Submitted to: Insect Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2017
Publication Date: 6/7/2017
Citation: Rehner, S.A., Kepler, R.M. 2017. Species limits, phylogeography and reproductive mode in the Metarhizium anisopliae complex. Insect Pathology. doi.org/10.1016/j.jip.2017.05.008.
Interpretive Summary: Insect pests annually cause billions of dollars of agricultural losses. The use of beneficial fungi to control pest insects is needed to reduce reliance on chemical pesticides that are expensive and damaging to the environment and human health. In this study we used molecular methods (i.e., DNA sequencing) to determine relationships and differences within a group of fungi parasitic on a wide range of insects, including many important crop pests. Using DNA sequencing and phylogenetic analysis we demonstrate that the insect pathogenic fungal genus Metarhizium includes multiple, evolutionarily distinct groups of species. This information is significant and will lead toward more precise classifications enabling greater accuracy in the identification of these important insect pathogens. This information will be used by insect mycologists and plant pathologists developing and implementing integrated pest management strategies of field crop pests.
Technical Abstract: An essential first step toward understanding the ecology and life histories of Metarhizium anisopliae-group species as entomopathogens, endophytes and soil-adapted fungi is the ability to accurately define species limits and confidently infer a species tree. Here we present a multilocus phylogeny of the core Metarhizium anisopliae species complex. The majority of isolates sampled here group within the currently defined limits of M. pingshaense, M. anisopliae, M. robertsii and M. brunneum, a clade of four species designated informally as the “PARB” clade. However, the increased resolution achieved with IGS sequences reveals congruent phylogenetic structure within each PARB species, suggesting that each species likely represents a species complex in and of itself. However, further taxonomic dissection of the PARB clade is not advocated at this time, although acknowledgment of these intraspecific partitions can provide a useful conceptual framework to inform understanding of the geography, ecology and reproductive biology of the PARB species radiation. As one example of the utility of IGS markers, the commercially registered M. anisopliae strain F52, which is widely used for pest control in North America and Europe, is shown to be a member of the M. brunneum complex. In addition, we demonstrate the presence of two functional mating types among individuals in each PARB species, diagnostic of a heterothallic mating system and evidencing a history of and potential for sexual reproduction.