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

    Authors

    K. M. Fedorka; V. Lee;W. E. Winterhalter

    Comments

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    Abbreviated Journal Title

    Evol. Ecol.

    Keywords

    Thermal melanism; Encapsulation; Pro-phenoloxidase; Season length; Body; size; Trade-off; DENSITY-DEPENDENT PROPHYLAXIS; DROSOPHILA-MELANOGASTER; CALOPTERYX-SPLENDENS; DISEASE RESISTANCE; COLIAS BUTTERFLIES; ANOPHELES-GAMBIAE; SEPHADEX BEADS; GROWTH LAYERS; POPULATIONS; INSECTS; Ecology; Evolutionary Biology; Genetics & Heredity

    Abstract

    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.

    Journal Title

    Evolutionary Ecology

    Volume

    27

    Issue/Number

    3

    Publication Date

    1-1-2013

    Document Type

    Article

    Language

    English

    First Page

    521

    Last Page

    531

    WOS Identifier

    WOS:000316639100005

    ISSN

    0269-7653

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