Browsing by Author "Murphy, John F."

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    The ecology and population biology of two litter decomposing basidiomycetes
    Murphy, John F. (Virginia Tech, 1992)
    Four 286m2 plots on alternate sides of the spur ridges on Brush Mt. were established and their plant communities characterized. Agaric and Bolete basidiomycetes were sampled for two years. Fifty species were recorded on the plots. Phenologically, decomposer species were highly dependent upon rainfall events, whereas mycorrhizal species were more seasonal. Two species emerged as dominant litter decomposers. Marasmiellus praeacutus (Ellis) Halling is dominant on southwest facing slopes and occurs on a wide variety of coniferous and hardwood detritus. Collybia subnuda (Ellis ex. Peck) Gilliam is dominant on northeast facing slopes, and occurs on hardwood leaves and small woody detritus. The population structure of both of these species was investigated using tests of somatic incompatibility. Genets of both species are able to persist for more than one year. The observed minimum population density is 0.071 - 0.121 genets/m² for M. praeacutus and 0.039 - 0.093 genets/m² for g. subnuda. Mating tests indicate that M. praeacutus is heterothallic and tetrapolar, and that C. subnuda is heterothallic and bipolar. Preliminary crosses between monokaryotic tester sets indicate a surprisingly low number of mating alleles in both species. Decomposition studies suggest that while the restricted distribution of ~. subnuda to the northeast slopes may be affected by substrate specificity, the restriction of M. praeacutus to the southwest slopes is due to other factors.
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    Microevolutionary studies in Marasmiellus praeacutus and Collybia subnuda, two litter-decomposing basidiomycetes
    Murphy, John F. (Virginia Tech, 1995)
    The distributions of mating alleles in local populations of the litter-decomposing agarics Marasmiellus praeacutus and Collybia subnuda were determined by mating crosses. The tetrapolar M. praeacutus has an unexpectedly low mating allele diversity at both the local and the regional level. This is probably due to a combination of factors which results in limited spore dispersal. The pattern of mating allele distribution among closely adjacent genets suggests that di-mon crossing (the Buller phenomenon) may contribute to the population structure of this species. Collybia subnuda has a mating allele diversity estimated at 45 for the species, with a 95% confidence interval of 19 to 187. On a local scale, closely adjacent genets of C. subnuda did not share mating alleles, indicating that C. subnuda is an outcrossing species. Two partially intersterile groups were identified within the C. subnuda morphospecies. They were not differentiated morphologically, geographically, or by the DNA sequence of the intergenic transcribed spacer (ITS) region of the ribosomal RNA-encoding gene family. Intersterility group (ISG) 1 is usually found on oak leaf litter, and ISG 2 is usually found associated with oak wood. Collection records, mating crosses, and spore-catching experiments indicate that the two ISGs are distributed sympatrically throughout the sampled range. Both ISGs produce binucleate spores in low frequency, and thus have the potential for secondary homothallism. Spore-catching experiments indicate that the spore rain of C. subnuda varies greatly over space and time. Spore viability studies show that C. subnuda spores have a limited viability. The implications of these observations for the population structure and speciation in C. subnuda are discussed.
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    Red imported fire ants (Hymenoptera : Formicidae) increase the abundance of aphids in tomato
    Coppler, Laura B.; Murphy, John F.; Eubanks, Micky D. (Florida Entomological Society, 2007-09)
    Red imported fire ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are abundant in many agroecosystems in the southern United States and can affect the abundance of arthropods in these systems. We determined the effects of red imported fire ants on the abundance of aphids, other herbivorous insects, and beneficial arthropods in Alabama tomato (Lycopersicon esculentum) by manipulating the density of red imported fire ants in plots of tomato plants and by sampling fresh market tomato farms for two years (2003 and 2004). In both years of our study, aphid abundance was significantly greater in tomato plots with high densities of fire ants than in plots where fire ant densities were suppressed. Further, the abundance of fire ants was positively correlated with the abundance of aphids on intensely managed tomato farms in both years. These aphids included many species that are the primary vectors of economically-important plant viruses of tomato and other vegetable crops. The positive effect of fire ants on aphid abundance was likely due to facultative fire ant-aphid mutualisms. Other studies have demonstrated that fire ants protect honeydewproducing insects from natural enemies, and we found that fire ants reduced the abundance of beneficial arthropods in the second year of our field experiment. However, red imported fire ants did not significantly reduce the abundance of non-aphid herbivores in either year of our field experiment, suggesting that fire ants are not important biological control agents of these insects in tomato. Fire ants may disrupt biological control of aphids in tomato fields and suppression of fire ants on tomato farms may decrease the abundance of aphids.