Spatio-temporal variations in larval digenean assemblages ofHeleobia parchappii(Mollusca: Cochliopidae) inhabiting four human-impacted streams

Abstract

In the last years, a growing number of studies have focused on the search for biological indicators of human impact in freshwater environments. Given their susceptibility to different types of impact, larval digeneans have been considered as useful tools for the study of temporal variations in parasite communities. However, few studies have been carried out in lotic environments. For that reason, the spatio-temporal variations of the larval digenean assemblages parasitizing the gastropod Heleobia parchappii were analysed in four human-impacted streams, located on the coast of Argentina. In total, 4800 specimens of H. parchappii were collected seasonally, and 12 digenean species belonging to eight families were registered. Three of the streams showed similar species presence but, during spring and summer, the streams located within the city presented lower species presence than the streams located in the urban periphery. By contrast, the spatial prevalence values evidenced a higher variation between the environments. Streams located in the urban periphery showed higher prevalence values throughout the year, compared to those calculated for streams located within the city. The spatio-temporal variations of larval digenean assemblages parasitizing H. parchappii seem to be mainly influenced by the diversity and vagility of definitive hosts, the types of digenean life cycles and habitat characteristics. However, environmental disturbances derived from anthropogenic activities are highlighted as the probable main factors that may affect the composition and dynamic of these parasite assemblages.

Diversity and dynamics in larval digenean assemblages parasitizingHeleobia parchappiiin a freshwater shallow lake from the Southeastern Pampa plain, Argentina

“…Also, this lake is located in the vicinity of Mar Chiquita Coastal Lagoon Basin, a biosphere reserve under the UNESCO Man and Biosphere Program since 1996. The low human disturbance in this environment may explain the larger diversity registered in this lake, in contrast with the other environments already studied in the region (Merlo et al, 2019;Parietti et al, 2020).…”

“…1 (Notocotylidae), M. simillimus (Microphallidae) and Levinseniella cruzi (Microphallidae) were registered in all seasons and all sites, the two first have a two-host life cycle, and the third a typically three-host life cycle. Also, these three species were recorded in the same host in other freshwater ecosystems (Martorelli, 1986a(Martorelli, , 1986b(Martorelli, , 1986cMerlo et al, 2019;Parietti et al, 2020), in other molluscs species of the same genus, as H. conexa in Mar Chiquita lagoon (Martorelli, 1986a(Martorelli, , 1986b(Martorelli, , 1986cEtchegoin andMartorelli, 1998, Merlo andEtchegoin, 2011) and H. australis in estuarial habitats (Alda and Martorelli, 2014;Parietti et al, 2013), and even in other mollusc genus, as B. peregrina in a temporary pond near to Mar Chiquita lagoon (Parietti et al, 2021). In Notocotylidae sp.…”

“…The larval digenean assemblage of H. parchappii has been studied in other shallow lakes, urban and peri-urban streams in Argentina, and 12-13 digenean species were found. The low specific richness found in those environments was mainly associated with heavily human-impact ecosystems due to recreation and agriculture (Merlo et al, 2019;Parietti et al, 2020). The shallow lake studied in this work is a very unstable environment, but with a lower human impact over it.…”

“…In the last 20 years, much progress has been made to increase the knowledge of the diversity of digeneans in the lotic and lentic environments of Argentina, as well as their temporal and spatial dynamics in several mollusc hosts (Flores et al, 2010(Flores et al, , 2015Merlo and Etchegoin, 2011;Fernández et al, 2013;Parietti et al, 2013Parietti et al, , 2020Parietti et al, , 2021Merlo et al, 2019;among others). However, due to the large number of water bodies that cover the Argentine territory, we are still far away from having adequate knowledge of the diversity of digeneans and the factors that determine their distribution that allows us to perform robust macroecological and biogeographical studies.…”