Evolution and Systematics

Functional Adaptations

Functional adaptation

Humidity changes exoskeleton color: Hercules beetle
 

The exoskeleton of the Hercules beetle changes from green to black with increasing humidity using thin film interference by reversible modification of layer thickness.

   
  "The Hercules beetle, Dynastes Hercules [sic] L., can change the colour of its elytra—horny fore-wings—from black to greenish yellow and back again to black all within a few minutes. It does this in a way previously unknown among insects. Apart from the reversible migrations of pigment granules in the iris cells, physiological or rapidly reversible colour changes are very rare in insects. Among beetles, CoptocycliaAspidomorpha, and many other Cassidinae can change the colour of their elytra by varying the amount of water in the cuticle and thereby the thickness of the thin films responsible for the interference colours." (Hinton and Jarman 1972:160)

"The elytra from dry specimens of the hercules beetle, Dynastes hercules appear khaki-green in a dry atmosphere and turn black passively under high humidity levels. New scanning electron images, spectrophotometric measurements and physical modelling are used to unveil the mechanism of this colouration switch. The visible dry-state greenish colouration originates from a widely open porous layer located 3μm below the cuticle surface. The structure of this layer is three-dimensional, with a network of filamentary strings, arranged in layers parallel to the cuticle surface and stiffening an array of strong cylindrical pillars oriented normal to the surface. Unexpectedly, diffraction plays a significant role in the broadband colouration of the cuticle in the dry state. The backscattering caused by this layer disappears when water infiltrates the structure and weakens the refractive index differences." (Rassart et al. 2008:1)


"The visible dry-state greenish coloration originates from a open porous layer located at 3 μm below the cuticle surface. This layer has three-dimensional photonic crystal structures, which are a network of filamentary strings, arranged in layers parallel to the cuticle surface [Fig. 1d]. In dry state, nanosized holes in the layer are occupied with air (refractive index 1) but the empty holes are filled with water (refractive index 1.33) under high humidity. The change in refractive index with respect to the humidity level induces the variation in the visible color." (Kim et al. 2010:103701-1)

  Learn more about this functional adaptation.
  • Hinton, HE; Jarman, GM. 1972. Physiological color change in the Hercules beetle. Nature. 238: 160-161.
  • Rassart, M; Colomer, J-F; Tabarrant, T; Vigneron, JP. 2008. Diffractive hygrochromic effect in the cuticle of the hercules beetle Dynastes hercules. New Journal of Physics. 10(033014): 14 pp.
  • Kim JH; Moon JH; Lee S-Y; Park J. 2010. Biologically inspired humidity sensor based on three-dimensional photonic crystals. Applied Physics Letters. 97: 103701-1 - 102701-3.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Dynastes hercules

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Specimens with Barcodes: 5
Species With Barcodes: 1
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Wikipedia

Hercules beetle

The Hercules beetle (Dynastes hercules) is the most famous and the largest of the rhinoceros beetles. It is native to the rainforests of Central America, South America, and the Lesser Antilles. The beetle has also been observed as far north as Southern Veracruz in Mexico. Their title is well deserved, with some able to lift more than 850 times (up to 8 kg lifted) their own weight and some males, rarely, reaching 17 cm (6.75 inches) in length.[1] It is the largest of the six species in the Dynastes genus, and one of the largest beetles known, being exceeded in length by only two other beetles in the family Cerambycidae, Macrodontia cervicornis (specimens of 17–17.5 cm are known) and Titanus giganteus (also up to 17–17.5 cm; several 18+ cm specimens are reputed/alleged to exist). However, if the horns are excluded, both M. cervicornis and D. hercules drop considerably farther down in the size rankings, leaving T. giganteus on top. One reason for this is that the development of the horns is allometric, as well as sexually dimorphic, and thus not strictly correlated to actual body size; it is possible for a female to be much longer, measured from eyes to abdomen, than a male, yet be considered "smaller" simply due to the absence of horns.

As noted above, Hercules beetles are highly sexually dimorphic, with the females generally being larger-bodied but much shorter, as they lack horns entirely. The larval stage of the Hercules beetle will last one to two years, with the larva growing up to 4.5 inches (11 cm) in length and weighing more than 100 grams. Much of the life of the larva is spent tunneling through its primary food source of rotting wood. After the larval period, transformation into a pupa, and moulting, the beetle then emerges as an adult. Adults will roam the forest floor in search of decaying fruit.

Subspecies[edit]

  • Dynastes hercules baudrii Pinchon, 1976
    • Origin: Martinique
    • Male size: 50–100 mm; female: 45–55 mm
  • Dynastes hercules bleuzeni Silvestre and Dechambre, 1995
    • Origin: Venezuela
    • Male size: 55–155 mm; female: 45–75 mm
  • Dynastes hercules ecuatorianus Ohaus, 1913
    • Origin: Colombia, Peru, Ecuador, Brazil
    • Male size: 55–165 mm; female: 50–80 mm
  • Dynastes hercules hercules Linnaeus, 1753.
    • Origin: Guadeloupe, Dominica
    • Male size: 45–178 (max: 220 mm?); female: 50–80 mm
  • Dynastes hercules septentrionalis
    • Origin: Extreme Southern Mexico, Central America
    • Male size: 50–150 mm; female: 40–80 mm
  • Dynastes hercules tuxtlaensis Moron, 1993
    • Origin: Mexico
    • Male size: 70–110 mm; female: 45–60 mm
  • Dynastes hercules occidentals

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References[edit]

Further reading[edit]

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