Ecological and Genetic Aspects of the Population Biology of the Littoral Rotifer Euchlanis Dilatata
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UNLV Retrospective Theses & Dissertations 1-1-1989 Ecological and genetic aspects of the population biology of the littoral rotifer Euchlanis dilatata Elizabeth Jensen Walsh University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Walsh, Elizabeth Jensen, "Ecological and genetic aspects of the population biology of the littoral rotifer Euchlanis dilatata" (1989). UNLV Retrospective Theses & Dissertations. 2954. http://dx.doi.org/10.25669/s2xt-3g8q This Dissertation is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. 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Ml 48106-1346 USA 313/761-4700 800/521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Order Number 9225454 Ecological and genetic aspects of the population biology of the littoral rotiferEuchlanis dilatata Walsh, Elizabeth Jensen, Ph.D. University of Nevada, Las Vegas, 1992 UMI 300 N. ZeebRd. Ann Arbor, MI 48106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ECOLOGICAL AND GENETIC ASPECTS OF THE POPULATION BIOLOGY OF THE LITTORAL ROTIFER EUCHLANIS DILATATA by Elizabeth Jensen Walsh A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor in Philosophy in Environmental Biology Department of Biological Sciences University of Nevada, Las Vegas May, 1992 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Dissertation of Elizabeth J. Walsh for the degree of Doctor of Philosophy in Environmental Biology is approved. Chairperson, Peter L. Starkweather, Ph.D. n Examining Committee'Member, Daniel B. Thompson, Ph.D. ittee Member, Robert F. Geever, Ph.D.Examinin , Eugene I. Smith, Ph.D External Refere D.N. Hebert, Ph.D Graduate Dean, Ronald W. Smith, Ph.D. University of Nevada, Las Vegas December 1991 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract Littoral rotifers are associated with vegetation and thus live in highly structured habitats. This structural complexity increases the possibilities of forming local subpopulations differing in a) plant substrate used, b) biotic interactions, and c) genetic structure. I explore some of these topics in populations of the littoral rotifer Euchlanis dilatata. I investigated several aspects of egg-laying behavior in 3 clones of E. dilatata. Individuals lay their eggs randomly within culture dishes in the absence of substrate, while eggs laid in the presence of an artificial substrate are deposited in clumps by 2 clones. When given a choice among artificial substrates with and without eggs or eggshells of conspecifics, rotifers lay most eggs on those substrates containing eggs followed by those with eggshells. I found E. dilatata most often associated with the macrophyte Mvriophvllum exalbescens at 3 sites in Devils Lake (Lincoln Co., OR). In general, rotifers laid most of their eggs on this macrophyte in laboratory preference experiments. I also assessed habitat-specific predation susceptibilities for rotifers cultured in the presence of aquatic macrophytes (M. exalbescens. Elodea canadensis, or CeratophvHum demersum) and two invertebrate predators (damselfly nymphs Hydra). Rotifer survival was greatest on Mvriophvllum. This rotifer population iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. consisted of individuals of two distinct size classes. Females of the larger size class are up to 1.5 times longer than those of the smaller size class. I determined chromosome numbers for individuals of each morphotype. Large morphotype females average 21 chromosomes, small morphotype females 14. Individuals of both ploidy levels were most often associated with Mvriophvllum. While there was no evidence of spatial habitat segregation, their temporal distributions varied. Diploid individuals were present only in late spring and summer collections, while triploids were present throughout the year. These distribution patterns were reflected in life history characteristics under various temperature treatments. Diploid clones produced significantly more young and lived longer under high temperature regimes (25°C) whereas triploid individuals survived longer at low temperatures (12°C). In addition, diploid and triploid also differed in their relative susceptibilities to invertebrate predators. Both damselfly nymphs and Hvdra were more effective in reducing the survival of the larger triploid rotifers. IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Abstract.................................................. iii List of Illustrations................................... vii List of Tables............................................ Acknowledgements....................................... xiii General Introduction...................................... 1 References............................................ 9 Chapter 1. Oviposition behavior in the littoral rotifer Euchlanis dilatata..................................... 13 Abstract.............................................. 13 Introduction.......................................... 14 Study Organism....................................... 17 Materials and Methods................................. 18 I. Artificial substrates and egg deposition pattern........................................ 18 II. Natural substrates and egg deposition pattern....21 III. Neonate hatching behavior........................23 Results................................................ 24 I. Artificial substrates and egg deposition pattern........................................ 24 II. Natural substrates and egg deposition pattern.... 28 III. Neonate hatching behavior........................31 Discussion............................................ 34 References............................................ 39 Chapter 2. Habitat preferences and habitat-specific predation susceptibilities............................. 42 Abstract.............................................. 42 Introduction.......................................... 43 Materials and Methods................................. 45 I. Habitat associations............................ 45 II. Laboratory substrate preferences................. 48 III. Plant-animal associations and relative predation risk................................. 51 Results............................................... 56 I. Habitat associations............................ 56 II. Laboratory substrate preferences................ 62 III. Plant-animal associations and relative predation risk................................. 70 Discussion............................................ 90 References........................................... 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter 3. Polyploidy and size variation in a natural population of the rotifer Euchlanis dilatata........... 108 Abstract............................................. 108 Introduction......................................... 109 Materials and Methods................................