Evolutionary Ecology

, Volume 27, Issue 3, pp 521–531 | Cite as

Thermal environment shapes cuticle melanism and melanin-based immunity in the ground cricket Allonemobius socius

  • Kenneth M. Fedorka
  • Vivian Lee
  • Wade E. Winterhalter
Original Paper


The thermal melanin hypothesis posits that ectothermic individuals of larger size or from colder environments exhibit darker cuticles due to melanin’s efficacy in absorbing solar radiation. However, melanin is also a crucial component of arthropod immunity. Thus, thermal selection for increased cuticle darkness may profoundly influence melanin-based immune function. In this study, we address the relationships between the thermal environment (season length), cuticular melanism and two aspects of melanin-based immunity across nine thermally distinct populations of the cricket Allonemobius socius. We found that season length (i.e. degree days) and body size had a positive association with cuticle melanism in both sexes across populations, supporting the thermal melanism hypothesis. Despite their smaller size, males were found to have darker cuticles and superior melanin-based immunity. This pattern may be the result of additional selection on males due to sex-specific temperature-dependent activities, such as male calling song. Perhaps most interestingly, we found that short season length populations (i.e. colder) exhibited a greater phenoloxidase activity (aspect of the melanin-based immune system) in addition to darker cuticles in both sexes. This pattern is consistent with direct thermal selection on cuticular color, coupled with indirect selection on melanin-based immunity due to pleiotropy. Thus, thermal selection on cuticle darkness appears to indirectly shape the evolution of pathogen resistance in this system, and potentially for other terrestrial arthropod systems whose ranges encompass a significant thermal gradient.


Thermal melanism Encapsulation Pro-phenoloxidase Season length Body size Trade-off 



We thank John Hayes, Alex Taraboletti and Kati Lindholm, who assisted with cricket maintenance and data collection. We thank Emily Copeland for testing the cricket age and cuticle melanization hypothesis. This work was supported by a Department of Energy grant to W.E.W. and K.M.F. (#DE-PS02-07ER07-11).


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Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  • Kenneth M. Fedorka
    • 1
  • Vivian Lee
    • 1
  • Wade E. Winterhalter
    • 1
  1. 1.Department of BiologyUniversity of Central FloridaOrlandoUSA

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