Six decades of museum collections reveal disruption of native ant assemblages by introduced species.

There is a looming environmental crisis characterized by widespread declines in global biodiversity,1,2,3,4,5,6 coupled with the establishment of introduced species at accelerated rates.7,8,9,10,11,12,13,14 We quantified how multi-species invasions affect litter ant communities in natural ecosystems by leveraging museum records and contemporary collections to assemble a large (18,990 occurrences, 6,483 sampled local communities, and 177 species) 54-year (1965-2019) dataset for the entire state of Florida, USA. Nine of ten species that decreased most strongly in relative abundance ("losers") were native, while nine of the top ten "winners" were introduced species. These changes led to shifts in the composition of rare and common species: in 1965, only two of the ten most common ants were introduced, whereas by 2019, six of ten were introduced species. Native losers included seed dispersers and specialist predators, suggesting a potential loss of ecosystem function through time, despite no obvious loss of phylogenetic diversity. We also examined the role of species-level traits as predictors of invasion success. Introduced species were more likely to be polygynous than native species. The tendency to form supercolonies, where workers from separate nests integrate, also differed between native and introduced species and was correlated with the degree to which species increased in their rank abundances over 50 years. In Florida, introduced ants now account for 30% of occurrence records, and up to 70% in southern Florida. If current trends continue, introduced species will account for over half of occurrence records in all Florida's litter ant communities within the next 50 years.

Testing the predictive value of functional traits in diverse ant communities.

Associating morphological features with ecological traits is essential for understanding the connection between organisms and their roles in the environment. If applied successfully, functional trait approaches link form and function in an organism. However, functional trait data not associated with natural history information provide an incomplete picture of an organism's role in the ecosystem. Using data on the relative trophic position of 592 ant (Formicidae) samples comprising 393 species from 11 subfamilies and 19 widely distributed communities, we tested the extent to which commonly used functional proxies (i.e., morphometric traits) predict diet/trophic position as estimated from stable isotopes (δ15N). We chose ants as a group due to their ubiquity and abundance, as well as the wealth of available data on species traits and trophic levels. We measured 12 traits that have previously been identified as functionally significant, and corrected trait values for size and evolutionary history by using phylogenetically corrected trait residuals. Estimated trophic positions varied from 0.9 to 4.8 or roughly 4 trophic levels. Morphological data spanned nearly the entire size range seen in ants from the smallest (e.g., Strumigenys mitis total length 1.1 mm) to the largest species (e.g., Dinoponera australis total length 28.3 mm). We found overall body size, relative eye position, and scape length to be informative for predicting diet/trophic position in these communities, albeit with relatively weak predictive values. Specifically, trophic position was negatively correlated with body size and positively correlated with sensory traits (higher eye position and scape length). Our results suggest that functional trait-based approaches can be informative but should be used with caution unless clear links between form and function have been established.

The spongiform tissue in Strumigenys ants contains exocrine glands.

The insect cuticle is multifunctional and often includes projections used for support, communication or protection. Ants in the genus Strumigenys exhibit a peculiar honeycomb-like spongiform tissue that covers their petiole, postpetiole and sometimes also the posterior mesosoma and anterior part of the first gastral segment. The tissue is abundantly developed in workers and queens, and much reduced in males. We found this spongiform tissue is associated with a novel exocrine gland that is made up by class-3 secretory cells that are clustered underneath the major pillars of the cuticular extensions, their associated narrow ducts enter these extensions and open at the surface through small pores. The chemical nature and function of the secretion are still unknown. The honeycomb texture may act in the storage and dispersion of the glandular secretions. In addition to the spongiform tissue gland, the posterior region of the petiole and postpetiole also contain intersegmental petiole and postpetiole glands, of which the ducts open through the intersegmental membrane that forms the connection with the next segment. Future work aimed at identifying the chemicals secreted by these glands will shed light onto the function of these unusual structures.

Land use and soil characteristics affect soil organisms differently from above-ground assemblages.

BACKGROUND: Land-use is a major driver of changes in biodiversity worldwide, but studies have overwhelmingly focused on above-ground taxa: the effects on soil biodiversity are less well known, despite the importance of soil organisms in ecosystem functioning. We modelled data from a global biodiversity database to compare how the abundance of soil-dwelling and above-ground organisms responded to land use and soil properties. RESULTS: We found that land use affects overall abundance differently in soil and above-ground assemblages. The abundance of soil organisms was markedly lower in cropland and plantation habitats than in primary vegetation and pasture. Soil properties influenced the abundance of soil biota in ways that differed among land uses, suggesting they shape both abundance and its response to land use. CONCLUSIONS: Our results caution against assuming models or indicators derived from above-ground data can apply to soil assemblages and highlight the potential value of incorporating soil properties into biodiversity models.

Muscle fatigue in the latch-mediated spring actuated mandibles of trap-jaw ants.

Muscle fatigue can reduce performance potentially affecting an organism's fitness. However, some aspects of fatigue could be overcome by employing a latch-mediated spring actuated system (LaMSA) where muscle activity is decoupled from movement. We estimated the effects of muscle fatigue on different aspects of mandible performance in six species of ants, two whose mandibles are directly actuated by muscles and four that have LaMSA "trap-jaw" mandibles. We found evidence that the LaMSA system of trap-jaw ants may prevent some aspects of performance from declining with repeated use, including duration, acceleration and peak velocity. However, inter-strike interval increased with repeated strikes suggesting that muscle fatigue still comes into play during the spring loading phase. In contrast, one species with directly actuated mandibles showed a decline in bite force over time. These results have implications for design principles aimed at minimizing the effects of fatigue on performance in spring and motor actuated systems.

Addressing Diverse Motivations to Enable Bioinspired Design.

Bioinspired design (BID) is an inherently interdisciplinary practice that connects fundamental biological knowledge with the capabilities of engineering solutions. This paper discusses common social challenges inherent to interdisciplinary research, and specific to collaborating across the disciplines of biology and engineering when practicing BID. We also surface best practices that members of the community have identified to help address these challenges. To accomplish this goal, we address challenges of bioinspiration through a lens of recent findings within the social scientific study of interdisciplinary teams. We propose three challenges faced in BID: (1) complex motivations across collaborating researchers, (2) misperceptions of relationships and benefits between biologists and engineers, and (3) institutionalized barriers that disincentivize interdisciplinary work. We advance specific recommendations for how to address each of these challenges.

ATLANTIC ANTS: a data set of ants in Atlantic Forests of South America.

Ants, an ecologically successful and numerically dominant group of animals, play key ecological roles as soil engineers, predators, nutrient recyclers, and regulators of plant growth and reproduction in most terrestrial ecosystems. Further, ants are widely used as bioindicators of the ecological impact of land use. We gathered information of ant species in the Atlantic Forest of South America. The ATLANTIC ANTS data set, which is part of the ATLANTIC SERIES data papers, is a compilation of ant records from collections (18,713 records), unpublished data (29,651 records), and published sources (106,910 records; 1,059 references), including papers, theses, dissertations, and book chapters published from 1886 to 2020. In total, the data set contains 153,818 ant records from 7,636 study locations in the Atlantic Forest, representing 10 subfamilies, 99 genera, 1,114 ant species identified with updated taxonomic certainty, and 2,235 morphospecies codes. Our data set reflects the heterogeneity in ant records, which include ants sampled at the beginning of the taxonomic history of myrmecology (the 19th and 20th centuries) and more recent ant surveys designed to address specific questions in ecology and biology. The data set can be used by researchers to develop strategies to deal with different macroecological and region-wide questions, focusing on assemblages, species occurrences, and distribution patterns. Furthermore, the data can be used to assess the consequences of changes in land use in the Atlantic Forest on different ecological processes. No copyright restrictions apply to the use of this data set, but we request that authors cite this data paper when using these data in publications or teaching events.

Effect of social structure and introduction history on genetic diversity and differentiation.

Invasive species are a global threat to biodiversity, and understanding their history and biology is a major goal of invasion biology. Population-genetic approaches allow insights into these features, as population structure is shaped by factors such as invasion history (number, origin and age of introductions) and life-history traits (e.g., mating system, dispersal capability). We compared the relative importance of these factors by investigating two closely related ants, Tetramorium immigrans and Tetramorium tsushimae, that differ in their social structure and invasion history in North America. We used mitochondrial DNA sequences and microsatellite alleles to estimate the source and number of introduction events of the two species, and compared genetic structure among native and introduced populations. Genetic diversity of both species was strongly reduced in introduced populations, which also differed genetically from native populations. Genetic differentiation between ranges and the reduction in microsatellite diversity were more severe in the more recently introduced and supercolonial T. tsushimae. However, the loss of mitochondrial haplotype diversity was more pronounced in T. immigrans, which has single-queen colonies and was introduced earlier. Tetramorium immigrans was introduced at least twice from Western Europe to North America and once independently to South America. Its monogyny might have limited genetic diversity per introduction, but new mutations and successive introductions over a long time may have added to the gene pool in the introduced range. Polygyny in T. tsushimae probably facilitated the simultaneous introduction of several queens from a Japanese population to St. Louis, USA. In addition to identifying introduction pathways, our results reveal how social structure can influence the population-genetic consequences of founder events.

Functional innovation promotes diversification of form in the evolution of an ultrafast trap-jaw mechanism in ants.

Evolutionary innovations underlie the rise of diversity and complexity-the 2 long-term trends in the history of life. How does natural selection redesign multiple interacting parts to achieve a new emergent function? We investigated the evolution of a biomechanical innovation, the latch-spring mechanism of trap-jaw ants, to address 2 outstanding evolutionary problems: how form and function change in a system during the evolution of new complex traits, and whether such innovations and the diversity they beget are repeatable in time and space. Using a new phylogenetic reconstruction of 470 species, and X-ray microtomography and high-speed videography of representative taxa, we found the trap-jaw mechanism evolved independently 7 to 10 times in a single ant genus (Strumigenys), resulting in the repeated evolution of diverse forms on different continents. The trap mechanism facilitates a 6 to 7 order of magnitude greater mandible acceleration relative to simpler ancestors, currently the fastest recorded acceleration of a resettable animal movement. We found that most morphological diversification occurred after evolution of latch-spring mechanisms, which evolved via minor realignments of mouthpart structures. This finding, whereby incremental changes in form lead to a change of function, followed by large morphological reorganization around the new function, provides a model for understanding the evolution of complex biomechanical traits, as well as insights into why such innovations often happen repeatedly.

Pervasive and persistent effects of ant invasion and fragmentation on native ant assemblages.

Biological invasions are a leading cause of global change, yet their long-term effects remain hard to predict. Invasive species can remain abundant for long periods of time, or exhibit population crashes that allow native communities to recover. The abundance and impact of nonnative species may also be closely tied to temporally variable habitat characteristics. We investigated the long-term effects of habitat fragmentation and invasion by the Argentine ant (Linepithema humile) by resurveying ants in 40 scrub habitat fragments in coastal southern California that were originally sampled 21 yr ago. At a landscape scale, fragment area, but not fragment age or Argentine ant mean abundance, continued to explain variation in native ant species richness; the species-area relationship between the two sample years did not differ in terms of slope or intercept. At local scales, over the last 21 yr we detected increases in the overall area invaded (+36.7%, estimated as the proportion of occupied traps) and the relative abundance of the Argentine ant (+121.95%, estimated as mean number of workers in pitfall traps). Argentine ant mean abundance also increased inward from urban edges in 2017 compared to 1996. The greater level of penetration into fragments likely reduced native ant richness by eliminating refugia for native ants in fragments that did not contain sufficient interior area. At one fragment where we sampled eight times over the last 21 yr, Argentine ant mean abundance increased over time while the diversity of native ground-foraging ants declined from 14 to 4 species. Notably, native species predicted to be particularly sensitive to the combined effect of invasion and habitat loss were not detected at any sites in our recent sampling, including the army ant genus Neivamyrmex. Conversely, two introduced ant species (Brachymyrmex patagonicus and Pheidole flavens) that were undetected in 1996 are now common and widespread at our sites. Our results indicate that behaviorally and numerically dominant invasive species can maintain high densities and suppress native diversity for extended periods.

Analysis of Recent Interception Records Reveals Frequent Transport of Arboreal Ants and Potential Predictors for Ant Invasion in Taiwan.

We uncovered taxonomic diversity, country of origin and commodity type of intercepted ants at Taiwanese borders based on an 8 year database of 439 interception records. We found intercepted ants arrived predominantly via timber, a pattern likely reflecting the high domestic demand for foreign timber in Taiwan. The most frequently intercepted species were either arboreal or wood-dwelling ants, raising a concern of these ants constituting a next wave of ant invasion in Taiwan. Further analyses indicate that the taxonomic composition of intercepted ants does not match that of established non-native ant species, suggesting that interception data alone fails to provide adequate power to predict the establishment success of ants. Yet, interception frequency and selected life-history traits (i.e., flexible colony founding mode and general nesting habits) were shown to jointly serve as a practical predictor of the establishment risk of non-native ants. Consistent with other border interception databases, secondary introduction (i.e., species arriving from their introduced ranges instead of their native ranges) also represents a major pathway for transport of invasive ants into Taiwan, suggesting its role in shaping the global invasion of ants. Our findings offer baseline information for constructing a prediction framework for future ant invasions and assist in the decision-making process of quarantine authorities in Taiwan.

The evolution of conspecific acceptance threshold models.

How do organisms balance different types of recognition errors when cues associated with desirable and undesirable individuals or resources overlap? This is a fundamental question of signal detection theory (SDT). As applied in sociobiology, SDT is not limited to a single context or animal taxon, therefore its application can span what may be considered dissimilar systems. One of the applications of SDT is the suite of acceptance threshold models proposed by Reeve (1989), which analysed how individuals should balance acceptance and rejection errors in social discrimination decisions across a variety of recognition contexts, distinguished by how these costs and benefits relatively combine. We conducted a literature review to evaluate whether these models' specific predictions have been upheld. By examining over 350 research papers, we quantify how Reeve's models (Reeve 1989 Am. Nat.133, 407-435 (doi:10.1086/284926)) have influenced the field of ecological and behavioural recognition systems research. We found overall empirical support for the predictions of the specific models proposed by Reeve, and argue for further expansion of their applications into more diverse taxonomic and additional recognition contexts. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

"Simple" Biomechanical Model for Ants Reveals How Correlated Evolution among Body Segments Minimizes Variation in Center of Mass as Heads Get Larger.

The field of comparative biomechanics strives to understand the diversity of the biological world through the lens of physics. To accomplish this, researchers apply a variety of modeling approaches to explore the evolution of form and function ranging from basic lever models to intricate computer simulations. While advances in technology have allowed for increasing model complexity, insight can still be gained through the use of low-parameter "simple" models. All models, regardless of complexity, are simplifications of reality and must make assumptions; "simple" models just make more assumptions than complex ones. However, "simple" models have several advantages. They allow individual parameters to be isolated and tested systematically, can be made applicable to a wide range of organisms and make good starting points for comparative studies, allowing for complexity to be added as needed. To illustrate these ideas, we perform a case study on body form and center of mass stability in ants. Ants show a wide diversity of body forms, particularly in terms of the relative size of the head, petiole(s), and gaster (the latter two make-up the segments of the abdomen not fused to thorax in hymenopterans). We use a "simple" model to explore whether balance issues pertaining to the center of mass influence patterns of segment expansion across major ant clades. Results from phylogenetic comparative methods imply that the location of the center of mass in an ant's body is under stabilizing selection, constraining the center of mass to the middle segment (thorax) over the legs. This is potentially maintained by correlated rates of evolution between the head and gaster on either end. While these patterns arise from a model that makes several assumptions/simplifications relating to shape and materials, they still offer intriguing insights into the body plan of ants across ∼68% of their diversity. The results from our case study illustrate how "simple," low-parameter models both highlight fundamental biomechanical trends and aid in crystalizing specific questions and hypotheses for more complex models to address.

Development but not diet alters microbial communities in the Neotropical arboreal trap jaw ant Daceton armigerum: an exploratory study.

To better understand the evolutionary significance of symbiotic interactions in nature, microbiome studies can help to identify the ecological factors that may shape host-associated microbial communities. In this study we explored both 16S and 18S rRNA microbial communities of D. armigerum from both wild caught individuals collected in the Amazon and individuals kept in the laboratory and fed on controlled diets. We also investigated the role of colony, sample type, development and caste on structuring microbial communities. Our bacterial results (16S rRNA) reveal that (1) there are colony level differences between bacterial communities; (2) castes do not structure communities; (3) immature stages (brood) have different bacterial communities than adults; and 4) individuals kept in the laboratory with a restricted diet showed no differences in their bacterial communities from their wild caught nest mates, which could indicate the presence of a stable and persistent resident bacterial community in this host species. The same categories were also tested for microbial eukaryote communities (18S rRNA), and (5) developmental stage has an influence on the diversity recovered; (6) the diversity of taxa recovered has shown this can be an important tool to understand additional aspects of host biology and species interactions.

Author Correction: Factors Associated with Variation in Cuticular Hydrocarbon Profiles in the Navel Orangeworm, Amyelois transitella (Lepidoptera: Pyralidae).

The original version of this article unfortunately contained a mistake. When filing the final publication details, we failed to include the following statement in our Acknowledgments paragraph: We thank the Almond Board of California for research funding.

Effects of Abdominal Rotation on Jump Performance in the Ant Gigantiops destructor (Hymenoptera, Formicidae).

Jumping is an important form of locomotion, and animals employ a variety of mechanisms to increase jump performance. While jumping is common in insects generally, the ability to jump is rare among ants. An exception is the Neotropical ant Gigantiops destructor (Fabricius 1804) which is well known for jumping to capture prey or escape threats. Notably, this ant begins a jump by rotating its abdomen forward as it takes off from the ground. We tested the hypotheses that abdominal rotation is used to either provide thrust during takeoff or to stabilize rotational momentum during the initial airborne phase of the jump. We used high speed videography to characterize jumping performance of G. destructor workers jumping between two platforms. We then anesthetized the ants and used glue to prevent their abdomens from rotating during subsequent jumps, again characterizing jump performance after restraining the abdomen in this manner. Our results support the hypothesis that abdominal rotation provides additional thrust as the maximum distance, maximum height, and takeoff velocity of jumps were reduced by restricting the movement of the abdomen compared with the jumps of unmanipulated and control treatment ants. In contrast, the rotational stability of the ants while airborne did not appear to be affected. Changes in leg movements of restrained ants while airborne suggest that stability may be retained by using the legs to compensate for changes in the distribution of mass during jumps. This hypothesis warrants investigation in future studies on the jump kinematics of ants or other insects.

Spanish: Efectos de la rotación abdominal en el desempeño del salto de la hormiga Gigantiops destructor (Hymenoptera, Formicidae) El salto es una forma importante de locomoción y muchos animales utilizan diversidad de mecanismos al saltar para mejorar su desempeño. A pesar de que el salto es común en insectos, en general, las hormigas presentan una habilidad limitada. La hormiga neotropical Gigantiops destructor (Fabricius 1804) es una excepción, y utiliza el salto para capturar presas o escapar de potenciales amenazas. Esta especie empieza el salto rotando el abdomen anteriormente al impulsarse desde el suelo. Se evaluaron las hipótesis que la rotación abdominal se usa tanto para la proporción de empuje durante el impulso, así como en la estabilización de la cantidad de movimiento rotacional durante la fase inicial del salto mientras se encuentra en el aire. Se usó videografía de alta velocidad para caracterizar el desempeño del salto entre dos plataformas. Posteriormente, un grupo de hormigas fueron anestesiadas, y con el uso de pegamento, se restringió el movimiento del abdomen para evitar la rotación de éstos en la subsecuente caracterización del desempeño al saltar. Los resultados apoyan la hipótesis que la rotación abdominal proporciona impulso adicional. La distancia máxima, el peso máximo y la velocidad del impulso durante el salto fueron reducidos cuando el abdomen está fijo comparados con los saltos de las hormigas que no sufrieron manipulación y las que se usaron en el tratamiento control. En contraste, no hubo evidencia que la estabilidad de rotación de las hormigas mientras se encontraban en el aire fuera afectada. Las hormigas con abdómenes fijos presentaron cambios en el movimiento de las patas que sugieren que la estabilidad se puede mantener al usar las patas y compensar la distribución de la masa durante el salto. Esta hipótesis justifica futuros estudios evaluando la cinemática del salto en hormigas y otros grupos de insectos. Translated to Spanish by Rafael Achury (rafaelachury@gmail.com).

French: Effet de la rotation abdominal sur les performances du saut chez la fourmi Gigantiops destructor (Hymenoptera, Formicidae) Sauter est une importante forme de locomotion, et les animaux utilisent une diversité de mécanismes pour améliorer les performances de leurs sauts. Meme si sauter est commun chez les insectes en général, la capacité de sauter est rare chez les fourmis. La fourmi néotropicale Gigantiops destructor (Fabricius 1804) est une exception, elle est reconnue pour sauter sur ces proies ou pour s'échapper des menaces. Singulièrement, cette fourmi commence un saut par une rotation de son abdomen vers l'avant au moment de décoller du sol. Nous avons testé l'hypothèse que la rotation abdominale est utilisée pour soit générer une poussée au décollage, soit stabiliser l'élan rotatif pendant la phase aérienne initiale du saut. Nous avons utilisé l'enregistrement vidéo de grande vitesse pour caractériser la performance du saut des ouvrières G. destructor entre deux plateformes. Ensuite, nous avons anesthesié les fourmis et utilisé de la colle pour empêcher leurs abdomens de pivoter durant les prochains sauts, pour de nouveau caractériser la performance du saut suite à la restriction dudit abdomen de cette manière. Nos résultats soutiennent l'hypothèse que la rotation de l'abdomen entraine une poussée supplementaire vu que la distance maximale, la hauteur maximale et la vitesse de décollage des sauts sont réduites par la restriction du mouvement de l'abodmen comparer aux sauts des fourmis non manipulées du groupe témoin. Au contraire, la stabilité rotative des fourmis en phase aérienne ne semble pas être affectée. Les changements dans le mouvement des pattes des fourmis restraintes suggèrent que la stabilité peut être conservée en utilisant les pattes pour compenser les variations de la distribution de la masse pendant le saut. Cette hypothèse garantie, dans de futures études, l'exploration la cinématique du saut chez les fourmis et autres insectes. Translated to French by Jules Chabain (chabain2@illinois.edu).

Portuguese: Efeitos de Rotação Abdominal no Desempenho de Salto na Formiga Gigantiops destructor (Hymenoptera, Formicidae) O salto é uma forma importante de locomoção, e os animais empregam uma variedade de mecanismos para aumentar a performance de salto. Embora o salto seja comum nos insetos em geral, a capacidade de saltar é rara entre as formigas. Uma exceção é a formiga neotropical Gigantiops destructor (Fabricius 1804), conhecido por saltar para capturar presas ou escapar de ameaças. Notavelmente, essa formiga começa um salto girando seu abdômen para a frente enquanto sai do chão. Testamos as hipóteses de que a rotação abdominal é usada para fornecer impulso durante a saída do chão ou para estabilizar o momento de rotação durante a fase inicial do salto no ar. Utilizamos videografia de alta velocidade para caracterizar o desempenho de saltos de formigas operárias de G. destructor saltando entre duas plataformas. Em seguida, anestesiamos as formigas e aplicamos cola para impedir que o abdômen gire durante os saltos subsequentes, caracterizando novamente o desempenho do salto após restringir o abdômen dessa maneira. Nossos resultados suportam a hipótese de que a rotação abdominal fornece impulso adicional, pois a distância máxima, a altura máxima e a velocidade de saída dos saltos foram reduzidas pela restrição do movimento do abdômen, em comparação aos saltos das formigas não manipuladas e de controle. Em contraste, a estabilidade rotacional das formigas no ar não pareceu ser afetada. Alterações nos movimentos das pernas no ar das formigas restringidas sugerem que a estabilidade pode ser mantida usando as pernas para compensar as mudanças na distribuição da massa durante os saltos. Essa hipótese merece investigação em estudos futuros sobre a cinemática do salto de formigas ou outros insetos.Translated to Portuguese by Diego Vaz (dbistonvaz@vims.edu).

Factors Associated with Variation in Cuticular Hydrocarbon Profiles in the Navel Orangeworm, Amyelois transitella (Lepidoptera: Pyralidae).

Cuticular hydrocarbons (CHCs) are the main components of the epicuticular wax layer that in many insects functions as a barrier against desiccation. CHCs also play many other roles, including serving as sex pheromones, kairomones, primer pheromones, and colony-, caste-, species- and sex-recognition signals. In insects, CHC profiles can vary depending upon age, species, sex, and strain. Understanding factors associated with variation in hydrocarbon profiles is important for identifying potential vulnerabilities relating to pest ecology and life histories and for developing tools for pest monitoring and management strategies. In this study, we assessed potential sources of variation in CHC profiles in the navel orangeworm Amyelois transitella (Walker) (Lepidoptera: Pyralidae), an economically important pest of nut crops in California. Using coupled gas chromatography-mass spectrometry, we characterized and compared CHC profiles between adults of pyrethroid-resistant (R347) and susceptible (ALMOND) strains. We further compared CHC profiles from adults differing in age (1, 3, 5, and 7 d post-eclosion) and sex. Hydrocarbon profiles comprised 47 different CHCs in detectable quantities that ranged from C17 to C43 in chain length and included straight-chain alkanes and a variety of mono-, di-, and tri-methylalkanes. Adults from resistant populations had greater quantities of CHCs in total than those from susceptible strains, but relative quantities of individual components were similar. The six most abundant compounds were n-pentacosane, n-heptacosane, n-nonacosane, n-hentriacontane, 11,25 + 13,23 + 15,21-dimethylpentatriacontane, and 13,23 + 11,25 + 9,17-dimethylheptatriacontane. Post-eclosion, total CHCs increased with adult age, with males producing greater quantities than females at all ages. Our results show that CHC profiles vary depending on age, sex, and strain and suggest that CHC profiles may be useful as biomarkers to differentiate between insecticide- resistant and susceptible populations.

Genetic Diversity and Wolbachia Infection Patterns in a Globally Distributed Invasive Ant.

Understanding the phylogeographic history of an invasive species may facilitate reconstructing the history and routes of its invasion. The longhorn crazy ant, Paratrechina longicornis, is a ubiquitous agricultural and household pest throughout much of the tropics and subtropics, but little is known about the history of its spread. Here, we examine worldwide genetic variation in P. longicornis and its associated Wolbachia bacterial symbionts. Analyses of mtDNA sequences of 248 P. longicornis workers (one per colony) from 13 geographic regions reveal two highly diverged mtDNA clades that co-occur in most of the geographic regions. These two mtDNA clades are associated with different Wolbachia infection patterns, but are not congruent with patterns of nDNA (microsatellite) variation. Multilocus sequence typing reveals two distinct Wolbachia strains in P. longicornis, namely, wLonA and wLonF. The evolutionary histories of these two strains differ; wLonA appears to be primarily transmitted maternally, and patterns of mtDNA and nDNA variation and wLonA infection status are consistent with a relatively recent Wolbachia-induced selective sweep. In contrast, the observed patterns of mtDNA variation and wLonF infections suggest frequent horizontal transfer and losses of wLonF infections. The lack of nDNA structure among sampled geographic regions coupled with the finding that numerous mtDNA haplotypes are shared among regions implies that inadvertent long-distance movement through human commerce is common in P. longicornis and has shaped the genetic structure of this invasive ant worldwide.

Co-occurrence Patterns in a Subtropical Ant Community Revealed by Complementary Sampling Methodologies.

Ants are abundant and ecologically dominant insects in most terrestrial communities. In subtropical ecosystems, there is a high turnover of species from the canopy to the top layers of the soil. Additionally, ant communities are often influenced by inter-specific competition. Collectively, these two processes (abiotic filtering and competition) make ants ideal for studies of community structure. We examined composition, co-occurrence, and species interactions in a sub-tropical forest ant community to examine how ground-foraging ant species partition microhabitats. We used four methods: pitfall traps, litter samples, surface baits, and subterranean baits. Surface baiting was employed at three different time periods to examine how foraging activity and species interactions at baits varied with time of day and temperature. Each method sampled a particular assemblage of the 97 total ant species. Pitfall traps shared ~50% of species with surface baits and litter samples. Subterranean baits had the fewest total species but included some uncommonly sampled ants. The majority of interactions between species at baits were neutral, but a few agonistic interactions were also observed when bait occupancy was highest. Species co-occurrence patterns suggest that this ant community may not be heavily influenced by interspecific competition. Our results reinforce the advantages of applying complementary sampling techniques to examine ant community structure, and suggest that competition and dominance is best considered in the context of resource type, foraging strategy and time of sampling. Finally, we discuss the lack of two conspicuous Neotropical groups in our samples, leaf-cutting ant and army ants.

Taxon cycle predictions supported by model-based inference in Indo-Pacific trap-jaw ants (Hymenoptera: Formicidae: Odontomachus).

Nonequilibrium dynamics and non-neutral processes, such as trait-dependent dispersal, are often missing from quantitative island biogeography models despite their potential explanatory value. One of the most influential nonequilibrium models is the taxon cycle, but it has been difficult to test its validity as a general biogeographical framework. Here, we test predictions of the taxon cycle model using six expected phylogenetic patterns and a time-calibrated phylogeny of Indo-Pacific Odontomachus (Hymenoptera: Formicidae: Ponerinae), one of the ant genera that E.O. Wilson used when first proposing the hypothesis. We used model-based inference and a newly developed trait-dependent dispersal model to jointly estimate ancestral biogeography, ecology (habitat preferences for forest interiors, vs. "marginal" habitats, such as savannahs, shorelines, disturbed areas) and the linkage between ecology and dispersal rates. We found strong evidence that habitat shifts from forest interior to open and disturbed habitats increased macroevolutionary dispersal rate. In addition, lineages occupying open and disturbed habitats can give rise to both island endemics re-occupying only forest interiors and taxa that re-expand geographical ranges. The phylogenetic predictions outlined in this study can be used in future work to evaluate the relative weights of neutral (e.g., geographical distance and area) and non-neutral (e.g., trait-dependent dispersal) processes in historical biogeography and community ecology.