Behavioral choice across leech species: chacun à son goût

Abstract

SUMMARYAt any one time, animals are simultaneously bombarded with many sensory stimuli, but they typically choose to respond to only a few of them. We used multidimensional analysis to determine the behavioral responses of six species of leeches to stimulation, as the responses are affected by species identity, diet, behavioral state and stimulus location. Our results show that each of the species tested while not feeding displayed remarkably similar behaviors in response to tactile stimulation of the surface of the body. When not feeding, stimulus location was the most reliable factor in determining behavioral response. While feeding, the three sanguivorous (bloodsucking) species tested ignored stimulation, whereas the three carnivorous leeches abandoned feeding in favor of locomotory responses, regardless of phylogenetic relationships. In the sanguivorous leeches, feeding abolished all mechanically elicited responses and mechanical stimulation in turn had no effect on feeding. We also show that the behavioral hierarchy of leeches was fixed and unchanging even in species that can consume both a carnivorous and a sanguivorous diet.

Serotonin as an integrator of leech behavior and muscle mechanical performance

“…Immediately after feeding, Retzius cell activity increases to pre-feeding levels (Wilson et al, 1996a). The distension that accompanies feeding inhibits the swimming motor pattern (Gaudry et al, 2010). Increased urine production during and after feeding rapidly expels blood plasma and reduces body volume (Zerbst-Boroffka et al, 1997;Claflin et al, 2009).…”

“…5-HT influences leech behavior both through modulation of motor pattern generation by the central nervous system and peripheral effects on tissue function (Mason and Kristan, 1982;Nusbaum and Kristan, 1986;Lent et al, 1988;Tian et al, 2007;Brodfuehrer et al, 2008;Gaudry et al, 2010). Elevated 5-HT levels are associated with pre-feeding search behavior, increased swimming activity and increased biting frequency (Willard, 1981;Lent and Dickinson, 1984;Lent et al, 1988;Wilson et al, 1996a).…”

Feeding-Mediated Distention Inhibits Swimming in the Medicinal Leech

“…First, the front sucker always remains attached to the food source. Second, this behavior is never elicited through mechanical stimulation in a variety of sanguivorous leech species, including Hirudo (Misell et al 1998; Gaudry et al 2010). This oscillatory behavior appears to distribute blood throughout the gut and illustrates a behavior that is “spontaneously” generated during feeding (i.e., it is not caused by mechanosensory stimulation) and does not interfere with feeding.…”

The Role of the Gustatory System in the Coordination of Feeding

“…For example, when feeding on blood, leeches can endure aversive chemicals applied to the animal’s chemosensory organ (Kornreich and Kleinhaus, 1999) and electric shocks (Gaudry et al, 2010). Strikingly, highly dissected leeches lacking a body wall and internal organs will still initiate and commit to feeding, showing that they can even ignore severe trauma to obtain a meal (Gaudry and Kristan, 2009).…”