Walker, Donald M. , Struwe, Lena , Castlebury, Lisa A. , Rossman, Amy Y. .
Host niche conservatism or specialization? Evolutionary host patterns in Ophiognomonia (Diaporthales: Ascomycota) and the relationship of species diversification to ecological vicariance and plant host niches.
Species of Ophiognomonia (Gnomoniaceae) are leaf- and stem-inhabiting perithecial fungi occurring on host tree species of the Betulaceae, Fagaceae, Juglandaceae, Lauraceae, Malvaceae, Platanaceae, Rosaceae, Salicaceae, and Sapindaceae (mostly rosids or more basally placed angiosperms). In this study host plant patterns at the order, family, genus, and species level were analyzed using SEEVA (Spatial Evolutionary and Ecological Vicariance Analysis) using a multi-gene phylogeny of 45 species of Ophiognomonia to better understand speciation events and host associations in this genus. Host taxonomic data were coded for four variables: species, genus; family; and order level. Eight temperature and precipitation variables were also analyzed in SEEVA in order to integrate evolutionary hypotheses from phylogenetic data and detailed specimen records with environmental (climate) information. Our objectives were to: 1) determine if patterns of fungal diversification in this genus are influenced by host plant association and/or other climate constraints, and 2) determine if speciation events in Ophiognomonia are associated with host switching or host conservation at certain taxonomic host ranks. The differences between sister clades in host and climate variables were interpreted using the divergence index (D), ranging from 0 for no difference, to 1 for maximum possible difference. One basal node in the phylogeny of Ophiognomonia independently displayed significantly differing D-values (0.58*-0.91*) for all ranks of taxonomic host variables, indicating a major ecological vicariance event within Ophiognomonia related to host specialization. More recent nodes showed both ecological conservatism as related to host order and families, and with a few relatively recent host leaps (novel niches) to new plant species of unrelated host groups. Two species of Ophiognomonia with syngeneric hosts and sympatric geographic ranges show patterns of ecological vicariance in three different temperature and precipitation variables (D-values> 0.72), indicating climate-based niche specialization without spatial or host changes. Host specificity and environmental effects are mechanisms strongly contributing to speciation patterns in this genus, and this method of analyzing host and environmental data provides a visual and statistically solid understanding of evolutionary mechanisms influencing speciation events, host switches, and climate niche evolution in the genus Ophiognomonia. This methodology could be useful for plant pathologists, mycologists, and plant quarantine officials for making predictions about host specificity or environmental constraints of plant pathogens, as well as evolutionary histories of host-parasite relationships.
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1 - Rutgers University, Department of Plant Biology and Pathology, 59 Dudley Rd, New Brunswick, NJ, 08901, USA
2 - Rutgers University, ROOM 237 FORAN HALL, ROOM 237 FORAN HALL, 59 DUDLEY RD, NEW BRUNSWICK, NJ, 08901, USA
3 - USDA Agricultural Research Service, Systematic Mycology and Microbiology Laboratory, Room 224, Bldg 010A, BARC-WEST, 10300 Baltimore Blvd, Beltsville, MD, 20705, USA
4 - USDA Agricultural Research Service, Systematic Mycology and Microbiology Laboratory, 10300 Baltimore Blvd, Room 224, Building 010A, BARC-WEST, Beltsville, MD, 20705, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union C/Hyatt
Date: Monday, July 9th, 2012
Time: 2:00 PM