Freshwater ostracods (Crustacea: Ostracoda) of the plateaus of the northern Western Ghats, India
Yugandhar Satish Shinde 1, Reginald Victor 2 & Kalpana Pai 3
1,3 Department of Zoology, University of Pune, Pune, Maharashtra 411007, India
1 Department of Zoology, Modern College, Shivajinagar, Pune, Maharashtra 411005, India
2 Department of Biology, Sultan Qaboos University, Sultanate of Oman, Muscat, Oman
1 email@example.com (corresponding author), 2 firstname.lastname@example.org, 3 email@example.com
Ostracoda, a class of Crustacea, can be found in all types of aquatic habitats. They are also known as “seed-shrimps” because of their tiny seed like appearance that differentiates them from much larger “clam shrimps”, Conchostraca with concentric rings on valves (Smith 2001).
Temporary waters are unique habitats in comparison to permanent lotic and lentic habitats and are characterised by the cyclic process of drying and filling (Williams 2006). Their biodiversity is remarkably high consisting of species with adaptations to withstand draught or frozen periods. Indian temporary freshwater habitats in particular have a high ostracod biodiversity (Deb 1972 & 1983; Victor & Michael 1975; Battish 1977; 1978 & 1981; Victor & Fernando 1979; George et al. 1993; Shinde 2012).
The northern Western Ghats consists of flat table-topped hills which are the result of collective geological events involving basalt flows (Watve 2013). Such flattable tops are popularly called ‘rocky outcrops’. This part of the Western Ghats has a dry period of about eight months and an approximately four-month period of monsoon with heavy rains (Dahanukar et al. 2004) during which a large number of temporary water bodies are formed. These habitats host an impressive array of freshwater micro- and macroinvertebrate fauna including ostracods.
Studies on Indian Ostracoda commenced in 1859 and from then till now 208 species of non-marine Ostracoda, both extinct and extant have been reported (Battish 2000). When compared to states like Tamil Nadu, Kerala and Punjab, studies on Ostracoda in Maharashtra State are very scarce. Before the study by Shinde (2012), the only investigations on ostracods were those of Deb (1972, 1973). This review specifically reports on the ostracods of the northern Western Ghats including the ‘rocky outcrop’.
Methods: Sampling was carried out in eight different sites present on hilltops including six forts of the northern Western Ghats from 2008–2012 (Fig. 1; Table 1). Three sites were on ‘ferricretes’ type of outcrops and five sites were on ‘basaltic mesa’ where there are hill forts (Watve 2013) (Images 1 a,b). Mapping of the sites was carried out using DIVA-GIS 7.5, while geographic data were obtained using handheld GPS and Google Earth (http://earth.google.com).
In our study, qualitative samples for ostracods were collected using a circular plastic frame hand net (diameter = 15cm, mesh size 150μm). The net was swept through disturbed sediments of shallow water bodies and through the aquatic vegetation. Samples were collected in 100ml plastic containers and fixed in the field using 5% formaldehyde. In the laboratory, samples were washed under tap water using the same net and preserved in 70% ethanol. Ostracods were separated under a stereo binocular microscope (Magnus MS24) using micropipettes. Soft part dissections and mounting of dissected appendages were done on a slide containing a drop of polyvinyl lactophenol tinted with lignin pink. Detailed observations were made under a compound microscope (Olympus BX40). Valve details were studied under a JEOL Analytical Scanning Electron Microscope. The ostracod genera were preliminarily identified using Victor & Fernando (1981). For further confirmation of genus and species identifications we consulted the original papers describing the taxon for the first time and as many redescriptions of the same taxa by other authors. In all, we consulted around 50 publications and citing them all here is beyond the scope of this Note.
Results and Discussion: Our study carried out from 2009–2012 revealed the presence of 17 species of ostracods in various localities (Tables 1, 2). Deb’s (1972, 1983) collections were mainly from the Ajinkyatara Fort area and the Tableland of Panchgani; her work reported only six species.
Ostracods from ferricretes were reported by Deb (1972) for the first time with the description of a new species Stenocypris krishnakantai; later on this species (Image 2a) was assigned to the genus Chrissia (Victor & Fernando 1979). We found this species at the type locality, Ajinkyatara Fort. Other taxa reported by Deb (1983) from the Tableland of Panchgani were Cypricercus indrani, Cypris elongata, Eucypris compressa, E. indica as new species and an unknown Sclerocypris sp. All these taxa were also found during our study indicating the integrity of habitat conditions favouring their existence.
We also found a species belonging to the genus Humphcypris from only one representative sample collected from Chalkewadi Plateau. This is the first report of this genus from Maharashtra and this species, pending further study could probably be new to science.
Many of the species described by Deb (1972, 1983), such as C. indrani, E. compressa, E.indica, C. elongata, need taxonomic revision. The descriptions and diagrams provided by the author are no longer adequate to confirm their generic identities and the type specimens. Though allegedly deposited in the Zoological Survey of India, Kolkata they are not accessible for study. However, based on the original descriptions and diagrams and by comparing the material collected by us in the type localities, it is possible to assign these species to other genera. Species of the genera Eucypris and Cypricercus should be assigned to one of the genera in the Strandesia group; some species may even require the establishment of a new genus in the subfamily Cypricercinae (Battish 2000; Shinde 2012).
Of the 17 species of ostracods recorded here, 13 were found in the pools on the basaltic mesa. Plesiocypridopsis dispar (Hartmann, 1964) (Image 2b) was found almost on every plateau made up of basaltic mesa. Chrissia biswasi (Deb, 1972) is the largest (giant ostracod) species found on basaltic mesa. Some of the species which were found commonly on basaltic mesa were not found on ferricretes. Sclerocypris sp. is a large taxon found only in the pools formed on ferricretes rock while P. dispar is only known from basaltic mesa.
Stenocypris sohni described by Deb (1983) was collected in a water body from Khopoli (Maharashtra); a very similar species was found in Visapur and Koraigad water pools on the basaltic mesas (Table 2). We are tentatively referring to this species as Stenocypris cf. sohni Deb, 1983, pending further study.
The number of species currently known from the northern Western Ghats is likely to be an underestimation. An intensive sampling effort, probably as a part of a larger program for studying freshwater biodiversity is likely to bring more taxa to light. Our study on ostracods indicates that the freshwater habitats on the rocky plateaus of the northern Western Ghats are unique, holding a treasure of diversity, yet to be discovered. Most of these habitats are temporary, characterized by seasonal drying and filling cycles in a regular frequency and their residents are adapted to these environmental conditions with some of them even requiring the drought as a prerequisite for subsequent resurgence (Williams 2006). Even the ephemeral habitats of unpredictable reoccurrence formed during the monsoons are microcosms of interest to investigate phenomena such as dispersal and colonization of micro-and macroinvertebrates. All these habitats are under severe threat from anthropogenic activities and their conservation requires attention.
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