EFFECTS OF DEVELOPMENTAL THERMAL REGIMES ON TWO MAYFLY SPECIES AND THEIR TAXONOMIC INTERPRETATION
Abstract
Hexagenia limbata (Serville) and Stenacron interpunctatum (Say) are two mayflies that have been most recently classified as several subspecies. Such classification is highly suspect due to a high degree of variability between and within populations. Both species were studied in the field and laboratory to determine the significance of variability. Life cycles at two study sites in Indiana were found to be complex, with at least two coherts. Maturation times determined in the laboratory for test groups of single populations varied inversely with experimental developmental thermal regimes (6-25(DEGREES)C, 12-26(DEGREES)C, 18-26(DEGREES)C, 24-26(DEGREES)C). Mean degree day accumulation was important for H. limbata at the two colder regimes, whereas a minimum water temperature of 18(DEGREES)C was necessary for S. interpunctatum adults to emerge. Reared adults varied in phenotypic characters previously used taxonomically. Such variability was either correlated with developmental thermal regime, or randomly expressed and temperature independent. Size, intensity of color and maculation were temperature dependent and increased as maturation time increased. The study of museum specimens from throughout the species' ranges substantiated the relationship between color types and developmental thermal regimes. Since ecophenotypes corresponding to supposed geographic subspecies could be produced from single populations manipulated in the laboratory and are present in nature along spatial and temporal gradients related to developmental temperature, and since proposed taxonomic characters are either temperature dependent or individually variable, previous specific and subspecific classifications of H. limbata and S. interpunctatum are not considered valid.
Degree
Ph.D.
Subject Area
Entomology
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