Count Your Eggs Before They Invade: Identifying and Quantifying Egg Clutches of Two Invasive Apple Snail Species (Pomacea)

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.

Insights from an Integrated View of the Biology of Apple Snails (Caenogastropoda: Ampullariidae)

“…Most Pomacea species lay them well above the water line on stems of emergent plants, trunks of riparian trees, rocks and other hard structures, such as bridge supports, and Pila deposit them on vegetation at the water line or directly on the soil surface at the margin of the water (Hurdle, 1973;Hanning, 1979;Turner, 1996;Cowie, 2002;Hayes et al, 2009a;Burks et al, 2010;Kyle et al, 2013). Some Pila species dig a depression in the mud near the shore in which to deposit their eggs (Bahl, 1928;Cowie, 2002).…”

“…Oviposition may last up to several hours and occurs with the right side of the foot forming a longitudinal groove that conducts the eggs from the vagina to the substrate at intervals that depend on species (Bahl, 1928;Bachman, 1960;Andrews, 1964;Hanning, 1979;Albrecht et al, 1996;Estebenet & Martín, 2003). Among species, the average number of eggs per egg mass is inversely related to egg size (Turner & McCabe, 1990;Cowie, 2002;Barnes et al, 2008;Burks et al, 2010;Kyle et al, 2013).…”

Tolerance of embryos and hatchlings of the invasive apple snail Pomacea maculata to estuarine conditions

“…The low hatching efficiency demonstrated here is likely due to artificial light and temperature conditions present indoors, yet conditions were consistent among treatments in this experiment and thus comparable. Moreover, Barnes et al (2008) found considerable variability between egg counts and clutch mass, and Kyle et al (2013) found differences between invaded and native range of P. maculata. Our regression from the Mobile, Alabama, population indicates more predictability in the relationship, and future work should be directed at why this discrepancy exists both within and between separate populations.…”

The ecophysiology of apple snails in rice: implications for crop management and policy

“…The lifetime fecundity of P. canaliculata and other apple snails in rice has been difficult to determine because of their normally long life and possible changes to life history under laboratory conditions (where life‐history observations are normally conducted). Clutch sizes are large, that is, 200 ( P. canaliculata, P. dolioides ) to >2000 eggs ( P. maculata ) (Cowie, ; Kyle et al ., ; Horgan et al ., ). However, snails may have significantly smaller (e.g.…”