Evan P. Economo

Basiceros dirt ants are morphologically distinct and widely distributed members of Neotropical communities. These ants possess features that aid in leaf litter camouflage and are larger than other closely related lineages with similar cryptic adaptations. Here, we report the first fossil of this genus group, Basiceros enana sp. nov., from Miocene-aged Dominican amber, which reveals a pattern of body size evolution and disjunct biogeography. The fossil evidences the local extinction of Basiceros in the Caribbean, even as living Basiceros are known from Honduras to Southern Brazil. Using combined morphological and molecular datasets of all closely related lineages, we recover the evolutionary trajectory for body size within the group, demonstrating that body size was initially small in these ants and followed by a rapid expansion of body size in the common ancestor of all living species. Results reflect the capacity for early morphological evolution to influence perceived patterns of body size increase through a mosaic of ancestral legacy and continuous enlargement.

Communication is essential for social organisms. In eusocial insects, olfaction facilitates communication and recognition between nestmates. The study of certain model organisms has led to the hypothesis that odorant receptors are expanded in eusocial Hymenoptera. This has become a widely mentioned idea in the literature, albeit with conflicting reports, and has not been tested with a broad comparative analysis. Here we combined existing genomic and new neuroanatomical data, including from an approximately 100 Myr old fossil ant, across a phylogenetically broad sample of hymenopteran lineages. We find no evidence that variation in the size and evolutionary tempo of odorant receptor repertoires is related to eusociality. Post hoc exploration of our data hinted at loss of flight as a possible factor shaping some of the variation in OR repertoires in Hymenoptera. Nevertheless, our analyses revealed a complex pattern of evolutionary variation, and raise new questions about the ecological, behavioural and social factors that shape olfactory abilities.

Climate change is a major threat to the Middle East and North Africa (MENA) region, which can cause significant harm to its plant and animal species. We predicted the habitat distribution of Cataglyphis nodus (Brullé, 1833) in MENA using MaxEnt models under current and future climate conditions. Our analysis indicates that the cooler regions of the MENA are projected to experience temperature increases of 1–2 °C by 2040 and 2–4 °C by the 2070s. Similarly, the warmer regions may anticipate rises of 0.5–2 °C by 2040 and 2–4 °C by the 2070s. MaxEnt model results for the current climate show good agreement with observations (mean area under the curve value of 0.975 and mean true statistical skill value of 0.8), indicating good potential habitat suitability for C. nodus. Significant factors affecting habitat suitability are elevation, mean monthly precipitation of the coldest quarter, temperature seasonality, and precipitation amount of the driest month. The research predicts that under Shared Socioeconomic Pathway (SSP) 1.2.6, the habitat suitability area may increase by 6% in 2040, while SSP 3.7.0 (0.3%) and SSP 5.8.5 (2.6%) predict a decrease. For 2070, SSP 5.8.5 predicts a 2.2% reduction in habitat suitability, while SSP 1.2.6 (0.4%) and SSP 3.7.0 (1.3%) predict slight increases. The results provide insight into the potential impacts of climate change on the species and regional biodiversity changes associated with the projected species distribution.

Three-dimensional (3D) imaging, such as micro-computed tomography (micro-CT), is increasingly being used by organismal biologists for precise and comprehensive anatomical characterization. However, the segmentation of anatomical structures remains a bottleneck in research, often requiring tedious manual work. Here, we propose a pipeline for the fully-automated segmentation of anatomical structures in micro-CT images utilizing state-of-the-art deep learning methods, selecting the ant brain as a test case. We implemented the U-Net architecture for 2D image segmentation for our convolutional neural network (CNN), combined with pixel-island detection. For training and validation of the network, we assembled a dataset of semi-manually segmented brain images of 94 ant species. The trained network predicted the brain area in ant images fast and accurately; its performance tested on validation sets showed good agreement between the prediction and the target, scoring 80% Intersection over Union (IoU) and 90% Dice Coefficient (F1) accuracy. While manual segmentation usually takes many hours for each brain, the trained network takes only a few minutes. Furthermore, our network is generalizable for segmenting the whole neural system in full-body scans, and works in tests on distantly related and morphologically divergent insects (e.g., fruit flies). The latter suggest that methods like the one presented here generally apply across diverse taxa. Our method makes the construction of segmented maps and the morphological quantification of different species more efficient and scalable to large datasets, a step toward a big data approach to organismal anatomy.

Adaptive radiations are of particular interest owing to what they reveal about the ecological and evolutionary regulation of biodiversity. This applies to localized island radiations such as Darwin's finches, and also to rapid radiations occurring on a global scale. Here we analyse the macroevolution and macroecology ofPheidole,a famously hyperdiverse and ecologically dominant ant genus. We generate and analyse four novel datasets: (i) a robust global phylogeny including 285Pheidolespecies, (ii) a global database on regionalPheidolerichness in 365 political areas summarizing over 97 000 individual records from more than 6500 studies, (iii) a global database ofPheidolerichness from 3796 local communities and (iv) a database ofPheidolebody sizes across species. Analysis of the potential climate drivers of richness revealed that the patterns are statistically very similar across different biogeographic regions, with both regional and local richness associated with the same coefficients of temperature and precipitation. This similarity occurs even though phylogenetic analysis shows thatPheidolereached dominance in communities through serial localized radiations into different biomes within different continents and islands.Pheidolebody size distributions have likewise converged across geographical regions. We propose these cases of convergence indicate that the global radiation ofPheidoleis structured by deterministic factors regulating diversification and diversity.