1. Body Size of Emerging Arctic Chironomids Correlates with Temperature
Alec R Lackmann, Ewelina S Bielak-Lackmann, Kevin M Cortes, Dan C McEwen, Malcolm G Butler
Department of Biological Sciences and Environmental & Conservation Sciences, North Dakota State University
Introduction
Results
Discussion
Temperature plays a major role in determining organism size, especially for ectotherms [1].
Flies play a critical role in arctic ecosystems, especially during the short summer, with nonbiting midges (Diptera: Chironomidae) the predominant freshwater invertebrates [2].
Over 6 million migratory shorebirds (~30 species) breed in the National Petroleum Reserve—Alaska (NPRA) [3]. Millions of other tundra-breeding birds also depend upon the seasonal pulse of adult chironomids emerging from tundra ponds [2].
In the current Anthropogenic Climate Change Era, the Arctic is the fastest warming region on earth [4].
What effect will rising temperatures in the Arctic have on chironomid size and fecundity?
Most Barrow chironomids illustrate the temperature size-rule [1]: they decrease in size as temperatures rise.
Temperature is rising in the Arctic, with some regions 4°C warmer compared to a thirty year average of the mid-late 20th century [8].
The annual average temperature of the Arctic is hypothesized to warm another 8°C by the end of the 21st century [9], potentially resulting in a 20% reduction in fly biomass and 25% reduction in fecundity/female for some midge species.
This may negatively affect tundra-breeding birds.
Can these lab results be applied to the field?
Rearing these chironomids over more of their life cycle, a better simulation of their experience under global warming, would strengthen our results and predictive power.
Figure 3. Response of dry weight to rearing temperature for ten chironomid species. Five of 20 regressions (male and female for each species) were statistically significant. Larvae/pupae spent only a small portion of their lifespan [6] in these lab rearings, yet when sufficient data are present there is a clear trend toward smaller adult body size at warmer temperatures for males and females. Psectrocladius II is a curious exception.
Barrow (BRW), AK (71°17′44″N 156°45′59″W) is located above the Arctic Circle.
Figure 1. Left: A map of Northern Alaska adapted from [3] showing Barrow, the NPRA (blue line) and Arctic Coastal Plain (red line). Right: image taken by M G Butler of our general field site near Barrow on 30 June 2014.
Species
Sex
Rearing min (C)
Rearing max (C)
Δ mass overall
Δ mass/degree
HypothesizedΔ eggs overall
Hypothesized Δ eggs/degree
C. tardus ♀ 6 24
-28%
-1.56%
-35%
-1.92% ♂*
-20%
-1.10%
Chironomus V 9 18
-17%
-1.94%
-22%
-2.39%
T. alaskensis
-30%
-2.47%
-37%
-3.05% ♂
-1.80%
Psectrocladius II 21
36%
2.41%
45%
2.98%
Photo courtesy of Ewelina
Table 1. Temperature effect on size and fecundity for significant results in Figure 3. *C. tardus males were nearly significant (P=0.06). Most species are projected to decrease in mass by 1-2% per degree C increase. Fecundity (as indicated by estimated number of eggs/female) will likely decrease even more [7]. Psectrocladius II shows an opposite trend.
Methods
Acknowledgements and References
Chironomid larvae were collected following thaw (2015) from tundra ponds sorted by source, species, and developmental stage.
Larvae were then distributed among a range of temperature treatments in the lab and reared to emergence of the winged adult fly.
Upon emergence, insects were immediately photographed under a dissecting microscope, later measured for thorax size to estimate dry weight [5].
We would like to thank Rick Lanctot and the rest of the CEWISH team for help in conceptualizing the relationship between wetlands, birds, and bugs. We would also like to thank Shane Braegelman and the rest of the Butler lab group for comments and advice.
9°C
21°C
Poster completed 22 February 16
1. Kingsolver, J. G., & Huey, R. B. (2008). Size, temperature, and fitness: three rules. Evolutionary Ecology Research, 10(2),
2. Hodkinson, I. D., Coulson, S. J., Webb, N. R., Block, W., Strathdee, A. T., Bale, J. S., & Worland, M. R. (1996). Temperature and the biomass of flying midges (Diptera: Chironomidae) in the high Arctic. Oikos,
3. Johnson, J. A., Lanctot, R. B., Andres, B. A., Bart, J. R., Brown, S. C., Kendall, S. J., & Payer, D. C. (2007). Distribution of breeding shorebirds on the Arctic Coastal Plain of Alaska. Arctic,
4. IPCC (2014) Synthesis Report
5. Welch, H. E., Jorgenson, J. K., & Curtis, M. F. (1988). Emergence of Chironomidae (Diptera) in fertilized and natural lakes at Saqvaqjuac, NWT. Canadian Journal of Fisheries and Aquatic Sciences, 45(4),
6. Butler, M. G. (1982). A 7-year life cycle for two Chironomus species in arctic Alaskan tundra ponds (Diptera: Chironomidae). Canadian Journal of Zoology,60(1),
7. Butler, M. G., & Walker, L. (1992). Fecundity, reproductive effort, and pupal size in the profundal midge Chironomus cuccini (Diptera: Chironomidae).Netherland Journal of Aquatic Ecology, 26(2-4),
8. Arctic Climate Impact Assessment (2004): Arctic Climate Impact Assessment. Cambridge University Press, ISBN , siehe online
9. IPCC (2007) Report
Photos courtesy of Ewelina
Figure 2. Left: Chironomid larvae are sorted by species (e.g. Chironomus tardus) to be distributed among the 10 temperature treatments ranging from 5 to 28°C (right); photos courtesy of Alec & Dan