Title

Seasonality influences cuticle melanization and immune defense in a cricket: support for a temperature-dependent immune investment hypothesis in insects

Authors

Authors

K. M. Fedorka; E. K. Copeland;W. E. Winterhalter

Comments

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Abbreviated Journal Title

J. Exp. Biol.

Keywords

temperature-dependent immunity; plasticity; seasonality; phenoloxidase; lytic; ecoimmunology; ALLONEMOBIUS-SOCIUS; DISEASE RESISTANCE; TRADE-OFFS; PROPHYLAXIS; MELANISM; SYSTEM; SIZE; Biology

Abstract

To improve thermoregulation in colder environments, insects are expected to darken their cuticles with melanin via the phenoloxidase cascade, a phenomenon predicted by the thermal melanin hypothesis. However, the phenoloxidase cascade also plays a significant role in insect immunity, leading to the additional hypothesis that the thermal environment indirectly shapes immune function via direct selection on cuticle color. Support for the latter hypothesis comes from the cricket Allonemobius socius, where cuticle darkness and immune-related phenoloxidase activity increase with latitude. However, thermal environments vary seasonally as well as geographically, suggesting that seasonal plasticity in immunity may also exist. Although seasonal fluctuations in vertebrate immune function are common (because of flux in breeding or resource abundance), seasonality in invertebrate immunity has not been widely explored. We addressed this possibility by rearing crickets in simulated summer and fall environments and assayed their cuticle color and immune function. Prior to estimating immunity, crickets were placed in a common environment to minimize metabolic rate differences. Individuals reared under fall-like conditions exhibited darker cuticles, greater phenoloxidase activity and greater resistance to the bacteria Serratia marcescens. These data support the hypothesis that changes in the thermal environment modify cuticle color, which indirectly shapes immune investment through pleiotropy. This hypothesis may represent a widespread mechanism governing immunity in numerous systems, considering that most insects operate in seasonally and geographically variable thermal environments.

Journal Title

Journal of Experimental Biology

Volume

216

Issue/Number

21

Publication Date

1-1-2013

Document Type

Article

Language

English

First Page

4005

Last Page

4010

WOS Identifier

WOS:000325806300016

ISSN

0022-0949

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