M.A. BarnesM.A. Barnes11,, B.B. BolandB.B. Boland11, M. Meerhoff, M. Meerhoff22, C. Folsaba, C. Folsaba22, N. Mazzeo, N. Mazzeo22, and R.L. Burks, and R.L. Burks11

That’s the way the egg hatches:That’s the way the egg hatches:Determining patterns in egg size, clutch variability, and hatchling Determining patterns in egg size, clutch variability, and hatchling emergence in an exotic versus native population of applesnailsemergence in an exotic versus native population of applesnails

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Establishment of a reproductively viable population announces invasion success. Although adults are cryptic, the appearance of bright pink egg clutches provides the first undeniable sign of the presence of applesnails (Pomacea). Our study compares and contrasts egg and hatchling life history traits between an exotic (Texas) and a native (Uruguay) population of Pomacea. Exotic Pomacea deposit eggs on any hard surface. Uruguayan Pomacea preferentially deposited eggs on Schoenoplectus californicus near the shoreline. Native Pomacea laid fewer eggs per clutch than exotic populations. Furthermore, a much stronger relationship existed between clutch mass and egg number (R2 = 0.88) in Uruguay, suggesting higher clutch size variability in the exotic population. Most eggs from Uruguay hatched successfully, while Texas clutch hatching efficiency varied more considerably. For Texas snails, we did not find any relationship between hatching date and hatchling size, instead clearly determining a threshold hatching size of 1.1-mm. In Uruguay, hatchlings emerged significantly larger, 1.9-mm on average. Thus, we found considerable differences between native and exotic species of Pomacea. Additionally, we demonstrated that Texas hatchlings of similar size exhibit different growth patterns when presented with fish cues or grown in salt water. Overall, our work may lend insight into how reproduction and early survival facilitates invasion success.

1001 E. University Ave.Georgetown, TX 78626

Departamento de EcologíaFacultad de CienciasUniversidad de la RepublicaMontevideo 11400, Uruguay

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(mbarnes3@nd.edu) (burksr@southwestern.edu)

INTRODUCTIONINTRODUCTION

ABSTRACTABSTRACT RESULTSRESULTS

DISCUSSIONDISCUSSION

•Texas clutches average 8x larger Texas clutches average 8x larger than Uruguayan clutches (Fig 1A), than Uruguayan clutches (Fig 1A), but Uruguayan eggs measure 50% but Uruguayan eggs measure 50% larger than Texas eggs (Fig 1B).larger than Texas eggs (Fig 1B).

•In Uruguay, a strong predictive In Uruguay, a strong predictive relationship exists between clutch relationship exists between clutch mass and egg number (Fig. 2A).mass and egg number (Fig. 2A).

•The relationship strengthens when The relationship strengthens when considering wet and dry clutches considering wet and dry clutches separately (Figs. 2B and 2C).separately (Figs. 2B and 2C).

•A poor (RA poor (R22 = 0.148) overall = 0.148) overall predictive relationship exists predictive relationship exists between Texas clutch mass and between Texas clutch mass and egg number.egg number.

•A strong predictive relationship A strong predictive relationship exists in April but deteriorates as exists in April but deteriorates as the reproductive season progresses the reproductive season progresses (Figs. 3A-3C).(Figs. 3A-3C).

•A predictive relationship does not A predictive relationship does not exist between clutch weight and egg exist between clutch weight and egg size in either the Texas (Fig. 4A) or size in either the Texas (Fig. 4A) or Uruguayan (Fig. 4B) populations.Uruguayan (Fig. 4B) populations.

•Though Texas hatchlings emerged Though Texas hatchlings emerged similar in size, the presence of a fish similar in size, the presence of a fish predator cue in fresh water predator cue in fresh water increased growth (Fig. 8A).increased growth (Fig. 8A).

•Salt water decreased growth Salt water decreased growth independent of predator cue independent of predator cue (Fig. 8B).(Fig. 8B).

•Uruguayan clutches demonstrated Uruguayan clutches demonstrated higher hatching efficiency and less higher hatching efficiency and less variation than Texas clutches variation than Texas clutches (Fig. 7A).(Fig. 7A).

•Hatchlings in Texas emerged with a Hatchlings in Texas emerged with a noticeably uniform operculum width. noticeably uniform operculum width. Also uniform, Uruguay hatchlings Also uniform, Uruguay hatchlings emerged larger on average (Fig. 7B).emerged larger on average (Fig. 7B).

•Uruguayan applesnails deposited Uruguayan applesnails deposited eggs an average of 2.5-cm above the eggs an average of 2.5-cm above the water surface, though considerable water surface, though considerable variation existed. Native applesnails variation existed. Native applesnails deposited eggs significantly closer deposited eggs significantly closer to the water surface (1.8-cm high), to the water surface (1.8-cm high), with less variation (Fig. 6).with less variation (Fig. 6).

•Texas applesnails deposit eggs on Texas applesnails deposit eggs on any hard emergent substrate.any hard emergent substrate.•Uruguayan applesnails tend to Uruguayan applesnails tend to oviposit on oviposit on Schoenoplectus Schoenoplectus californicus californicus (Fig. 5A) located near (Fig. 5A) located near the shore (i.e. within 3.0-m, Fig. 5B).the shore (i.e. within 3.0-m, Fig. 5B).

•Enhanced fecundity represents one of the most noticeable and quantifiable life history traits that routinely contributes to invasive success (Sakai et al. 2001).

•An invasive snail, Pomacea canaliculata, has spread to new systems around the world through aquaculture and trade (Carlsson et al. 2004). Native to South America, P. canaliculata, commonly referred to as channeled applesnails, has gained considerable attention since its recent invasion into the United States (Howells et al. 2006).

•One population of exotic applesnails occurs in Armand Bayou, near Houston, Texas. Initially identified as P. canaliculata based on morphological traits, recent investigations have identified it as P. insularum (R. Cowie and K. Hayes, personal communication).

•Female snails deposit eggs in clutches (Photos A, B), ovipositing multiple egg clutches annually on plants and other structures above the waterline to avoid predators (Estebenet and Martín 2002). New hatchlings (Photos C, D) fall into the water below.

•Little information currently exists on any species of Pomacea, especially P. insularum. In particular, few studies have compared fecundity traits of exotic and native Pomacea populations.

•Although closely related, exotic populations of P. insularum and native populations of P. canaliculata possess strikingly different life history traits (see Table to the right).

•Limited literature on applesnails exists. Most reports on fecundity resemble our Uruguayan findings, suggesting that the exotic Texas population is unique enough to warrant further investigation.

•Differences in egg size and hatching efficiency in the two populations might serve as evidence of ecological bet hedging by the exotic population in Texas. Indeed, 25% hatching efficiency of a 3000-egg clutch yields many offspring (750) and 75% would release even more propagules into the environment (2250).

•The decreasing predictive relationship between egg number and clutch weight at the end of the reproductive season in Texas may represent 2 extremes. Highly fecund snails may exhaust their resources by September. Alternatively, some snails may save resources to maximize fitness at the end of the season.

•Differences in oviposition support the idea that native applesnails experience limitation by predation whereas snails in Texas do not.

•Our growth data confirms that applesnails are more likely to thrive in freshwater systems.

•Overall, high fecundity of invasive applesnails and variable life history traits suggest a need for more comparative research of native and exotic applesnail populations.

METHODSMETHODS

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Thanks to undergraduate students Jessie Carrier, Colin Kyle, Amber Hoerauf, Sarah Hensley, Scott

Manusov, and Ryan Ubias who all helped with data collection for this project. Also, thanks to Becca

Marfurt (pictured below) for introducing the lab to the world of applesnails.

Texas Parks and Wildlife, our colleagues at Armand Bayou Nature Center, and our colleagues in la

Facultad de Ciencias de La Universidad de Republica in Uruguay helped with applesnail

collection. Funding for this project was provided by Southwestern University and the Biology Summer

Research Program.

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS

•Carlsson, N.O.L., C. Brönmark, and L. Hansson. 2004. Invading herbivory: the golden apple snail alters ecosystem functioning in Asian wetlands. Ecology 85: 1575-1580.

•Estebenet, A. L. and P. R. Martín. 2002. Pomacea canaliculata (Gastropoda: Ampullariidae): Life-history Traits and their Plasticity. Biocell 26: 83-89.

•Howells, R.G, L. E. Burlakova, A. Y. Karatayev, R K. Marfurt, and R L. Burks. 2006. Native and introduced Ampullaridae in North America: History, Status and Ecology. Book chapter in Golden Apple Snail, R. C. Joshi (editor).

•Sakai, A.K., F.W. Allendorf, J.S. Holt, D.M. Lodge, J. Molofsky, K.A. With, S. Baughman, R.J. Cabin, J.E. Cohen, N.C. Ellstrand, D.E. McCauley, P. O’Neil, I.M. Parker, J.N. Thompson, and S.G. Weller. 2001. The population biology of invasive species. Annual Review of Ecological Systems. 32: 305-332.

WORKS CITEDWORKS CITED