Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Andrew M. Kramer, Ph.D.

Committee Member

Bradford J. Gemmell, Ph.D.

Committee Member

Mark J. Margres, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Keywords

Allee effect, Escape, Evolution, Mate, Zooplankton

Abstract

This dissertation investigates the swimming behavior and population dynamics of the marine copepod, Acartia tonsa. This copepod is of interest as it utilizes hydromechanical signals within the environment to navigate its surroundings, resulting in a distinctive hop/sink swimming pattern. This adaptive trait serves several purposes including searching for mates, obtaining food, and detecting predators, however the evolution of this unique swimming style has not been explored. To address this knowledge gap, the first chapter of this dissertation explores the swimming characteristics and escape responses of captive-reared and wild-caught A. tonsa. When reared in aquaculture, A. tonsa populations experience higher populations densities and lower predation compared to wild population of A. tonsa. To understand how these differences may drive adaptive evolution of swimming behavior in this species, several components of routine swimming were compared for groups of captive reared and wild caught A. tonsa, revealing that wild caught copepods swim faster and jumped more frequently than captive reared copepods. Following this, the escape responses of the two groups were compared to gain insight into how captive rearing affects A. tonsa response to hydromechanical predator cues.

Next, to further investigate A. tonsa swimming behavior, the second chapter of this dissertation uses quantitative modeling techniques to investigate how mating behavior and life history traits impact the population growth and net reproductive rate of A. tonsa. In addition, this chapter also investigates the evolution of swimming speed in A. tonsa using hydromechanical encounter rate models (Kiørboe and Bagøien, 2005) and individual-based models (Berec et al., 2017). The models demonstrate how positive density dependence (an Allee effect) and a realistic movement-fecundity trade-off influence the population dynamics and evolution of swimming speed in A. tonsa, further addressing the knowledge gap identified in Chapter 1. Chapter 2 therefore aims to expand on the knowledge gained in Chapter 1 by providing a mechanistic understanding of how population density and mortality affect the net reproductive rate and evolution of swimming behavior in copepods that use hydromechanical mate-finding strategies. By using quantitative modeling techniques, this chapter offers insight into the ecological and evolutionary dynamics of A. tonsa, beyond what is possible to obtain from experimental research alone.

The third and final chapter of this dissertation is slightly different from the preceding chapters as it moves away from copepod physiology and instead focuses on Allee effects in experimental ecology. As copepods are known to experience Allee effects, this chapter provides an important and relevant dimension to this work. Using meta-analysis, this chapter reviews experimental studies on Allee effects, with the primary goal of determining whether Allee mechanism (e.g., mate-finding) or taxonomic group impact Allee effect magnitude in low density populations. This chapter provides the first quantitative synthesis of experimental Allee effect research and aims to improve our understanding of how the different Allee mechanisms manifest in different taxonomic groups. As population density is a recurring theme throughout the first two chapters of this dissertation, this final chapter complements this research by exploring the theory of low-density population dynamics. This is an area of increasing importance in ecology as a growing number of species face issues caused by low population density around the world.

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