducted in 2003 (open circle) and 2004 (open square)

Color cued directly to temperature and not photoperiod

Color can change at each molt depending on temperature experienced by larva

Drop in proportion of red larvae late in the season allegedly due to unseasonably cold temperatures (no evidence given)

Apr 10Jun 19

experimental methods effect of temperature on larval color and performance
Experimental MethodsEffect of temperature on larval color and performance
  • Common garden experiment in temperature-controlled environments to assess the relative contributions of heritable variation and phenotypic plasticity to color variation
  • Origins of larvae: Ten half-sib (possibly full-sib given sperm precedence) families, 2 populations (CA and TX)
  • Treatments. Reared under conditions of constant temperature (24, 30, 36, 40 oC) and darkness (0L:25D)
  • Responses: Larval performance measured in two ways: time to pupation (days) and pupal mass (mg)
  • Analysis: Two mixed model ANOVAs used to test for effects of family, population (CA vs. TX), and temperature on time to pupation and pupal weight
probability of red larval phenotype increases with max daily temperature over range 24 36 o c
Probability of red larval phenotype increases with max daily temperature over range 24-36 oC
  • Critical temperature (50% red) ~ 30-31 o C

No among-family or between-population variation in coloration detected, but there were effects of temperature on days to pupation and pupal mass

Significant terms from ANOVAs

A, Response: Time to pupation –

Population – CA take longer than TX

Temperature – shorter at higher T

Family (Population)

Family (Population) x Temperature

(lines appear to be parallel) ??

B. Response: Pupal Mass

Population – CA heavier at low T

Temperature – lighter at high T

Population x Temperature

Family (Population) x Temperature

Note: 40oC lethal maximum

red larvae maintain lower body temperatures in full sunlight
Red larvae maintain lower body temperatures in full sunlight
  • Fig. 5  Effects of larval color on internal body temperatures in Battus philenor. Body temperatures (mean±SE) of 11 pairs of black (filled circle) and red (open diamonds) larvae exposed to sunlight for 17 min

6.85 oC > ambient

3.81 oC > ambient

However, mean (± SE) body temperatures

Black 44.91 ± 1.16 o C

Red 41.87± 1.46 o C

Appear to be above the lethal maximum of 40 o C - so we lack evidence to conclude ‘red phenotype… a mechanism to avoid internal temperatures above the lethal maximum’

morphology and thermoregulation
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 as in Bumblebee
stilts and parasols tenebrionidae of the namib desert
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).

apache cicada sonoran desert dicerooproctoa apache
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
warming up by shivering
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)
bumblebees out in the cold
Bumblebees out in the cold
  • Bumblebees occur throughout the temperature region and on cool mountaintops in the tropics
  • They can forage and fly at or near 0 o C after they are heated up (depending on body size and availability of fuel)

Books by Bernd Heinrich

  • Bumblebee Economics
  • The hot-blooded insects: strategies and mechanisms of thermoregulation.
  • Insect Thermoregulation.

Photo by John Ascher

Bombus vosnesenskii female queen Note: Keys to species found at

regulation of body temperature in bumblebees ch 6 in heinrich
Regulation of body temperature in bumblebees (Ch 6 in Heinrich)
  • Pubescence – How can the contribution to thermoregulation be separated from alternative functions?
  • Body Mass – Small bees cool faster than larger bees, but both large and small bees maintain similar Tth. How?
  • Brood incubation – How is heat generated in the thorax transferred to abdomen and brood?
  • Ovary incubation – Arctic queens maintain higher Tabd than New England counterparts. Why?
  • Circulatory Anatomy – How do counter-current exchange and alternating current regulate body temperatures?
  • Evaporative cooling by regurgitation – How does regurgitation help regulate head temperature?
thoracic and abdominal temperatures of bumblebee bombus vosnesenskii queen in continuous flight
Thoracic and Abdominal Temperatures of bumblebee Bombus vosnesenskii Queen in continuous flight

Tth is stabilized independently of ambient temperature

countercurrent and alternating current
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  prevents excessive cooling
  • Alternating current removes heat from thorax by alternating warm outgoing and cool incoming flow  prevents excessive heating
high artic bumblebee bombus polaris
High artic bumblebeeBombus polaris

By incubating brood with abdomen, queen can produce a batch of workers in ~2 weeks

  • 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
  • Thermoregulation has consequences from individual insects to populations and communities