Behavioral hierarchy in the medicinal leech, Hirudo medicinalis: feeding as a dominant behavior

Stimuli in the environment, as well as internal states, influence behavioral choice. Of course, animals are often exposed to multiple external and internal factors simultaneously, which makes the ultimate determinants of behavior quite complex. We observed the behavioral responses of European leeches, Hirudo verbana, as we varied one external factor (surrounding water depth) with either another external factor (location of tactile stimulation along the body) or an internal factor (body distention following feeding). Stimulus location proved to be the primary indicator of behavioral response. In general, anterior stimulation produced shortening behavior, midbody stimulation produced local bending, and posterior stimulation usually produced either swimming or crawling but sometimes a hybrid of the two. By producing a systematically measured map of behavioral responses to body stimulation, we found wide areas of overlap between behaviors. When we varied the surrounding water depth, this map changed significantly, and a new feature -rotation of the body along its long axis prior to swimming -appeared. We found additional interactions between water depth and time since last feeding. A large blood meal initially made the animals crawl more and swim less, an effect that was attenuated as water depth increased. The behavioral map returned to its pre-feeding form after approximately 3 weeks as the leeches digested their blood meal. In summary, we found multiplexed impacts on behavioral choice, with the map of responses to tactile stimulation modified by water depth, which itself modulated the impact that feeding had on the decision to swim or crawl.

Section: Research Articlementioning

confidence: 85%

Section: Research Articlementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Multiplexed modulation of behavioral choice

Palmer

Barnett

Copado

et al. 2014

“…I included the group of fed individuals expecting that they might show a different response to UVR than the unfed leeches. It has been well established that satiety strongly influences sensory responses (Gaudry and Kristan, 2009) and the probability of evoking certain behaviors, such as swimming or crawling (Gaudry and Kristan, 2010;Misell et al, 1998). Many of the interactions influencing motivation, behavioral choice and responses to stimuli are regulated by amines (Crisp and Mesce, 2006;Esch et al, 2002;Nusbaum, 1982-1983;Puhl and Mesce, 2008) and these transmitter systems strongly interact with feeding behavior, swimming and crawling (Brodfuehrer and Friesen, 1984;Lent and Dickinson, 1984;Willard, 1981).…”

Section: Research Articlementioning

confidence: 99%

Detection and selective avoidance of near ultraviolet radiation by an aquatic annelid: the medicinal leech

Jellies

2013

Medicinal leeches are aquatic predators that inhabit surface waters during daylight and also leave the water where they might be exposed to less screened light. Whereas the leech visual system has been shown to respond to visible light, leeches in the genus Hirudo do not appear to be as negatively phototactic as one might expect in order to avoid potential ultraviolet radiation (UVR)-induced damage. I used high intensity light emitting diodes to test the hypothesis that leeches could detect and specifically avoid near UVR (395-405 nm). Groups of unfed juvenile leeches exhibited a robust negative phototaxis to UVR, but had no behavioral response to blue or red and only a slight negative phototaxis to green and white light. Individual leeches also exhibited a vigorous negative phototaxis to UVR; responding in 100% of trials compared with modest negative responses to visible light (responding in ~8% of the trials). The responses in fed and unfed leeches were comparable for UVR stimuli. The responses depended upon the stimulus site: leeches shortened away from UV light to the head, and extended away from UV light to the tail. Electrophysiological nerve recordings showed that the cephalic eyes responded vigorously to UVR. Additionally, individual leech photoreceptors also showed strong responses to UVR, and a higher-order neuron associated with shortening and rapid behavioral responses, the S-cell, was activated by UVR, on both the head and tail. These results demonstrate that the leech can detect UVR and is able to discriminate behaviorally between UVR and visible light.

“…For a leech, for instance, interrupting a meal can be a costly choice because the animal might only eat once every several months (Sawyer, 1986). Accordingly, it is not surprising that feeding is the top priority in the leech behavioral hierarchy (Misell et al, 1998). Stimuli that normally elicit locomotory responses such as swimming and crawling -or even escape behaviors such as local bending and full-body shorteningevoke little or no response while a leech is feeding.…”

Section: Behavioral Hierarchies: Don't Bother Me While I'm Eatingmentioning

confidence: 99%

A classic model animal in the 21st century: recent lessons from the leech nervous system

Wagenaar

2015

The medicinal leech (genus Hirudo) is a classic model animal in systems neuroscience. The leech has been central to many integrative studies that establish how properties of neurons and their interconnections give rise to the functioning of the animal at the behavioral level. Leeches exhibit several discrete behaviors (such as crawling, swimming and feeding) that are each relatively simple. Importantly, these behaviors can all be studied -at least at a basal level -in the isolated nervous system. The leech nervous system is particularly amenable to such studies because of its distributed nature; sensory processing and generation of behavior occur to a large degree in iterated segmental ganglia that each contain only ∼400 neurons. Furthermore, the neurons are relatively large and are arranged with stereotyped topography on the surface of the ganglion, which greatly facilitates their identification and accessibility. This Commentary provides an overview of recent work on the leech nervous system, with particular focus on circuits that underlie leech behavior. Studies that combine the unique features of the leech with modern optical and genetic techniques are also discussed. Thus, this Commentary aims to explain the continued appeal of the leech as an experimental animal in the 21st century.