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Reproductive Biology of Isolated Fern Gametophytes Carol Jacobs Peck Iowa State University

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Reproductive Biology of Isolated Fern Gametophytes Carol Jacobs Peck Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1985 Reproductive biology of isolated fern gametophytes Carol Jacobs Peck Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Botany Commons Recommended Citation Peck, Carol Jacobs, "Reproductive biology of isolated fern gametophytes " (1985). Retrospective Theses and Dissertations. 8762. https://lib.dr.iastate.edu/rtd/8762 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This reproduction was made from a copy of a manuscript sent to us for publication and microfilming. While the most advanced technology has been used to pho­ tograph and reproduce this manuscript, the quality of the reproduction is heavily dependent upon the quality of the material submitted. Pages in any manuscript may have indistinct print. In all cases the best available copy has been Slmed. The following explanation of techniques is provided to help clarify notations which may appear on this reproduction. 1. Manuscripts may not always be complete. When it is not possible to obtain missing pages, a note appears to indicate this. 2. When copyrighted materials are removed from the manuscript, a note ap­ pears to indicate this. 3. Oversize materials (maps, drawings, and charts) are photographed by sec­ tioning the original, beginning at the upper left hand comer and continu­ ing from left to right in equal sections with small overlaps. E)ach oversize page is also filmed as one exposure and is available, for an additional charge, as a standard 35mm slide or in black and white paper format. * 4. Most photographs reproduce acceptably on positive microfilm or micro­ fiche but lack clarity on xerographic copies made from the microfilm. For an additional charge, all photographs are available in black and white standard 35mm slide format.* *Fcr more information about black and white slides or enlarged paper reproductions, please contact the Dissertations Customer Services Department. IMversity Microfilms loternadonal 8604509 Peck, Carol Jacobs REPRODUCTIVE BIOLOGY OF ISOLATED FERN GAMETOPHYTES Iowa State University PH.D. 1985 University Microfilms I ntBrnSltiOnâl 300 N. zeeb Road, Ann Arbor, Ml 48106 PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark •/ . 1. Glossy photographs or pages 2. Colored illustrations, paper or print 3. Photographs with dark background 4. Illustrations are poor copy 5. Pages with black marks, not original copy 6. Print shows through as there is text on both sides of page 7. Indistinct, broken or small print on several pages 8. Print exceeds margin requirements 9. Tightly bound copy with print lost in spine 10. Computer printout pages with indistinct print 11. Page(s) lacking when material received, and not available from school or author. 12. Page(s) seem to be missing in numbering only as text follows. 13. Two pages numbered . Text follovfs. 14. Curling and wrinkled pages 15. Dissertation contains pages with print at a slant, filmed as received 16. Other University Microfilms international Reproductive biology of isolated fern gametophytes ...z:s1/ by /9g'~ ;°33~ Carol Jacobs Peck <! • ·~:2/ A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major: Botany Signatures have been redacted for privacy Iowa State University Ames, Iowa 1985 ii TABLE OF CONTENTS Page INTRODUCTION 1 LITERATURE REVIEW II MATERIALS AND METHODS 87 RESULTS AND DISCUSSION I: SPECIES ACCOUNTS 95 RESULTS AND DISCUSSION II: REPRODUCTIVE PHENOMENA 180 CONCLUDING REMARKS 210 REFERENCES 213 ACKNOWLEDGEMENTS 236 1 INTRODUCTION Ferns are pteridophytes, land plants with two distinct plant forms which alternate in the life cycle. The more conspicuous form is the diploid generation, consisting of a vascularized sporophyte plant which meiotically produces large numbers of wind dispersed spores. Derived from those spores is the haploid generation, consisting of a non-vascularized gametophyte plant that produces gametes by mitosis. Male and female gametes fuse to form a zygote which develops into a new sporophyte plant. Within the ferns, there are two variations of this basic life cycle; heterospory and homospory. The heterosporous ferns, like seed plants, produce two types of spores, smaller microspores which give rise to strictly male gametophytes which bear antheridia with sperm cells, and larger megaspores which give rise to female gametophytes which bear archegonia, each containing an egg cell. For heterosporous ferns, two gametophytes are required for reproduction and establishment of new populations by sexual reproduction. Homosporous ferns produce a single kind of spore which gives rise to a gametophyte that is viewed as potentially bisexual. Theoretically, a single gametophyte of a homosporous fern could self-fertilize to establish a new population. Three distinct types of mating are possible in homosporous pteridophytes (Klekowski, 1969a), each representing a different 2 level of inbreeding. Mating between male and female gametes from the same gametophyte has been termed intragametophytic mating or intragametophytic selfing (Klekovski, 1969a). Because gametes are produced mitotically, this type of mating will result in a totally homozygous sporophyte. This level of inbreeding is unparalleled in heterosporous plants. There are two requirements for the success of this type of reproduction. Male and female sex organs must be produced simultaneously, and the gametophyte genotype must be free of any lethal genetic defects. If these requirements are met, the resultant sporophyte will be entirely free of genetic load. If mating occurs between male and female gametes derived from two gametophytes descended from the same parent sporophyte, this is referred to as intergametophytic selfing (Klekowski, 1969a). Because gametes are derived from separate meiotic events, this type of mating is equivalent to the highest level of inbreeding possible in heterosporous plants. Although such inbreeding tends to lower the level of heterozygosity, total homozygosity is not very likely to be attained in a single generation. Finally, mating between gametes derived from gametophytes descended from two different sporophyte plants is referred to as intergametophytic crossing (Klekowski, 1969a). This is equivalent to outbreeding in heterosporous plants. The more general term intergametophytic mating is used if 3 gametes are derived from separate gametophytes, but the parentage of the gametophytes is not specified (Klekowski, 1969a). In populations where intergametophytic mating predominates, some level of heterozygosity and genetic load will probably be maintained due to sheltering of recessive genes, including lethals, in the heterozygous condition. If some deleterious or lethal genes are favored in the heterozygous state (heterosis), the level of genetic load maintained in the population will be even higher (Goodenough, 1978). Because the unit of dispersal is the spore, the establishment of new sporophyte populations is dependent upon spore dispersal and upon the subsequent establishment, growth, and reproductive potential of the gametophyte generation. Two kinds of dispersal may be considered, multispore dispersal close to the spore source and single spore dispersal some greater distance from the spore source. Sites near parent sporophyte plants are likely to be saturated with spores. Conditions favorable for gametophyte growth may result in development of dense gametophyte populations, and sporophytes nay result from intergametophytic mating. As the distance from the spore source increases, spore density decreases rapidly, such that for most species, colonization of distant sites is probably by single spores. Although there are some spectacular instances of long distance dispersal in ferns, most families and genera of ferns 4 have the same basic geographic patterns as flowering plants (Smith, 1972; Wagner, 1972). Thus, the advantage of producing a large number of wind dispersed spores, each theoretically capable of initiating a new fern population, has not been sufficient to give fern species a significant dispersal advantage over seed plants. This apparent contradiction may be explained in part by ineffectiveness of single spore reproduction. The consequences of a fern species relying on the success of a single, isolated spore to initiate a new population are far- reaching in terms of genetics, development, sexuality, and ecology. The isolated spore must germinate and develop into a bisexual gametophyte free of genetic load. Since any sporophyte produced from such a gametophyte will be load free, and may have inherited a tendency toward bisexuality, such sporophytes would initially have a high probability of reproductive success by isolated spores. However, genetic load may develop in populations over time. The sources of genetic load include somatic mutations which may be accumulated in long-lived individuals or clones. These mutations, along with mutations originating during the meiotic
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