Symbiont diversification in ambrosia beetles: Diversity of fungi associated with exotic scolytine beetles

In virtually every forest habitat, ambrosia beetles (Coleoptera: Curculionidae: Scolytinae, Platypodinae) plant and maintain symbiotic fungus gardens inside dead or dying wood. Some introduced ambrosia beetles aggressively attack live trees and can damage tree crops, lumber, and native woody plant taxa by inoculating ambrosia fungi. Non-native ambrosia beetle introductions have become increasingly abundant in the United States, yet there is almost nothing known about their fungal symbionts. These fungi may have significant impacts to native economic and ecological systems, and their identity is critical for understanding the specificity and diversity of beetle-symbiont communities.

To determine the identity and diversity of symbiotic ambrosia fungi, exotic beetles were collected in Florida and their fungi were isolated. Strength of relationships to beetles was inferred by frequency of isolation and location on the beetle where the fungi were found. Our results support the hypothesis that some beetles carry highly specific monocultures of fungi, while others have a diverse community of symbionts and may swap symbionts with other ambrosia beetles. This trend is likely to be clade-specific among ambrosia beetles. This study provides a the first comprehensive dataset on the taxonomic identity and symbiotic specificity of fungal symbionts of an invaded and homogenized symbiotic community. These results are now used to formulate and test hypotheses and models of evolution of pathogenicity within ambrosia fungi and invasion ability within beetle-fungus complexes.