Mating‐Associated Changes in the Behaviour of Leptothorax gredleri Ant Queens

Throughout their lives, animals adapt their behaviour to environmental fluctuations and to their own requirements. In social insects, behavioural changes are often particularly conspicuous. For example, in many ant species, reproductive sexuals leave their maternal nests and engage in risky mating and dispersal activities. Female sexuals experience, during a short period of time, dramatic changes in terms of behaviour and environmental conditions. But because sexual activities of ants are not easily observed, few studies have quantified in detail how behaviour alters with maturation and mating. We studied how various behavioural traits of Leptothorax gredleri female sexuals, a species in which female sexuals attract males by ‘female calling’, change before and after mating. We tested the hypothesis that behavioural variation reflects the altered requirements of queens to adapt to a particular situation. To this end, we compared geotactic, phototactic and locomotor behaviour across a wide range of life stages from lightly coloured, unmated female sexuals to old, mated queens. The results showed that female sexuals of L. gredleri change conspicuously their geotactic, phototactic and locomotor behavioural traits over their life stages. Three different behavioural states were evident (1) from light to dark female sexuals, individuals have negative phototaxis and reduced locomotor activity; (2) mature female sexuals during the daily period of sexual activity have strong phototaxis, negative geotaxis and an important locomotor activity; and (3) freshly mated and old mated queens avoid light and decrease their locomotor activity. These sharp differences in behaviour between stages match the transition from the relative safety of the nest chamber to the adversary world outside the nest , and back.     

Proximate Determinants of Reproductive Skew in Polygyne Colonies of the Ant Formica fusca

Understanding the determinants of reproductive skew (the partitioning of reproduction among co‐breeding individuals) is one of the major questions in social evolution. In ants, multiple‐queen nests are common and reproductive skew among queens has been shown to vary tremendously both within and between species. Proximate determinants of skew may be related to both queen and worker behaviour. Queens may attempt to change their reproductive share through dominance interactions, egg eating and by changing individual fecundity. Conversely, workers are in a position to regulate the reproductive output of queens when rearing the brood. This paper investigates queen behaviour at the onset of egg laying and the effect of queen fecundity and worker behaviour on brood development and reproductive shares of multiple queens in the ant Formica fusca. The study was conducted in two‐queen laboratory colonies where the queens produced only worker offspring. The results show that in this species reproductive apportionment among queens is not based on dominance behaviour and aggression, but rather on differences in queen fecundity. We also show that, although the queen fecundity at the onset of brood rearing is a good indicator of her final reproductive output, changes in brood composition occur during brood development. Our results highlight the importance of queen fecundity as a major determinant of her reproductive success. They furthermore suggest that in highly derived polygyne species, such as the Formica ants, direct interactions as a means for gaining reproductive dominance have lost their importance.     

The Use of Edges in Visual Navigation by the Ant Leptothorax albipennis

Certain navigating insects home in on their goal by moving so that currently viewed images of landmarks fall on the same retinal locations memorized during previous visits. Here we show that ants can use similar retinotopic learning to guide lengthy routes, by memorizing and walking parallel to a distinct visual edge. We induced workers of the ant Leptothorax albipennis to travel parallel to a prominent wall. When the wall's height was changed, the ants' paths consistently shifted toward a lowered wall and away from a raised wall, as would be expected if they attempt to keep the wall's image at a constant retinal position. These path shifts were smaller than would be expected if the wall was the only guide to navigation, suggesting that other cues are also important. Significantly larger shifts were seen when edge guidance was enhanced by using two walls, one on each side of the path.     

Leptothorax (Mychothorax) muscorum Nylander undLeptothorax (M.) gredleri Mayr zwei gute Arten

Zusammenfassung Körpergrösse, Epinotaldornlänge, Kopulationsorgane der , Form des Clypeus und Färbung von und sind beiLeptothorax (Mychothorax) muscorum Nyl. undL. (M.) gredleri Mayr so verschieden, dass beide Arten eindeutig zu unterscheiden sind. In der Umgebung von Würzburg kommen beide Arten eng nebeneinander vor und schwärmen zur gleichen Zeit ohne sich zu kreuzen. Sie sollten daher als gute Arten betrachtet werden.

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Summary Length of body and epinotal spines, male genitalia, structure of clypeus and colour of and ofLeptothorax (Mychothorax) muscorum Nyl. andL. (M.) gredleri Mayr are as much different that the two species are clearly to distinguish. Around Würzburg both species are found closely together and swarm simultaneously without crossbreeding. Therefore they should be considered as valable species.

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Résumé La longueur du corps et des épines épinotales, les génitalia mâles, la façon du clypeus et la coloration de et deLeptothorax (Mychothorax) muscorum Nyl. etL. (M.) gredleri Mayr sont assez différentes que l'on peut distinguer les deux espèces nettement. Autour de Würzburg les deux espèces sont trouvées souvent ensemble; l'essaimage a lieu au même temps sans croisement. C'est pourquoi elles doivent être considérées comme des espèces valables.

     

Dynamics and Consequences of Hierarchy Formation in the Ant Leptothorax sp. A

In the Nearctic ant Leptothorax sp. A, aggressive interactions among wingless intermorphic queens and primarily winged gynomorphic queens lead to the formation of dominance hierarchies, in which the highest-ranking individual is the only egg-layer in a colony. Fighting occurs during two periods of the annual cycle: in late summer, newly adopted young queens are integrated into the colony's hierarchy; after hibernation, fighting resumes and the high aggressiveness of α-queens may now lead to the emigration of β and other middle-ranking queens. The α-position appears to be very stable over successive fighting periods, though an estimate of nestmate relatedness by allozyme electrophoresis (Polyacrylamide gels and cellulose acetate plates) suggests that queen replacement occasionally occurs. The mean relatedness determined for adult workers in a functionally monogynous population of Leptothorax sp. A was 0.54 and their effective number of mothers therefore 1.5. This is lower than expected and found for monogynous colonies. Dominance rank is apparently not correlated with queen morph, weight, and size, but an influence of insemination, age, or previous reproductive experience is likely.     

Apparent Dear-enemy Phenomenon and Environment-based Recognition Cues in the Ant Leptothorax nylanderi

Inter- and intraspecific competition was investigated in ants of the myrmicine genus leptothorax in a deciduous woodland near Würzburg, Germany. The most common species, A. (Myrafant) nylanderi, lives in rotting pine, oak, and elder sticks and may locally reach densities of 10 nests per m². In the studied sites, only a small fraction of colonies were polydomous, i.e. single colonies typically did not inhabit several nest sites. The home ranges of nylanderi colonies overlap the ranges of other conspecific colonies and colonies of other species, especially L. (s.str.) gredleri. Foragers from different colonies encountering one another in the field back off without exhibiting strong aggression, suggesting that colonies do not defend absolute foraging territories. In laboratory experiments, the frequency and severity of agonistic interactions among workers from different colonies, all living in pine sticks, increased significantly with the distance between their nests. Workers from colonies nesting in different types of wood exhibited significantly more aggression. Experiments in which we transferred colonies from pine sticks into artificial pine or oak nests corroborate the hypothesis that nesting material strongly influences colony odour in L. nylanderi. The evolutionary significance of this apparent dear-enemy phenomenon is discussed.     

Suppression subtractive hybridization analysis reveals expression of conserved and novel genes in male accessory glands of the ant Leptothorax gredleri

An issue arising from recent progress in establishing the placental mammal Tree of Life concerns the nomenclature of high-level clades. Fortunately, there are now several well-supported clades among extant mammals that require unambiguous, stable names. Although the International Code of Zoological Nomenclature does not apply above the Linnean rank of family, and while consensus on the adoption of competing systems of nomenclature does not yet exist, there is a clear, historical basis upon which to arbitrate among competing names for high-level mammalian clades. Here, we recommend application of the principles of priority and stability, as laid down by G.G. Simpson in 1945, to discriminate among proposed names for high-level taxa. We apply these principles to specific cases among placental mammals with broad relevance for taxonomy, and close with particular emphasis on the Afrotherian family Tenrecidae. We conclude that no matter how reconstructions of the Tree of Life change in years to come, systematists should apply new names reluctantly, deferring to those already published and maximizing consistency with existing nomenclature.     

Ant Colonies Do Not Trade-Off Reproduction against Maintenance

The question on how individuals allocate resources into maintenance and reproduction is one of the central questions in life history theory. Yet, resource allocation into maintenance on the organismic level can only be measured indirectly. This is different in a social insect colony, a “superorganism” where workers represent the soma and the queen the germ line of the colony. Here, we investigate whether trade-offs exist between maintenance and reproduction on two levels of biological organization, queens and colonies, by following single-queen colonies of the ant Cardiocondyla obscurior throughout the entire lifespan of the queen. Our results show that maintenance and reproduction are positively correlated on the colony level, and we confirm results of an earlier study that found no trade-off on the individual (queen) level. We attribute this unexpected outcome to the existence of a positive feedback loop where investment into maintenance (workers) increases the rate of resource acquisition under laboratory conditions. Even though food was provided ad libitum, variation in productivity among the colonies suggests that resources can only be utilized and invested into additional maintenance and reproduction by the colony if enough workers are available. The resulting relationship between per-capita and colony productivity in our study fits well with other studies conducted in the field, where decreasing per-capita productivity and the leveling off of colony productivity have been linked to density dependent effects due to competition among colonies. This suggests that the absence of trade-offs in our laboratory study might also be prevalent under natural conditions, leading to a positive association of maintenance, (= growth) and reproduction. In this respect, insect colonies resemble indeterminate growing organisms.     

Ant Colonies Prefer Infected over Uninfected Nest Sites

During colony relocation, the selection of a new nest involves exploration and assessment of potential sites followed by colony movement on the basis of a collective decision making process. Hygiene and pathogen load of the potential nest sites are factors worker scouts might evaluate, given the high risk of epidemics in group-living animals. Choosing nest sites free of pathogens is hypothesized to be highly efficient in invasive ants as each of their introduced populations is often an open network of nests exchanging individuals (unicolonial) with frequent relocation into new nest sites and low genetic diversity, likely making these species particularly vulnerable to parasites and diseases. We investigated the nest site preference of the invasive pharaoh ant, Monomorium pharaonis, through binary choice tests between three nest types: nests containing dead nestmates overgrown with sporulating mycelium of the entomopathogenic fungus Metarhizium brunneum (infected nests), nests containing nestmates killed by freezing (uninfected nests), and empty nests. In contrast to the expectation pharaoh ant colonies preferentially (84%) moved into the infected nest when presented with the choice of an infected and an uninfected nest. The ants had an intermediate preference for empty nests. Pharaoh ants display an overall preference for infected nests during colony relocation. While we cannot rule out that the ants are actually manipulated by the pathogen, we propose that this preference might be an adaptive strategy by the host to “immunize” the colony against future exposure to the same pathogenic fungus.     

The Role of Non-Foraging Nests in Polydomous Wood Ant Colonies

A colony of red wood ants can inhabit more than one spatially separated nest, in a strategy called polydomy. Some nests within these polydomous colonies have no foraging trails to aphid colonies in the canopy. In this study we identify and investigate the possible roles of non-foraging nests in polydomous colonies of the wood ant Formica lugubris. To investigate the role of non-foraging nests we: (i) monitored colonies for three years; (ii) observed the resources being transported between non-foraging nests and the rest of the colony; (iii) measured the amount of extra-nest activity around non-foraging and foraging nests. We used these datasets to investigate the extent to which non-foraging nests within polydomous colonies are acting as: part of the colony expansion process; hunting and scavenging specialists; brood-development specialists; seasonal foragers; or a selfish strategy exploiting the foraging effort of the rest of the colony. We found that, rather than having a specialised role, non-foraging nests are part of the process of colony expansion. Polydomous colonies expand by founding new nests in the area surrounding the existing nests. Nests founded near food begin foraging and become part of the colony; other nests are not founded near food sources and do not initially forage. Some of these non-foraging nests eventually begin foraging; others do not and are abandoned. This is a method of colony growth not available to colonies inhabiting a single nest, and may be an important advantage of the polydomous nesting strategy, allowing the colony to expand into profitable areas.     

Further Evidence of Lack of Pheromonal Inhibition among Queens of the Ant Leptothorax acervorum

Queens in some species of ant with several queens per colony are believed to inhibit one another's fecundity pheromonally. This paper describes a repeat of an experimental test of this idea in the multiple-queen ant Leptothorax acervorum. The three most fecund queens from a field-collected colony were housed together in an experimental nest. This was then filmed for 10 h per day over 36 consecutive days (i.e. for 360 h in total). Over the first 12 d, all queens were present in the colony. For the middle 12 d, the two most fecund queens were removed, but were returned for the final 12 d. The queen that was observed throughout the experiment failed to show a rise in fecundity when the other queens were removed. Instead, her egg-laying rate fell, although this drop was not significant. These results confirm previous findings that short-term, strong pheromonal inhibition of fecundity does not occur among L. acervorum queens. The phenomena of pheromonal inhibition in other species may be a result of workers treating queens differentially in response to rapid, short-term changes in the numbers of queens and eggs. If so, the results presented here could stem from the relative infrequency of such changes in L. acervorum.     

Absence of Nepotism in Genetically Heterogeneous Colonies of a Clonal Ant

Insect societies are normally closed entities from which alien individuals are excluded. The occasional fusion of unrelated colonies of the thelytokous ant Platythyrea punctata is therefore puzzling, because it strongly intensifies competition among nestmates for the replacement of an old reproductive. Most colonies of P. punctata have only one or few reproductives, which produce female offspring from unfertilized eggs, and therefore have a clonal structure. Fusion leads to multi‐clone colonies. We compared the occurrence of dominance and policing behavior between single‐ and double‐clone colonies. We find that the frequency of aggression is higher in double‐clone colonies, but that individuals do not preferentially direct attacks toward non‐clonemates. This matches observations in other species that social insects perceive genetic homogeneity but are not capable of reliable discrimination among nestmates of different degree of relatedness.     

Behavioral Plasticity in Ant Queens: Environmental Manipulation Induces Aggression among Normally Peaceful Queens in the Socially Polymorphic Ant Leptothorax acervorum

The behavioral traits that shape the structure of animal societies vary considerably among species but appear to be less flexible within species or at least within populations. Populations of the ant Leptothorax acervorum differ in how queens interact with other queens. Nestmate queens from extended, homogeneous habitats tolerate each other and contribute quite equally to the offspring of the colony (polygyny: low reproductive skew). In contrast, nestmate queens from patchy habitats establish social hierarchies by biting and antennal boxing, and eventually only the top-ranking queen of the colony lays eggs (functional monogyny: high reproductive skew). Here we investigate whether queen-queen behavior is fixed within populations or whether aggression and high skew can be elicited by manipulation of socio-environmental factors in colonies from low skew populations. An increase of queen/worker ratio and to a lesser extent food limitation elicited queen-queen antagonism in polygynous colonies from Nürnberger Reichswald similar to that underlying social and reproductive hierarchies in high-skew populations from Spain, Japan, and Alaska. In manipulated colonies, queens differed more in ovarian status than in control colonies. This indicates that queens are in principle capable of adapting the magnitude of reproductive skew to environmental changes in behavioral rather than evolutionary time.     

The Spatial Development of Spartina Colonies Growing without Competition

The spatial development of circular auxoclones of Spartina townsendiicolonizing bare mud or muddy sand is described. It is shownthat enlargement of the auxoclones is accompanied by a changein shoot density distribution and development of a concentricpattern. Additional ‘rings’ of high shoot densityare added as the auxoclone increases in diameter and those inthe centre are maintained. The number of rings is proportionalto the diameter, and auxoclones reached the same complexityat the same diameter on different substrates. This type of developmentis discussed in relation to Spartina morphology.     

Absence of Within‐Colony Kin Discrimination in a Multiple‐Queen Ant,Leptothorax acervorum

Inclusive fitness theory predicts that, other things equal, individuals within social groups should direct altruistic behaviour towards their most highly related group‐mates to maximise indirect fitness benefits. In the social insects, most previous studies have shown that within‐colony kin discrimination (nepotism) is absent or weak. However, the number of studies that have investigated within‐colony kin discrimination at the level of individual behaviour remains relatively small. We tested for within‐colony kin discrimination in the facultatively multiple‐queen (polygynous) ant, Leptothorax acervorum. Specifically, we tested whether workers within polygynous colonies treated queens differently as a function of their relatedness to them. Colonies containing two egg‐laying queens were filmed to measure the rate at which individually marked workers antennated and groomed or fed each queen. Relatedness between individual queens and workers was calculated from their genotypes at four microsatellite loci. The results showed there were no differences in the rates at which workers antennated or groomed/fed their more related queen and their less related queen. Workers interacted preferentially with their potential mother queen with respect to grooming/feeding but not with respect to antennation. However, because of high queen turnover, the frequency of adult workers with their potential mother queen still present within the colony was relatively low. Overall, therefore, we found no evidence for within‐colony kin discrimination in the context of the average worker's treatment of queens in polygynous L. acervorum colonies.     

Reproductive Systems and Sibling Competition in Plants

Abstract Competition among relatives can modify the genetic structure of plant populations; in turn, competitive outcomes can depend on the genetic relatedness of the individuals competing. The offspring from individual parents exhibit a continuum of genetic relatedness, depending on parental reproductive systems. Competition among relatives may have evolutionary significance as a selection pressure; sibling competition, for example, has been invoked to explain the evolution of sexual systems, seed packaging within fruits, seed dispersal dimorphisms, and germination behavior.
Density-dependent fitness consequences of sibling competition have been documented in a population of the annual grass Sporobolus vaginiflorus . This species produces seeds matured in cleistogamous spikelets within leaf sheaths along tillers in autumn: when seeds along the tillers of a maternal parent (i.e. a sibship) germinate in situ the following spring in close proximity to one another, sibling competition results in a high-density zone centered around the original senescent parent. Both intra- and intersibship interactions can occur within a population. Although fitness is much reduced for siblings inside the zone of competition, potential seed rain and net primary productivity per unit area are significantly higher relative to outside the zone. This annual is functionally analogous to a perennial ramet producer with a phalanx growth strategy and the unit of selection may be the sibling group. It is not yet known whether sibling competition is a significant selection pressure in other species, but indirect evidence suggests it may be relatively widespread.     

Biomantling and Bioturbation by Colonies of the Florida Harvester Ant,Pogonomyrmex badius

In much of the world, soil-nesting ants are among the leading agents of biomantling and bioturbation, depositing excavated soil on the surface or in underground chambers. Colonies of the Florida harvester ant, Pogonomyrmex badius excavate a new nest once a year on average, depositing 0.1 to 12 L (3 L average) of soil on the surface. Repeated surveys of a population of about 400 colonies yielded the frequency of moves (approximately once per year), the distance moved (mean 4 m), and the direction moved (random). The area of the soil disc correlated well with the volume and maximum depth of the nest, as determined by excavation and mapping of chambers. The population-wide frequency distribution of disc areas thus yielded the frequency distribution of nest volumes and maximum depths. For each surveyed colony, the volume of soil excavated from six specified depth ranges and deposited on the surface was estimated. These parameters were used in a simulation to estimate the amount of soil mantled over time by the observed population of P. badius colonies. Spread evenly, P. badius mantling would create a soil layer averaging 0.43 cm thick in a millennium, with 10–15% of the soil deriving from depths greater than 1 m. Biomantling by P. badius is discussed in the context of the ant community of which it is a part, and in relation to literature reports of ant biomantling.