Birth order as a source of diversification in spring phenology and its potential effects on performance in greater duckweed, Spirodela polyrhiza

Abstract

Organisms must be able to adapt in order to persist in dynamic and unstable environments. Now, in the face of rapid environmental change, questions about plants' intrinsic tolerance to variability and unpredictable environments are especially relevant. The timing of both winter freeze-up and spring thaws are unpredictable and under these variable environments, clonal populations of Spirodela polyrhiza (greater duckweed) provide an excellent case study of phenotypic diversification as a risk aversion strategy. Previous research on this species has demonstrated that potential diversification bet hedging in the phenology of the production of turions-the quiescent overwintering structure that rests at the sediment surface-is generated by birth order within clones. Like production of turions which occurs in the fall, the timing of turion reactivation the following spring may also have profound fitness consequences due to the risk of the thaw and re-freezing of the water's surface. I therefore hypothesize that variance in turion reactivation phenology within clones is influenced by birth order of turions. This was tested through a laboratory study that determined the source of observed phenological variability, and an outdoor mesocosm study that further examined fitness consequences of variance in the timing of turion reactivation under different temperature treatments. The results showed that both temperature and birth order play a role in reactivation timing in that early birth order turions generally reactivate before later birth orders. The effect size of this birth order interaction was found to decrease with temperature. Furthermore, although an effect of turion birth order on lineage performance was not seen, temperature was shown to be positively associated with performance. This research suggests mechanisms whereby clones may generate diversification strategies. If various phenotypes (birth orders) perform differently depending on the environment, a "phenotype-by-environment interaction" generates potential diversification bet hedging. Such diversification could mitigate impacts of both seasonal unpredictability and larger scale climate trends. This thesis could not have been done without the help and support of a number of individuals. I would first like to thank my thesis supervisor Dr. Andrew Simons, who has been a wonderful research supervisor and mentor and has endlessly supported me throughout my studies in his lab. His expertise in research and writing have been a great example for me as I navigated my way through my degree program.

Latitudinal variation in norms of reaction of phenology in the greater duckweed Spirodela polyrhiza

“…Overwintering buds called turions (Hillman, 1961; Krajnčič & Devidé, 1979; Krajnčič & Slekovec‐Golob, 1991; Wang, Haberer, et al, 2014) are produced through vegetative propagation (Wang, Haberer, et al, 2014) from the same meristematic tissue as normal fronds. These starch‐rich structures sink to the bottom of water bodies and remain in a dormant state until favourable conditions resume (Appenroth, Teller, & Horn, 1996; Jacobs, 1947), at which point reactivation is thought to be initiated by light (Appenroth et al., 1996; Newton, Shelton, Disharoon, & Duffey, 1978) and temperature cues (Morris, 2018).…”

Studying Whole-Genome Duplication Using Experimental Evolution of Spirodela polyrhiza

“…We grow our cultures at 40-45 μmol m −2 s −1 PPFD. Open outdoor systems are commonly covered by nets to reduce direct radiation and to create some shading (e.g., [43,44]). Within such systems, it is possible to make smaller enclosures to quantify growth parameters.…”

Geographic variation in reaction norms of phenological traits in the greater duckweed, Spirodela polyrhiza

“…It has been used extensively in physiological (Bieleski, 1968;Ley et al, 1997), environmental remediation (Ansari & Khan, 2009) and toxicological studies (Caicedo et al, 2000;Doǧanlar, 2013;Qiao et al, 2012;Su et al, 2017). Recently, it and other duckweed species have emerged as a useful system in evolutionary ecological research (Barks & Laird, 2016;Barks et al, 2018;Mejbel & Simons, 2018;Morris, 2018).…”