Evaluating the status and identity of ”︁Melania”jugicostisHanley & Theobald, 1876 - an enigmatic thiarid gastropod in Thailand (Caenogastropoda, Cerithioidea)

Abstract

Given the importance in tropical diseases caused by food-borne trematodes infecting humans, it is essential to understand the taxonomy and distribution of its first intermediate hosts, which are in Southeast Asia freshwater Cerithioidean gastropods such as the widely distributed Melanoides tuberculata. Next to the occurrence of this type species in Thailand there is a second, congeneric thiarid neglected and, therefore, remained enigmatic to date. Described as "Melania" jugicostis by Hanley & Theobald (1876) it was originally reported and only known from the type locality, "Tenasserim River" (i.e. Tanintharyi River) of Southeast Burma (today Myanmar), but later recorded also for Thailand based on shell morphology. In evaluating the status of this taxon, we here report on its geographical occurrence ranging from the Kanchanaburi Province to the southern most provinces in Thailand (anticipating that it might extend further south on the Malay Peninsula and even into Sumatra). Based on the more detailed study of material from five locations we provide conchological and anatomical evidence for the comparison with other thiarids, in particular the closely related Melanoides tuberculata and Pseudoplotia scabra. Interestingly, with respect to its reproductive mode we found in one population of M. jugicostis from Erawan waterfall, Kanchanaburi Province, the lack of any sign of a subhaemocoelic brood pouch otherwise typical for viviparous thiarids. This is discussed in context of climatic factors (e.g. seasonal changing precipitation), but anticipated to be caused by an unusually high infection rate of human intestinal trematodes. These parasites having infected 98 of 222 snails studied, resulting in an infection rate of 44.14 %, are assumed to be responsible for the sterility of the females in this particular population, in comparison with considerable lower infection rates in two other populations, viz. Raman waterfall (1.74 % in 5/288) and Klong Chalung (9.46 % in 7/74), respectively.

Trematodes obtained from the thiarid freshwater snail Melanoides tuberculata (Müller, 1774) as vector of human infections in Thailand

“…The positions of collection sites were recorded by GPS (Garmin PLUS III, Taiwan). The localities of the relevant samples were mapped on a dot-by-dot basis to a digitally reduced version of the drainage pattern map of Thailand, as developed in Dechruksa et al (2013). This map was created using a Reliefkarte on the basis of the Global 30-Arc-Second Elevation Data (GTOPO30) from the U.S. Geological Survey and a river map from the Map/server Aquarius Geomar, and then compiled using Adobe Photoshop CS3 and Adobe Illustrator.…”

Molecular phylogeography and reproductive biology of the freshwater snail Tarebia granifera in Thailand and Timor (Cerithioidea, Thiaridae): morphological disparity versus genetic diversity

“…This is in contrast to a pronounced correlation as to reproductive biology in Thiaridae from Australia (Glaubrecht et al 2009), where all ovo-viviparous taxa that release veligers paradoxically exhibit very restricted distributional ranges in the Jardinian biogeographical region only. It is also in contrast to differences in the Thai thiarid Melanoides jugicostis (see Dechruksa et al 2013), that was found to lack viviparous populations at least in some geographical regions and during some time of the year.…”

“…The development of an accurate and rapid method for the detection of males in aphallic thiarids, in order to evaluate the frequency of parthenogenesis in individual populations and species or higher-level taxa, respectively, remain an essential desideratum in biosystematics research on these snails. In addition, it remains to be analysed thoroughly whether and in how far there is a correlation of partially or completely parthenogenetic populations with parasite infections by digenic trematodes, for example, in the thiarids Melanoides tuberculata (see Krailas et al 2011Krailas et al , 2012Krailas et al , 2014, in M. jugicostis (see Dechruksa et al 2013) and Tarebia granifera (Veeravechsukij et al 2018).…”

“…Accordingly, as is typical in thiarids, a plethora of species names has been applied, irrespective of the fact that their known polymorphic phenotype, in combination with their viviparity and mainly parthenogenetic reproduction, renders unequivocal species delimitation quite problematic; see for detailed discussion e.g. Glaubrecht 2009, 2011, Maaß and Glaubrecht 2012, Dechruksa et al 2013.…”

A glimpse in the dark? A first phylogenetic approach in a widespread freshwater snail from tropical Asia and northern Australia (Cerithioidea, Thiaridae)

“…Glaubrecht et al (2009) and Maaß and Glaubrecht (2012) surveyed the thiarid fauna of Australia. Dechruska et al (2013) evaluated the status and identity of the nominal taxon Melania jugicostis Hanley & Theobald, 1876 from the Southeast Asian mainland, and Veeravechsukij et al (2018aVeeravechsukij et al ( , 2018b investigated the phylogeography and reproductive biology of T. granifera and its trematode parasites. However, many other named taxa have been rarely studied and, thus, remain enigmatic and even pure nomenclatorial "ghosts" with highly questionable status as evolutionary relevant entities, which hampers further insights into the systematics, biogeography, and evolution of these freshwater gastropods otherwise under scrutiny, e.g., in speciation and/ or radiation studies.…”