Pink eggs and snails: field oviposition patterns of an invasive snail, Pomacea insularum, indicate a preference for an invasive macrophyte

Abstract

Oviposition of non-calcareous or thinly shelled eggs represents an important life stage of many insects, amphibians, and several gastropods. A recently identified invasive species of apple snail, Pomacea insularum, exhibits alarming invasive characteristics of high reproductive rates and generalist consumption patterns. This snail takes the opposite approach to egg laying compared to most aquatic insects as adult snails crawl out of the water to place clutches on emergent, or terrestrial, substrates. As fecundity best indicates invasive potential for mollusks, control or management efforts need to understand reproductive behavior in P. insularum to predict, and hopefully impede, its spread throughout the Gulf Coast of the United States. Specific characteristics of wetlands and shallow lakes may facilitate the invasion process of P. insularum by providing females with conditions that permit successful oviposition. In order to investigate this possibility, we studied P. insularum oviposition behavior in an invasive population at two times during the reproductive season in Texas, USA. Based on a subsequent survey (August 2009), plants comprised 78% of the available habitat. Wild taro (Colocasia esculenta) and alligator weed (Alternanthera philoxeroides) represented 48 and 43% of that proportion, respectively. During 2008-2009, no new concrete or metal structures appeared in our sampling reach and consistent amounts of plant stands and woody debris remained dominant. Given this distribution, P. insularum laid disproportionately more clutches on wild taro compared to its availability and less on alligator weed and bulrush (Schoenoplectus californicus) than expected. Owing to limited metal and concrete substrates, we found a higher proportion of clutches on these artificial substrates than expected in both May and August 2008. However, artificial substrates comprised less than 2% of available substrates in the bayou. Our results suggest that wetlands and shallow lakes surrounded by large emergent macrophytes, particularly wild taro, likely provide ideal oviposition sites for P. insularum, promote egg supply, and possibly facilitate invasion into new aquatic ecosystems.

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

“…The eggs of ampullariids are fertilized internally and develop externally in calcareous or non-calcareous eggs, deposited in clutches or in gelatinous masses respectively, on submerged vegetation, rocks or other firm substrates (Hayes et al, 2009aBurks et al, 2010;Tiecher et al, 2014). The eggs of some species contain pigmented proteins collectively referred to as perivitellins, the colors of which range from white to vivid pink, orange and green, which play diverse functions in the developing embryo (see Egg Laying under Reproductive Behavior and Egg Proteins, for details; Heras et al, 2007;Dreon et al, 2008Dreon et al, , 2013Hayes et al, 2009a).…”

Repair process and enzymatic activity associated with induction of shell regeneration in the invasive speciesPomacea canaliculata

“…Harper et al 2012). The spread and increase of P. canaliculata in various aquatic environments, especially paddy fields and reservoirs, is facilitated by its high fecundity (Burks et al 2010); but is it also possible that this species' shell repair and regeneration abilities are another factor in its invasive success? In natural environments, the shell repair process frequently takes place after accidental shell breakage, shell boring by epibionts (Marshall and Day 2001;Nollens et al 2002;Huchette et al 2006), or predation by fish.…”

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

“…Because estuaries of the region are productive and diverse ecosystems (Lydeard and Mayden 1995), the threat of P. maculata invasion is of concern given the high aquatic macrophyte diversity and nekton assemblages that these estuaries support Valentine 2011, 2012;Rozas et al 2013). P. maculata deposit masses of eggs above the water surface on emergent vegetation or structures, and as eggs hatch, juvenile snails fall into underlying waters (Horn et al 2008;Burks et al 2010;Kyle et al 2011).…”