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Graham 1 Food finding using olfaction by scorpion mud turtles (Kinosternon scorpioides) Megan M. Graham Department of Ecology and Evolutionary Biology University of California, Santa Cruz EAP Tropical Biology and Conservation Program, Spring 2018 8 June 2018 ABSTRACT The mechanism used to locate food varies between animals, whether it be by olfaction, vision, hearing, touch, taste, or some combination of these. Many turtle species rely on vision and olfaction to find prey. I designed an experiment to test if scorpion mud turtles (Kinosternon scorpioides) can find food using olfaction by placing the turtles in Rio Cuajiniquil with three nondescript capsules containing sardine chunks and three empty, control capsules. Observations of six turtles’ interactions with the capsules suggested that they can locate food through olfaction; however, only one statistical analysis was significant which was that the turtles were more likely to bite full capsules than empty capsules. El descubrimiento de alimento por medio del olfato en las tortugas candado (Kinosternon scorpioides) RESUMEN Los mecanismos utilizados para localizar alimentos varían entre las especies de animales, ya sea por olfato, visión, audición, tacto, gusto o alguna combinación de estos. Muchas especies de tortugas dependen de la visión y el olfato para encontrar sus presas. Diseñé un experimento para probar si las tortugas candado (Kinosternon scorpioides) podían encontrar comida usando el olfato. Coloqué las tortugas en el Río Cuajiniquil con tres cápsulas que contenían trozos de sardina y tres cápsulas vacías de control. Las observaciones de las interacciones de seis tortugas con las cápsulas sugirieron que pueden localizar los alimentos a través del olfato; sin embargo, solo uno de los análisis estadísticos fue significativo, la cual fue que las tortugas tenían mayor probabilidad de morder las cápsulas completas que las cápsulas vacías. INTRODUCTION The ability to locate food is important for survival in all species. Different organisms rely more heavily on certain senses to find prey items and often use more than one sense at a time. Turtles typically depend on vision and olfaction to locate food (Savage 2002). Since many semi- aquatic turtles, including Kinosternon scorpioides, live in murky water, olfaction may be one of the more reliable methods to detect objects (Bowden 2010). Scientists are unsure of exactly how turtles smell underwater. One possibility is that both in and out of water, turtles pulsate their throats to move air or water through their mouth and nostrils where different chemicals can be detected on the olfactory tract and taste buds (Savage 2002; Bowden 2010). Additionally, scorpion mud turtles, along with other mud and musk turtles, have barbels on their chins. Barbels are whisker-like protrusions that are thought to function as sensory receptors (Ramdial 2014; Fergus 2007). Most turtles are omnivorous, but scorpion mud turtles (Kinosternon scorpioides) are primarily carnivores and scavengers, feeding on insects, spiders, fish, shrimp, frogs, snails, and Scorpion mud turtle olfaction Graham 2 worms (Berry and Iverson 2011). They will also feed on aquatic plants, algae, fruits, and seeds, but given the choice, they prefer the former foods (Ramdial 2014). While these turtles can survive on land, they spend most of their time in the water, particularly in ponds, swamps, marshes, and slow-moving rivers (Ramdial 2014). Another species of turtle in the same genus, Kinosternon sonoriense, has been reported to forage by moving slowly along the bottom of a body of water with its head and neck fully extended, swinging back and forth. Once prey is detected, the turtle retracts its head slightly and lunges. When eating, small prey items will be swallowed whole and larger items will be torn apart and chewed (Hulse 1974). Little is known about how Kinosternon scorpioides locates prey. One study was done in which two scorpion mud turtles were captured and one was observed for three months. The researchers believe that these turtles locate prey visually because the turtle did not eat prey while their tank was in a light-tight bag for 46 hours but did eat the prey once exposed to light (Monge- Nájera and Morera-Brenes 1987). This leads into the question my study attempts to answer: can Kinosternon scorpioides locate food through olfaction? MATERIALS AND METHODS I caught six turtles in Rio Cuajiniquil in Cuajiniquil, Guanacaste, Costa Rica with the help of several people. I kept the turtles in captivity outside for the duration of the experiment. The turtles were kept in the shade in separate clear plastic tubs with about two centimeters of river water and a rock to climb onto. I took measurements of each turtle’s carapace length and width and plastron length and width to the nearest millimeter and their mass. I also took note of identifying marks on the turtles such as scars, shell damage, and pronounced features to differentiate them. After the last night of testing, I returned the turtles to the exact location I had found them in Rio Cuajiniquil. I constructed small capsules made of two black bottle caps per capsule, secured together by two black zip ties. Half of the capsules had sardine chunks inside, and the other half were empty and served as controls. All of the capsules had the same number of holes cut in them to allow the sardine scent to better flow into the water. Tests were performed in an approximately 2.5 meter by 2.5 meter pool in Rio Cuajiniquil; three boundaries of the pool were marked by rows of rocks and the fourth was marked by a barbed wire fence (Figure 1). The water was about 20 centimeters deep at the deepest point. Three pairs of capsules were used for each test, except for the tests conducted on the first night where only one pair was used and placed in the ‘left’ position (Fig. 1). A pair consisted of one capsule with food (full) and one capsule without (empty). The capsules in each pair were placed approximately 20 centimeters apart. The pairs of capsules were placed in the river pool in a triangle formation. One pair was placed upstream by the barbed wire fence, and the other two pairs were placed in the downstream corners of the pool (Figure 1). Each capsule was held down by a small rock so that the capsule was still accessible to the turtle. If a turtle tried to escape under the fence or over the rocks, I picked it up and placed it back at the starting point, roughly halfway between the downstream capsules. One at a time, I would place a turtle roughly halfway between the downstream capsules, facing upstream (Figure 1). Once the turtle was in the water, I started the timer. Each test lasted 30 minutes unless a turtle bit one of the capsules at which time I ended the trial. I recorded the times of when a turtle would touch a capsule with its nose, bite a capsule, and when a turtle had Scorpion mud turtle olfaction Graham 3 to be reset after trying to leave the pool. With this, I took note of what the first contact was. Tests were performed nightly from 15 May 2018 through 18 May 2018, usually starting around 8:00 pm. I tested the turtles at night because they are primarily nocturnal (Forero-Medina and Costaño-Mora 2011), partially evidenced by the fact that it took roughly six hours of searching during the day to find one turtle and 30 minutes at night to find four turtles. Each turtle was tested once per night. Four of the turtles were tested three times each, and the other two were each tested twice. Key Rock wall Barbed wire fence Empty capsule Full capsule Direction of water flow Turtle starting position Figure 1. Set up of testing pool in Rio Cuajiniquil. The pool was approximately 2.5 by 2.5 meters. Three pairs of capsules were placed in a triangle formation. A pair consisted of one capsule with food (full) and one without food (empty). Capsules within a pair were approximately 20 centimeters apart. Not to scale. After each test on the last two nights, I replaced the sardine chunks in the full capsules and switched the locations of the empty and full capsules within a pair. I replaced the bait to ensure that the scent wasn’t being washed away between tests, so each turtle would have the same strength olfactory cue. The capsules were switched between trials to somewhat randomize the location and help control for any other factors that may have been causing a turtle to go to a particular capsule such as other cues already present in the river. I performed a chi-squared test on the total number of times full and empty capsules were touched, the number of times full and empty capsules were touched first during a test, and the Scorpion mud turtle olfaction Graham 4 number of times full and empty capsules were bitten. I also did a Wilcoxon signed rank test on the first contacts per turtle and the total contacts per turtle to test the statistical significance of these data. An alpha level of .05 was used for all statistical tests. RESULTS Even though the majority of my data was not statistically significant, my observations provide evidence that scorpion mud turtles may use olfaction to find food. Each turtle bit a full capsule at least once across all of its trials. In the seven instances that an empty capsule was touched, five of those times a full capsule was contacted afterward, during the same trial. Four of those five full capsule contacts were bites (Figure 2). I define a touch as a turtle touching a capsule with its nose, and I define a contact as a turtle touching a capsule with its nose or biting a capsule.

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