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Biosystematics of the grylloblattodea

University of British Columbia

The North American Grylloblattidae are either hygro-philic occupants of the alpine-subalpine or facultative cavernicoles of lava ice caves. The'research indicates that the habitats preferred by Grylloblatta must be cold and moist but not wet. The preferred alpine-subalpine hypolithion was found to be beneath stones 50 to 150 cm. buried 20 to 50 cm. deep in the substrate. Grylloblatta also temporarily occupied glaciers, snow fields, rotting logs and borders of glacial springs. The optimum microclimate in the alpine-subalpine habitats was within - 3 to + 6° C. with a humidity above 70 per cent. Humidity evidently governs the occupancy of the hypolithion more than temperature. The insect will not inhabit hypolithion with relative humidities less than 70 per cent, regardless of temperature. The cavernicolous habitat for Grylloblatta is a micro-environment limited to a few ice caves in lava fields. Sufficient ice must be present to maintain a spring-to-fall temperature of - 3 to + 8° C. and over 80 per cent relative humidity. During the winter the Ice cave is recharged with cold air below the tolerance of Grylloblatta at which time the Insect inhabits the hypolithion. The temperature preference of Grylloblatta, established in the laboratory, was between - 3.5 and + 5° C. at 90 to 99 per cent relative humidity, - 2.2 to + 4.5° C. at relative humidities between 70 and 90 per cent, and - 1.1 to + 1.6° C. at 50 to 70 per cent relative humidities. Temperature tolerance at humidities above 95 per cent ranges between - 4 and + 11° C. Four-hour exposure to + 16° C. and one-hour exposure at - 5.5° C. produces 50 per cent mortality. Lethal extremes were - 8° C. and + 23° C. All stages of the insect were found to be active year around with no dormant period. The mean freezing point depression of the hemolymph was measured at - 0.98° C. therefore, the insect remains active in a supercooled state. Twenty-six new populations were found during this research, extending the distribution from the Yukon-British Columbia border to the southern Sierra Nevada of California. Five new species and three new subspecies are here described The distributional data indicate the presence of four divergent groups characterized by isolated endemic populations or species. The present disjunct distribution and zoogeography have been fundamentally influenced by the geologic and climatic events of the late Pleistocene. Further, regional and sometimes highly localized volcanic activity during the post Pleistocene, the warm dry Hypsi-thermal period, and the re-birth of summit and cirque glaciers, commencing approximately 2500 years ago, have affected the distributional patterns of Grylloblatta. The recent zoogeography of the various species and populations in western North America is discussed. A comparative lipid analysis of Grylloblattidae and six other insects from related orders, and with varying temperature preferences, shows differences in fatty acid composition. The composition in Grylloblatta is more like that in Dermaptera, but the affinity is as remote as is demonstrated in the numerical analysis. Analysis of Grylloblatta shows 65.8 per cent of the total fatty acids are unsaturated, 91 per cent of which have melting points below its maximum tolerated temperature. These data clearly indicate the low temperature adaptation of Grylloblatta; such composition is not seen in the warmer tolerance forms. In a numerical analysis of 164 external and internal morphological characters in Grylloblatta and seven other related orthopteroid insects, Dermaptera has the closest affinity to the Grylloblatta. The phenetic affinities and relationships of the Grylloblatta, as shown in the analysis, place the taxon at the ordinal level. The most acceptable systematic treatment of this group is as the order Grylloblattodea.

Text

2011-03-04

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http://hdl.handle.net/2429/32023

Zoology

University of British Columbia

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