Biology subjects

Casadei-Ferreira, A.

Publications and source records attributed to Casadei-Ferreira, A..

6 recordsLinked to original sources

bioRxiv2026

Evolutionary diversification of the biological screw joint in weevils

Complex biomechanical innovations are often treated as discrete evolutionary breakthroughs, yet their diversification within large radiations remains poorly understood. Beetle leg joints provide a striking example: some weevils possess screw-like coxa-trochanteral articulations in which rotation and axial displacement are mechanically coupled, resembling engineered screw-and-nut mechanisms. Whether these joints represent isolated mechanical extremes, discrete adaptive types or part of a broader continuum of phenotypic variation has remained unknown. Here we combine synchrotron X-ray microtomography, landmark-free atlas-based morphometrics, quantitative functional morphology and phylogenetic comparative analyses to examine the mesocoxa-trochanteral joint in 68 specimens representing seven sampled family-level groups across early-diverging and derived weevil lineages. We show that screw joint evolution combines continuous variation in trochanteral shape with a restricted set of mechanically plausible joint-character combinations, rather than forming sharply separated morphological classes. True screw-and-nut joints are not confined to a distinct region of morphospace, indicating that overall form and mechanical configuration are not necessarily coupled. The occurrence of this configuration in the early diverging Caridae shows that it is not restricted to more derived families. Three-dimensional helix fitting revealed a mosaic geometry, with winding angle showing the clearest relationship with overall shape and joint architecture, whereas axial pitch varied largely independently of shape, size and lineage. Together, these patterns show that screw joint components diversified with different degrees of evolutionary integration. These results recast the weevil screw joint from a singular biomechanical curiosity into a diversified evolutionary system. They suggest that complex functional structures can evolve through the gradual recombination and differential persistence of structurally constrained and evolutionary flexible components, rather than through a single shift from simple to fully specialized designs.

zoology↗

bioRxiv2025

High-throughput phenomics of global ant biodiversity

The big data era in biology is underway, but the study of organismal form has been slow to capitalize on advances in imaging and computation. Modern imaging can digitize whole organisms, but low throughput has limited the effort to document morphological diversity. Within the open science initiative Antscan, we applied high-throughput synchrotron X-ray microtomography to capture phenotypes across a diverse and ecologically dominant insect group -- ants. We provide 2193 whole-body 3D ant datasets from 792 species to broadly cover the ant phylogeny with a global scope, also pairing phenomic data with genome sequencing projects. Scans acquired with standardized parameters facilitate automated analysis and free access to data can broaden the audience and incentivize methods development. Antscan presents a scalable approach to create libraries of diverse anatomies, heralding a new era of studies on the evolution, structure, and function of organismal phenotypes.

zoology↗

bioRxiv2025

Pumping Venom: Valvilli Architecture and Implications for Stinger Functionality

The internal structure of the insect stinger plays a central role in venom delivery, yet critical components in this process remain poorly understood. Of these, the valvilli, a pair of articulated structures within the valve chamber that act as flaps, have often been overlooked or described only superficially. Here, we use high-resolution micro-computed tomography (micro-CT), histological sectioning, and confocal laser scanning microscopy (CLSM) to characterize the fine morphology and material composition of the cuticle of ant valvilli. We report structural differentiation within the valvilli, including sharply delimited material zones that may correspond to distinct mechanical properties. CLSM imaging highlights variation in sclerotization, resilin distribution, and ultrastructure, indicating that the valvilli are not uniform flap-like elements but rather complex, partially deformable structures. Furthermore, comparative micro-CT scans of stingers fixed in different actuation states indicate the involvement of a non-antiphasic pattern of valvilli movement during stinger deployment, challenging the current understanding of valvilli-assisted pumping based on rhythmic, alternating movements, as inferred from European honeybees. These findings offer new anatomical insight into the architecture of the ant stinger and provide a refined morphological basis for future studies of venom delivery mechanisms in Hymenoptera; to also foster our understanding of the complex functionality of micro-scale injection and pumping systems in insects.

zoology↗

bioRxiv2025

Ant head shape evolved to compromise bite-induced mechanical demands

Heads of ant workers harbour the mouthparts and respective musculature, varying drastically in morphology. The mandible adductor muscles occupy most of the heads internal volume, and their contraction generates forces that could risk cuticle failure. Here we quantified ant worker plane head shape disparity and explored how it influences stress dissipation under biting conditions. We combined a geometric morphometric approach under a phylogenetic comparative framework and biomechanical simulations to test the hypothesis that idealized head shapes poorly explored by current ant lineages exhibit biomechanical limitations that could be negatively selected, while an idealized shape representing the median ant worker head shape would present a superior mechanical performance. Our results revealed that narrow heads with deep vertex depressions distribute stresses more evenly, but usually at high levels. Broader heads with convex posterior margins, in contrast, concentrate stresses around the mandibular articulations, making them more prone to failure under high bite forces. Most ant lineages exhibit a head shape that allows mild stresses to spread along the head while concentrating higher stresses around the mandibular articulations. This evolutionary pattern results in a limited morphospace occupation, with most ants clustering around a typical shape and only a few lineages exploring extreme morphologies.

zoology↗

bioRxiv2022

Incorporating sampling bias into permutation tests for niche and distribution models

Randomization tests are often used with species niche and distribution models to estimate model performance, test hypotheses, and measure methodological biases. Many of these tests involve building null models representing the hypothesis that there is no association between the species occurrences and the environmental predictors, then comparing the empirical model to null distributions built from these models. These null models are commonly based on points randomly selected with a uniform probability from the study area. However, spatial sampling bias, a near-universal feature of the occurrence data used to build niche and distribution models, results in a non-uniform probability of observing species in different areas even when species occurrences are unrelated to environmental predictors. Failing to account for this bias in randomization tests results in null distributions that do not accurately represent the null hypothesis, potentially leading to incorrect conclusions. In this study, we use simulations to demonstrate that uniform sampling in randomization tests can lead to unacceptable rates of type I error and poor estimates of methodological bias when spatial sampling bias is present in the occurrence data. We present a new method that incorporates a bias estimate into replicate simulations for these randomization tests, and show that this adjustment can reduce type I error rates to an acceptable level.

ecology↗

bioRxiv2020

Mandibular morphology, task specialization, and bite mechanics in Pheidole ants (Hymenoptera: Formicidae)

The remarkable ecological and evolutionary success of ants was associated with the evolution of reproductive division of labor, in which sterile workers perform most colony tasks whereas reproductives become specialized in reproduction. In some lineages, the worker force became further subdivided into morphologically distinct subcastes (e.g. minor vs. major workers), allowing for the differential performance of particular roles in the colony. However, the functional and ecological significance of morphological differences between subcastes is not well understood. Here, we applied Finite Element Analysis (FEA) to explore the functional differences between major and minor ant worker mandibles. Analyses were carried out on mandibles of two Pheidole species, a dimorphic ant genus. In particular, we test whether major mandibles evolved to minimize stress when compared to minors using combinations of tooth and masticatory margin bites under strike and pressure conditions. Majors performed better in pressure conditions yet, contrary to our expectations, minors performed better in strike bite scenarios. Moreover, we demonstrate that even small morphological differences in ant mandibles might lead to substantial differences in biomechanical responses to bite loading. These results also underscore the potential of FEA to uncover biomechanical consequences of morphological differences within and between ant worker castes.

ecology↗