PARENTAL INVESTMENT DECISIONS IN A BIPARENTAL CICHLID FISH, THE CONVICT CICHLID (AMATITLANIA NIGROFASCIATA), WHEN THREATENED WITH A DIMORPHIC PREDATORY-PAIR A Thesis Presented to the faculty of the Department of Biological Sciences California State University, Sacramento Submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE in Biological Science (Ecology, Evolution, and Conservation) by Colleen Moore SPRING 2020 © 2020 Colleen Moore ALL RIGHTS RESERVED ii PARENTAL INVESTMENT DECISIONS IN A BIPARENTAL CICHLID FISH, THE CONVICT CICHLID (AMATITLANIA NIGROFASCIATA), WHEN THREATENED WITH A DIMORPHIC PREDATORY-PAIR A Thesis by Colleen Moore Approved by: __________________________________, Committee Chair Ronald M. Coleman, Ph.D. __________________________________, Second Reader Timothy Davidson, Ph.D. __________________________________, Third Reader Jamie Kneitel, Ph.D. ____________________________ Date iii Student: Colleen Moore I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for electronic submission to the Library and credit is to be awarded for the thesis. __________________________, Graduate Coordinator _______________________ James W. Baxter, Ph.D. Date Department of Biological Sciences iv Abstract of PARENTAL INVESTMENT DECISIONS IN A BIPARENTAL CICHLID FISH, THE CONVICT CICHLID (AMATITLANIA NIGROFASCIATA), WHEN THREATENED WITH A DIMORPHIC PREDATORY-PAIR by Colleen Moore How much a parent invests in its offspring has been a focus in many studies assessing parental care dynamics across taxa. An animal with offspring must make investment decisions and behave in a way that will maximize its lifetime reproductive success. Biparental species face a unique conflict in terms of parental investment: the parent must take into consideration how much it invests itself, and also how much its partner invests. A lack of care by both parents may lead to brood loss, but parental care is energetically costly to each parent, resulting in cooperation and conflict. Previous studies have examined investment allocation by a single parent or how parents in a biparental system allocate their investment against a single attacker. However, very few studies have examined investment allocation decisions when a biparental pair is threatened with multiple predators that also differ in size - a realistic threat in the wild. The convict cichlid (Amatitlania nigrofasciata), is a biparental species that provides prolonged parental care, and is therefore an ideal species for examining this question. v Parental defense is critical for offspring survival, and therefore, involves appropriate decision making by the breeding pair. That is, each member of the guarding pair does not simply strike at the closest attacker or attack at random, but instead assesses the threat level and responds with a consistent behavior. The objective of this research is to explore this behavioral response by a pair of parents that differed in size (i.e., a large male and small female). To investigate this research question, a constructed predatory- pair model (two model fish, differing in size) was presented to a pair of convict cichlids that were actively guarding fry, simulating a predator attack. For each experimental trial the model was presented to the pair and moved in a figure-8 pattern towards the pair for 30 seconds, pulled away for 30 seconds, and presented for a final 30 seconds. During each model presentation, the number of bites that each fish took at each of the predators was recorded, producing four scores. The four scores from the first presentation were added to the four scores from the second presentation, to produce four scores for the trial (i.e., male versus large, male versus small, female versus large, and female versus small). This procedure was replicated for 5 consecutive days. The four scores from each day were summed to produce four scores for the pair for the experiment (i.e., male versus large, male versus small, female versus large, and female versus small). The hypotheses for this experiment were as follows: (1) the larger parental fish (the male) in the convict cichlid pair will bite the large model attacker fish more than he will bite the small model attacker fish, and (2) the smaller parental fish (the female) will bite the small model attacker fish more than she will bite the large model attacker fish. vi A total of twelve convict cichlid pairs were used in the behavioral experiment, which was performed over a nine month period (May 2019 – January 2020). A paired t- test was used to examine the impact of predator size (small vs. large) on parental investment decisions within each sex, measured by the number of bites each parent took at each model fish during the duration of the experiment. Results revealed a consistent pattern within each sex, with significant differences in the number of bites at the model fish predators by both the male (p-value = 0.0001) and by the female (p-value = 0.0003) of the twelve pairs examined. Specifically, the large fish (the male) within a pair bit the large model attacker significantly more than the small model attacker and the small fish (the female) bit the small model attacker more than the large model attacker, supporting the hypotheses. Results from this research suggest that the size of a predator, when multiple are present, influences the decision-making of a biparental pair. This research builds off of a solid foundation of theory and experimentation and expands our understanding of investment allocation decisions in biparental fishes. ______________________________________, Committee Chair Ronald M. Coleman, Ph.D. ______________________________________ Date vii ACKNOWLEDGEMENTS First, I would like to thank my thesis advisor, Dr. Ron Coleman, for the support and guidance throughout my time in graduate school. I will leave this program with an even deeper fascination and appreciation for fish after being a part of your lab. Thank you for always making the time to chat whether it was about research or just a friendly conversation about everyday life. Lastly, thank you for the endless amounts of chocolate in the lab for us students on the more difficult days. Thank you to the other members of my committee, Dr. Jamie Kneitel and Dr. Timothy Davidson, for your thoughtful comments and support while writing this paper. I would like to acknowledge my family for the support and encouragement throughout my graduate school journey. First, I would like to thank my mom for allowing me to have a flexible work schedule so I could leave daily to conduct research trials or check my fish for eggs. I also want to thank my dad for my love and fascination of fish that I initially developed while being raised on the sturgeon farm and for the nonstop encouragement to pursue my Master’s degree. Thank you to my twin sister Sarah, who of course, finished grad school before I did. Sarah, thank you for helping me with my figures and statistics, for the tedious grammar-checks, and for being a great sister during the lows of graduate school and for celebrating my small victories with me, even if it was over the phone. To my other siblings, Kevin and Lauren, thank you for supporting me in your own ways along this journey. You never asked too many questions in regards to my research, which is something I needed – to forget the stressful times and appreciate the small moments with family. viii Lastly, I would like to thank my partner Ty. I met you a month before I started my first semester in grad school in 2016 and you’ve been nothing but encouraging along the way. Thank you for the weekend fishing trips during the stressful periods of graduate school that brought me so much joy. Most importantly, thank you for always reminding me of how proud you are of me. ix TABLE OF CONTENTS Page Acknowledgments ..................................................................................................... viii List of Figures ............................................................................................................. xii Chapter 1. INTRODUCTION ………………………………………………………………......1 Parental Investment Theory………………………………………………………....1 Size-based Decision-making……………………………………………………......3 The Convict Cichlid.………………………………………………………………..6 Field Observation and Unanswered Questions……………………………………..7 Objectives and Hypotheses…………………………………………………………8 2. MATERIALS AND METHODS…………………………………………………….9 Preliminary Fieldwork: Costa Rica………………………………………………....9 Laboratory Experiment: Sacramento State………………………………………...11 Experimental Fish………………………………………………………………….11 Aquaria Configuration………...………………………………………………........12 Predatory-pair Model...……………… …………………………………………….12 Predatory-pair Behavioral Experiment……………………………………….…….15 Data Analysis……………….…………………………………………………........16 3. RESULTS……………………………………………………………………….......18 Behavioral Experiment...…………………………………………………………..18 4. DISCUSSION……………………………………………………………………….21 x Appendix A. Raw Data of Convict Cichlid Pairs………………………………………..25 Appendix B. Daily Data From Predatory-pair Experiment………………………...……27 Appendix C. Data Used in the Paired t-test….……………………………………...…...34 References………………………………………………………………………………..35 xi LIST OF FIGURES Figures 1. Relevant Research Flowchart…………………………………………………………5 2. Predatory-pair Fieldwork Model……………………………………………………..10 3. Aquaria Set-up for the Behavioral Experiment……………………………………...13 4. Predatory-pair Lab Model……………………………………………………………14 5. Male