This semester I took an Animal Behavior class at California State University, Sacramento. One of the projects was to conduct our own experiment. I thought I’d share what I did on my blog!
The family Pachychelidae contains freshwater snails that live throughout tropical habitats worldwide. The family belongs to the superfamily Cerithoidea. There are roughly 200 species of Pachychelid snails (Strong et al. 2011). One of the family’s most interesting genera is Tylomelania. Tylomelania snails form an adaptive radiation of gastropods endemic to the island of Sulawesi, Indonesia, formerly known as Celebes (Glaubrecht & Rintelen, 2008). There are currently 53 described species with many undescribed species known to exist (Rintelen et al., 2010). Tylomelania are found in both the rivers and crater lakes of the island.
While the evolutionary history, phylogenetics, and taxonomy of Tylomelania is fairly well studied, very little is known of the ecology and behavior of these species (Rintelen et al., 2007a, Glaubrecht & Rintelen, 2008, Rintelen et al., 2010). While Tylomelania have a diverse radula morphology indicating trophic diversity, little is known about their actual diet in the wild. Aquarium observations have shown most species may be kept maintained successfully on an omnivorous diet. One area of Tylomelania ecology well studied is their breeding behavior. All species are known to be ovoviviparous giving birth to a few offspring that are miniature copies of the adults (Fig. 2) (Rintelen et al., 2007a).
In this study, I tested whether or not Tylomelania sp. “poso orange” (fig. 1) has a food preference between a high and low protein food source. Tylomelania sp. “poso orange” is an undescribed species that inhabits the crater lake Lake Poso. It is found over hard substrates throughout the lake. Tylomelania sp. “poso orange” is commonly referred to as the Poso Orange Elephant Snail in the aquarium trade due to its orange coloration and its long “nose”. Tylomelania sp. “poso orange” is one of the largest species in the genus reaching a size of around 7.5-10 cm (Glaubrecht & Rintelen, 2008). I hypothesized that if there was a preference for a certain type of food in Tylomelania sp. “poso orange” then there would be a statistical difference in the number of grazes per food. My null hypothesis was that there would be no statistical difference in the number of grazes per food.
Materials and Methods:
All of the Tylomelania sp. “poso orange” used in the study were wild caught and imported from Lake Poso, Sulawesi, Indonesia. A total of twelve Tylomelania sp. “poso orange” were purchased for the study. Every snail used was an adult and ranged from 6-9 cm.
This study was conducted in the Evolutionary Ecology of Fishes Lab at California State University, Sacramento. Two ten gallon aquariums were used in this study. One aquarium was used as a stock tank while the other was used as an experimental tank. Both aquariums contained a heater set to 25oC and a sponge filter. The substrate used in the tanks was a mixture between sand and gravel and was 1.25 cm deep. The aquariums contained no other decorations. Weekly 50% water changes were conducted on the tanks. The aquariums were refilled with water that was aged for at least 24 hours to remove chlorine. The only additive added to the water was 1/16th teaspoon of calcium in the form of crushed cuttlefish bone to promote healthy shell maintenance in the snails.
Repashy gel foods were used in this study (Fig. 3). The two foods used in this study varied in their amount of protein content. For this study I used Repashy Meat Pie, which contains 55% protein as the high protein food and Repashy Soilent Green as the low protein food with a 45% protein content. The foods are made by combining three parts boiling water to one part powdered food. After the mixture is allowed to cool it forms into a gel.
In order to quantify this study I needed to be able to expose each snail to both types of food that and be able numerically record their responses. This was done by creating a 4X4 grid out of ½” egg crate. For each trial, I set up this grid with eight squares of each type of food. In order to get an unbiased and randomized placement of where the food was placed I used an electronic sixteen sided dice application called “dice” for an Android phone. Each square of the egg crate was given a number starting with the top left corner being number one and the far bottom right corner being number 16. The numbers for every row ran left to right. Each roll alternated between the high protein and low protein food. Once a number was rolled once it was not used again. A piece of slate was used as the substrate to hold the gel mixture. The egg crate grid was placed on top of the slate and was held in place with rubber bands (Fig. 4). While the egg crate grid was on the slate for the first time, I etched the slate with a razor to mark the placement of the grid. This ensured that the egg crate grid was placed in the same spot on the slate for the entire experiment. Before the food set into a gel and was still liquid, I pipetted .5 ml of the food into each designated position on the egg crate grid. Once the gel set, the grid was removed. This created 16 gel food “gum drops” comprised of eight “gum drops” of both the low and high protein food (Fig. 5).
The snails were starved 48 hours before they were subject to a trial. Each trial was performed by placing an individual Tylomelania sp. “poso yellow” into the experiment tank and allowing it to acclimate for 15 minutes. After acclimation was completed, the piece of slate with the gel food attached was added to the aquarium and the snails were left to graze for an hour. As the snails have extremely sharp teeth on their radula (mouth parts), they leave a visible mark of where they have fed (Fig. 6). After the one hour grazing period had passed, the number of food squares for each food the snail had grazed upon was recorded. The snail was also removed from the experimental aquarium and bagged for transfer to an aquarium at my house, guaranteeing that no individual would be used more than once. This was repeated for a total of twelve trials involving twelve different Tylomelania sp. “poso orange”.
Microsoft excel was used to organize the data as well as perform statistical analysis. A paired t-test was performed to analyze the data as I looked at the response of the same individual snail given to different food options.
A total of 39 grazes and 20 grazes were recorded for the low protein and high protein food respectively from the twelve Tylomelania sp. “poso orange”. The most grazes by one snail for the low protein food was seven while it was 4 for the high protein food. The least number of grazes recorded for both foods was 0. Paired t-test analysis yielded a p-value=0.01 (Fig. 7 & 8).
With a calculated p-value of 0.01 being less than alpha, which was 0.05, we can conclude that there was a significant difference in the number of grazes between the high and low protein foods. We thus reject the null hypothesis. Results of this study show that the snails preferred the low protein food over the high protein food.
This seems to be the first behavioral experiment performed on Tylomelania sp. “poso orange”. This is most likely due to the difficulty of performing an experiment in the wild on Sulawesi as well as the difficulty to obtain enough specimens for a large sample size. There are also very few captive bred specimens available as they are not a fecund species with females having only one offspring every six weeks.
I believe the most likely reason that Tylomelania sp. “poso orange” preferred the low protein food may be due to the habitat in which it is found in the wild. As stated above, this species is found over hard rocky substrates in Lake Poso. These hard rocky substrates are perfect for the growth of biofilm. Biofilm contains algae and diatoms, and microbes. This biofilm could possibly be a main food source for Tylomelania species living in habitats with hard substrate as it does for a vast majority of the endemic freshwater shrimp species of the genus Caridina (Rintelen, 2010). As these snails are not predators and carrion is probably few and far between for these snails as they are simply beat to the carrion by faster scavengers, it would not be surprising if biofilm is the main component of their diet. However, they most likely are not obligate biofilm feeders.
One area to investigate beyond this study is whether or not Tylomelania sp. “poso orange” can see different colors. The low protein food, Repashy Soilent Green, was a very dark green, while the high protein Repashy Meat Pie was a much brighter orange coloration (Fig. 4). Color may have influenced the snail’s choice on whether or not to feed on a certain food. A future study could be designed using foods of that have been dyed the same color but have different protein contents.
Another factor that may have affected the study is the snail’s behavior to pick up the food. Tylomelania sp. “poso orange” have incredibly strong foot muscles. I’ve observed Tylomelania sp. “poso orange” feeding on floating food items throughout an aquarium as well as dead fish. I was unable to find any scientific research on this phenomenon. In these cases, the snails have used their foot to physically grab the food item and use their long “nose” to feed on the item while they hold it in their foot (Fig. 9). I found a few food “gum drops” not attached to the rock after the one hour grazing period and observed one snail holding a food “gum drop” in his foot at the end of the grazing period. I counted these as a grazes. These are not instances of the gel food breaking down in the aquarium and detaching from the slate. Detached gel food were only seen in three of the trials and a test soak for one hour with no snails present in the tank yielded no detachment of the food from the slate. It is also possible that in some instances the snail simply ripped the food gum drop off the piece of slate. This would affect the outcome of the study as they may rip the food from the substrate but not actually graze it if they were to move across it. If I were to reproduce the study in the future, I’d observe each grazing session. Future studies addressing the observed foraging behavior of grabbing food with the snail’s foot and holding it to consume could yield valuable information on this snail’s behavior.
Glaubrecht, M. & von Rintelen, T. (2008) The species flocks of lacustrine gastropods: the Sulawesi lakes as model system in speciation and adaptive radiation. Hydrobiologia, 615, 181-199.
Rintelen T von, Glaubrecht M (2005) Anatomy of an adaptive radiation: a unique reproductive strategy in the endemic freshwater gastropod Tylomelania (Cerithioidea: Pachychilidae) on Sulawesi, Indonesia, and its biogeographic implications. Biological Journal of the Linnean Society 85, 513–542.
Rintelen T. von, Bouchet, P, Glaubrecht, M. (2007a) Ancient lakes as hotspots of diversity: a morphological review of an endemic species flock of Tylomelania (Gastropoda: Cerithioidea: Pachychilidae) in the Malili lake system on Sulawesi, Indonesia. Hydrobiologia 592:1–94.
Rintelen, T. von, Rintelen, K. von. & Glaubrecht, M. (2010) The species flocks of the viviparous freshwater gastropod Tylomelania (Mollusca: Cerithioidea: Pachychilidae) in the ancient lakes of Sulawesi, Indonesia – the role of geography, trophic morphology and colour as driving forces in adaptive radiation. pp. 485-512, In Evolution in Action (Glaubrecht, M., ed),. Springer, Berlin, 586 pp.
Rintelen, K. v., Glaubrecht, M., Schubart, C. D., Wessel, A., & Rintelen, T. v. (2010). Adaptive radiation and ecological diversification of Sulawesi’s ancient shrimp. Evolution, 64, 3287-3299.
Strong, E. E., Colgan, D. J., Healy, J. M., Lydeard, C., Ponder, W. F., & Glaubrecht, M. (2011) Phylogeny of the gastropod superfamily Cerithioidea using morphology and molecules. Zoological Journal of the Linnean Society, 162, 43-89.