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Gynaephora groenlandica

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Arctic woolly bear moth
Arctic woolly bear caterpillar, Baffin Island
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Superfamily: Noctuoidea
Family: Erebidae
Genus: Gynaephora
Species:
G. groenlandica
Binomial name
Gynaephora groenlandica
(Wocke, 1874)
Synonyms
  • Dasychira groenlandica Woke, 1874[1]

Gynaephora groenlandica, commonly referred to as the arctic woolly bear moth, is an erebid moth endemic to the High Arctic, specifically the Canadian Archipelago and Greenland.[2] It is best known for its slow rate of development, as its full life cycle may extend up to 14 years, and it remains in its larval stage for the vast majority of its life.[2][3] It is unique among Lepidoptera in its ability to withstand temperatures as low as −70°C, and it does so during a period of diapause that lasts for much of the calendar year.[4] Encasing itself within hibernacula during diapause serves several functions: protection from parasitoids that affect a large proportion of larvae and pupae, avoidance of decreased nutrients in their primary food source, Salix arctica, degradation of mitochondria linked to hypometabolism and antifreeze synthesis, and conservation of energy reserves.[3][4][5]

This species has alpine subspecies which are notable for their geographic distribution south of the High Arctic. Females generally do not fly, while males are much more active in this capacity.[4][6] Basking is a key behavior in this species which aids in temperature regulation and digestion in addition to having effects on metabolism and oxygen consumption.[2][3] G. groenlandica may also represent a useful indicator species for the effects of global warming in the High Arctic due to temperature-based feeding tendencies.[7]

The Natural History Unit of the BBC filmed G. groenlandica in their natural habitat on Ellesmere Island during June 2009. The sequence became part of the BBC's sequel to Planet Earth called Frozen Planet, broadcast on BBC One in Autumn 2011 (with the US broadcast following on Discovery Channel in spring 2012).[8]

Geographic Range

G. groenlandica is endemic to the Canadian Arctic Archipelago and Greenland, above 70°N latitude.[6][2] It is known as one of the most northern members of the Lepidoptera order in the Northern hemisphere.[4] It is officially classified as a High Arctic endemic species.[6] Data published in December 2013 presented the first records of G. groenlandica south of the arctic circle, in alpine environments in southwest Yukon, 900 kilometers south of their previously established distribution. These populations were subsequently designated as the subspecies G.g. beringiana.[6]

Habitat

G. groenlandica is extremely adapted to living under conditions of extreme heat deficiency in the High Arctic.[4]

Home Range and Territoriality

The G. groenlandica caterpillar moves up to several meters per day.[9] To understand movement for the acquisition of resources, an experiment was performed in which one group of caterpillars was physically transferred between Salix arctica (arctic willow) plants. A second group of caterpillars were individually restricted to a single willow. This arrangement was maintained throughout the active period of the caterpillars, and it was observed that those caterpillars which were moved demonstrated higher herbivory and growth rates compared to the stationary group. This suggests that the acquisition of high quality resources may be a principle motivation for G.groenlandica caterpillars to move from one plant to another.[9]

Food Resources

Host Plant Preferences and Selection

As G. groenlandica spends much of its life as a caterpillar, and 20% of its time feeding, food resources in general apply to its larval stage of development. The primary host plant and source of food for this species is the patchily-distributed Salix arctica, the arctic willow.[9][3] However, larvae can feed on plants of other families, such as the flowers of Saxifraga oppositifolia and the senescent leaves of Dryas integrifolia. Less than 3% of larvae, though, have been found to choose these alternatives.[2]

Compared to High Arctic populations, it was found that in lower and warmer sites in Canada, G. groenlandica exhibits lower consumption of Salix arctica; for instance, the G. groenlandica beringiana subspecies found in the alpine environments of southwest Yukon feed on a broader spectrum of plants than populations of the High Arctic.[6][10][11] Furthermore, the highest herbivory in this species was discovered to be at sites of intermediate temperature for its range in Canada. This is attributed to the narrow thermal adaptation of this species, meaning that it is not able to increase its levels of herbivory at warmer sites in its geographical distribution.[11]

While the catkins of S. arctica are rarely eaten by the larvae, they are known to eat its leaves: 97% of larvae which were actively eating at the onset of their feeding season were consuming primarily new leaf buds of this plant. Removal of nitrogen and potassium by the feeding larvae is hypothesized to occur due to nutrient concentrations of the leaves of the plant compared to those in larval frass.[9] Examining the feeding patterns of larvae, it was found that the larvae only fed in June when the leaves of S. arctica had the highest concentrations of nutrients and total non-structural carbohydrates, and larvae decreased their food intake towards the end of the month and into the summer, when the energy and nutrient content of the plant, specifically the level of total non-structural carbohydrates, decreased.[2][3]

Life History

The life history traits of G. groenlandica are dictated by the short, cold nature of summers in the High Arctic.[10] Due to the restricted seasonal growth period of G. groenlandica, this species has a life cycle that is generally 10 years, but is known to extend to at least 14 years at the Alexandra Fiord lowland and at Ellesmere Island.[6][2][3] It is much shorter (2-3 years) in alpine environments.[6] They remain larvae for the vast majority of their lives, with the exception of up to 3-4 weeks of a single summer.[3] While they remain in their larval stage, G. groenlandica experience numerous winter diapauses.[4]

Life Cycle

In general, G. groenlandica caterpillars are characterized as large and densely pubescent, and they have a hair tuft on the eighth abdominal segment.[6][4] The later instars of the larvae can be characterized by the color patterns of their dorsal hair tufts and the form of their spinulose hairs.[6]

Larval activity is confined to a short period following snowmelt. The High Arctic presents a short growing season of 45-70 days, and the G. groenlandica cease foraging after 3-4 weeks in June, prior to mid-summer.[2] Larvae tend to spend 95% of their time either basking in the sun, feeding, or moving, and only 5% of their time immobile.

At the end of this period, the larvae openly prepare to overwinter by weaving a hibernacula and entering diapause until the subsequent snowmelt.[6][4] This typically occurs when daytime temperatures are at a maximum of 5-10°C, but in this state they are able withstand temperatures as low as -70°C.[4][12]

Cocoons of this species are spun on exposed sites such as rocks, and they have silk cocoons of two layers, into which they incorporate larval hairs.[6][12]

The developmental stages of pupation, emergence, mating, egg laying, eclosion, and molting to the second instar stage are all confined to a period of 3-4 weeks during a single summer, and emergence and reproduction may occur in a 24-hour period.[6][2]

Because the lifespan of adult, fully mature individuals is so brief, adults are difficult to find in the field.[6]

Enemies

Predators

G. groenlandica has a distinct defense reaction to bat signals.[4] When the moths hear the ultrasound, the males reverse their flight course in response. However, females have a degenerating bat-sensing system for multiple reasons. First, females tend to be flightless and thus do not need this adaptation. Second, an auditory system would compete for space with the ovaries, and thus could be more costly than beneficial to reproducing females.[13]

Parasitoids

The primary enemies of G. groenlandica caterpillars are parasitoids, namely Exorista thula and Hyposoter diechmanni, an ichneumonid wasp. [9][14] In general, more than two thirds of Gynaephora are killed by parasitoids, and parasitism in G. groenlandica specifically causes more than 50% mortality.[3][11] The probability of parasitism increases towards the end of the species’ active period, which coincides with declining rates of feeding.[4]

The tachinid fly Exorista thula also poses a threat to G. groenlandica. [5] The wasp, a solitary parasitoid, kills about 20% of the third and fourth instars of the host. The Gregarious Bristle Fly causes about 50% mortality in instar 5 and 6, and pupae.

Genetics

Subspecies

While G. groenlandica is generally classified as a High Arctic endemic species, an article published in December 2013 contained the first reports of G. groenlandica in alpine environments. Specifically, two neighboring populations were discovered in southwest Yukon, 900 kilometers south of their previously-defined southern distributive border. Due to the distinct habitat, geography, DNA barcode, and wing phenotype of these two populations, they were classified as a subspecies, G.g.beringiana[citation needed].

Hybridization

While G. groenlandica is a close relative of G. rossii, the two species are reproductively isolated and no hybridization occurs[citation needed].

Physiology

Flight

While the females of this species have fully developed wings and can take flight for a short time, they do not usually fly; however, it is worth noting that while Arctic-inhabiting females tend to be flightless, alpine subspecies females are usually more mobile.[6][4]

Males, on the other hand, tend to fly high, fast, and erratically during the day.[6]

Thermoregulation: Basking, Metabolism, Oxygen Consumption

In general, the period of maximal activity in G. groenlandica occurs during the annual period of maximal solar radiation. During this time, the body temperatures of feeding larvae tend to be similar to those of molting and spinning larvae, while those of “basking” larvae tend to be higher.[3] G. groenlandica larvae spend approximately 60% of their time basking, which is a behavior in which a caterpillar orients its body so as to maximize sun exposure and avoid wind, thus raising its body temperature by up to 20°C. Generally, maximal body temperature is about 30°C.[2][4][3] This maximum temperature is generally only reached when larvae lie in midday sun, surrounded by snow, on a day with minimal wind.[3] The preferred angle of orientation is towards the sun and away from the wind, and larvae tend to follow the direct angle of the sun’s rays in order to maintain maximal absorption of sunlight. They do this by orienting perpendicularly to the sun’s angle of insolation.[3]

While larvae utilize solar radiation to promote growth, and basking may therefore increase developmental rates, it may also interfere with other activities such as feeding.[2][3] When comparing growth rates at 5, 10, and 30°C, respectively, the growth rate was found to be lowest at 5°C and metabolism rates were maximized at 30°C.[2] Thus, basking tends to increase body temperature. As body temperature increases, metabolic rate increases exponentially, even when larvae are starved or seemingly inactive.[2][3] Because feeding larvae tend to have lower body temperatures than basking larvae, their body temperature drops, and their maintenance metabolism increases simultaneously. Consequently, larvae tend to feed during the day, when temperatures are highest, and they bask when they can’t reach these higher temperatures (more than 5 -10°C) needed for activity.[2]

Changes in metabolic state and body temperature also affect oxygen consumption.[2][3] Oxygen consumption was found to be much lower when body temperatures were below 10°C.[3] It was also found to be lowest for inactive larvae, while it was higher for caterpillars with were moving or starved, higher still for those who were digesting, and highest for feeding larvae.[2]

Digestion

After feeding, larvae may move to a new feeding site, but they often bask for about 5 hours.[2][3] The increase in body temperature that results from basking increases digestion rate because it stimulates gut enzyme activity.[3] G. groenlandica’s level of efficiency for the conversion of ingested food exceeds the mean value of the level in other Lepidopteran species.[2]

Diapause

G. groenlandica experience a winter diapause period during which they form a hibernacula. In this state, they can withstand temperatures up to -70°C.[4]

During the active season, larvae orient towards solar radiation and spin two-layer cocoons over a 24-hour period.[4][3] When they finish, they tend to pupate with their head facing south, in a north-south orientation.[3] In addition to dense pubescence, their cocoon helps to accumulate heat more effectively, accelerating pupal development.[4] As temperatures decrease during the late arctic summer, larvae also begin to synthesize cryoprotective compounds, such as glycerol and betaine. Accumulation of these "antifreezes“ is aided by bottle-necking of oxidative phosphorylation through mitochondrial degradation. While G. groenlandica obtain energy from stored glycogen in their frozen state, this mitochondrial degradation causes their metabolism to become so low as to almost stop entirely. Mitochondrial functioning may be restored in the spring after a period of only several hours of resumed larval activity.[4][15]

Conservation

Warming Temperatures and Herbivory

When investigating Arctic moth caterpillars, it was found that larvae generally tended to have higher respiration rates and lower growth rates at warmer temperatures. They also tended to shift their diets to more nutrient-rich foods. Salix arctica and Dryas octopetala herbivory rates thus changed.[7] Results such as this suggest host plant plasticity in G. groenlandica depending on their environment and suggest that increases in temperature due to global warming events, for instance, may have profound effects on the performance of cold-adapted herbivore invertebrates such as G. groenlandica, and herbivory rates of their food sources, suggesting that G. groenlandica may represent an indicator species for climate change.[4][10][7]

See also

References

  1. ^ von Homeyer, Alexander (1874). "Lepidopteren". Wissenschaftliche Ergebnisse. Die zweite Deutsche Nordpolarfahrt. Vol. 2. Leipzig: F. A. Brockhaus. pp. 409–410.
  2. ^ a b c d e f g h i j k l m n o p q r Kukal, Olga; Dawson, Todd E. (1989-06-01). "Temperature and food quality influences feeding behavior, assimilation efficiency and growth rate of arctic woolly-bear caterpillars". Oecologia. 79 (4): 526–532. doi:10.1007/BF00378671. ISSN 0029-8549.
  3. ^ a b c d e f g h i j k l m n o p q r s t Kukal, Olga (March 24, 1988). "Behavioral Thermoregulation in the Freeze-Tolerant Arctic Caterpillar, Gynaephora groenlandica" (PDF). The Company of Biologists Limited. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  4. ^ a b c d e f g h i j k l m n o p q r Makarova, O. L.; Sviridov, A. V.; Klepikov, M. A. (2013-04-01). "Lepidoptera (Insecta) of polar deserts". Entomological Review. 93 (2): 225–239. doi:10.1134/S0013873813020115. ISSN 0013-8738.
  5. ^ a b Morewood, W. Dean; D. Monty Wood (2002). "Host utilization by Exorista thula Wood (sp. nov.) and Chetogena gelida (Coquillett) (Diptera: Tachinidae), parasitoids of arctic Gynaephora species (Lepidoptera: Lymantriidae)". Polar Biology. 25: 575–582. doi:10.1007/s00300-002-0382-y.
  6. ^ a b c d e f g h i j k l m n o "WU Libraries: Proxy Server Login" (PDF). www.jstor.org.libproxy.wustl.edu. Retrieved 2017-10-25.
  7. ^ a b c Barrio, Isabel C.; Bueno, C. Guillermo; Hik, David S. (2016-01-01). "Warming the tundra: reciprocal responses of invertebrate herbivores and plants". Oikos. 125 (1): 20–28. doi:10.1111/oik.02190. ISSN 1600-0706.
  8. ^ Levin, Gary (April 8, 2008). "Another sweeping nature special when 'Planet' freezes over". USA Today. Retrieved May 25, 2010. {{cite news}}: Italic or bold markup not allowed in: |publisher= (help)
  9. ^ a b c d e Greyson-Gaito, Christopher J.; Barbour, Matthew A.; Rodriguez-Cabal, Mariano A.; Crutsinger, Gregory M.; Henry, Gregory H. R. (2016/12). "Freedom to move: Arctic caterpillar (Lepidoptera) growth rate increases with access to new willows (Salicaceae)". The Canadian Entomologist. 148 (6): 673–682. doi:10.4039/tce.2016.22. ISSN 0008-347X. {{cite journal}}: Check date values in: |date= (help)
  10. ^ a b c Barrio, I. C.; Hik, D. S.; Liu, J. Y. (2015/04). "Diet breadth of Gynaephora groenlandica (Lepidoptera: Erebidae): is polyphagy greater in alpine versus Arctic populations?". The Canadian Entomologist. 147 (2): 215–221. doi:10.4039/tce.2014.35. ISSN 0008-347X. {{cite journal}}: Check date values in: |date= (help)
  11. ^ a b c Birkemoe, Tone; Bergmann, Saskia; Hasle, Toril E.; Klanderud, Kari (2016-10-01). "Experimental warming increases herbivory by leaf-chewing insects in an alpine plant community". Ecology and Evolution. 6 (19): 6955–6962. doi:10.1002/ece3.2398. ISSN 2045-7758.
  12. ^ a b Laity, Peter R.; Holland, Chris (2017-02-01). "Thermo-rheological behaviour of native silk feedstocks". European Polymer Journal. 87 (Supplement C): 519–534. doi:10.1016/j.eurpolymj.2016.10.054.
  13. ^ Rydell, J., et al. “Persistence of Bat Defence Reactions in High Arctic Moths (Lepidoptera).” Proceedings of the Royal Society B: Biological Sciences, vol. 267, no. 1443, 2000, pp. 553–557., doi:10.1098/rspb.2000.1036.
  14. ^ Varkonyi, Gergely; Tomas Roslin (2013). "Freezing cold yet diverse: dissecting a high-Arctic parasitoid community associated with Lepidoptera hosts". Canadian Entomologist. 145: 193–218. doi:10.4039/tce.2013.9.
  15. ^ Hoffmann, Klaus H. (2014-12-19). Insect Molecular Biology and Ecology. CRC Press. ISBN 9781482231892.

Further reading

  • Bernd Heinrich (1993). The hot-blooded insects: strategies and mechanisms of thermoregulation. Harvard University Press.
  • R. F. Chapman (1998). The insects: structure and function. Cambridge University Press. ISBN 978-0-521-57890-5.
  • Kukal, O. and P.G. Kevan. (1987) The influence of parasitism on the life history of a high arctic insect, Gynaephora groenlandica (Wöcke) (Lepidoptera: Lymantriidae). Can. J. Zool. 65: 156-163.
  • Kukal, O. 1988. Caterpillars on ice. Natural History 97: 36-41.
  • Kukal, O., Duman, J.G. and A.S. Serianni. (1988) Glycerol metabolism in a freeze-tolerant arctic insect: An in vivo 13-C NMR study. J. Comp. Physiol. B 158: 175-183.
  • Kukal, O., Heinrich, B. and J.G. Duman. (1988) Behavioural thermoregulation in the freeze-tolerant arctic caterpillar, Gynaephora groenlandica. J. Exp. Biol. 138: 181-193.
  • Kukal, O. and T.E. Dawson. (1989) Temperature and food quality influences feeding behavior, assimilation efficiency and growth rate of arctic woolly-bear caterpillars. Oecologia 79: 526-532.
  • Kukal, O., Duman, J.G. and A.S. Serianni. (1989) Cold-induced mitochondrial degradation and cryoprotectant synthesis in freeze-tolerant arctic caterpillars. J. Comp. Physiol. B 158: 661-671.
  • Kukal, O. 1990. Energy budget for activity of a high arctic insect, Gynaephora groenlandica (Wöcke) (Lepidoptera: Lymantriidae). In: C.R. Harington (ed) Canadian Arctic Islands: Canada's Missing Dimension. National Museum of Natural History, Ottawa, Canada.
  • Kukal, O. 1991. Behavioral and physiological adaptations to cold in a freeze-tolerant arctic insect. In: R.E. Lee and D.L. Denlinger (eds) Insects at Low Temperature. Chapman and Hall, N.Y.
  • Kukal, O. 1993. Biotic and abiotic constraints on foraging of arctic caterpillars. In: N.E. Stamp and T.M. Casey (eds) Caterpillars: Ecological and Evolutionary Constraints on Foraging. Chapman and Hall, N.Y.
  • Kevan, P.G. and O. Kukal. (1993) A balanced life table for Gynaephora groenlandica (Lepidoptera: Lymantriidae) a long-lived high arctic insect, and implications for the stability of its populations. Can. J. Zool. 65: 156-163.
  • Danks, H.V., Kukal, O. and R.A. Ring. (1994) Insect cold-hardiness: Insights from the arctic. Arctic 47 (4): 391-404.
  • Kukal, O. (1995) Winter mortality and the function of larval hibernacula during the 14-year life cycle of an arctic moth, Gynaephora groenlandica. Can. J. Zool. 73: 657-662.
  • Bennett, V. A, Kukal, O. and R.E. Lee. (1999) Metabolic opportunists: Feeding and temperature influence the rate and pattern of respiration in the high arctic woollybear caterpillar, Gynaephora groenlandica (Lymantriidae). J. Exp. Biol. 202: 47-53.
  • Bennett, V.A., Lee, R. E., Jr., Nauman, J.S. and Kukal, O. (2003) Selection of overwintering microhabitats used by the arctic woollybear caterpillar, Gynaephora groenlandica. CryoLetters 24(3): 191-200.
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