DOI: 10.5061/dryad.9zw3r22r6
title: Mechanical properties and cuticle organisation in mandibles are related to the task specialisation in leafcutter ants (<em>Atta laevigata</em>, Attini, Formicidae)

description: Leafcutter ants show a high degree of task division among the workers of
 different castes. For example, the smallest workers, the minims, care for
 the brood and the symbiotic fungus, whereas the larger mediae cut and
 transport plant material. This is reflected in the size and morphology of
 the mandibles, but also in their mechanical properties as mediae possess
 the hardest and stiffest cuticle and the minims - the softest and most
 flexible one. This is directly related to the content of the cross-linking
 transition metal zinc (Zn). The cuticle microstructure, which can be more
 or less anisotropic depending of the orientation of cuticle layers, is
 known to determine the resistance to loads and stresses and thus
 contributes to the biomechanical behaviour of the structure. To study how
 the mandible tasks are related to the cuticular organisation, we here
 documented the microstructure of the mandibles from the mediae and the
 minims by scanning electron microscopy. Afterwards, the mechanical
 properties (Youngs’ modulus, E and hardness, H) of the exo-, meso- and
 endocuticle were identified by nanoindentation. Tests were performed along
 the longitudinal and the circumferential axes of the mandibles. We found,
 that the minims possess mandibles, which are more isotropic, whereas the
 mandibles of the mediae are rather anisotropic. This difference was never
 determined within one species before and is probably linked to the task of
 the individual ant. To gain insight into the origins of these properties,
 we characterized the elemental composition of the different cuticle layers
 along the circumferential axis, revealing that only the exocuticle of the
 mandible cutting edge contains Zn. All other mechanical property gradients
 thus must be the result of the chitin fibre bundle architecture or the
 properties of the protein matrix, which awaits further investigation.
description: Nanoindentation was performed with the same samples and at the
 same regions in circumferential direction (along the length of the
 mandible; terminology of testing direction after Li et al., 2019). They
 were attached to the sample holders following established protocols
 (Krings et al., 2022a, 2022b). Each region of interest was tested at room
 temperature with an SA2 nanoindenter (MTS Nano Instruments, Oak Ridge,
 USA) with a Berkovich diamond tip and a dynamic contact module (DCM) head
 was utilized. Nanoindentation tip calibration was performed with glass and
 the resulting force/displacement curves were stable in the depth from 150
 to 1500 nm (which was the end of the test). The Young’s modulus
 (<em>E</em>) was calculated via the Oliver–Pharr method
 (Oliver & Pharr, 1992). Hardness (<em>H</em>) and
 <em>E </em>were determined from force-distance curves using
 the continuous stiffness mode (CSM). The Poisson’s ratio was set to 0.3
 and the allowable drift rate to 0.1 nm/s. All tests were conducted under
 normal room conditions (relative humidity 28–30%, temperature 22–24 °C),
 with each indent and corresponding curve manually controlled. Due to the
 Pt sputter coating, <em>E</em> and <em>H</em> were
 determined at penetration depth ranging from 600 to 800 nm. Approximately
 40 values were obtained from this indentation depth for each site, which
 were then averaged to calculate one mean <em>H</em> and one
 mean <em>E </em>value per indent.
description: # Mechanical properties and cuticle organisation in mandibles are related
 to the task specialisation in leafcutter ants (*Atta laevigata*, Attini,
 Formicidae) Dataset DOI:
 [10.5061/dryad.9zw3r22r6](10.5061/dryad.9zw3r22r6) ## Description of the
 data and file structure **These files are the raw files from the
 nanoindentor.** The Excel file is provided as an accessible version of the
 data. ### Files and variables #### File: Data.xlsx **Description:** Data
 on each measurement point. One sheet contains the elemental data, each
 elemental content given in atomic %. One sheet contains the
 nanoindentation data, hardness and Young's modulus, each given in
 GPa. The ant castes, the testing direction, mandible side, mandible region
 of each test are given. #### File: L01_circumferential_02.mss
 **Description:** Tested in circumferential direction, large ant caste ####
 File: L01_circumferential_01.mss **Description:** Tested in
 circumferential direction, large ant caste #### File:
 L02_circumferential_01.mss **Description:**  Tested in circumferential
 direction, large ant caste #### File: L02_circumferential_02.mss
 **Description:**  Tested in circumferential direction, large ant caste
 #### File: L01_circumferential_03.mss **Description:**  Tested in
 circumferential direction, large ant caste #### File: L02_longitudinal.mss
 **Description:**  Tested in longitudinal direction, large ant caste ####
 File: L01_longitudinal.mss **Description:**  Tested in longitudinal
 direction, large ant caste #### File: L03_circumferential_01.mss
 **Description:**  Tested in circumferential direction, large ant caste
 #### File: L03_longitudinal.mss **Description:**  Tested in longitudinal
 direction, large ant caste #### File: L04_circumferential_02.mss
 **Description:** Tested in circumferential direction, large ant caste ####
 File: L04_circumferential_01.mss **Description:** Tested in
 circumferential direction, large ant caste #### File: L04_longitudinal.mss
 **Description:** Tested in longitudinal direction, large ant caste ####
 File: L05_circumferential_01.mss **Description:** Tested in
 circumferential direction, large ant caste #### File:
 L05_circumferential_02.mss **Description:** Tested in circumferential
 direction, large ant caste #### File: L03_circumferential_02.mss
 **Description:** Tested in circumferential direction, large ant caste ####
 File: S01_longitudinal.mss **Description:** Tested in longitudinal
 direction, small ant caste #### File: S01_circumferential_02.mss
 **Description:** Tested in circumferential direction, small ant caste ####
 File: L05_longitudinal.mss **Description:** Tested in longitudinal
 direction, large ant caste #### File: S01_circumferential_01.mss
 **Description:** Tested in circumferential direction, small ant caste ####
 File: S02_circumferential_01.mss **Description:** Tested in
 circumferential direction, small ant caste #### File:
 S02_circumferential_02.mss **Description:** Tested in circumferential
 direction, small ant caste #### File: S02_longitudinal.mss
 **Description:** Tested in longitudinal direction, small ant caste ####
 File: S03_circumferential_01.mss **Description:** Tested in
 circumferential direction, small ant caste #### File: S03_longitudinal.mss
 **Description:** Tested in longitudinal direction, small ant caste ####
 File: S04_longitudinal.mss **Description:** Tested in longitudinal
 direction, small ant caste #### File: S04_circumferential_01.mss
 **Description:** Tested in circumferential direction, small ant caste ####
 File: S05_longitudinal.mss **Description:** Tested in longitudinal
 direction, small ant caste #### File: S05_circumferential_01.mss
 **Description:** Tested in circumferential direction, small ant caste ##
 Code/software Testworks 4, by MTS Systems, Excel ## Access information
 Other publicly accessible locations of the data: * n/a Data was derived
 from the following sources: * n/a