Graduate Thesis Or Dissertation
 

Life history studies of Cinygma integrum Eaton (Ephemeroptera : Heptageniidae) and other mayflies associated with wood substrates in Oregon streams

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  • Wood debris serves an important substrate for macroinvertebrates in streams. Particle size reduction due to feeding and other activities can be an important role of the fauna in wood degradation. In this study the Ephemeroptera associated with wood were investigated, with the objective of assessing their impact in the degradation process. Emphasis was placed on Cinygma integrum Eaton which appeared to be the only mayfly that showed a predilection for wood substrates. The abundance of mayfly larvae on wood at Berry Creek, Benton County, Oregon was compared with that on stones and composite substrates (kick samples) for one year. Nine taxa were encountered. Proportions on wood compared with other substrates were: C. integrum, 76%; Baetis, 46%; Ironodes nitidus (Eaton), 43%. Although Baetis was the most abundant species on wood, it was also common on the other substrates. It uses wood for attachment and as an emergence platform--activities that have little effect on wood degradation. C. integrum and I. nitidus showed feeding habits that are related to wood decomposition. Their mouth parts are adapted for scraping the aufwuchs on wood substrates. Epeorus (Iron), Cinygmula and Rhithrogena were less associated with wood substrates, apparently exploiting similar food resources on mineral substrates. Three methods of analysis revealed that C. integrum had a univoltine, slow seasonal (S1) type of life cycle (Hynes, 1970). I. nitidus had a univoltine, fast seasonal (F1) type. These differences are perhaps related to differential effects of temperature on developmental stages. Eggs of I. nitidus were the only stage present in the summer and appeared to undergo a period of quiescence. C. integrum eggs apparently hatched over a longer period. Both species were cool adapted with the majority of growth occurring from November to February. Three millimeter larvae of C. integrum were reared to adults using a constant temperature of 9°C, 12 hours daylength and a restricted diet of only the aufwuchs present on wood. Success at rearing indicated that this species is perhaps a suitable candidate for future ecological, physiological and biochemical laboratory investigations of wood decomposition. Mayfly feeding activity appears to be responsible for some biological degradation of wood. Superficial layers of wood that have been partially degraded by microbial activity are ingested and wood particles up to a millimeter in length were present in the guts. Ingestion of wood particles probably accompanies the ingestion of the aufwuchs layer. Fungal mycelia and spores were commonly ingested. C. integrum showed maximum consumption of fungi with I. nitidus second to it. Aquatic Hyphomycetes, Ascomycetes and Luteromycetes spores were present in the gut and fecal material, indicating a potential role of spore dispersal. Seasonal periodicity of mycelial ingestion occurred, with a maximum in winter. Small larvae of C. integrum consumed more detritus than did the mature larvae which had large quantities of fungal material in their guts. Annual productivity for C. integrum was 0.28g/m² (dry weight). Larvae ingested an average of 53% of their body weight of mycelia per day. An annual estimate of mycelial ingestion by the woodassociated mayfly complex was about lg/m². Mycophagy in woodassociated mayfly larvae thus make a contribution (although an indirect one) to wood processing and mineralization in aquatic habitats. Removal of senescent populations of fungi make available fresh areas for further fungal colonization. Benefits accrued by mayflies from an association with wood are related to emergence, shelter and feeding. As a result of these biological activities, particularly the latter, this group plays both an indirect and direct ecological role in wood decomposition in aquatic habitats.
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Déclaration de droits
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  • File scanned at 300 ppi (Monochrome) using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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