Biology subjects

Holzman, R.

Publications and source records attributed to Holzman, R..

7 recordsLinked to original sources

bioRxiv2025

Twist and Snout: Head and Body Morphologies Determine Feeding Kinematics in Substrate-Biting Fishes

Across teleosts, feeding by biting substrate-attached prey has evolved multiple times and is associated with convergent morphologies that include a deep body and an elongated, tapered head. However, the functional role of these morphologies in substrate-biting fish is not established. Here, we tested the hypothesis that these morphologies function as control surfaces that affect feeding kinematics during biting. To test this hypothesis, we used simplified physical models of substrate-biting fish and examined the role of head, body, and fin morphology in determining feeding kinematics that facilitate the removal of substrate-attached prey. Models simulated the swift lateral movement of the head, previously documented in species biting substrate-attached algae. Using models that capture the natural morphological variation of biters, we tested (i) how different head morphologies affect the speed of the head and (ii) how different body morphologies affect the stability of the body during head movements. We found that the moment of inertia (MOI) of the head and body explained most of the variation in head speed and body displacement. A decrease in head MOI resulted in faster lateral head movements, known to facilitate removal of attached prey. An increase in body MOI, relative to that of the head, stabilized the lateral displacement of the body during bites. Overall, our results suggest that the laterally compressed bodies and tapered snouts function as control surfaces during feeding in substrate-biting fish. We propose that a selective pressure to extend the lateral surface area underlies the prevailing morphological convergence of biting reef fishes.

zoology↗

bioRxiv2023

Multiple performance peaks for scale-biting in an adaptive radiation of pupfishes

The physical interactions between organisms and their environment ultimately shape their rate of speciation and adaptive radiation, but the contributions of biomechanics to evolutionary divergence are frequently overlooked. Here we investigated an adaptive radiation of Cyprinodon pupfishes to measure the relationship between feeding kinematics and performance during adaptation to a novel trophic niche, lepidophagy, in which a predator removes only the scales, mucus, and sometimes tissue from their prey using scraping and biting attacks. We used high-speed video to film scale-biting strikes on gelatin cubes by scale-eater, molluscivore, generalist, and hybrid pupfishes and subsequently measured the dimensions of each bite. We then trained the SLEAP machine-learning animal tracking model to measure kinematic landmarks and automatically scored over 100,000 frames from 227 recorded strikes. Scale-eaters exhibited increased peak gape and greater bite length; however, substantial within-individual kinematic variation resulted in poor discrimination of strikes by species or strike type. Nonetheless, a complex performance landscape with two distinct peaks best predicted gel-biting performance, corresponding to a significant nonlinear interaction between peak gape and peak jaw protrusion in which scale-eaters and their hybrids occupied a second performance peak requiring larger peak gape and greater jaw protrusion. A bite performance valley separating scale-eaters from other species may have contributed to their rapid evolution and is consistent with multiple estimates of a multi-peak fitness landscape in the wild. We thus present an efficient deep-learning automated pipeline for kinematic analyses of feeding strikes and a new biomechanical model for understanding the performance and rapid evolution of a rare trophic niche.

evolutionary biology↗

bioRxiv2022

Analysis of Larval Fish Feeding Behavior under Naturalistic Conditions

Modern research efforts concerned with animal behavior rely heavily on image and video analysis. While such data are now quick to obtain, extracting and analyzing complex behaviors under naturalistic conditions is still a major challenge, specifically when the behavior of interest is sporadic and rare. In this study, we present an end-to-end system for capturing, detecting and analyzing larval fish feeding behavior in unconstrained naturalistic environments. We first constructed a specialized system for imaging these tiny, fast-moving creatures and deployed it in large aquaculture rearing pools. We then designed an analysis pipeline using several action classification backbones, and compare their performance. A natural feature of the data was the extremely low prevalence of feeding events, leading to low sample sizes and highly imbalanced datasets despite extensive annotation efforts. Nevertheless, our pipeline successfully detected and classified the sparsely-occurring feeding behavior of fish larvae in a curated experimental setting from videos featuring multiple animals. We introduce three new annotated datasets of underwater videography, in a curated and an uncurated setting. As challenges related to data imbalance and experts annotation are common to the analysis of animal behavior under naturalistic conditions, we believe our findings can contribute to the growing field of computer vision for the study and understanding of animal behavior.

zoology↗

bioRxiv2020

A power amplification dyad in seahorses

Ubiquitous constraints derived from the muscles structure limit the power capacity of fast contracting muscles. Correspondingly, organisms evolved elastic elements that store energy which, when released, can be used to rapidly accelerate appendages. Such latch-mediated spring actuation (LaMSA) systems comprise of a single elastic element and are used to actuate a single mass. Here we reveal a dual LaMSA system in seahorses, in which two elastic elements actuate two masses: the head as they rapidly swing it towards the prey, and the water mass sucked into the mouth to prevent the prey from escaping. This power-amplified system enhances the speeds of both head rotation and suction flows by x10 compared to similarly-sized fish. Furthermore, the dual system provides temporal coordination between head rotation and suction flows, a novel function for LaMSA. These findings extend the known function, capacity and design of LaMSA systems.

biophysics↗

bioRxiv2019

Hydrodynamic regime drives flow reversals in suction feeding larval fishes during early ontogeny

Fish larvae are the smallest self-sustaining vertebrates. As such, they face multiple challenge that stem from their minute size, and from the hydrodynamic regime in which they dwell. This regime of intermediate Reynolds numbers (Re) was shown to affect the swimming of larval fish and impede their ability to capture prey. Numerical simulations indicate that the flow fields external to the mouth in younger larvae result in shallower spatial gradients, limiting the force exerted on the prey. However, observations on feeding larvae suggest that failures in prey capture can also occur during prey transport, although the mechanism causing these failures is unclear. We combine high-speed videography and numerical simulations to investigate the hydrodynamic mechanisms that impede prey transport in larval fishes. Detailed kinematics of the expanding mouth during prey capture by larval Sparus aurata were used to parameterize age-specific numerical models of the flows inside the mouth. These models reveal that, for small larvae that slowly expand their mouth, not all the fluid that enters the mouth cavity is expelled through the gills, resulting in flow reversal at the mouth orifice. This efflux at the mouth orifice was highest in the younger ages, but was also high (>8%) in slow strikes produced by larger fish. Our modeling explains the observations of \"in-and-out\" events in larval fish, where prey enters the mouth but is not swallowed. It further highlights the importance of prey transport as an integral part in determining suction feeding success.

zoology↗

bioRxiv2019

Suction feeding performance and prey escape response interact to determine feeding success in larval fish

The survival of larval marine fishes during early development is strongly dependent on their ability to capture prey. Most larval fish capture prey by expanding their mouth cavity, generating a \"suction flow\" that draws the prey into their mouth. Larval fish dwell in a hydrodynamic regime of low Reynolds numbers, which has been shown to impede their ability to capture non-evasive prey. However, the marine environment is characterized by an abundance of evasive prey such as Copepods. These organisms can sense the hydrodynamic disturbance created by approaching predators and perform high-acceleration escape maneuvers. Using a 3D high-speed video system, we characterized the interaction between 8-33 day post hatching Sparus aurata larvae and prey from a natural zooplankton assemblage that contained evasive prey, and assessed the factors that determine the outcome of these interactions. Larvae showed strong selectivity for large prey that was moving prior to the initialization of the strike. As previously shown in studies with non-evasive prey, larval feeding success increased with increasing Reynolds numbers. However, larval feeding success was also strongly dependent on the preys escape response. Feeding success was lower for larger, more evasive prey, indicating that larvae might be challenged in capturing their preferred prey. The kinematics of successful strikes resulted in shorter response time but higher hydrodynamic signature available for the prey. Thus, despite being \"noisier\", successful strikes on evasive prey depended on preceding the preys escape response. Our results show that larval performance, rather than larval preferences, determines their diet during early development.

zoology↗

bioRxiv2017

A complex performance landscape for suction-feeding reveals constraints and adaptations in a population of reef damselfish

The ability to predict how multiple traits interact in determining performance is key to understanding the evolution of complex functional systems. Similar to Simpsons adaptive landscape, which describes the fitness consequences of varying morphological traits, performance landscapes depict the performance consequences of varying morphological traits. Mapping the populations location with respect to the topographic features of the landscape could inform us on the selective forces operating on the traits that underlie performance. Here, we used a mechanistic model derived from first principles of hydrodynamics to construct a hypothetical performance landscape for zooplankton prey capture using suction feeding. We then used the landscape to test whether a population of Chromis viridis, a coral reef zooplanktivore, is located on a performance peak or ridge based on measurements of kinematic variables recorded in-situ during undisturbed foraging. Observed trait combinations in the wild population closely matched regions of high feeding performance in the landscape, however the population was not located on a local performance peak. This sub-optimal performance was not due to constraints stemming from the observed trait correlations. The predominant directions of variation of the phenotypic traits was tangent to the path of steepest ascent that points towards the local peak, indicating that the population does not reside on a \"performance ridge\". Rather, our analysis suggests that feeding performance is constrained by stabilizing selection, possibly reflecting a balance between selection on feeding performance and mechanical or genetic constraints.

evolutionary biology↗