Environmental Variability and Intraspecies Diversification in Arctic Charr (Salvelinus Alpinus)
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Environmental Variability and Intraspecies Diversification in Arctic Charr (Salvelinus alpinus) by Wendy Michaud A thesis presented to the University of Waterloo in fulfilment of the thesis requirement for the degree of Doctor of Philosophy in Biology Waterloo, Ontario, Canada, 2016 © Wendy Michaud 2016 Author’s Declaration I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract Arctic charr (Salvelinus alpinus) exhibit what is arguably the greatest observed range of phenotypic and ecological diversity within a single vertebrate species. The patterns of adaptive diversity that have developed among populations over evolutionary timescales have been well studied in this species. However, much less is known about the patterns of diversification occurring within populations over contemporary timescales. To better understand the mechanisms involved in the processes of diversification and speciation, this thesis investigates the relationship between environmental variability and phenotypic diversity of Arctic charr over different spatial and temporal scales. To examine the relationship between environmental variability and phenotypic diversity over contemporary time scales, we tested the prediction that shifts in the growth patterns of wild Arctic charr would coincide with temperature fluctuations over a 29-year period. A significant portion of the variation in size-at-age among cohorts of Arctic charr was explained by the cumulative lifetime temperatures, but temperature had mixed effects on growth observed within a single growing season. These changes in cohort growth patterns with temperature demonstrated that environmental fluctuations can have cumulative effects on growth dynamics over an individual’s lifetime. However, the observed changes in growth were better explained by the combined coincident changes in species community dynamics, Arctic charr behavioral patterns, and exploitation rates and practices in the Northwest Atlantic region than by the direct effects of temperature fluctuations alone. Phenotypic diversity over a small spatial scale was examined in the context of a polymorphic population of Arctic charr in a high-latitude lake. An unbiased, Bayesian analysis indicated the size-at-age data collected from Lake Hazen was best described by three discrete clusters of individuals. Life history, diet, and morphological characteristics observed for two of these clusters were consistent with previous descriptions of a cannibalistic and a benthivorous morph. The third cluster represented an early-maturing group that attained adult body sizes smaller than those reported for the previously identified forms. Although there are alternative explanations for the occurrence of distinct size-at-age groups within a fish population, polymorphism is the most consistent explanation for the combination of differences observed iii in life history (growth and age-at-maturity), trophic ecology (diet), and morphology among the three groups of Arctic charr identified here. The unusual patterns of diversification observed within this population highlight some of the holes in our broader understanding of the mechanisms of diversification in Arctic charr and other species. The effect of spatial variation in environmental characteristics on intrapopulation diversity was directly examined by testing the prediction that intraspecific competition and ecological opportunity promote morphological diversity within populations of Arctic charr. The relative importance of morphological variation to inter-individual differences in diet was also examined, by testing the prediction that the covariation between diet and morphological variation was greater in populations experiencing less interspecific competition and greater ecological opportunity. The patterns of morphological and diet variation observed in the eleven populations of Arctic charr examined here did not support the predictions tested, though the broader conclusions that can be drawn from this study are limited by the relatively small samples sizes available for analysis. This chapter is best viewed as a pilot project to developing a larger study to test these predictions, as it revealed a suite of potentially interactive effects on the extent of ecological and phenotypic variation within populations of Arctic charr. Phenotypic diversity in Arctic charr and other northern fish species is typically linked with ecological diversity, which is increasingly being quantified using stable isotope data. The final data chapter included in this thesis is a methods-based study meant to compliment the use of stable isotopes as a tool for quantifying diet diversity within and among populations of Arctic charr. Specifically, this chapter tests whether the effects of ecological factors on the differences in δ13C and δ15N values between muscle and liver tissues were large enough to affect the biological interpretation of isotope data when reconstructing temporal diet patterns. Our results demonstrated that life history, diet specialization, reproductive status and gender had significant effects on the difference in stable isotope values between tissues. These factors 13 15 appear to affect δ C(M-L) and δ N(M-L) values indirectly, due to their physiological impacts on metabolism and tissue composition. Most of the ecological factor effects observed here were not large enough to cause misinterpretation when examining major changes in diet, but could confound studies concerned with more subtle changes in omnivory. iv Acknowledgements This thesis would not have been possible without the collaborative support and hard work of a number of people. I have to first thank my supervisory committee, Michael Power, Jim Reist, Brian Dempson, and Brian Dixon for the many lessons I learned about mentoring as a result of working with you. I also want to express my gratitude to Kirsten Müller and Sue Fraser for your support and mentorship, and for empowering me to finish this project. I would like to thank everyone who collected and processed the samples from Labrador and Ellesmere Island included in this thesis, including: John Babaluk, Marc Bloom, George Furey, Colin Gallagher, Klaus Gantner, Tracey Loewen, Rob Perry, and Milton Shears. To everyone I met while working in St. John’s and Winnipeg, especially the Rymans and the Loewens, thank you so much for welcoming me into your lives, making me laugh, and keeping me well fed while I was away from home. I want to acknowledge the work done by Bill Mark, Lois Graham and the rest of the staff of the University of Waterloo Environmental Isotope Laboratory (uwEILAB). All of the stable isotope data I was able to use here is the result of your hard work and patience, and I am thankful to have had the opportunity to work with you. I would also like to thank David Garson at North Carolina State for being the best stats teacher I never met. To my lab mates; I want you to know that I learned more from you than I did from anyone else during this process. Our conversations about statistics, homebrewing, ecology, fish, politics, careers, knitting, and life in general were, by far, the most valuable part of my graduate education. I would also like to thank Sarah Wilder, Jane Godiksen, and Tracey Loewen for your thoughtful insights, support, encouragement and, most of all, your friendship from afar. I am incredibly lucky to have so many supportive friends and colleagues, and I would not have made it through this experience without you! Lastly, I would like to thank my family. I am forever grateful for the encouragement, patience, and unconditional support I have received from my mother, father, and sisters throughout my life. Mark Waldick, you deserve a special thank you for standing beside me through the highs and lows of this long process. v Financial support for the work conducted as part of this thesis project was provided by ArcticNet, the Canadian International Polar Year (IPY) Programme, NSERC, and the University of Waterloo. Logistical support for sample collection on Ellesmere Island was provided by the Polar Continental Shelf Project. vi Table of Contents Author’s Declaration ........................................................................................................................ii Abstract ........................................................................................................................................... iii Acknowledgements .......................................................................................................................... v Table of Contents ........................................................................................................................... vii List of Figures ................................................................................................................................... x List of Tables ................................................................................................................................. xiii Chapter 1 - Introduction ................................................................................................................. 1 Intraspecies diversity in Arctic charr and other northern fish species ....................................... 2 Why are Arctic charr so diverse? ...............................................................................................