| Research
Interests
Evolutionary and ecological physiology of insects
My research focus is on the physiological interactions of
insects and other terrestrial arthropods with various abiotic
factors in their immediate environments over time.
Temperature
Short term and long term mechanisms and strategies allowing
insects to survive what could be considered lethal extremes.
Metabolic and life history responses to variable thermal
regimes.
Water
Physiological and behavioural strategies allowing insects
to maximize desiccation tolerance and desiccation resistance.
Gas exchange responses in relation to water balance requirements.
Interactions between water balance mechanisms and thermal
conditions.
Atmospheric components
The evolution and ecological significance of controlled
gas exchange mechanisms in insects and other tracheated
arthropods in relation to levels of oxygen, carbon dioxide
and water vapour.
The effects of available oxygen on insects’ body
sizes and tracheal constructions in physiological, ecological
and historical contexts.
Research Interests
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Current Research
I am investigating the effects of different atmospheric
oxygen concentrations on adult body size of insects and
also its effects, during development, on their tracheal
structures, scaling, dimensions and respiratory functioning.
Drosophila melanogaster is the primary model species.
Rearing medium sized D. melanogaster populations
(ca. 100 founding adults) at three atmospheric concentrations
– low or hypoxia at 10 kPa atmospheric partial oxygen
pressure (aPO2), ambient or normoxia at 21 kPa aPO2, and
high or hyperoxia at 40 kPa aPO2 – allowed me to assess
possible changes in body size related to the various aPO2
levels. After several generations the populations reared
in hypoxia and hyperoxia are returned to normoxia for up
to five additional generations. These procedures make it
possible to determine to what extent increases and decreases
in aPO2 affect final body size and also to determine whether
these changes are as a result of phenotypic plasticity (physiological
and developmental flexibility) or whether the flies actually
underwent laboratory natural selection and acquired genetically
fixed size changes upon returning to normoxia from their
respective selective oxygen regimes – i.e. did these
flies evolve different sizes. As it turned out, the flies
did show size changes. Those reared in hypoxia became smaller
while those reared in hyperoxia increased in size. In addition,
the changes in size were the combined results of phenotypic
plasticity and genetic selection. All lines showed marked
size deviations while in the test aPO2s. However, only some
of the selection lines retained these changes in size.
In addition to changes in size I also looked at the effects
of rearing oxygen on the development and dimensions of the
flies’ tracheae. One would hypothesise that in hypoxia
flies should increase tracheal diameters to compensate for
the decrease diffusive capacity of oxygen whereas in hyperoxia
one could expect a decrease in tracheal diameters. High
definition X-ray synchrotron imaging allowed me to measure
the tracheal diameters of flies reared for several generation
in the above aPO2 levels. The various aPO2 levels did indeed
lead to increases in tracheal diameters in hypoxic reared
flies and decreases in hyperoxic reared flies. However,
these changes were not universal in all tracheae. The leg
tracheae, a fair distance from the spiracles that feeds
air in and most likely more dependent on diffusive gas exchange,
showed these responses. Abdominal tracheae, on the other
hand, those close to the spiracles found on the abdominal
segments and also likely to benefit from convective movements
in the abdomen, showed no changes in diameter.
Research Interests
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History | Collaborators
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Interest | Top
Research History
Research Interests
| Current Research | Research
History | Collaborators
| Publications | General
Interest | Top
Collaborators
Present
Argonne National Laboratories – Jake Socha and
Wah-Keat Lee
Midwestern University – Alex Kaiser and Michael
Quinlan
Past
University of Stellenbosch – Centre for Invasion
Biology – Steven Chown, John Terblanche
Iowa State University – Elliot Krafsur
Kenyan Agricultural Research Institute – Trypanosomiasis
Unit – Mathu N’Dungu
International Atomic Energy Agency – Agricultural
Unit – Andrew Parker
New Zealand Antarctica
South African National Antarctic Programs
Australian Antarctic Division
Sheffield University – Animal and Plant Sciences
– Kevin Gaston
Research Interests
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History | Collaborators
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Publications
Klok CJ & Chown SL. 1993. Karyotypes of five Myrmeleontidae
species from southern Africa. African Entomology 1, 29-33.
Chown SL, Scholtz CH, Klok CJ, Joubert FJ & Coles KS.
1995.Ecophysiology, range contraction and survival of a
geographically restricted African dung beetle (Coleoptera:
Scarabaeidae). Functional Ecology 9, 30-39.
Klok CJ & Chown SL. 1997. Critical thermal limits, temperature
tolerance and water balance of a sub-Antarctic caterpillar,
Pringleophaga marioni Viette (Lepidoptera: Tineidae). Journal
of Insect Physiology 43, 685-694.
Klok CJ & Chown SL. 1998. Field thermal ecology and
water relations of gregaria phase african armyworm caterpillars,
Spodoptera exempta (Lepidoptera: Noctuidae). Journal of
Thermal Biology 23, 131-142.
Klok CJ & Chown SL. 1998. Interactions between desiccation
resistance, host-plant contact and the thermal biology of
a leaf-dwelling sub-Antarctic caterpillar, Embryonopsis
halticella (Lepidoptera: Yponomeutidae). Journal of Insect
Physiology 44, 615-628.
Klok CJ & Chown SL. 1999. Assessing the benefits of
aggregation: thermal biology and water relations of anomalous
emperor moth caterpillars. Functional Ecology 13, 417-427.
Klok CJ & Chown SL. 2000. Lack of cold tolerance in
a small, brachypterous sub-Antarctic fly, Apetaenus litoralis
Eaton (Diptera: Tethinidae), from Marion Island. African
Entomology 8, 305-308.
Klok CJ & Chown SL. 2001. Critical thermal limits, temperature
tolerance and water balance of a sub-Antarctic kelp fly,
Paractora dreuxi (Diptera: Helcomyzidae). Journal of Insect
Physiology 47, 95-109.
Chown SL & Klok CJ. 2001. First record of Palirhoeus
eatoni (Coleoptera: Curculionidae) from sub-Antarctic Heard
Island. African Entomology 9, 193-194.
Chown SL & Klok CJ. 2001. Habitat use, diet and body
size of Heard Island weevils. Polar Biology 24, 706-712.
Klok CJ, Mercer RD & Chown SL. 2002. Discontinuous gas
exchange in centipedes and its convergent evolution in tracheated
arthropods. Journal of Experimental Biology 205, 1031-1036.
Chown SL & Klok CJ. 2003. Altitudinal body size clines:
latitudinal effects associated with changing seasonality.
Ecography, 26, 445-455.
Klok CJ & Chown SL. 2003. Resistance to temperature
extremes in sub-Antarctic weevils: interspecific variation,
population differentiation and acclimation. Biological Journal
of the Linnean Society, 78, 401-414.
Klok CJ, Gaston KJ & Chown SL. 2003. The geographical
range structure of the Holly Leaf-Miner. III. Cold hardiness
physiology. Functional Ecology 17, 858-868.
Sinclair BJ, Klok CJ, Scott MB, Terblanche J & Chown
SL. 2003. Diurnal variation in supercooling points of three
species of Collembola from Cape Hallett, Antarctica. Journal
of Insect Physiology 49, 1049-1061.
Sinclair BJ, Vernon P, Klok CJ & Chown SL. 2003. Insects
at low temperatures: an ecological perspective. Trends in
Ecology and Evolution 18, 257–262.
Chown, SL, Klok, CJ & McGeoch MA. 2004. Weather to go
out: activity of Bothrometopus brevis (Curculionidae) at
Heard Island. Polar Biology 27, 217-221.
Sinclair BJ, Klok CJ & Chown SL. 2004. Metabolism of
the sub-Antarctic caterpillar Pringleophaga marioni during
cooling, freezing and thawing. Journal of Experimental Biology
207, 1287-1294.
Terblanche JS, Klok CJ & Chown SL. 2004. Metabolic rate
variation in Glossina pallidipes (Diptera: Glossinidae):
gender, ageing and repeatability. Journal of Insect Physiology
50, 419-428.
Klok CJ, Sinclair BJ & Chown SL. 2004. Upper thermal
tolerance and oxygen-limitation in terrestrial arthropods.
Journal of Experimental Biology 207, 2361-2369.
Terblanche JS, Klok CJ & Chown SL. 2004. Metabolic rate
in the whip-spider, Damon annulatipes (Arachnida: Amblypygi).
Journal of Insect Physiology 50, 637-645.
Klok CJ & Chown SL. 2005. Inertia in physiological traits:
Embryonopsis halticella caterpillars (Yponomeutidae) across
the Antarctic Polar Frontal Zone. Journal of Insect Physiology
51 (1): 87-97.
Klok CJ & Chown, SL. 2005. Temperature- and body mass-related
variation in cyclic gas exchane characteristics and metabolic
rate of seven weevil species: Broader implications. Journal
of Insect Physiology 51 (7): 789-801.
Terblanche JS, Klok CJ & Chown SL. 2005. Temperature-dependence
of metabolic rate in Glossina morsitans morsitans (Diptera,
Glossinidae) does not vary with gender, age, feeding, pregnancy
or acclimation. Journal of Insect Physiology 51 (8): 861-870.
Terblanche JS, Sinclair BJ, Klok CJ, et al. 2005. The effects
of acclimation on thermal tolerance, desiccation resistance
and metabolic rate in Chirodica chalcoptera (Coleoptera
: Chrysomelidae). Journal of Insect Physiology 51 (9): 1013-1023.
Sinclair BJ, Terblanche JS, Scott MB Blatch, GL, Klok CJ,
& Chown SL. 2006. Environmental physiology of three
species of Collembola at Cape Hallett, North Victoria Land,
Antarctica Journal of Insect Physiology 52 (1): 29-50.
Chown SL, Gibbs AG, Hetz SK, Klok CJ, Lighton JRB &
Marais E. 2006. Discontinuous gas exchange in insects: a
clarification of hypotheses and approaches. Physiol. Biochem.
Zool. 79 (2): 333-343.
Marais E., Klok CJ, Terblanche J.S. & Chown SL 2005.
Insect gas exchange patterns: a phylogenetic approach. Journal
of Experimental Biology 208 (23): 4495-4507.
Terblanche JS, Klok CJ, Krafsur ES, et al. 2006. Phenotypic
plasticity and geographic variation in thermal tolerance
and water loss of the tsetse Glossina pallidipes (Diptera
: Glossinidae): Implications for distribution modelling
American Journal of Tropical Medicine and Hygiene 74 (5):
786-794.
Klok CJ, Veldtman R, Terblanche JS, McGeoch MA & Chown
SL.
The physico-physiological function of wild silk moth cocoons:
CO2 and water vapour exchange. In prep.
Harrison JF, Henry J, Kaiser K, Klok CJ, Rascon B &
Frazier MR. In the burrow or the oxygen bar: responses of
terrestrial insects to hypoxia or hyperoxia. In press.
Klok CJ, Kaiser A & Harrison JF. The effects of variable
rearing oxygen atmospheres on body size, development and
tracheal structure in Drosophila melanogaster across single
and multiple generations. In prep.
Kaiser A, Klok CJ, Socha J; Lee WK; Quinlan MC; Harrison
JF. No giants today: oxygen supply to appendages limits
insect size. Submitted to Nature.
Research Interests
| Current Research | Research
History | Collaborators
| Publications | General
Interest | Top
General Interest
Photography
Skeptical Inquiry
Research Interests
| Current Research | Research
History | Collaborators
| Publications | General
Interest | Top
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