Dissertation
The influence of environmental stress, reproductive mode, and ploidy variation on life-history trait expression.
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.007872
Abstract
Environmental stressors are amongst the most important of all components of evolution because they shape life-history traits, critical traits that guide life cycle and are variable within and across species. One potential mechanism that underlines this variation is environmental stress. In my dissertation, I address how environmental stress (nutrient availability and population density) connects to life-history trait variation and evolution, with a particular focus on ploidy level, reproductive mode, and invasion status. I investigate these questions using Potamopyrgus antipodarum, a powerful and appropriate model because of its unique combination of ploidy- and reproductive mode- polymorphism and its status as a worldwide invasive species. In chapter 2, I explored how phosphorus (P) availability can influence growth and body-P content differentially between ploidy levels and reproductive modes, specifically sexual diploids and asexual triploids. My work revealed higher performance of asexual triploid snails relative to sexual diploid counterparts, suggesting advantages of asexual reproduction and polyploidy outweigh the advantages of sexual reproduction and diploidy. In Chapter 3, I explored the effects of P availability on reproduction among diploids, triploids, and tetraploids; I found novel evidence that dietary-P and maternal-P influences reproductive investment and does so differentially across ploidy levels. In Chapter 4, I explored an inherent connection between biological invasions and intraspecific variation for sensitivity to population density. These results revealed that the growth and reproduction of native but not invasive lineages of P. antipodarum counterparts was found to be sensitive to population density, suggesting that the insensitivity displayed by invasive snails could play a role in invasion success. Altogether, my dissertation illuminates how the interplay between fundamental organismal characteristics and environmental factors can influence the expression and maintenance of variation in life-history traits.
Details
- Title: Subtitle
- The influence of environmental stress, reproductive mode, and ploidy variation on life-history trait expression.
- Creators
- Briante Shevon Lewis Najev
- Contributors
- Maurine Neiman (Advisor)Amy Krist (Advisor)Andrew Forbes (Committee Member)John Logsdon (Committee Member)Sander Heather (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Integrated Biology
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.007872
- Publisher
- University of Iowa
- Number of pages
- xv, 159 pages
- Copyright
- Copyright 2025 Briante Shevon Lewis Najev
- Language
- English
- Date submitted
- 04/28/2025
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
- In stressful environments, organisms have three choices: adapt, leave, or die. If they are to adapt to a stressful environment, they must change their life-history strategy which would change their life cycle. This is important because life cycle drives evolution and they are very different for all organisms. For example, the African bush elephant takes 22 months to birth a calf while the most mice species take less than 30 days to produce a litter of pups. An organism’s internal makeup, for example the number of chromosomes they have, and environmental factors also drive evolution. I studied how fundamental components of the environment like nutrient availability and crowding can affect the evolution of an organism, specifically growth and reproduction. My research uses a freshwater snail (Potamopyrgus antipodarum) that has invaded aquatic systems across the world, can that reproduce sexually vs. clonally, and has different numbers of chromosomes. I found that clonal snails often have an advantage in nutrient-limited environments, deepening the mystery of why most organisms still reproduce sexually. I discovered that nutrient availability, and its interplay with chromosome number, shapes maternal investment and offspring quality. I also asked how crowding affects snails that were native or invasive and invasive species seem to do well because they are resilient to crowded conditions, while the snails collected from their native range in New Zealand perform poorly in crowds. Altogether, my dissertation research demonstrates that environmental and organismal biology interact to shape how an organism survives and thrives.
- Academic Unit
- Biology
- Record Identifier
- 9984830729702771
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