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Head and mandible shapes are highly integrated yet represent two distinct modules within and among worker subcastes of the ant genus Pheidole.

ABSTRACT: Ants use their mandibles for a wide variety of tasks related to substrate manipulation, brood transport, food processing, and colony defense. Due to constraints involved in colony upkeep, ants evolved a remarkable diversity of mandibular forms, often related to specific roles such as specialized hunting and seed milling. Considering these varied functional demands, we focused on understanding how the mandible and head shape vary within and between Pheidole subcastes. Using x-ray microtomography and 3D geometric morphometrics, we tested whether these structures are integrated and modular, and how ecological predictors influenced these features. Our results showed that mandible and head shape of majors and minor workers tend to vary from robust to slender, with some more complex changes related to the mandibular base. Additionally, we found that head and mandible shapes are characterized by a high degree of integration, but with little correlation with feeding and nesting habits. Our results suggest that a combination of structural (allometric) constraints and the behavioral flexibility conferred by subcaste dimorphism might largely buffer selective pressures that would otherwise lead to a fine-tuning between ecological conditions and morphological adaptation.

SUBMITTER: Casadei-Ferreira A

PROVIDER: S-EPMC8207162 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Breaking out of biogeographical modules: range expansion and taxon cycles in the hyperdiverse ant genus <i>Pheidole</i>.

Project description:AimWe sought to reconstruct the biogeographical structure and dynamics of a hyperdiverse ant genus, Pheidole, and to test several predictions of the taxon cycle hypothesis. Using large datasets on Pheidole geographical distributions and phylogeny, we (1) inferred patterns of biogeographical modularity (clusters of areas with similar faunal composition), (2) tested whether species in open habitats are more likely to be expanding their range beyond module boundaries, and (3) tested whether there is a bias of lineage flow from high- to low-diversity areas.LocationThe Old World.MethodsWe compiled and jointly analysed a comprehensive database of Pheidole geographical distributions, the ecological affinities of different species, and a multilocus phylogeny of the Old World radiation. We used network modularity methods to infer biogeographical structure in the genus and comparative methods to evaluate the hypotheses.ResultsThe network analysis identified eight biogeographical modules, and a suite of species with anomalous ranges that are statistically more likely to occur in open habitat, supporting the hypothesis that open habitats promote range expansion. Phylogenetic analysis shows evidence for a cascade pattern of colonization from Asia to New Guinea to the Pacific, but no 'upstream' colonization in the reverse direction.Main conclusionsThe distributions of Pheidole lineages in the Old World are highly modular, with modules generally corresponding to biogeographical regions inferred in other groups of organisms. However, some lineages have expanded their ranges across module boundaries, and these species are more likely to be adapted to open habitats rather than interior forest. In addition, there is a cascade pattern of dispersal from higher to lower diversity areas during these range expansions. Our findings are consistent with the taxon cycle hypothesis, although they do not rule out alternative interpretations.

| S-EPMC5014176 | biostudies-literature

Division of labor in the hyperdiverse ant genus Pheidole is associated with distinct subcaste- and age-related patterns of worker brain organization.

Project description:The evolutionary success of ants and other social insects is considered to be intrinsically linked to division of labor among workers. The role of the brains of individual ants in generating division of labor, however, is poorly understood, as is the degree to which interspecific variation in worker social phenotypes is underscored by functional neurobiological differentiation. Here we demonstrate that dimorphic minor and major workers of different ages from three ecotypical species of the hyperdiverse ant genus Pheidole have distinct patterns of neuropil size variation. Brain subregions involved in sensory input (optic and antennal lobes), sensory integration, learning and memory (mushroom bodies), and motor functions (central body and subesophageal ganglion) vary significantly in relative size, reflecting differential investment in neuropils that likely regulate subcaste- and age-correlated task performance. Worker groups differ in brain size and display patterns of altered isometric and allometric subregion scaling that affect brain architecture independently of brain size variation. In particular, mushroom body size was positively correlated with task plasticity in the context of both age- and subcaste-related polyethism, providing strong, novel support that greater investment in this neuropil increases behavioral flexibility. Our findings reveal striking levels of developmental plasticity and evolutionary flexibility in Pheidole worker neuroanatomy, supporting the hypothesis that mosaic alterations of brain composition contribute to adaptive colony structure and interspecific variation in social organization.

| S-EPMC3281964 | biostudies-literature

DNA barcodes for species identification in the hyperdiverse ant genus Pheidole (Formicidae: Myrmicinae).

Project description:DNA sequencing is increasingly being used to assist in species identification in order to overcome taxonomic impediment. However, few studies attempt to compare the results of these molecular studies with a more traditional species delineation approach based on morphological characters. Mitochondrial DNA Cytochrome oxidase subunit 1 (CO1) gene was sequenced, measuring 636 base pairs, from 47 ants of the genus Pheidole (Formicidae: Myrmicinae) collected in the Brazilian Atlantic Forest to test whether the morphology-based assignment of individuals into species is supported by DNA-based species delimitation. Twenty morphospecies were identified, whereas the barcoding analysis identified 19 Molecular Operational Taxonomic Units (MOTUs). Fifteen out of the 19 DNA-based clusters allocated, using sequence divergence thresholds of 2% and 3%, matched with morphospecies. Both thresholds yielded the same number of MOTUs. Only one MOTU was successfully identified to species level using the CO1 sequences of Pheidole species already in the Genbank. The average pairwise sequence divergence for all 47 sequences was 19%, ranging between 0-25%. In some cases, however, morphology and molecular based methods differed in their assignment of individuals to morphospecies or MOTUs. The occurrence of distinct mitochondrial lineages within morphological species highlights groups for further detailed genetic and morphological studies, and therefore a pluralistic approach using several methods to understand the taxonomy of difficult lineages is advocated.

| S-EPMC3735075 | biostudies-literature

Tradeoffs in the evolution of caste and body size in the hyperdiverse ant genus Pheidole.

Project description:The efficient investment of resources is often the route to ecological success, and the adaptability of resource investment may play a critical role in promoting biodiversity. The ants of the "hyperdiverse" genus Pheidole produce two discrete sterile castes, soldiers and minor workers. Within Pheidole, there is tremendous interspecific variation in proportion of soldiers. The causes and correlates of caste ratio variation among species of Pheidole remain enigmatic. Here we test whether a body size threshold model accounts for interspecific variation in caste ratio in Pheidole, such that species with larger body sizes produce relatively fewer soldiers within their colonies. We evaluated the caste ratio of 26 species of Pheidole and found that the body size of workers accounts for interspecific variation in the production of soldiers as we predicted. Twelve species sampled from one forest in Costa Rica yielded the same relationship as found in previously published data from many localities. We conclude that production of soldiers in the most species-rich group of ants is regulated by a body size threshold mechanism, and that the great variation in body size and caste ratio in Pheidole plays a role in niche divergence in this rapidly evolving taxon.

| S-EPMC3485035 | biostudies-literature

Global phylogenetic structure of the hyperdiverse ant genus Pheidole reveals the repeated evolution of macroecological patterns.

Project description: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 of Pheidole, a famously hyperdiverse and ecologically dominant ant genus. We generate and analyse four novel datasets: (i) a robust global phylogeny including 285 Pheidole species, (ii) a global database on regional Pheidole richness in 365 political areas summarizing over 97 000 individual records from more than 6500 studies, (iii) a global database of Pheidole richness from 3796 local communities and (iv) a database of Pheidole body 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 that Pheidole reached dominance in communities through serial localized radiations into different biomes within different continents and islands. Pheidole body size distributions have likewise converged across geographical regions. We propose these cases of convergence indicate that the global radiation of Pheidole is structured by deterministic factors regulating diversification and diversity.

| S-EPMC4262160 | biostudies-literature

Fire ant worker brain transcriptomes

Project description:Transcriptomes of dissected brains from workers from polygyne fire ants were analyzed. Four replicates were obtained.

2020-07-18 | GSE117432 | GEO

Mechanical demands of bite in plane head shapes of ant (Hymenoptera: Formicidae) workers.

Project description:Food processing can exert significant evolutionary pressures on the morphological evolution of animal appendages. The ant genus Pheidole displays a remarkable degree of morphological differentiation and task specialization among its workers. Notably, there is considerable variation in head shape within worker subcastes of Pheidole, which could affect the stress patterns generated by bite-related muscle contraction. In this study, we use finite element analysis (FEA) to investigate the effect of the variation in head plane shape in stress patterns, while exploring the morphospace of Pheidole worker head shapes. We hypothesize that the plane head shapes of majors are optimized for dealing with stronger bites. Furthermore, we expect that plane head shapes at the edges of each morphospace would exhibit mechanical limitations that prevent further expansion of the occupied morphospace. We vectorized five head shapes for each Pheidole worker type located at the center and edges of the corresponding morphospaces. We conducted linear static FEA to analyze the stresses generated by mandibular closing muscle contraction. Our findings indicate that plane head shapes of majors exhibit signs of optimization to deal with stronger bites. Stresses are distinctly directed along the lateral margins of the head, following the direction of muscle contraction, whereas the stresses on the plane head shapes of minors tend to concentrate around the mandibular articulations. However, the comparatively higher stress levels observed on majors' plane head shapes suggest a demand for cuticular reinforcement, like increased cuticle thickness or sculpturing pattern. Our results align with the expectations regarding the main colony tasks performed by each worker subcaste, and we find evidence of biomechanical limitations on extreme plane head shapes for majors and minors.

| S-EPMC10244895 | biostudies-literature

Large deformation diffeomorphic mapping of 3D shape variation reveals two distinct mandible and head capsule morphs in Atta vollenweideri leaf‐cutter worker ants

Project description: Not available

| S-EPMC11021802 | biostudies-literature

Fire ant worker brain transcriptomes

Project description:Fire ant worker brain transcriptomes

| PRJNA482105 | ENA

Functional richness shows spatial scale dependency in <i>Pheidole</i> ant assemblages from Neotropical savannas.

Project description:There is a growing recognition that spatial scale is important for understanding ecological processes shaping community membership, but empirical evidence on this topic is still scarce. Ecological processes such as environmental filtering can decrease functional differences among species and promote functional clustering of species assemblages, whereas interspecific competition can do the opposite. These different ecological processes are expected to take place at different spatial scales, with competition being more likely at finer scales and environmental filtering most likely at coarser scales. We used a comprehensive dataset on species assemblages of a dominant ant genus, Pheidole, in the Cerrado (savanna) biodiversity hotspot to ask how functional richness relates to species richness gradients and whether such relationships vary across spatial scales. Functional richness of Pheidole assemblages decreased with increasing species richness, but such relationship did not vary across different spatial scales. Species were more functionally dissimilar at finer spatial scales, and functional richness increased less than expected with increasing species richness. Our results indicate a tighter packing of the functional volume as richness increases and point out to a primary role for environmental filtering in shaping membership of Pheidole assemblages in Neotropical savannas.Open research badgesThis article has been awarded Open Materials, Open Data, Preregistered Research Designs Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5061/dryad.31201jg.

| S-EPMC6822040 | biostudies-literature

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