Scaling and development of elastic mechanisms: the tiny strikes of larval mantis shrimp

Latch-mediated spring actuation (LaMSA) is used by small organisms to produce high acceleration movements. Mathematical models predict that acceleration increases as LaMSA systems decrease in size. Adult mantis shrimp use a LaMSA mechanism in their raptorial appendages to produce extremely fast strikes. Until now, however, it was unclear whether mantis shrimp at earlier life-history stages also strike using elastic recoil and latch mediation. We tested whether larval mantis shrimp (Gonodactylaceus falcatus) use LaMSA and, because of their smaller size, achieve higher strike accelerations than adults of other mantis shrimp species. Based on microscopy and kinematic analyses, we discovered that larval G. falcatus possess the components of, and actively use, LaMSA during their fourth larval stage, which is the stage of development when larvae begin feeding. Larvae performed strikes at high acceleration and speed (mean: 4.133×105 rad s−2, 292.7 rad s−1; 12 individuals, 25 strikes), which are of the same order of magnitude as for adults – even though adult appendages are up to two orders of magnitude longer. Larval strike speed (mean: 0.385 m s−1) exceeded the maximum swimming speed of similarly sized organisms from other species by several orders of magnitude. These findings establish the developmental timing and scaling of the mantis shrimp LaMSA mechanism and provide insights into the kinematic consequences of scaling limits in tiny elastic mechanisms.ReadMe File: "README.pdf" The ReadMe file steps through the contents for each file and folder contained in this repository. Please review this file first, it includes helpful information on how to connect the R code and data together. Rcode: "LarvalMantisShrimpKinematicsCode_FINAL.rmd" This R code includes all of the kinematics code and statistical analyses used in this study. Larval Mantis Shrimp ID and Metadata: "Larval.ID_forkinematics.csv" This is the metadata file and general information needed for running the kinematics Rcode. Larval LaMSA Mechanism: "LarvalLaMSAMechanism.csv" This spreadsheet contains data used to infer the LaMSA mechanism from a highspeed video (20,000 frames s-1) of a larval mantis shrimp strike under a microscope slide. Comparative Mantis Shrimp Kinematics: "MantisShrimpComparativeKinematics.csv" This spreadsheet contains data used to compare larval mantis shrimp strike kinematics to various adult mantis shrimp kinematics. Larval Speed Comparisons: "LarvalSpeedComparisons.csv" This spreadsheet includes data used to compare larval strike speeds to speeds produced by other small larval aquatic organisms. Larval Strike Kinematics - "StrikeKinematicsData.zip" This folder contains data used to calculate the kinematics of the larval mantis shrimp strike. There are two different file types, '.csv' files and '.mdf' files. The '.mdf' files are the output files from the manual tracking of larval mantis shrimp strikes using the MtrackJ plugin in FIJI. Measuring Error From Tracking - "KinematicErrorData.zip" This folder contains data used to calculate the measurement error from manual tracking of the larval mantis shrimp strikes. Funding provided by: Company of BiologistsCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000522Award Number: JEBTF181185Funding provided by: Army Research LaboratoryCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006754Award Number: W911NF - 15-1-058Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: NSF - IOS - 1439850Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: EPSCoR RII 1738567Funding provided by: Office of Naval ResearchCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000006Award Number: N00014-19-1-2035 and N00014-17-1-2062Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: NSF - IOS - 2034043Larval mantis shrimp raptorial appendage strikes were collected using high speed video (20,000 frames s-1; 25 strikes, 12 individuals, 1-6 strikes per individual). Kinematics were determined by manually tracking the raptorial appendage over the course of a strike using MTrackJ plug-in (V1.5.1, Meijering et al., 2012) in ImageJ (v2.0.0, Schneider et al, 2012). Strike kinematics (angular and linear velocity and acceleration) were compared to a previously compiled dataset of adult mantis shrimp strike kinematics (McHenry et al., 2016). The speed of the larval mantis shrimp strike was compared to a newly compiled dataset collected from the literature of swimming and feeding speeds from other larval aquatic organisms