Statistical characterization of social interactions and collective behavior in medicinal leeches

Abstract

Bisson G, Torre V. Statistical characterization of social interactions and collective behavior in medicinal leeches. J Neurophysiol 106: 78 -90, 2011. First published March 16, 2011 doi:10.1152/jn.01043.2010In the present study we analyzed the behavior and interactions among leeches in the same observation tank. Colored beads were glued onto their skin so that their behavior could be followed and quantified. When two or three leeches were present in the observation tank, they searched around for a maximum of 2 h and their motion and behavior were independent from those of their conspecifics. When the number of leeches in the tank was increased to 10, leeches were attracted to each other and exhibited episodes of highly correlated behavior. Solitary leeches injected with serotonin or dopamine increased the portion of time spent pseudoswimming and crawling, respectively. The behavior of three to five leeches injected with serotonin was not statistically independent, and leeches were attracted to their conspecifics and exhibited episodes of correlated behavior. Therefore, serotonin not only induces pseudoswimming in leeches but also promotes social interactions, characterized by a mutual attraction and by episodes of correlated/collective behavior.

Settlement preferences of leeches (Clitellata: Hirudinida) for different artificial substrates

“…This may be due to several factors, primarily leeches tend to inhabit the edges of various submerged elements, which were observed in our study (GarciaPerez et al, 2007;Bisson & Torre, 2011). The substrate is even more attractive for them, when circumference to the surface area ratio is higher, which ensures a greater availability of attractive places for leeches to inhabit.…”

“…According to the literature, some taxa are more numerous on artificial substrates in relation to the natural bottom (Czarnecka et al, 2009); this particularly applies to thigmotactic organisms, which include leeches (Czerniawska-Kusza, 2004). In general, they inhabit tightfitting places to achieve maximum body contact (Bisson & Torre, 2011). This study indicates that leech assemblages on artificial substrates are dominated by predatory taxa.…”

“…Leech density also depends on the presence of conspecifics (Lang, 1974;Garcia-Perez et al, 2007;Bisson & Torre, 2011;Bisson et al, 2012). When choosing a place to colonize, leeches actively penetrate Hydrobiologia (2015) 758:275-286 283 micro-habitats (Garcia-Perez et al, 2007).…”

“…When choosing a place to colonize, leeches actively penetrate Hydrobiologia (2015) 758:275-286 283 micro-habitats (Garcia-Perez et al, 2007). If this exploratory phase is accompanied by sufficient physical contact with conspecifics, leeches form a group and inhabit such regions (Bisson & Torre, 2011;Bisson et al, 2012). In order to settle they must exceed a certain threshold of meetings.…”

“…Most attention has been devoted to biological and chemical agents (Mazzoni et al, 2005;Garcia-Perez et al, 2007;Bisson & Torre, 2011;Bisson et al, 2012) and the role of light (Pawłowski, 1936;Elliott, 1973;Sawyer, 1986;Bielecki, 1999;Bielecki et al, 2011a). However, there is a lack of information concerning physical properties of substrates, particularly those of anthropogenic origin, which often represent the more frequent substrate type for settlement by these invertebrates.…”