Biology subjects

Ukrow, J.

Publications and source records attributed to Ukrow, J..

3 recordsLinked to original sources

bioRxiv2025

Disentangling Cephalopod Chromatophores Motor Units with Computer Vision

Cephalopod chromatophores are skin pigment organs that enable unmatched camouflage through rapid, flexible and neurally controlled deformation. Although their morphology is well known, the organization of their motor control is not entirely understood. Here, we combine high-resolution videography with a dedicated computer-vision pipeline (CHROMAS) to investigate chromatophore control and their likely innervation in Euprymna berryi and Sepia officinalis. By segmenting chromatophores into radial slices and analyzing anisotropic deformations, we applied dimensionality reduction (PCA) and source separation (ICA) to estimate the number and spatial influence of motor neurons responsible for the control of individual and groups of chromatophores. On average, four independent components were detected (suggesting innervation by four motor neurons), each forming contiguous petal-shaped domains rather than causing uniform expansion. Clustering thousands of components revealed motor units spanning multiple chromatophores, most involving fewer than 14 but occasionally spanning more widely. These motor units displayed a wide variety of geometries, ranging from compact local groups to elongated or fragmented structures; they often overlapped, with repeated co-innervation of chromatophore pairs occurring more often than expected by chance. Expansion was consistently faster and more stereotyped than relaxation, consistent with active contraction (corresponding to chromatophore expansion) and passive recoil (chromatophore contraction). Together, these results show that individual chromatophores are not singular or uniform pixels, but rather contrast elements that can be fractionated into smaller territories, themselves coordinated with those of other chromatophores. This geometry of neural control enables, among others, the generation of "virtual" chromatophores, i.e., functional groupings of adjacent chromatophore territories that act as single units, as well as that of noise in the distribution of pixel shapes.

neuroscience↗

bioRxiv2025

CHROMAS: A Computational Pipeline to Track Chromatophores and Analyze their Dynamics

Cephalopod chromatophores are small dermal neuromuscular organs, each consisting of a pigment-containing cell and 10-20 surrounding radial muscles. Their expansions and contractions, controlled and coordinated by the brain, are used to modify the animals appearance during camouflaging and signaling. Building up on tools developed by this lab, we propose a flexible computational pipeline to track and analyse chromatophore dynamics from high-resolution videos of behaving cephalopods. This suite of functions, which we call CHROMAS, segments and classifies individual chromatophores, compensates for animal movements and skin deformations, thus enabling precise and parallel measurements of chromatophore dynamics and long-term tracking over development. A high-resolution tool for the analysis of chromatophore deformations during behavior reveals details of their motor control and thus, their likely innervation. When applied to many chromatophores simultaneously and combined with statistical and clustering tools, this analysis reveals the complex and distributed nature of the chromatophore motor units. We apply CHROMAS to the skins of the bobtail squid Euprymna berryi and the European cuttlefish Sepia officinalis, illustrating its performance with species with widely different chromatophore densities and patterning behaviors. More generally, CHROMAS offers many flexible and easily reconfigured tools to quantify the dynamics of pixelated biological patterns.

animal behavior and cognition↗

bioRxiv2024

Modelling coordinated nocturnal rhythms in ungulates

Studying animal behavior is an important aspect of ethology and behavioral biology and a prerequisite to improving animal management in zoos. As the nocturnal behavior of many ungulate species is, in contrast to the behavior during daylight, poorly studied, a better understanding of nocturnal behavior is necessary to improve animal welfare. We analyse the nocturnal behavior of ungulates recorded in a large number of German and Dutch zoos. These animals show a switching between standing and lying phases, which can be associated with a certain degree of regularity. Interestingly, this regularity is not always captured in the simple length distributions of behavioral phases but shows in the autocorrelation and in the coordination of standing and lying across animals. Particularly, this phenomenon often occurs in younger animals. We provide an explanation to this phenomenon by proposing a stochastic model that can describe these processes. For individual behavior, regular standing cycles are assumed to be potentially interrupted by short lying phases, such that a regular background rhythm appears in the autocorrelation but not necessarily in the raw length distribution of the activity phases. For coordinated behavior, crosscorrelation functions allow to analyse the degree to which pairs of animals that are sharing the same stable box show a synchronization of their standing-lying rhythms. In the data set, our analyses suggest that indeed, baseline regularity does not seem to be reduced in younger animals. Instead, younger animals showed increased probabilities for interruption of standing phases by short lying phases. In addition, the coordination of the standing-lying rhythm between animals in the same box ranged up to 100% and decreased with the distance between boxes. We also found systematic delays between the standing activity of young and adult animals. Author summaryIn this paper, we investigate rhythms observed in the nocturnal behavior of a large number of ungulates housed in zoos. Motivated by the observation that younger individuals, in particular, exhibit irregular standing-lying cycles, we propose and analyze a mathematical model to describe the basic rhythms of the observed animals and quantify the regularity of their standing-lying behavior. Our model enables us to measure both the regularity and synchronization of behavior among individuals. The results suggest that even individuals initially perceived as highly irregular actually follow a strict base rhythm during the night, but single standing phases may be interrupted. Moreover, we observe that animals stalled together typically synchronize their behavior, particularly in the case of a dam and her calf.

animal behavior and cognition↗