Behavioural and physiological traits to thermal stress tolerance in two Spanish desert ants

In Mediterranean open habitats, dominant ant species are heat-intolerant and risk-averser, foraging very far from their critical thermal limits (CTM). Subordinate are heat-tolerant (thermophilic) and risk-proner, foraging very near their CTM, running a high heat mortality risk, but having better performance at high temperatures. Thermal tolerance allows a far greater dominance in the ecosystem by subordinates than might be expected from their relative abundance and fighting abilities. Foraging of subordinates is more influenced by temperature than by competition of dominants. The mutual exclusion between dominant and subordinate species seems the result of physiological specialization to different temperature ranges. Focussing on two Cataglyphis species (subordinate and thermophilic), two alternative mechanisms facing extreme heat are described: C. velox polymorphism (large workers are more resistant than small ones), and physiological and behavioural adaptations of C. rosenhaueri workers (all of them of small size).Peer Reviewe

Patterns of diversity and composition of Mediterranean ground ant communities tracking spatial and temporal variability in the thermal environment

The present study analyzed ant community structure and the factors affecting it in the Spanish Mediterranean area. The aim of this study was to test whether temperature controls the composition and diversity of the ground ant fauna and the spatial and temporal distribution of dominance groups along adjacent communities. The main descriptors of community structure (except perhaps species richness) were found to vary along the gradient of vegetation cover: increased vegetation cover resulted in an increase in the relative abundance of the most common species, which led to a significant decrease in species evenness, together with a reduction in total ant density on the ground. In open habitats, dominant and subordinate species were abundant during different periods of the day, and this led to an increase in species evenness. In areas with high vegetation cover, dominants benefited from the lower temperatures by lengthening their periods of activity. This resulted in a decrease in the abundance of subordinate species, and in lower evenness. Seasonal patterns in community structure tracked temperature fluctuations and varied between habitat types. Evenness was similar in the two habitat types in spring, but increased in grasslands and decreased in shrublands/forests in summer. Species richness did not vary between seasons or habitat types. The relative abundance of dominance groups in the two types of habitats showed a different pattern between seasons. In grasslands, subordinates increased and dominants decreased their relative abundance from spring to summer, while in shrublands/forests, the opposite pattern was found. The overall conclusion from this study is that ground ant communities in open areas are primarily regulated by temperature variations, while in shrublands and forests, dominant species are more abundant, and competitive interactions appear to be the major structuring force.Peer Reviewe

Sobre la fundación de la sociedad en la hormiga Cataglyphis iberica (Emery, 1906) (Hymenoptera, Formicidae)

Colony founding in Cataglyphis iberica, a monogynous and polydomous ant species, has been studied. Nest population, worker size distribution and queeníworker dimorphism has been analyzed. Males and virgin females are found only in queenless nests. Virgin females have a relatively small fat content (36+8%) and after mating, they fly and go away from their original nest. Solitary mated queens are usually found in the field, but they never reach to found new societies in laboratory conditions. The contribution of these results to clarify the colony founding process, and the relationships between this process and polydomy phenomenon is discussed.Se ha estudiado el modo de fundación de la sociedad en la hormiga Cataglyphis iberica, especie monogínica y policálica. Se ha analizado la población de 10s nidos, la biometria de las obreras y el dimorfisme reina/obrera. Los sexuados se encuentran únicamente en 10s nidos sin reina de las colonias. Las hembras vírgenes tienen un contenido relativamente bajo en lípidos (36f 8%). Tras la cópula (siempre en el suelo: carrera nupcial) las hembras emprenden el vuelo y se alejan del nido madre. Se encuentran hembras solitarias y fecundadas por el campo, pero instaladas en el laboratorio mueren sin descendencia. Se discute la aportación de estos resultados en favor de 10s diversos tipos posibles de fundación, y su relación con la policalia

A multidimensional functional trait analysis of resource exploitation in European ants

The major factors explaining ecological variation in plants have been widely discussed over the last decade thanks to numerous studies that have examined the covariation that exists between pairs of traits. However, multivariate relationships among traits remain poorly characterized in animals. In this study, we aimed to identify the main multivariate trait dimensions that explain variance in important functional traits related to resource exploitation in ants. To this end, we created a large ant trait database. This database includes information on 11 traits that are important in ant resource exploitation; data were obtained for 150 European species found in different biomes. First, we examined the pairwise correlations between the traits included in the database. Second, we used multivariate analyses to identify potential trait dimensions. Our study shows that, to a great extent, resource exploitation strategies align along two main trait dimensions. The first dimension emerged in both the overall and group-specific analyses, where it accounted for the same pairwise trait correlations. The second dimension was more variable, as species were grouped by levels of taxonomy, habitat, and climate. These two dimensions included most of the significant pairwise trait correlations, thus highlighting that complementarity, but also redundancy, exists among different pairs of traits. The first dimension was associated with behavioral dominance: dominance was associated with large colony size, presence of multiple nests per colony, worker polymorphism, and a collective foraging strategy. The second dimension was associated with resource partitioning along dietary and microhabitat lines: it ranged from species that consume liquid foods, engage in group foraging, and mainly nest in the vegetation to species that consume insects and seeds, engage in individual foraging, and demonstrate strictly diurnal activity. Our findings establish a proficient ecological trait-based animal research that minimizes the number of traits to be measured while maximizing the number of relevant trait dimensions. Overall, resource exploitation in animals might be framed by behavioral dominance, foraging strategy, diet, and nesting habitat; the position of animal species within this trait space could provide relevant information about their distribution and abundance, for today as well as under future global change scenarios.Peer reviewe

The role of competition by dominants and temperature in the foraging of subordinate species in Mediterranean ant communities

In this paper we test the influence of temperature and interference competition by dominant species on the foraging of subordinate species in Mediterranean ant communities. We have analyzed the changes in resource use by subordinate species in plots with different abundances of dominant ants, and in different periods of the day and the year, i.e., at different temperatures. The expected effects of competition by dominant species on foraging of subordinates were only detected for two species in the number of baits occupied per day, and for one species in the number of foragers at pitfall traps. In all three cases, subordinate species were less represented at baits or in traps in plots with a high density of dominants than in plots with a medium or low density of dominants. The number of workers per bait, and the foraging efficiency of subordinate species did not differ in plots differing in dominant abundance. Daily activity rhythms and curves of temperature versus foraging activity of subordinate species were also similar in plots with different abundance of dominant species, indicating no effect of dominants on the foraging times of subordinates. Instead, temperature had a considerable effect on the foraging of subordinate species. A significant relationship was found between maximum daily temperature and several variables related to foraging (the number of foragers at pitfall traps, the number of baits occupied per day, and the number of workers per bait) of a number subordinate species, both in summer and autumn. These results suggest that the foraging of subordinate ant species in open Mediterranean habitats is influenced more by temperature than by competition of dominants, although an effect of dominants on subordinates has been shown in a few cases. In ant communities living in these severe and variable environments, thermal tolerance reduces the importance of competition, and the mutual exclusion usually found between dominant and subordinate species appears to be the result of physiological specialization to different temperature ranges.Peer Reviewe

Dispersal of non-myrmecochorous plants by a >keystone disperser> ant in a Mediterranean habitat reveals asymmetric interdependence

In contrast to other plant-animal mutualisms, seed dispersal interactions, and particularly seed dispersal by ants, are generally considered asymmetric, non-specialized relationships in which dispersers depend less on plants than vice versa. Although myrmecochory is well understood in many terrestrial ecosystems, dispersal of non-elaiosome-bearing seeds by ants has barely been studied outside the Neotropics. Aphaenogaster senilis, a common ant in Southern Spain, collects a great variety of non-myrmecochorous diaspores along with insect prey. At our study site, fleshy fruits of Arum italicum, Phillyrea angustifolia and Pistacia lentiscus represent up to one-fourth of the items collected by A. senilis from June to November. However, they are mostly ignored by other ants. In the laboratory, the addition of A. italicum fruits to A. senilis insect-based diet increased male production and both worker and queen pupae size. Seeds were transported up to 8 m away from the mother plant and deposited in a favorable habitat allowing a relatively high proportion of germination. Given important differences in seed production between species, our data suggest that A. senilis removes virtually all seeds of A. italicum, but a negligible fraction of P. lentiscus seeds. We conclude that in contrast to the common view, dispersal of non-myrmecochorous Mediterranean plants by ants might be an important phenomenon. Keystone disperser ants like A. senilis probably obtain an important fitness advantage from non-myrmecochorous diaspore collection. However, plant benefit may vary greatly according to the amount of seeds per individual plant and the existence of alternative dispersal agents. © 2012 International Union for the Study of Social Insects (IUSSI).Peer Reviewe

Estrategias alternativas en el ciclo de vida de tres hormigas mediterráneas

Se ha estudiado el ciclo biológico de tres especies de hormigas mediterráneas, y se han constatado importantes diferencias entre ellas. Cataglyphis cursor hibema sin descendencia y completa un ciclo de nidada entre los meses de abril y septiembre. Aphaenogaster senilis hibema sin nidada y produce pupas durante un amplio periodo de tiempo, desde abril hasta octubre, aunque los valores mtiximos (que coinciden con el pico de actividad exterior) se dan en primavera y principio de verano. Ambas especies fundan la sociedad por fisión colonial, por lo que la descendencia obrera es la que condiciona decisivamente el ciclo de vida de las colonias. En cambio, Camponotus cruentatus funda la sociedad de manera independiente, por lo que debe producir un elevado número de sexuados que contrarresten la elevada mortalidad que tiene lugar durante el apareamiento. Su ciclo difiere de los anteriores en que hay una importante producción primaveral de sexuados y de obreras, que se solapan en el tiempo en el interior de los nidos. Las variaciones en los ciclos de vida de las tres especies se discuten en relación con la actividad estacional y las características ecológicas de cada una de ellas.Colony life cycles of three mediterranean ants have been analyzed, and important differences have been found among them. Cataglyphis cursor does not keep brood during the winter, and rears new individuals from egg to adult in only one activity period, from April to September. Aphaenogaster senilis spends the winter with brood, and produces new workers during a long period of the year, from April to October. Both species produce a small number of alates because they form new colonies by fission. Therefore, worker brood is the decisive factor that determines colony life cycles of both species. Camponotus cruentatus has an independent mode of colony founding, in which colonies produce a high number of alates in order to override the extremely high mortality of colony-founding queens during mating. Its colony cycle differs from the others in that there is a high spring production of alates and workers, which overlap into the nests. Variations in colony life cycles of these species in relationship with their seasonal activity pattem and their ecological features are discussed

Which tone-mapping operator is the best? A comparative study of perceptual quality

Altres ajuts: CERCA Programme/Generalitat de CatalunyaPublicat sota la llicència Open Access Publishing Agreement, específica d'Optica Publishing Group https://opg.optica.org/submit/review/pdf/CopyrightTransferOpenAccessAgreement-2022-06-27.pdfTone-mapping operators (TMOs) are designed to generate perceptually similar low-dynamic-range images from high-dynamic-range ones. We studied the performance of 15 TMOs in two psychophysical experiments where observers compared the digitally generated tone-mapped images to their corresponding physical scenes. All experiments were performed in a controlled environment, and the setups were designed to emphasize different image properties: in the first experiment we evaluated the local relationships among intensity levels, and in the second one we evaluated global visual appearance among physical scenes and tone-mapped images, which were presented side by side. We ranked the TMOs according to how well they reproduced the results obtained in the physical scene. Our results show that ranking position clearly depends on the adopted evaluation criteria, which implies that, in general, these tone-mapping algorithms consider either local or global image attributes but rarely both. Regarding the question of which TMO is the best, KimKautz ["Consistent tone reproduction," in Proceedings of Computer Graphics and Imaging (2008)] and Krawczyk ["Lightness perception in tone reproduction for high dynamic range images," in Proceedings of Eurographics (2005), p. 3] obtained the better results across the different experiments. We conclude that more thorough and standardized evaluation criteria are needed to study all the characteristics of TMOs, as there is ample room for improvement in future developments

A proactive-reactive syndrome affects group success in an ant species

Social insects have been particularly evolutionarily successful: they dominate terrestrial ecosystems all over the globe. Their success stems from their social organization, where one or a few individuals reproduce, whereas others carry out different colony tasks. From an evolutionary standpoint, social species are particularly interesting because natural selection acts at both the individual and colony levels. Therefore, we might expect to see selection acting simultaneously on personality at the individual level and colony level. In this study, we tested whether captive colonies of the ant Aphaenogaster senilis exhibited different behavioral types and evaluated their consequences for intraspecific competition. Our results demonstrate that colonies of the same age exposed to standardized laboratory conditions did indeed have different personalities. In addition, we found that A. senilis demonstrated a behavioral syndrome that included proactive and reactive behaviors: colonies varied in their approaches to exploration, risk taking, food retrieval, and conspecific interactions. This syndrome appears to be associated with a trade-off between competition for food resources and temperature-related foraging risks. >Bold> colonies contained individuals who more readily explored novel environments, exhibited aggressive behaviors, and demonstrated higher food-retrieval efficiency during intraspecific competition trials. However, such colonies were also more risk prone: workers suffered higher mortality rates because they more frequently foraged over their critical thermal maximum. The trade-off we observed under laboratory conditions might be key in maintaining colony-level personality, thus driving local-level adaptations in collective behavior.Peer Reviewe