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Review
. 2012 Mar 22;3(1):339-66.
doi: 10.3390/insects3010339.

Ecological and Evolutionary Determinants of Bark Beetle -Fungus Symbioses

Diana L Six  1
Affiliations
Review

Ecological and Evolutionary Determinants of Bark Beetle -Fungus Symbioses

Diana L Six. Insects. .

Abstract

Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree of mutual dependence among the beetles and their fungal partners. Unfortunately, the processes that shaped current day beetle-fungus symbioses remain poorly understood. Phylogeny, the degree and type of dependence on partners, mode of transmission of symbionts (vertical vs. horizontal), effects of the abiotic environment, and interactions among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I provide an overview of these associations and discuss how evolution and ecological processes acted in concert to shape these fascinating, complex symbioses.

Keywords: Ambrosiella; Ceratocystiopsis; Ceratocystis; Grosmannia; Leptographium; Ophiostoma; Raffaelea; ambrosia beetle; cospeciation; host-switching; symbiont redundancy; symbiosis.

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Figures

Figure 1
Figure 1
Examples of ambrosia beetles and their galleries. From left to right, top to bottom: Diuncus gallery; Trypodendron gallery; Xyleborina ambrosia beetles; Xylosandrus crassiusculus gallery. All photos courtesy of Jiri Hulcr.
Figure 2
Figure 2
Examples of mycangia. From left to right, top to bottom: maxillary cardine of Dendroctonus ponderosae showing opening of sac mycangium (arrow) courtesy of Katherine Bleiker; Close up of mycangium of D. ponderosae showing fungal mass extruding from opening courtesy of Katherine Bleiker; Oval brush mycangium on female Pityoborus rubentris Mal Furniss; close up of brush mycangium of P. rubentris containing spores Mal Furniss; Ascospores in pit mycangium (puncture) of Ips pini Mal Furniss; mesonotal paired sac mycangia of Xylosandrus mutilates (dissected from beetle) courtesy of W. Doug Stone.
Figure 3
Figure 3
Examples of bark beetles and their galleries. Left to right, top to bottom: Pupal chambers containing Dendroctonus.ponderosae pupae and spore layers of fungi, courtesy of the author; D. ponderosae adult, courtesy of the author; Bark section showing extensive beetle development in light portions colonized by mutualistic fungal symbionts and lack of development in highly stained portion of bark colonized by the antagonistic fungus, O. minus (arrow) courtesy of Fred Stephen; I. pini courtesy of Jesse Logan.
See this image and copyright information in PMC

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