PREDATION ON THE TROPICAL FRESHWATER SHRIMP XIPHOCARIS ELONGATA: ROSTRUM INDUCIBILITY, ANTIPREDATOR RESPONSES AND CASCADE EFFECTS By MARÍA E. OCASIO TORRES A dissertation submitted to the DEPARTMENT OF BIOLOGY FACULTY OF NATURAL SCIENCES UNIVERSITY OF PUERTO RICO RÍO PIEDRAS CAMPUS In partial fulfillment of the requirements for the degree of DOCTOR IN PHILOSOPHY May 2014 Río Piedras, Puerto Rico i This dissertation has been accepted by faculty of the: DEPARTMENT OF BIOLOGY FACULTY OF NATURAL SCIENCES UNIVERSITY OF PUERTO RICO RÍO PIEDRAS CAMPUS In partial fulfillment of the requirements for the degree of DOCTOR IN PHILOSOPHY Dissertation Committee: __________________________________________ Alberto M. Sabat, Ph.D. Advisor __________________________________________ Todd A. Crowl, Ph.D. __________________________________________ Tugrul Giray, Ph.D. __________________________________________ Jorge Ortiz, Ph.D. __________________________________________ Eduardo Rosa Molinar, Ph.D. ii PREDATION ON THE TROPICAL FRESHWATER SHRIMP XIPHOCARIS ELONGATA: ROSTRUM INDUCIBILITY, ANTIPREDATOR RESPONSES AND CASCADE EFFECTS iii A mi familia, Julio, La Luna, La Michu, Cuatro Huesos, La Flaca, Pupi y Agatha iv ACKNOWLEDGMENTS First, I thank God for giving me the strength to pursue and finish a PhD in Biology. I thank my advisor Alberto M. Sabat for his mentoring and counseling throughout my graduate studies. I could not have done it without you. I also thank dearly Todd A. Crowl for all his ideas and help. I send my gratitude to the other members of my committee: Tugrul Giray, Jorge Ortiz and Eduardo Rosa Molinar for their valuable comments and recommendations. I thank Alan Covich for revision of my manuscripts. My gratitude to the Graduate Biology Program and the Department of Biology for their continued support and high quality education. A special thanks to the Puerto Rico Louis Stokes Alliance for Minority Participation (HRD-0832961), the National Science Foundation Graduate Research Fellowship Program and the Dean of Graduate Studies and Research Golf Tournament Fellowship for their financial support. Thanks to El Verde Field Station Staff, Alonso Ramírez, Karleen Wagner, Katie Hein, Omar Pérez, Diana Delgado, Carlos Toledo, Tomas Hrbek, Carla Restrepo, and Mitch Aide for their help in terms of logistics. Thanks to the field and laboratory assistance from Yanira Mejías, Julio Lazcano, Nicole Rivera, Francis Diroche, Frances Diroche, Cielo Figuerola, Daphne Pagán, Alejandra Estrada, Michael Torres, Guillermo Colón, Virnaliz Cruz, Kathiria Figueroa, Yanuska Zosh, Diane Mankin, Stephanie Amarante, Alexandra Salcedo, Robert Bencosme, Leira Marzán, Rebeca Bayrón, Rafael Vaquer, Raisa Hernández, Jonathan, Iris Torres, Ketzia Ocasio, Augustin Engman, Giomara La Quay, Diana Delgado, Pablo Hernández, Branko Hilje, Ana Sánchez, Oscar Ospina, Rita Cáceres, José Fumero, Dylan Rhea, D’Gleneis Valenzuela, and José Sánchez. I also want v to thank my family, Julio, and my dear friends for the hugs, laughs, food, and good times I had during this stage of my life. vi ABSTRACT Predators affect prey indirectly through inducible defenses that are only present when the predator is present, and have a measurable cost. This dissertation is focused on the effects of the predatory fish Agonostomus monticola on the morphology, anti-predator strategies, and ecological role of the amphidromous shrimp Xiphocaris elongata, which exhibits a phenotypic polymorphism (i.e. long or short rostrum) that has been correlated with the presence/absence of fish predators (Covich et al. 2009). I answer four questions: 1) is the long rostrum inducible by A. monticola, 2) is the long rostrum an effective defense mechanism against A. montocola, 3) is the long rostrum costly in terms of downstream displacement and reproduction, and 4) does predator presence create top- down cascade effects? Inducibility of the rostrum by A. monticola was evaluated through exposure experiments to juvenile, long-rostrum adult shrimp, and short-rostrum adult shrimp. The anti-predator strategies of X. elongata against A. monticola were addressed through behavioral and mortality experiments for long-rostrum and short-rostrum shrimp. The cost of the rostrum was assessed through experiments that manipulated the flow in which downstream displacement occurred for long-rostrum and short-rostrum shrimp, and through an egg count of gravid long-rostrum and short-rostrum females. Top-down trophic cascades were examined through experiments in artificial pools where long- rostrum and short-rostrum shrimp could forage or hide in refuge in the presence or absence of predators. The data indicated that: 1) the long rostrum is inducible by the presence of A. monticola, 2) the long rostrum is an effective defense mechanism against fish in terms of choice, rejections, and handling time, 3) the long rostrum is not costly in vii terms of downstream displacement, but there seems to be a trend that the long rostrum may be costly in terms of reproduction, and 4) predator presence creates trait-mediated top-down cascades effects by reducing the amount of shredding by X. elongata, this decreases decomposition rates of the riparian species Cecropia schreberiana. This study demonstrates that the long rostrum in X. elongata fits the criteria of an inducible defense against predatory fish and that predator presence affects the ecological role of X. elongata. viii TABLE OF CONTENTS Acknowledgements …………………………………...…………………………………. v Abstract …………………………...……………………………………………………. vii List of Tables …………………………………………………………………...……..... xi List of Figures ……………………..………..…………………………….………..….. xiv Prologue ...………………………………………………………………………..….... xvii Chapter 1: Long rostrum in an amphidromous shrimp induced by signals from a predatory fish……………………………………………………………………………...1 Abstract ………………………………………………………………………….. 2 Introduction...…………………………………………………………………….. 3 Methods ………………………………………………………………………….. 6 Results ………………………………………………………………………….. 11 Discussion ……………………………………………………………………… 11 Tables ……………………………………………………………………….….. 15 Figures ………………………………………………………………………….. 18 Chapter 2: Antipredator defense mechanism in the freshwater shrimp Xiphocaris elongata: rostrum length…………………………………………………………………20 Abstract ………………………………………………………………………….21 Introduction...…………………………………………………………………….22 Methods ………………………………………………………………………….24 Results …………………………………………………………………………...28 Discussion ……………………………………………………………………….29 ix Tables ……………………………………………………………………….….. 35 Figures ………………………………………………………………………….. 39 Chapter 3: Hydrodynamic and morphological differences between two phenotypes of the amphidromous shrimp Xiphocaris elongata……………………………………………..41 Abstract ………………………………………………………………………….42 Introduction...…………………………………………………………………….43 Methods ………………………………………………………………………….46 Results …………………………………………………………………………...50 Discussion ……………………………………………………………………….53 Tables ……………………………………………………………………….…...58 Figures …………………………………………………………………………...62 Chapter 4: Predatory fish causes top-down trophic cascades on the amphidromous shrimp Xiphocaris elongata ……………………………………………...………………..…………… 68 Abstract ………………………………………………………………………….69 Introduction...…………………………………………………………………….69 Methods ………………………………………………………………………….74 Results …………………………………………………………………………...79 Discussion ……………………………………………………………………… 81 Tables ……………………………………………………………………….….. 85 Figures ………………………………………………………………………….. 96 General Conclusions……………………………………………………………………102 Literature Cited ...………………………………………………………………..……..105 x LIST OF TABLES Table 1.1 The total of each phenotype of Xiphocaris elongata in each treatment replicate that survived the duration of the experiment……………………………………………16 Table 1.2 Results of 2-way analyses of variance of rostrum growth and rostrum growth relative to post-orbital carapace length of Xiphocaris elongata of 3 phenotypes (adult long-rostrum, adult short-rostrum, and juvenile) and 6 predator treatments………………17 Table 2.1 Average sizes and standard errors of the fish and the shrimp used for the behavioral and the mortality experiments………………………………………………..36 Table 2.2 Pearson's chi-square analysis for the fish choice trials (i.e., first shrimp phenotype attacked versus second shrimp phenotype attacked), unsuccessful and consumptions, and in terms of bites and consumptions; and Fisher’s exact test in terms of consumptions and rejections.…………………………………………………………….37 Table 2.3 Pearson's chi-squared tests in terms of the amount of shrimp alive and consumed by A. monticola after 24 hours………………………………………………38 Table 3.1 The average sizes (mm) and standard deviations of the shrimp used for the downstream displacement experiments, morphometric analysis and egg count analysis. LR[S] stands for the originally long-rostrum shrimp whose rostrums were cut by hand before the experiments…………………………………………………………………...59 Table 3.2 Statistical results (i.e. given by the p-values) of the Post-hoc Tukey Test on the effect of each phenotype on the flow in which downstream displacement occurred for the different X. elongata phenotypes (M.S. = 0.00178, d.f. = 87). LR[S] stands for the xi originally long-rostrum shrimp whose rostrums were cut by hand before the experiments. * stands for statistically significant………………………………………………………60 Table 3.3 Statistical results (i.e. given by the p-values) of the Post-hoc Tukey Test on the effect of each phenotype on the distance the different X. elongata phenotypes were flushed downstream (M.S. = 2.505, d.f. = 87). LR[S] stands for the originally long- rostrum shrimp whose rostrums were cut