title: Searching for motifs in the behaviour of larval Drosophila melanogaster and Caenorhabditis elegans reveals continuity between behavioural states.
abstract: We present a novel method for the unsupervised discovery of behavioural motifs in larval Drosophila melanogaster and Caenorhabditis elegans. A motif is defined as a particular sequence of postures that recurs frequently. The animal's changing posture is represented by an eigenshape time series, and we look for motifs in this time series. To find motifs, the eigenshape time series is segmented, and the segments clustered using spline regression. Unlike previous approaches, our method can classify sequences of unequal duration as the same motif. The behavioural motifs are used as the basis of a probabilistic behavioural annotator, the eigenshape annotator (ESA). Probabilistic annotation avoids rigid threshold values and allows classification uncertainty to be quantified. We apply eigenshape annotation to both larval Drosophila and C. elegans and produce a good match to hand annotation of behavioural states. However, we find many behavioural events cannot be unambiguously classified. By comparing the results with ESA of an artificial agent's behaviour, we argue that the ambiguity is due to greater continuity between behavioural states than is generally assumed for these organisms.
authors.affiliation: Neuroinformatics Doctoral Training Centre, University of Edinburgh, Edinburgh, UK b.szigeti@sms.ed.ac.uk.
authors.forename: Balázs
authors.initials: B
authors.lastname: Szigeti
authors.affiliation: EMBL-CRG Systems Biology Program, Barcelona, Spain.
authors.forename: Ajinkya
authors.identifier: http://orcid.org/0000-0003-3369-0370
authors.initials: A
authors.lastname: Deogade
authors.affiliation: School of Informatics, University of Edinburgh, Edinburgh, UK.
authors.forename: Barbara
authors.initials: B
authors.lastname: Webb
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D000066949:Biobehavioral Sciences; D017173:Caenorhabditis elegans / Q000502:physiology*; D004331:Drosophila melanogaster; D007814:Larva / Q000502:physiology; D008954:Models, Biological
keywords: Caenorhabditis elegans; Drosophila melanogaster larva; behavioural states; eigenmaggots; eigenworms; ethogram