Interaction between the Intermediate Host of Schistosomiasis in Brazil Biomphalaria glabrata (Planorbidae) and a Possible Competitor Melanoides tuberculata (Thiaridae): I. Laboratory Experiments

Abstract

(WHO 1984, Madsen 1990, Sturrock 1995, Pointier & Giboda 1999. In the West Indies, the thiarid Melanoides tuberculata was effective in the elimination or reduction of populations of Biomphalaria glabrata, the intermediate host in the cycle of schistosomiasis , 1991a, Pointier & McCullough 1989, Pointier & Guyard 1992, Pointier 1993, Schlegel et al. 1997. However, in Venezuela M. tuberculata was introduced in 20 sites, but only in three sites was Biomphalaria spp. eliminated or effectively reduced (Pointier et al. 1991c). In Brazil, the first occurence of M. tuberculata was reported in 1967, in Santos, State of São Paulo. After that, this snail has spread to other localities, probably as a result of successive accidental introductions associated with fish farms (Vaz et al. 1986). However, there are few reports of interaction between M. tuberculata and species of the genus Biomphalaria in Brazil. glabrata reached a larger size and produced more cercaria of S. mansoni (Moné 1991). These results point to the dangers of species introductions for biological control based on poor knowledge and weak assumptions of species interactions. The effectiveness of M. tuberculata for biological control of B. glabrata in a specific environment can be evaluated only when the ecology of these species and the nature of their interactions are understood.Here, our objectives were to test two hypotheses: that M. tuberculata has a negative effect on the growth and demography of B. glabrata (H1), and that a substance liberated by M. tuberculata causes this negative effect (H2). The second hypothesis was proposed previously for Thiara granifera, another thiarid (Prentice 1983, Gomez et al. 1990, Perez et al. 1991. Two laboratory experiments were performed to test these hypotheses. MATERIALS AND METHODSIndividuals of M. tuberculata and B. glabrata were collected in streams of two valleys in the municipality of Sumidouro, RJ, Brazil (22 o 02'59"S, 42 o 40'29"W). In laboratory, these individuals were raised in 74 x 237 x 330 mm plastic containers with 2 l of dechlorinated tap water. Dehydrated lettuce and rodent food pellets (3-4 mm large) were provided ad libitum, and temperature varied between 22 and 27 o C during the study. Containers were checked at least every two days to remove dead individuals, to guarantee ad libitum food, and that rodent pellets stayed on the bottom. The water was changed every fortnight to avoid any crowding effect, when the number of egg masses, embryos, young and adults was counted. These

Malacological assessment and natural infestation of Biomphalaria straminea (Dunker, 1848) by Schistosoma mansoni (Sambon, 1907) and Chaetogaster limnaei (K. von Baer, 1827) in an urban eutrophic watershed

“…Barbosa, personal communication). This fact probably favors the dominance of M. tuberculatus, which is an alien species with high adaptation capacity and also an efficient competitor (Guimarães et al, 2001;Giovanelli et al, 2002). Previous studies suggest the role of M. tuberculatus in diminishing the population of Biomphalaria spp., the invertebrate host of S. mansoni, on Santa Lucia Island (West Indies) and in Venezuela (Pointier, 1993;Pointier et al, 1994).…”

“…A promising new path for biological control of the snail intermediate hosts of human schistosomiasis is the introduction of other snail species, such as Melanoides tuberculatus (Pointier, 2001;Giovanelli et al, 2002), that act only as natural competitors, and whose competitive pressure on Biomphalaria spp. can lead to the latter's extinction.…”

Ecological assessment of a southeastern Brazil reservoir

“…One of the non-native mollusks recorded near the dam, Melanoides tuberculatus (Gastropoda: Thiaridae), is native to East Africa, Southeast Asia, China, and the Indo-Pacific Islands and is broadly distributed in Brazil (Silva & Barros 2011). Its introduction may be related to the trade of ornamental plants and fish (Fernandez et al 2003) and to control Biomphalaria glabrata (Say 1818), the intermediate host of Schistosoma mansoni, as it is a possible competitor of the snail (Giovanelli et al 2002). Another non-native mollusk collected, the bivalve Corbicula fluminea, also has a broad distribution in Brazil (Silva & Barros 2011).…”

Apparent competition through facilitation between Melanoides tuberculata and Biomphalaria glabrata and the control of schistosomiasis

“…Densities declined abruptly after this period, reaching its lowest densities until September 1999. In a laboratory study of M. tuberculata and B. glabrata collected in Sumidouro, the fecundity of B. glabrata increased when raised with M. tuberculata (Giovanelli et al 2002). This apparent contradiction suggests the occurrence of ACF.…”

“…At least in four studies of interspecific competition in freshwater snails, the inferior competitor initially increased in abundance when raised with the superior competition (Santos et al 1989, Gomez et al 1990, Stryker et al 1991, Giovanelli et al 2002. ACF is more likely in combinations of organisms and environment producing high intrinsic rates of natural increase.…”