Search

In some social insects, workers can produce females asexually through thelytokous parthenogenesis. This allows them to produce replacement queens (i.e. requeening) if the queen has died, but also to compete with the queen to produce females (i.e. reproductive cheating). For the first time, we experimentally tested the role of worker thelytoky under quasinatural conditions in the ant Cataglyphis cursor , where the queen uses both sexual and thelytokous reproduction. We reared pairs of orphaned and queenright colonies in enclosures for almost 3 months, during which they competed for resources. Orphaned colonies lost more workers than queenright colonies over the course of the experiment, presumably because of the costs of reproductive conflicts between workers. Nevertheless, they produced new queens through worker thelytoky and new colonies through colony fission. This is the first unambiguous demonstration that worker thelytoky allows requeening under natural conditions in this species. We further showed that worker thelytoky results in reproductive cheating in the form of a few workers reproducing in the presence of the queen (in queenright colonies) and a few worker lineages producing more new queens than other lineages (in orphaned colonies). In addition, it also results in rare instances of social parasitism, that is, workers entering and reproducing in foreign colonies. These benefits to workers seem too occasional and too low to drive the evolution of thelytoky in this species. We argue that thelytoky probably evolved in the queen caste, where it allows the production of young queens and confers frequent and large benefits by increasing gene transmission, but is also expressed in workers because of genetic correlations between the two castes. [ABSTRACT FROM AUTHOR]

Central place foragers are faced with the challenge to learn the position of their nest entrance in its surroundings, in order to find their way back home every time they go out to search for food. To acquire navigational information at the beginning of their foraging career, Cataglyphis noda performs learning walks during the transition from interior worker to forager. These small loops around the nest entrance are repeatedly interrupted by strikingly accurate back turns during which the ants stop and precisely gaze back to the nest entrance--presumably to learn the landmark panorama of the nest surroundings. However, as at this point the complete navigational toolkit is not yet available, the ants are in need of a reference system for the compass component of the path integrator to align their nest entrance-directed gazes. In order to find this directional reference system, we systematically manipulated the skylight information received by ants during learning walks in their natural habitat, as it has been previously suggested that the celestial compass, as part of the path integrator, might provide such a reference system. High-speed video analyses of distinct learning walk elements revealed that even exclusion from the skylight polarization pattern, UV-light spectrum and the position of the sun did not alter the accuracy of the look back to the nest behavior. We therefore conclude that C. noda uses a different reference system to initially align their gaze directions. However, a comparison of neuroanatomical changes in the central complex and the mushroom bodies before and after learning walks revealed that exposure to UV light together with a naturally changing polarization pattern was essential to induce neuroplasticity in these high-order sensory integration centers of the ant brain. This suggests a crucial role of celestial information, in particular a changing polarization pattern, in initially calibrating the celestial compass system. [ABSTRACT FROM AUTHOR]

Although extensive research has been carried out on the desert ants in the genus Cataglyphis in recent years, some of the specific intra- and interspecific relationships remain elusive. The present study disentangles the phylogenetic relationships among the C. bicolor complex in Israel using an integrative approach based on genetic markers, morphometric measurements, and chemical analyses (cuticular hydrocarbons). Several species delimitation approaches based on four nuclear, two mitochondrial, and eleven microsatellite markers, as well as 16 body measurements and 56 chemical variables, were employed to deciphering the occurrence of cryptic species in our data set. Our findings support the occurrence of at least four distinct species in the C. bicolor group in Israel, one of which may be a complex of three more recent species. The findings confirm the distinctiveness of C. isis and C. holgerseni . They attest the presence of a recently discovered species, C. israelensis, in the central mountain ridge and the occurrence of another clade distributed from the Negev to the Mediterranean coast, comprising the species C. niger, C. savignyi, and C. drusus . Although these three species are separated on the basis of mt DNA, this subgrouping was not supported by any of the nuclear sequence markers nor by the microsatellite analysis. This genetic structure may thus either reflect a possible recent speciation, or a geographical structuring of a single species. Overall, using these different sources of evidence we locate our samples within a global phylogeny of the bicolor group and discuss the processes that underlie speciation in this group. [ABSTRACT FROM AUTHOR]

Sexual activity is only a brief moment in the life of ant colonies, but it determines several characteristics of life history. Mating behaviour, distance of female dispersal and mode of colony foundation are interlinked. In species exhibiting 'male aggregation' (males and queens fly and mate away from natal nests), newly mated queens have no option but to found a colony alone (independent colony founding, ICF). In contrast, in 'female calling' species, queens mate close to the natal nests, then either fly or walk away for dispersal. In several species, they can also disperse on foot accompanied by nestmate workers (dependent colony founding, DCF). Here, we review field observations and genetic data to untangle dispersal strategies across the genus Cataglyphis. We complement these existing informations with queen thorax morphology and dissection of wing muscles. Our comparative study includes 18 species belonging to six species-groups. We found that female calling occurs across all clades, with only two species showing male aggregation. Although most species have normal flying queens specialized for ICF, species in three out of the six species-groups show DCF. Remarkably, species with DCF evolved short-winged 'brachypterous' queens that lack wing muscles. Relative size of their thorax sclerites can be used to predict lack of flight ability. Altogether, these results show a marked deviation from the breeding behaviour typical of most species in subfamily Formicinae. We discuss how reduction of female dispersal may be linked to harsh desert conditions. [ABSTRACT FROM AUTHOR]

Cataglyphis desert ants are famous navigators. Like all central place foragers, they are confronted with the challenge to return home, i.e. relocate an inconspicuous nest entrance in the ground, after their extensive foraging trips. When leaving the underground nest for the first time, desert ants perform a striking behavior, so-called learning walks that are well structured. However, it is still unclear how the ants initially acquire the information needed for sky- and landmark-based navigation, in particular how they calibrate their compass system at the beginning of their foraging careers. Using high-speed video analyses, we show that different Cataglyphis species include different types of characteristic turns in their learning walks. Pirouettes are full or partial rotations (tight turns about the vertical body axis) during which the ants frequently stop and gaze back in the direction of the nest entrance during the longest stopping phases. In contrast, voltes are small walked circles without directed stopping phases. Interestingly, only Cataglyphis ant species living in a cluttered, and therefore visually rich, environment (i.e. C. noda and C. aenescens in southern Greece) perform both voltes and pirouettes. They look back to the nest entrance during pirouettes, most probably to take snapshots of the surroundings. In contrast, C. fortis inhabiting featureless saltpans in Tunisia perform only voltes and do not stop during these turns to gaze back at the nest - even if a set of artificial landmarks surrounds the nest entrance. [ABSTRACT FROM AUTHOR]

The experimental study of rescue behaviour in ants, behaviour in which individuals help entrapped nestmates in distress, has revealed that rescuers respond to victims with very precisely targeted behaviour. In Cataglyphis cursor , several different components of rescue behaviour have been observed, demonstrating the complexity of this behaviour, including sand digging and sand transport to excavate the victim, followed by pulling on the victim’s limbs as well as the object holding the victim in place, behaviour that serves to free the victim. Although previous work suggested that rescue was optimally organized, first to expose and then to extricate the victim under a variety of differing circumstances, experimental analysis of that organization has been lacking. Here, using experimental data, we characterize the pattern of individual rescue behaviour in C. cursor by analysing the probabilities of transitions from one behavioural component to another. The results show that the execution of each behavioural component is determined by the interplay of previous acts. In particular, we show not only that ants move sand away from the victim in an especially efficient sequence of behaviour that greatly minimizes energy expenditure, but also that ants appear to form some kind of memory of what they did in the past, a memory that directs their future behaviour. [ABSTRACT FROM AUTHOR]

In ectotherms, high temperatures impose physical limits, impeding activity. Exposure to high heat levels causes various deleterious and lethal effects, including protein misfolding and denaturation. Thermophilic ectotherms have evolved various ways to increase macromolecular stability and cope with elevated body temperatures; these include the high constitutive expression of molecular chaperones. In this study, we investigated the effect of moderate to severe heat shock (37-45°C) on survival, heat hardening, protein damage and the expression of five heat tolerance-related genes (hsc70-4 h1, hsc70-4 h2, hsp83, hsc70-5 and hsf1) in two closely related Cataglyphis ants that occur in distinct habitats. Our results show that the highly thermophilic Sahara ant Cataglyphis bombycina constitutively expresses HSC70 at higher levels, but has lower induced expression of heat tolerance-related genes in response to heat shock, as compared with the more mesophilic Cataglyphis mauritanica found in the Atlas Mountains. As a result, C. bombycina demonstrates increased protein stability when exposed to acute heat stress but is less disposed to acquiring induced thermotolerance via heat hardening. These results provide further insight into the evolutionary plasticity of the hsp gene expression system and subsequent physiological adaptations in thermophilous desert insects to adapt to harsh environmental conditions. [ABSTRACT FROM AUTHOR]

The employment of an alternating tripod gait to traverse uneven terrains is a common characteristic shared among many Hexapoda. Because this could be one specific cause for their ecological success, we examined the alternating tripod gait of the desert ant Cataglyphis fortis together with their ground reaction forces and weight-specific leg impulses for level locomotion and on moderate (±30 deg) and steep (±60 deg) slopes in order to understand mechanical functions of individual legs during inclined locomotion. There were three main findings from the experimental data. (1) The hind legs acted as the main brake (negative weight-specific impulse in the direction of progression) on both the moderate and steep downslopes while the front legs became the main motor (positive weight-specific impulse in the direction of progression) on the steep upslope. In both cases, the primary motor or brake was found to be above the centre of mass. (2) Normalised double support durations were prolonged on steep slopes, which could enhance the effect of lateral shear loading between left and right legs with the presence of direction-dependent attachment structures. (3) The notable directional change in the lateral ground reaction forces between the moderate and steep slopes implied the utilisation of different coordination programs in the extensor-flexor system. [ABSTRACT FROM AUTHOR]

The present study focuses on the abundance, heavy metal content, and the impact of ecosystem engineering activities of two coal mine site-inhabiting ant species, Cataglyphis longipedem and Camponotus compressus. The abundance of Ct. longipedem increased while that of C. compressus decreased, with increasing soil pollution. Correspondence analysis reveals a close association between soil heavy metal concentrations and Ct. longipedem abundance, but this association is lacking in the case of C. compressus. Cataglyphis ants which occupy stress-characterized niches appear to be pre-adapted to tolerate heavy metal pollution. Higher concentrations of Zn and Mn in Ct. longipedem may contribute to the strengthening of the cuticular structures, necessary for nest excavation in the hard, arid soil and for single load carrying. C. compressus ants appear to be pollution sensitive. Their higher Fe content may be related to metal uptake via plant-derived liquids and species-specific regulatory mechanisms. The metal pollution index and biota-to-soil accumulation factors, calculated by using the ant body metal content of the two species, indicate an overall decrease of soil heavy metal concentrations with increase of the site age, which reflects the degree of pollution related to the mine site age. The concentrations of total and available heavy metals (Fe, Zn, Mn, Pb, and Cu) were significantly lower in the ant nest debris soil as compared to the reference soil. The results of the present study highlight the role of ants as bioindicators and in bioremediation of contaminated soil. [ABSTRACT FROM AUTHOR]

The desert ants Cataglyphis fortis inhabit the harsh salt pans of Tunisia. The individually foraging ants rely on path integration to navigate back to their nest. 1,2,3,4 However, as path integration accumulates errors 5 at a rate that increases with distance traveled, 6,7 it is supplemented by visual and olfactory cues. 8,9,10,11,12,13 We show that despite their impressive homing accuracy, ants returning from long foraging journeys face a mortality rate of up to 20%. To facilitate homing, colonies inhabiting the featureless center of the salt pan build tall nest hills as visual cues. Removing these hills triggers rebuilding, but visual artificial landmarks placed near the nest entrance are sufficient to suppress the ants' rebuilding activity. Our data suggest that the desert ant builds its own landmark on purpose in a featureless environment to increase its chances of successful homing and survival. [Display omitted] • Cataglyphis ants face high mortality during long foraging runs • Nests in the flat salt pan have taller nest hills than nests in structured areas • Ants use the nest hill as a visual cue to navigate home • Adding landmarks to nests in the salt pan suppresses hill-building behavior Freire et al. show that Cataglyphis ants build taller nest hills in environments with fewer visual cues to use them as landmarks, allowing them to locate their nests more efficiently in environments void of natural cues. [ABSTRACT FROM AUTHOR]

Organisms use an amazingly large diversity of mechanisms to pass on their genes to the next generation. Sex is ancestral in eukaryotes, where it remains the most widespread way of reproduction. By combining one's genes with those of a partner, sex entails a dilution of one's genes at each generation. Evolution has been particularly creative in devising mechanisms allowing females to avoid this dilution, from classical parthenogenesis to the elimination of male genes after fertilization (Bell, 1982). Moreover, the term parthenogenesis includes various forms. Parthenogenesis can be used for female (thelytoky) or male (arrhenotoky) production and it can be associated with different cytological mechanisms, from strict clonality to meiotic division with the fusion of two of the four products of meiosis to restore diploidy (Suomalainen, Saura, & Lokki, 1987). Understanding the evolution of these diverse reproductive systems remains one of the most exciting and longstanding questions in evolutionary biology. By characterizing the reproductive systems of 11 species from the thermophilic ant genus Cataglyphis, in this issue of Molecular Ecology, Kuhn, Darras, Paknia, and Aron (2020) show the high lability of parthenogenesis, with multiple independent evolution of facultative thelytoky from sexual ancestors. The diversity of life history traits and social characteristics of this genus (e.g., mode of colony foundation, female polyandry) provides a unique and exciting opportunity to investigate the social and environmental factors driving the evolution of reproductive systems in social Hymenoptera. [ABSTRACT FROM AUTHOR]

Air-cushioned spheres are widely used as treadmills to study behavioural and neurophysiological questions in numerous species. We describe an improved spherical treadmill design that reliably registers the path and walking behaviour of an animal walking on top of the sphere. The simple and robust set-up consists of a very light hollowed styrofoam ball supported by an air stream in a hollow half sphere and can be used indoors and outdoors. Two optical mouse sensors provided with lenses of 4.6 mmfocal length detect the motion of the sphere with a temporal resolution of more than 200 frames s-1 and a spatial resolution of less than 0.2 mm. The treadmill can be used in an open- or closed-loop configuration with respect to yaw of the animal. The tethering allows animals to freely adjust their body posture and in the closed-loop configuration to quickly rotate around their yaw axis with their own moment of inertia. In this account, we present the first evidence of naturalistic homing navigation on a spherical treadmill for two species of Cataglyphis desert ants. We were able to evaluate with good precision the walking speed and angular orientation at any time. During homing the ants showed a significant difference in walking speed between the approach and search phases; moreover, they slowed down significantly as soon as they reached zero vector state, the fictive nest position. [ABSTRACT FROM AUTHOR]

Unlike most desert-dwelling animals, Cataglyphis ants do not attempt to escape the heat; rather, they apply their impressive heat tolerance to avoid competitors and predators. This thermally defined niche has promoted a range of adaptations both at the individual and colony levels. We have also recently discovered that within the genus Cataglyphis there are incredibly diverse social systems, modes of reproduction, and dispersal, prompting the tantalizing question of whether social diversity may also be a consequence of the harsh environment within which we find these charismatic ants. Here we review recent advances regarding the physiological, behavioral, life-history, colony, and ecological characteristics of Cataglyphis and consider perspectives on future research that will build our understanding of organic adaptive responses to desertification. [ABSTRACT FROM AUTHOR]

Some species of Cataglyphis desert ants have evolved a hybridogenetic mode of reproduction at the social scale. In hybridogenetic populations, two distinct genetic lineages coexist. Non-reproductive offspring (workers) are hybrids of the two lineages, whereas sexual offspring (males and new queens) are produced by parthenogenesis and belong to the mother queen lineage. How this unusual reproductive system affects phylogeographic patterns and speciation processes remains completely unknown to date. Using one mitochondrial and four nuclear genes, we examined the phylogenetic relationships between three species of Cataglyphis ( C. hispanica , C. humeya and C. velox ) where complex DNA inheritance through social hybridogenesis may challenge phylogenetic inference . Our results bring two important insights. First, our data confirm a hybridogenetic mode of reproduction across the whole distribution range of the species C. hispanica . In contrast, they do not provide support for hybridogenesis in the populations sampled of C. humeya and C. velox . This suggests that these populations are not hybridogenetic, or that hybridogenesis is too recent to result in reciprocally monophyletic lineages on nuclear genes. Second, due to mitochondrial introgression between lineages (Darras and Aron, 2015), the faster-evolving COI marker is not lineage specific, hence, unsuitable to further investigate the segregation of lineages in the species studied. Different mitochondrial haplotypes occur in each locality sampled, resulting in strongly structured populations. This micro-allopatric structure leads to over-splitting species delimitation on mitochondrial gene, as every locality could potentially be considered a putative species; haploweb analyses of nuclear markers, however, yield species delimitations that are consistent with morphology. Overall, this study highlights how social hybridogenesis varies across species and shapes complex phylogeographic patterns. [ABSTRACT FROM AUTHOR]

At the beginning of their foraging lives, desert ants (Cataglyphis fortis) are for the first time exposed to the visual world within which they henceforth must accomplish their navigational tasks. Their habitat, North African salt pans, is barren, and the nest entrance, a tiny hole in the ground, is almost invisible. Although natural landmarks are scarce and the ants mainly depend on path integration for returning to the starting point, they can also learn and use landmarks successfully to navigate through their largely featureless habitat. Here, we studied how the ants acquire this information at the beginning of their outdoor lives within a nest-surrounding array of three artificial black cylinders. Individually marked 'newcomers' exhibit a characteristic sequence of learning walks. The meandering learning walks covering all directions of the compass first occur only within a few centimeters of the nest entrance, but then increasingly widen, until after three to seven learning walks, foraging starts. When displaced to a distant test field in which an identical array of landmarks has been installed, the ants shift their search density peaks more closely to the fictive goal position, the more learning walks they have performed. These results suggest that learning of a visual landmark panorama around a goal is a gradual rather than an instantaneous process. [ABSTRACT FROM AUTHOR]

How parents invest resources in offspring is a central aspect of life history. While investment strategies have been well studied in solitary organisms, comparatively little has been done on social species, including the many that reproduce by fission. Under colony fission, a parent colony divides resources (individuals) to form two or more offspring colonies. Because individuals differ in characteristics (e.g. size), there is opportunity for both quantitative and qualitative bias in their allocation. In this study we investigated the qualitative aspect of offspring investment during colony fission. Colonies of the ant Cataglyphis cursor fission into multiple offspring colonies as part of their lifecycle, and the distribution of workers is quantitatively biased. We found that investment is also qualitatively biased in terms of worker size and worker genetic characteristics (patrilines). This bias was mainly between the offspring colony that inherited the original nest and offspring colonies that dispersed to new nesting sites. In 74% of cases, dispersing colonies contained larger workers, and the distribution of genetic patrilines was biased in two of six cases in a manner that cannot be explained by the observed variation in worker size between patrilines. Fission also led to a reduction in diversity in offspring colonies compared to the parent colony, in terms of both worker size (70% of cases) and genetic diversity (40% of cases). These patterns are probably the result of differing dispersal probability between workers of different patrilines and of different size. This differential allocation may be adaptive because larger workers may be of disproportionate value to dispersing colonies, and their loss an acceptable cost to the colony inheriting the nest. [ABSTRACT FROM AUTHOR]

Cataglyphis desert ants display unique variation in their breeding systems, making this genus a particularly interesting model to study the evolution of derived reproductive traits in eusocial Hymenoptera. Colonies may be headed by a single or several queens, and queens may be singly or multiply mated. Furthermore, in a number of species, both the workers and queens do reproduce asexually by thelytokous parthenogenesis. We examined whether the variability in reproductive traits is the result of a single evolutionary transition or of multiple independent evolutionary transitions, per trait. First, we inferred a phylogenetic estimate for the genus by analyzing DNA sequence variation among several species at four independent loci. Our phylogenetic hypothesis confirms the monophyly of previously defined species groups. Second, we examined the evolution of four reproductive traits in the genus (queen mating frequency, colony queen number, as well as worker reproduction and queen reproduction by thelytokous parthenogenesis), by inferring the state of these traits at the ancestral nodes. Our results show that polyandry and monogyny are the most likely conditions for the ancestor of the genus; the status of worker and queen thelytoky remains ambiguous. Genetic diversity within colonies may have been a major driver for the evolution of derived reproductive traits in Cataglyphis. Significance statement: Kinship among group members has long been recognized as a main factor promoting the evolution of sociality and reproductive altruism. In eusocial Hymenoptera (ants, bees, wasps), at least three reproductive characteristics were shown to profoundly affect colony kin structure and may have played a key role in the evolution and maintenance of reproductive altruism: the queen mating frequency, the number of reproductive queens in a colony, and reproduction by parthenogenesis. We infer the evolution of these three reproductive traits in Cataglyphis desert ants, a genus displaying considerable variation in reproductive strategies. We propose a phylogenetic estimate for the genus, from variation at four loci. Then, we show that multiple evolutionary changes occurred for all three reproductive characters studied. Our results suggest that selection for enhanced colony genetic diversity has driven the evolution of reproductive traits away from their ancestral state. [ABSTRACT FROM AUTHOR]

Cataglyphis ants are renowned for their impressive navigation skills, which have been studied in numerous experiments during forward locomotion. However, the ants' navigational performance during backward homing when dragging large food loads has not been investigated until now. During backward locomotion, the odometer has to deal with unsteadymotion and irregularities in inter-leg coordination. The legs' sensory feedback during backward walking is not just a simple reversal of the forward stepping movements: compared with forward homing, ants are facing towards the opposite direction during backward dragging. Hence, the compass system has to cope with a flipped celestial view (in terms of the polarization pattern and the position of the sun) and an inverted retinotopic image of the visual panorama and landmark environment. The same is true for wind and olfactory cues. In this study we analyze for the first time backwardhoming ants and evaluate their navigational performance in channel and open field experiments. Backward-homing Cataglyphis fortis desert ants show remarkable similarities in the performance of homing compared with forward-walking ants. Despite the numerous challenges emerging for the navigational system during backward walking, we show that ants perform quite well in our experiments. Direction and distance gauging was comparable to that of the forwardwalking control groups. Interestingly, we found that backward-homing ants often put down the food itemand performed foodless search loops around the left food item. These search loops were mainly centred around the drop-off position (and not around the nest position), and increased in length the closer the ants came to their fictive nest site. [ABSTRACT FROM AUTHOR]

For insects, flexibility in the performance of terrestrial locomotion is a vital part of facing the challenges of their often unpredictable environment. Arthropods such as scorpions and crustaceans can switch readily from forward to backward locomotion, but in insects this behaviour seems to be less common and, therefore, is only poorly understood. Here we present an example of spontaneous and persistent backward walking in Cataglyphis desert ants that allows us to investigate rearward locomotion within a natural context. When ants find a food itemthat is too large to be lifted up and to be carried in a normal forward-faced orientation, they will drag the load walking backwards to their home nest. A detailed examination of this behaviour reveals a surprising flexibility of the locomotor output. Compared with forward walks with regular tripod coordination, no main coordination pattern can be assigned to rearward walks. However, we often observed leg-pair-specific stepping patterns. The front legs frequently step with small stride lengths, while the middle and the hind legs are characterized by less numerous but larger strides. But still, these specializations show no rigidly fixed leg coupling, nor are they strictly embedded within a temporal context; therefore, they do not result in a repetitive coordination pattern. The individual legs act as separate units, most likely to better maintain stability during backward dragging. [ABSTRACT FROM AUTHOR]

Cataglyphis cursor worker ants are capable of highly sophisticated rescue behaviour in which individuals are able to identify what has trapped a nestmate and to direct their behaviour towards that obstacle. Nonetheless, rescue behaviour is constrained by workers' subcaste: whereas foragers, the oldest workers, are able both to give and to receive the most help, the youngest workers, inactives, neither give nor receive any help whatsoever; nurses give and receive intermediate levels of aid, reflecting their intermediate age. Such differences in rescue behaviour across subcastes suggest that age and experience play a critical role. In this species, as in many others in which a sensitive period for nestmate recognition exists, newly enclosed ants, called callows, are adopted by ants belonging not only to different colonies but also to different species; foreign callows receive nearly the same special care provided to resident newborns. Because callows are younger than inactives, which are incapable of soliciting rescue, we wondered whether entrapped callows would receive such aid. In the present study, we artificially ensnared individual callows from their own colony (homocolonial), from a different colony (heterocolonial), and from a different species (heterospecific), and tested each one with groups of five potential C. cursor rescuers, either all foragers or all nurses. Our results show that all three types of callows are able to elicit rescue behaviour from both foragers and nurses. Nonetheless, nurse rescuers are better able to discriminate between the three types of callow victims than are foragers. [ABSTRACT FROM AUTHOR]

The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant’s dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat. In this paper, we further investigate how geometrical optical and high reflection properties account for the bright silver color of C. bombycina. Using optical ray-tracing models and attenuated total reflection (ATR) experiments, we show that, for a large range of incidence angles, total internal reflection (TIR) conditions are satisfied on the basal face of each hair for light entering and exiting through its upper faces. The reflection properties of the hairs are further enhanced by the presence of the corrugated surface, giving them an almost total specular reflectance for most incidence angles. We also show that hairs provide an almost 10-fold increase in light reflection, and we confirm experimentally that they are responsible for a lower internal body temperature under incident sunlight. Overall, this study improves our understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant’s body. [ABSTRACT FROM AUTHOR]

Under polyandry, males are selected to produce more competitive ejaculates. Theoretical models have explored how the mechanism of sperm competition drives males to partition investment within an ejaculate between sperm quantity and quality. The raffle-based competition model predicts that increased level of sperm competition selects for larger numbers of sperm in ejaculates. Sperm competition is also thought to promote the evolution of longer sperm, because longer sperm could be faster., In eusocial Hymenoptera, the mating system imposes unique selective pressures on male ejaculates. Males are short lived; they reach adulthood with a finite amount of spermatozoa, and they mate typically with a single or a few females and die. The actual number of spermatozoa stored in their accessory testes at emergence is thus a reliable measure of total investment into sperm production. In a comparative study of 15 species of Cataglyphis desert ants, we used phylogenetically controlled analyses to investigate relationships between levels of sperm competition, sperm production and sperm length. We measured sperm production by quantifying the number of spermatozoa present in testes, instead of using a proxy measure such as size of testes. Multiple queen mating is the ancestral state in the genus but reduction in mating frequency evolved secondarily and independently in some clades, providing a unique opportunity to examine how reduction from multiple to single mating influences sperm traits., Our results provide phylogenetically robust evidence that species experiencing greater levels of sperm competition produce more sperm. After controlling for male size, investment in sperm production decreases significantly according to the sequence obligatory multiple queen mating > multiple-single queen mating > single-double queen mating. Furthermore, the number of spermatozoa produced per male decreases significantly with reduction in paternity frequency for each species. In contrast, neither sperm length nor male size was significantly associated with the mating system classes or the number of patrilines., Our measures of sperm number provide the first direct evidence that sperm production covaries with the level of sperm competition in a eusocial insect. Given the reversal from multiple to single mating in Cataglyphis, our comparative analysis also shows convincingly that reduction in sperm competition influences sperm traits. [ABSTRACT FROM AUTHOR]

The nesting habits of ants play an important role in structuring ant populations. They vary from monodomy, a colony occupies a single nest, via polydomy, a colony occupies multiple adjacent nests, to supercoloniality, a colony spans over large territories comprising dozen to thousands nests without having any boundaries. The population structure of the desert ant Cataglyphis niger, previously considered to form supercolonies, was studied using genetic, chemical and behavioral tools in plots of 50x50 meters at two distinct populations. At the Palmahim site, the plot comprised 15 nests that according to the genetic analysis constituted three colonies. Likewise at the Rishon Leziyyon site 14 nests constituted 5 genetic colonies. In both sites, both chemical analysis and the behavioral (aggression) tests confirmed the colony genetic architecture. The behavioral tests also revealed that aggression between colonies within a population was higher than that exhibited between colonies of different populations, suggesting the occurrence of the nasty neighbor phenomenon. In contrast to supercolony structure previously reported in another population of this species, the presently studied populations were composed of polydomous colonies. However, both the genetic and chemical data revealed that the inter-colonial differences between sites were larger than those within site, suggesting some within-site population viscosity. Thus, C. niger exhibits flexible nesting characteristics, from polydomy to supercoloniality, and can be considered at the brink of supercoloniality. We attribute the differences in population structure among sites to the intensity of intraspecific competition.

Cataglyphis fisheri sp. n. is described and illustrated from the United Arab Emirates, Oman and Kingdom of Saudi Arabia based on the worker caste. It belongs to the C. pallida-group which is recorded for the first time from the Arabian Peninsula. Cataglyphis fisheri sp. n. is similar to C. pallida Mayr, 1877 from Kazakhstan. Differential diagnosis between these two species is given and a key to the species of the C. pallida-group is presented. Cataglyphis laylae Collingwood, 2011 is treated as a junior synonym of Cataglyphis saharae Santschi, 1929. Cataglyphis flavobrunnea Collingwood & Agosti, 1996 is redescribed and a lectotype for this species is designated. [ABSTRACT FROM AUTHOR]

Division of labor among workers is a hallmark of social insects that has largely contributed to their ecological success. In a number of species, ants in particular, environmental cues have long been recognized to determine the different phenotypes of workers. Recently, however, a genetic basis for worker polymorphism has been documented in some species. The silver ant Cataglyphis bombycina is characterized by the co-existence of two physiologically distinct castes of non-reproductive individuals: workers and soldiers. Soldiers are not a worker subcaste; they belong to a third caste, along with the queen and the worker castes. Using microsatellite DNA markers, we tested whether soldier caste determination has a genetic component, by comparing the distribution of patrilines between the soldier and the worker castes. Our data show evidence of genotypic variation in caste propensity in only 2 out of 7 colonies sampled. In addition, most patrilines produce both workers and soldiers across all colonies. These results support moderate genotypic influence to soldier caste determination and suggest that non-genetic, likely environmental factors, also influence caste fate among non-reproductive offspring in this species. We also provide new estimates of the queen mating frequency, which support biogeographic variations in mating behavior in C. bombycina. [ABSTRACT FROM AUTHOR]

Desert ants, Cataglyphis fortis , forage for dead arthropods in the Tunisian salt pans. Both the unpredictable food distribution and the high surface temperatures might account for the fact that the ants do not use any pheromone trails. However, Cataglyphis has been shown to still use olfactory cues for navigation. For instance, the ants locate sparsely distributed food or pinpoint their inconspicuous nest entrance by following odour plumes. In this study we found that, as well as using odours to pinpoint a target, the ants might use environmental odours as olfactory landmarks when following habitual routes. When analysing odours collected at 100 positions in the desert, we found spatially distinct gradients of a range of different environmental odorants. Furthermore we confirm that individual foragers followed forager-specific routes when leaving the nest. Therefore these ants could potentially learn such olfactory landscape features along their stable routes. We, hence, asked whether ants could learn and use olfactory cues for route guidance. We trained ants to visit a stable feeder and presented them with a sequence of four different odours along the way. Homing ants that had already passed the odour alley on their way back were displaced to a remote test field and released at the starting point of an identical alley. Control ants that experienced the alley only during the test situation focused their search on the release point. Ants that had experienced the odours during training, however, biased their nest search towards the odour alley and performed straight walking segments along the alley. Hence, we found that ants learnt the olfactory cues along their homeward route and used these cues in the absence of other navigational information. Hence, desert ants seem to be able to use odour information to follow routes. [ABSTRACT FROM AUTHOR]

The article focuses on research on the thermoregulatory effects of triangular hairs on Saharan silver ants which allows them to forage under extreme temperature conditions in the Saharan desert. It states that the ants' silvery appearance is caused by the hairs which enhances the reflectivity of the body surface of the antis in near-infrared and visible range of the spectrum. It mentions the hairs allow the ants to dissipate heat in the mid-infrared using blackbody radiation.

Sexual selection typically shapes the traits of individuals capable of reproduction. However, in social species, it may also affect the behaviour of non-reproductive individuals if this increases their inclusive fitness. We examined the potential role of workers during mating in the polyandrous ant Cataglyphis cursor. In this species, mating takes place on the ground near the nest entrance, and workers chase away foreign males trying to mate with young queens (gynes). We investigated the effects of worker aggression on male mating attempts by placing three or four males in the presence of one foreign gyne and 20 of her nestmate workers and contrasted this with a second group of 3-4 males in the presence of another gyne without nestmate workers (n = 8 paired replicates). Workers strongly attacked males (more than 20 aggressions per minute), although this did not affect the total number of mating attempts by the 3-4 males or the skew in the number of mating attempts among these males. However, there was an interaction between worker aggression and relative male weight, as relatively heavy males attempted to mate more often than lighter males in the absence of worker whereas the reverse occurred in the presence of workers. Our study is the first to experimentally test the potential role of non-reproductive individuals in sexual selection. It shows that workers could potentially change male mating success by disfavouring heavier males. [ABSTRACT FROM AUTHOR]

North African desert ants, Cataglyphis, use path integration to calculate a home vector during their foraging trips, constantly informing them about their position relative to the nest. This home vector is also used to find the way back to a productive feeding site the ant has encountered and thus memorized. When the animal fails to arrive at its goal after having run off the home or food vector, a systematic search is initiated. The basic search strategies are identical for nest and food searches, consisting of a search spiral superimposed by a random walk. While nest searches have been investigated in much detail, food site searches have received comparatively little attention. Here, we quantify and compare nest and food site searches recorded under similar conditions, particularly constant nest-feeder distance, and we observe notable differences in nest and food search performances. The parameters of nest searches are relatively constant and improve little with experience, although those small improvements had not been recognized previously. Food searches, by contrast, are more flexible and cover smaller or larger areas, mainly depending on the reliability of food encounter over several visits. Intriguingly, food site searches may be significantly more focussed than nest searches, although the nest should be the most important goal in an ant's life. These results demonstrate both adaptability and high accuracy of the ants' search programme. [ABSTRACT FROM AUTHOR]

Desert ants, Cataglyphis fortis, perform large foraging excursions during which they continuously compute a home vector that allows them to return to the nest on the shortest way. This type of navigation, termed path integration, needs a compass system and an odometer. Ants use several cues to determine their walking direction, two of the most important ones being the sun position and the polarization pattern of the sky. We tested whether an information transfer is possible from one compass system to the other, which depend on different anatomical substrates. Since the sky's polarization pattern is detected by UV-photoreceptors located in the dorsal rim area (DRA), we used an orange Perspex filter that eliminated the UV part of the spectrum to prevent the use of the polarization compass. The use of the sun compass could be excluded by appropriate screens. In the critical tests the ants had learned a nest-feeder direction with e.g. the sun compass only, and were later tested with the polarization compass, or vice versa. The results show that a transfer is possible in both directions. [ABSTRACT FROM AUTHOR]

North African desert ants, Cataglyphis fortis, use path integration as their primary means of navigation. The ants also use landmarks when these are available to improve navigation accuracy. Extended landmarks, such as walls and channels, may serve further functions, for example, local guidance or triggering of local vectors. The roles of such structures were usually examined in homing animals but not during food searches. When searching for familiar feeding sites, Cataglyphis may show intriguing deviations from expected search performances. These may result from the presence of extended landmarks, namely experimental channels. Here we scrutinise this hypothesis of landmark guidance in food searches. We prevented the ants from seeing the channel walls by covering their eyes, except the dorsal rim area. This experiment was repeated in the open test field with an alley of black cylinders to extend our findings to a more normal foraging environment. Ants with covered eyes did not deviate from expected search performances, whereas ants with normal eyes extended their searches along the axis of the leading structures by 15-20 %, in both channels and landmark alleys. This demonstrates that Cataglyphis orients along extended landmarks when searching for familiar food sources and alters its search pattern accordingly. [ABSTRACT FROM AUTHOR]

Desert ants, Cataglyphis fortis, navigate individually in the salt pans of Tunisia by means of path integration. However, as path integration is error-prone, the ants in addition use visual and olfactory cues to pinpoint their nest entrance. It has been shown that the accuracy of the path integrator as well as the ants' confidence in that egocentric navigational tool decreases with increasing foraging distance. Here, we show that despite the accumulating errors, even after far-reaching foraging runs path integration provides the ants with surprisingly accurate information regarding the nest position. However, in addition, the ants take into account distant visual cues that are most probably provided by the patterns along the horizon line behind the nest entrance. [ABSTRACT FROM AUTHOR]

Path integration, although inherently error-prone, is a common navigation strategy in animals, particularly where environmental orientation cues are rare. The desert ant Cataglyphis fortis is a prominent example, covering large distances on foraging excursions. The stride integrator is probably the major source of path integration errors. A detailed analysis of walking behaviour in Cataglyphis is thus of importance for assessing possible sources of errors and potential compensation strategies. Zollikofer (J Exp Biol 192:95-106, ) demonstrated consistent use of the tripod gait in Cataglyphis, and suggested an unexpectedly constant stride length as a possible means of reducing navigation errors. Here, we extend these studies by more detailed analyses of walking behaviour across a large range of walking speeds. Stride length increases linearly and stride amplitude of the middle legs increases slightly linearly with walking speed. An initial decrease of swing phase duration is observed at lower velocities with increasing walking speed. Then it stays constant across the behaviourally relevant range of walking speeds. Walking speed is increased by shortening of the stance phase and of the stance phase overlap. At speeds larger than 370 mms, the stride frequency levels off, the duty factor falls below 0.5, and Cataglyphis transitions to running with aerial phases. [ABSTRACT FROM AUTHOR]

Animals that travel large distances in search of food need to be equipped with navigation systems that are capable of keeping track of the distance and direction of travel throughout their outbound journey, so that they may return home expeditiously and without losing their way. The challenge of homing is especially acute when the environment is devoid of landmarks. Desert ants and honeybees are able to meet this challenge, despite their minuscule brains and restricted computational capacity. This article reviews some of the processes and mechanisms that underlie the homing abilities of these creatures, which are among the best-understood navigators in the animal kingdom. [ABSTRACT FROM AUTHOR]