1. TEMPLATE DESIGN © 2008 www.PosterPresentations.com Relationship of maternal flow environment to offspring size in Botrylloides violaceus Damion Delton 1,2, C. Sarah Cohen 2 California State University, Fresno 1, Romberg Tiburon Center for Environmental Studies, San Francisco State University 2 Abstract Colonial botryllid tunicates, such as Botrylloides violaceus, brood large, non-feeding offspring with extremely limited larval life spans of minutes to perhaps one day. Despite the importance of this transitory life history stage, there is little information on how environmental factors such as ambient water flow affect larval size among invertebrates. Background  We collected samples of tunicates from varying locations around the dock from Pillar Point Harbor in Half Moon Bay, CA (Image 4).  Water flow was measured hanging Life Savers TM (Koehl and Alberte, 1988) at each location a colony was collected for 10 minutes (Image 5).  The rate of dissolution for each trial was calculated as follows: Initial Mass (mg) – Final Mass (mg) /- Exposure Time (secs).  Swimming larvae were collected from each colony and then measured in mm at 400x magnification using a camera and ImageJ software.  Area of each larva calculated using the elliptical area formula (Image 7): Area = π * A * B (A= major radius of the ellipse and B=the minor radius of the ellipse). Methods The colonial, sessile ascidian Botrylloides violaceus is a marine invertebrate that is globally invasive and commonly found on the west coast of the United States, including the San Francisco Bay. Due to the rapid growth of this species, this tunicate causes a great deal of bio-fouling and can smother other marine invertebrates including mussels and barnacles. They are hermaphroditic and brood large, non-feeding larvae about 1 millimeter in body diameter. They have a relatively short larval cycle where they spend anywhere from a few hours to a day in the water column before attaching to substrate, creating a limited dispersal potential. B. violaceus filter feeds to acquire food and nutrients for survival which requires low energy expenditure (4). The zooids References/Acknowledgments Discussion tunicates, more food may be able to pass through the filtering system allowing the tunicate to potentially store more energy to be used for brooding of larger larva. Though flow plays an important part in tunicate survival there has been very little information on how environmental factors such as water flow affect invertebrate larva, so this study will test to see the possible relationship. By collecting various colonies, testing flow rates at our collection sites, and assaying for larval size we will be able to determine whether different flow rates play a factor in size. Results 1)Kokita, T. 2003. Potential latitudinal variation in egg size and number of a geographically widespread reef fish, revealed by common environments experiments. Marine Biology 143:593-601 2)Marshall, D., Russell Bonduriansky, and Luc F. Bussière. 2008. Offspring Size Variation within Broods as a Bet-Hedging Strategy in Unpredictable Environments. Ecological Society of America Vol. 89, No. 9, pp. 2506-2517 3)Sakai, S., and Y. Harada. 2001. Why do large mothers produce large offspring? theory and a test. American Naturalist 157:348-359 4)Paradis, K.L., and L.A. Pyzocha. "Energetics and Metabolism." Http://academics.smcvt.edu. Web. 21July. 2011. ***Special thanks to the Cohen Lab, STAR peers, RTC, and the STAR Program for making helping with my summer project. pump water through their own incurrent siphons which then filter small organisms such as phytoplankton, zooplankton, and other organic material suspended in the water column for food and nutrients. The filtered water then exits through a common excurrent siphon between the individual zooids (Washington Dept of Fish and Wildlife). Since tunicates feed by filtering food from the water flowing around the siphons, we reasoned that colonies of B. violaceus in high water flow may produce larger offspring. With higher flow passing by the Image 4 : Map of where colonies were collected at Pillar Point Harbor Figure 1: Larval size is negatively correlated with high and low flow environments of maternal colony (R 2 =.373, p<.01). Larger larvae are found in colonies from areas with lower flow. Figure 2: Large larvae come from colonies growing in lower flow environments, while smaller larvae are produced by colonies across the flow range measured (R 2 =.272, p<.02) Since adult tunicates feed by filtering particles from the water flowing around the siphons, we reasoned that colonies of B. violaceus in high water flow may produce larger offspring due to greater food availability. We tested to see whether there was a relationship between larval size and water motion in low and high flow environments. We collected colonies from Pillar Point Harbor in Half Moon Bay, CA from random locations, conducted flow measurements, and measured larvae released naturally in the lab from each colony. Contrary to our expectation, results showed a statistically significant inverse correlation between larval size and flow rate. Bigger larvae were produced by colonies located in slower flows, while smaller larvae were found in colonies from across the full spectrum of flow rates measured. Perhaps, low flow environments are actually high food environments allowing these colonies to have a dual reproductive strategy where they produce both large and small larvae as a bet-hedging strategy. Whereas, high flow, lower food environments may constrain reproductive options. Data indicates that larger larvae were produced from colonies in slower flow, whereas smaller larvae were produced from colonies across the flow spectrum. A possible reason why colonies in slower flow had both smaller larvae and larger larvae could be that this species has a dual reproductive strategy, when feeding conditions are advantageous. Contrary to our expectation of greater food availability in higher flows, perhaps feeding is actually more efficient at the slower flows found in this study. Larger offspring may have higher fitness, but producing smaller offspring hedges against uncertain success. This possible variation of offspring within broods can reflect a strategy of adaptation for dealing with the environment which can be variable depending on where the maternal colony is located (2). It could very well be due to an adaptive response by the maternal colony to the environmental conditions, which in this case is flow, which their offspring will experience (1). Based on preliminary data in this study, there is no evidence to show that single colonies produce both small and large larvae. The size of the colony could also possibly play a role, as larger mothers may be able to brood larger larvae. (3) In lower flow areas it may be that colonies are easily able to retrieve nutrients to supplement their broods, while the higher flows in this study may not be as efficient. Research on the dynamics of particle capture by internal filter feeding colonial ascidians is needed. "This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation.“ Image 5 : Life Savers TM in the water user to check water flow rates in the maternal environment Image 6 : Comparing dissolution rates of Life Savers TM Image 7 : Measurements used to calculate larval heads, where A= major radius of the ellipse and B=the minor radius of the ellipse. A B Image 1 : Tunicate at 200x magnification. Marker A is indicating a brooding larvae A Image 2 (left): Colony with a larva swimming in the water. Image 3 (right): Larva at 400x