Doctoral Dissertations

Date of Award

8-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Zoology

Major Professor

Dewey L. Bunting

Committee Members

Arthur C. Echternacht, James N. Liles, Melbourne C. Whiteside, David K. Smith

Abstract

The main objectives of this study were to (1) briefly review the history of experiments dealing with cryptobiosis over the lost 300 years, (2) obtain data comparing the revival of the eutardigrade Milnesium tordigradum Doyere with the heterotardigrodes Echiniscus perviridis Ramozzotti and Echiniscus viridissimus Peterfi from laboratory-controlled onhydrobiotic conditions, and (3) present new eidostic, metric, and meristic data concerning the taxonomy and instars of E. perviridis and E. viridissimus.

Saxicolous moss samples were collected from seven sites at The University of Tennessee in Knoxville and one site at East Tennessee State University in Johnson City. After being dried, these samples were soaked in aerated distilled or deionized water to extract co-habiting specimens of M. tordigradum and either of the two Echiniscus species. In each experiment, specimens of an Echiniscus species were simultaneously onhydrobiosed with M. tardigradum specimens inside identical relative humidity systems, in which internal humidity was controlled by various glycerol-woter dilutions. Randomly selected animals were dried under these respective drying conditions within a 2 ½ - 5 µl droplet for 65-85 minutes, and allowed to remain in the desiccated state for the post-droplet drying times of 1/2 hr, 1 hr, 2 hr, 4 hr, 14 hr, and 24 hr. The specimens then were reimmersed into aerated moss water, and observed for revival with a dissecting microscope at selected check intervals of up to 24 hr. In Series A, the relative humidities of 13%, 32%, 52%, 73%, and 94% were run at a constant temperature of 20°C. In Series B, the temperatures of 4°C, 12°C, 20°C, 28°C, end 36°C were used with the high humidity of 94%.

Overall revival from anhydrobiosis was found to be related to the physiological adaptation of tun formation, and the behavioural adaptation of clumping. In both Series A and B, clumping always was present for M. tardiqradum and E. perviridis, regardless of relative humidity or temperature, while clumping was absent in E. viridissimus. Clumping in M. tardiqradum and E. perviridis may function in a manner similar to the "eelworm wool" of nematodes or huddling in woodlice and slugs, and could account for the better revival of these two species over E. viridissimus. Tun formation was found to occur only under conditions of high humidities (73% and 94%) or lower temperatures (4°C, 12°C, and 20°C). The highest revival results and the quickest revival times were found in M. tardiqradum and E. perviridis when both clumps and tuns were formed.

Revival in M. tardiqradum was higher than that in either Echiniscus species, and rarely dropped below 80%. Revival for both E perviridis and E. viridissimus decreased across the longer post-droplet drying times at lower relative humidities and higher temperatures. Of the three species, revival of E. viridissimus was the poorest. Trends in the relative humidities, temperatures, and drying times of the three species were confirmed by interspecific and intraspecific ANOVA and Student-Newman-Keuls comparisons, and by stepwise multiple regressions. The hypothesized role of the dorsal plating in the two Echiniscus species to aid in the control of evaporative water loss was not substantiated by the revival data obtained in this study.

Although both E. perviridis and E. virldissimus taxonomically belong to the "viridis-group," they were reconfirmed as being distinct species. The diagnostic sculpturing patterns seen in these two Echiniscus species under brightfield and phase-contrast microscopies were found with S.E.M. to be partially divided and flattened protrusions in E. perviridis, and small depressions in E. viridissimus. The relationship of the cirrus A length (CA) to the body length (BL) and body width (BW), when expressed as ratios of CA/BL and CA/BW, also was found to be highly diagnostic, regardless of instar. These relationships were further substantiated by the exceptionally high r2 obtained for the simple regressions of CA with BW and CA with BL, and the R2 derived for the multiple regressions of CA with BW and BL. Three E. perviridis specimens with cirrus A anomalies also were found. Based on the frequency of BL, and supplemented by CA, BW and claw lengths (CL), E. perviridis was found to possess six definite adult instars, while E. viridissimus contained seven. Both species hod up to two juvenile instars.

This is the first report of E. perviridis from outside its type locality in Italy, and the second report of E. viridissimus from the southeastern United States.

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