Abstract
Winning the war against invasive species requires early detection of invasions. Compared to terrestrial invaders, aquatic species often thrive undetected under water and do not garner notice until too late for early action. However, fortunately for managers, apple snails (Family Ampullariidae, Genus Pomacea) provide their own conspicuous sign of invasion in the form of vibrantly colored egg clutches. Managers can potentially use egg clutches laid in the riparian zone as a means of early detection and species identification. To facilitate such efforts, we quantified differences in characteristics (length, width, depth, mass, egg number) of field-laid clutches for the two most common invasive species of apple snail, P. canaliculata and P. maculata, in native and non-native populations. Pomacea canaliculata native and non-native populations differed noticeably only in width. Native P. maculata clutches possessed significantly greater width, mass and eggs numbers compared with native P. canaliculata. Non-native P. maculata clutches significantly exceeded all other populations in all measured characteristics. Consequently, these traits may successfully distinguish between species. Fecundity data also allowed us to develop models that accurately estimated the number of eggs per clutch for each species based on clutch dimensions. We tested one, two and three dimensional models of clutches, including rendering a clutch as either a complete ellipsoid or an ellipsoid intersected by a cylinder to represent the oviposition site. Model comparisons found the product of length and depth, with a different function for each population, best predicted egg number for both species. Comparisons of egg number to clutch volume and mass implied non-native P. canaliculata may be food limited, while non-native P. maculata appeared to produce such enormous clutches by having access to greater nutrients than the native population. With these new tools, researchers and managers can quickly identify, quantify and begin eradication of new non-native apple snail populations.
Highlights
Most invasions of non-native species fail [1]
Non-native P. maculata clutches significantly exceeded all other populations in all measured characteristics (Figure 2)
When exploring our ability to predict eggs per clutch (EPC) based on clutch dimensions, we found the product of clutch length and depth best predicted EPC for both snail species (ΔAIC > 50; Table 2; Figure 3)
Summary
Most invasions of non-native species fail [1]. Early detection of non-native, invasive species (NIS) holds the best potential to avoid the considerable economic and ecological costs that often result from successful establishment [1,3,4,5]. Applications of molecular biology use environmental DNA (eDNA) to test for the presence of unwanted NIS [6,7,8]. While these methods prove successful for several species, the procedures take considerable time and expertise to develop and remain costly to execute. Such an investment will pay off for rare or cryptic species that leave few other signs of invasion [7]
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