Biodiversity of Hirudinea, in freshwater low-altitude mountainous environment (Provincia de Buenos Aires), Argentina.

Abstract

Leeches are important benthic members in rivers and streams of low altitude mountain environments and show a high grade of endemic species in the Neotropical Region (Ringuelet, 1944; 1947; 1985; Christoffersen, 2009). As members of food chains they act as predators or as preys. They are intermediate host in life cycles ofDigenea, Cestoda and parasitic Protozoa. Their medicinal use is known, as well as their rol as pollution bioindicator (Sawyer, 1986). On the other hand, there are many contributions to the knowledge of this group, particularly: the discovery of new species Siddall; et al. (2001, 2004), Gullo (2006, 2008); Kutchera et al (2013), the redescription of others in the basis of molecular analysis (Mosser, et al. 2012 a y b; 2013); the contruction of phylogeny (Siddall, et al. 2003, 2005) and the contribution to the global Hirudinea diversity (Sket, 2008). Despite their importance as benthic members, it is not common to include them in the analysis of benthic macroinvertebrates, because of their difficult identification. There is a lack of studies of leech biodiversity in Argentina and no antecedents for low altitude mountain environments are recorded. The heart of the investigation lies in the specific conditions of the area in question, where slightly varying environments provide the proper ecological requirements for a variety of species which are essential for biodiversity conservation. The specimens were collected in seasonal samplings during 2009, 2010 and 2011. The selected sampling locations were: Sauce Grande and Sauce Chico rivers; San Bernardo, El Negro, Rivera and El Divisorio streams. Physical and chemical parameters as temperature, pH, dissolved oxygen, oxygensaturation, conductivity and total disolved solids were recorded in each location. Three Surber samples (0.09 m2, 250 ?m mesh size) were taken in each stream. The collected specimens were fixed in 5% formaldehyde solution for 24 hours and preserved in alcohol 70%. Associations between species and environmental variables were analyzed using correspondence canonical analysis (CCA) taking into account the seven most plentiful species and four environment variables.Associations among species were analyzed using clustering analysis (UPGMA) and the Jaccard similarity index. Pearson´s correlation coefficient and Student's t-distribution were used as well. Ten leech species were recorded in a freshwater environment at Sierra de la Ventana: Helobdella simplex (Moore, 1911); Helobdella brasiliensis Weber, 1915; Helobdella triserialis triserialis (Blanchard, 1849); Helobdella adiastola Ringuelet, 1972; Helobdella hyalina (Ringuelet, 1942);Helobdella triserialis lineata (Verril, 1874), Helobdella duplicata duplicata (Moore, 1911); Theromyzon propinquum Ringuelet, 1947 and Helobdella cordobensis Ringuelet, 1943. Helobdella cordobensis represents the first recording of its kind in the Buenos Aires province. The three most frequent and abundant species (more than 150) individuals in total) were H. simplex (31,55% n=348), H. triserialis s. st. (30%, n=331) and H. brasiliensis (14,50%; n=160), while H. hyalina (6,98%, n=77), H. adiastola (5,25%, n=58), H. cordobensis (4,98% n=54), H. triserialis lineata (n=33, 2,99%), H. duplicata (2,17 n=24), H. michaelseni (1,17% n=13) and T. propinquum (0,36% n=4) showed lower frequency of occurrence and a lower number of individuals. Associations among species were analyzed using clustering analysis with the Jaccard index. The clustering analysis revealed two species assemblages. A first group is represented by six species: H. brasiliensis, H. triserialis s.st., H. triserialis lineata, H. simplex, H. hyalina and H. adiastola and thesecond group is constituted by only one species, H. cordobensis. Relationships between species and environmental variables were examined with CCA. Axis 1 ofthe ordination diagram shows 99.1 % correlation between species and environmental variables. The occurrence of H. simplex, H. triserialis s. st., H. triserialis lineata, H. brasiliensis and H. hyalina near the centre of the ordination diagram is a  consequence of their wide range of tolerance. H. adiastola (r = 0.44, p < 0.05) and H. brasiliensis (r = 0.30, p < 0.05) are positively correlated to pH, whereas H. cordobensis (r = -0.80, p < 0.01) is negatively correlated to that variable. In addition, H. adiastola (r = -0.90 p < 0.01) and H. brasiliensis (r = -0.77, p < 0.01) are negatively correlated to water temperature and the specific richness shows the same trend (r = -0.79, p < 0.01). Leeches in Sierra de la Ventana do not differ from that found in other lentic and lotic environments of Buenos Aires province (Gullo, 1991; Darrigran et al., 1998; Gullo, 2007; César et al., 2009). The present records in Buenos Aires province indicate that Helobdella cordobensis is only found in freshwater low-altitude mountainous environment at Sierra de la Ventana. Hirudinea are more abundant into submerged vegetation and their amount decreases with depthas a consequence of the lack of vegetation, adequate substrates and nutrients. Several factors limit the leech number and species found in an environment. In order of importance, they are: nutrient availability, type of substrate, water depth, stream, size and type of the water body, water hardness, pH, temperature, dissolved oxygen, cloudiness and salinity (Sawyer, 1986). The UPGMA clustering showed the  association among H. brasiliensis, H. triserialis s.st., H. simplex, H. triserialis lineata, H. hyalina and H. adiastola, being the first three species the more frequent and abundant in the sampling sites. It should be pointed out that H. triserialis s. st., H. simplex and H. hyalina were the more abundant and frequent species recorded by César et al. (2009) in Martín García Island. After analyzing the relationships among species and environment variables it is concluded that H. simplex, H. triserialis s. st., H. triserialis lineata, H. brasiliensis and H. hyalina, which are the more frequent species, have a wide range of tolerance to the fluctuations of environmental parameters, and as a consequence they are located close to the center of the ACC diagram. No statistically significant results were obtained for the correlation of H. simplex with pH and of H. hyalina with conductivity. In this respect, these results differ from those obtained by César et al., 2009. On the other hand, H. adistola and H. cordobensis, which are less frequent, seem to be more sensitive to pH fluctuations. Sawyer (1986) points out that this parameter could affect the organisms that leeches take for feeding. Hirudinea are considered organisms with great physiological plasticity because they can survive under anoxia conditions for some days and under hyperoxia during long periods of time (Davies & Govedich, 2001). No statistically significant results were obtained for the correlation with dissolved oxygen. The measured values of dissolved oxygen did not show fluctuations during the year.