Developmentally regulated multisensory integration for prey localization in the medicinal leech

Abstract

SUMMARYMedicinal leeches, like many aquatic animals, use water disturbances to localize their prey, so they need to be able to determine if a wave disturbance is created by prey or by another source. Many aquatic predators perform this separation by responding only to those wave frequencies representing their prey. As leechesʼ prey preference changes over the course of their development, we examined their responses at three different life stages. We found that juveniles more readily localize wave sources of lower frequencies (2Hz) than their adult counterparts (8-12Hz), and that adolescents exhibited elements of both juvenile and adult behavior, readily localizing sources of both frequencies. Leeches are known to be able to localize the source of waves through the use of either mechanical or visual information. We separately characterized their ability to localize various frequencies of stimuli using unimodal cues. Within a single modality, the frequency-response curves of adults and juveniles were virtually indistinguishable. However, the differences between the responses for each modality (visual and mechanosensory) were striking. The optimal visual stimulus had a much lower frequency (2Hz) than the optimal mechanical stimulus (12Hz). These frequencies matched, respectively, the juvenile and the adult preferred frequency for multimodally sensed waves. This suggests that, in the multimodal condition, adult behavior is driven more by mechanosensory information and juvenile behavior more by visual. Indeed, when stimuli of the two modalities were placed in conflict with one another, adult leeches, unlike juveniles, were attracted to the mechanical stimulus much more strongly than to the visual stimulus. Supplementary material available online at

Discontinuous locomotion and prey sensing in the leech

“…Adult medicinal leeches (Hirudo verbana Carena 1820) were obtained from Niagara Medicinal Leeches (Niagara, NY, USA) and maintained according to methods described previously (Harley et al, 2011).…”

“…This stimulator created waves in the testing arena containing the leech. Throughout this study, we used waves with a frequency of 8Hz, because those were found to be most readily localized by adult leeches under our experimental conditions (Harley et al, 2011). The arena was illuminated using a 750W halogen flood lamp (McMaster-Carr, Santa Fe, CA, USA).…”

“…Here we examine an aquatic predator, the leech Hirudo verbana, that determines prey location by sensing water disturbances using both visual sensors and mechanosensors (Young et al, 1981;Dickinson and Lent, 1984;Carlton and McVean, 1993;Harley et al, 2011). During prey localization, leeches readily switch between swimming, crawling and non-locomotion (for descriptions of these behaviors, see Fig.1) (Gray et al, 1938;Sawyer, 1986;SternTomlinson et al, 1986;Brodfuehrer et al, 1995a;Brodfuehrer et al, 2008), suggesting that leeches may serve as another example of stop-and-go predators.…”

“…Thus both sensory capabilities and sensory needs may differ between slow and fast locomotion. Our previous work described the visual and Leech prey sensing during locomotion mechanical stimuli that evoke prey localization in the medicinal leech (Harley et al, 2011). Here we consider whether swimming and crawling in the leech may serve distinct functions in prey localization, and use behavioral assays to determine the extent to which leeches are able to sense prey-like stimuli during various forms of locomotion.…”

Frontiers in Neuroscience

“…Leeches (Hirudo verbana) were maintained as previously reported (Harley et al, 2011). Nerve cords were extracted following the procedures of Baljon and Wagenaar (2015), except that here either a single ganglion or the entire nerve cord (sans the head brain, which would inhibit fictive swimming) was extracted rather than a short chain of ganglia.…”