Choosing exotic over the familiar taste: habitat-specific preferences of a malacophagous leech for freshwater snails as prey gastropod establishment?

Abstract

The spread of freshwater invasive species through aquarium trade poses a threat to the ecosystem, economy and human health. The availability of the exotic freshwater gastropod mollusc, Planorbarius corneus (Linnaeus, 1758) (Gastropoda: Planorbidae), in pet shops in Kolkata, West Bengal, India, raises concern for its potential establishment as an invasive species. Assuming the role of the native predators as a potential biotic barrier for invasion, observations on the predation pattern of the malacophagous leech, Glossiphonia weberi (Blanchard, 1897) (Clitellata: Glossiphoniidae) against P. corneus was made in single as well as in combination with the native snail Indoplanorbis exustus (Deshayes, 1834) (Gastropoda: Planorbidae). Using varying size classes and densities of P. corneus, the predation potential of G. weberi was estimated after a 24 hour period. In another set of experiments, the predation of G. weberi against the snail P. corneus was observed in the presence of I. exustus under four different habitat conditions. The purpose was to justify - (1) the effect of conspecific and heterospecific conditions of the prey availability and (2) the effect of habitat complexity on the predatory efficacy of G. weberi. The results indicated that G. weberi consumed varied numbers of P. corneus, depending on the size and the densities of the prey and predator. Although the prey heterogeneity and complex habitats caused significant reduction of predation on both of the prey species, G. weberi significantly preferred P. corneus over I. exustus in open (P < 0.0001), macrophyte (P = 0.002) and pebbles and macrophyte containing habitats (P < 0.0001). Apparently, G. weberi preferred the exotic snail P. corneus in presence of alternative prey snail I. exustus, under different habitat conditions. Therefore, G. weberi may act as a significant biotic resistance against the colonization and establishment of P. corneus in the Indian context. However, further studies including the multiple prey and predators are required to ascertain the food web level impact of the exotic snail P. corneus in invaded freshwater ecosystems.

Predation of Glossiphonia weberi (Blanchard, 1897) on the invasive snail Physella acuta (Draparnaud, 1805) in the presence of an alternative prey

“…Following this proposition, we investigated how habitat elements like macrophytes and pebbles influence the predation rate and whether G. weberi showed any preference for P. acuta over G. convexiusculus with the intent if G. weberi can be used as a prospective biological control agent for invasive snail P. acuta. The results of the present study will extend the earlier findings on the ability of G. weberi as predator of exotic snail (Paul et al 2020). The findings will also be useful in promoting the malacophagous leech in the biological control of the freshwater snails, whether invasive or involved in the disease transmission.…”

“…As stated in the "exotic prey naiveté hypothesis", non-native species can suffer higher predation pressure from the native predators than the native prey species (Li et al 2011), which may provide biotic resistance against the establishment of non-native species in newer habitats. The hypothesis can be sustained through the observation that G. weberi preferred an exotic snail, P. corneus, over a native snail, I. exustus, under different complex habitats (Paul et al 2020) and as observed for P. acuta in this experiment. Hence, the novelty of invasive or exotic prey does not seem problematic for G. weberi as it readily consumed and preferred the non-native prey species over alternative indigenous prey.…”

“…Despite the structural complexity and prey heterogeneity resulted in reduced predation on P. acuta in some conditions, in all habitats, predation on P. acuta remained higher than G. convexiusculus, and G. weberi preferred P. acuta over G. convexiusculus (except P habitat). In a similar experiment, G. weberi consumed higher number of an indigenous snail, Indoplanorbis exustus, in the habitat characterized with the presence of pebbles (Paul et al 2020). Perhaps, the movement of the planospiral shelled G. convexiusculus and I. exustus are affected due to the pebbles which may have eased the prey capture by the leeches.…”

“…Aside from insect predators, empirical studies showed that many native leech predators preyed upon a significant number of invading snail species. The leech, G. weberi, was reported as a potential biological control agent against invasive P. acuta and exotic snails such as Planorbarius corneus and Pomacea bridgesii in India (Aditya and Raut 2002a;Aditya and Raut 2005;Paul et al 2020). However, the prey preference of predator is an essential factor for the successful regulation of invasive snails.…”

“…However, the vertebrates are not satisfactory biological control agents of snails as most of them are general predators of snails and do not threaten the prey species until confined with it. The predatory efficiency of shell-invading marsh fly larva (Diptera: Sciomyzidae), water bugs (Hemiptera: Belostomatidae) and glossiphoniid leeches (Hirudinea: Glossiphoniidae) are well documented (Eckblad 1973;Young and Ironmonger 1980;Raut and Nandi 1985;Aditya and Raut 2002a, b;Aditya and Raut 2005;Paul et al 2020). Among the native predators, the leech Glossiphonia weberi (Blanchard, 1897) had been proposed as a potential biological control agent of P. acuta (Aditya and Raut 2002a) as it is common in the ponds, lakes and ditches in India (Ghosh 1998).…”