Individual and collective choice: parallel prospecting and mining in ants

Decision making is of crucial importance in the lives of both animals and humans. How decisions of group members scale up to group decisions is of great interest. Accordingly, we gave homeless ant colonies (n = 67) in three experiments a choice between two nest sites (with small, big or mixed sand grains), each of which had to be excavated to be habitable. Among the colonies that chose only one of the new nest sites, all preferred the ones that could be excavated most easily and quickly. There are interesting parallels between the collective choice of mining sites and the ability of certain ants to select short cuts; both involve positive feedback. However, in this paper, we discuss a mechanism whereby collective co-ordination in the production of social infrastructure can occur in the absence of signalling.     

Genetic caste polymorphism and the evolution of polyandry in <Emphasis Type="Italic">Atta</Emphasis> leaf-cutting ants

Multiple mating by females with different males (polyandry) is difficult to explain in many taxa because it carries significant costs to females, yet benefits are often hard to identify. Polyandry is a derived trait in social insects, the evolutionary origins of which remain unclear. One of several leading hypotheses for its evolution is that it improves division of labour by increasing intra-colonial genetic diversity. Division of labour is a key player in the ecological success of social insects, and in many successful species of ants is based on morphologically distinct castes of workers, each with their own task specialisations. Atta leaf-cutting ants exhibit one of the most extreme and complicated forms of morphologically specialised worker castes and have been reported to be polyandrous but with relatively low mating frequencies (~2.5 on average). Here, we show for the first time that there is a significant genetic influence on worker size in Atta colombica leaf-cutting ants. We also provide the first estimate of the mating frequency of Atta cephalotes (four matings) and, by analysing much higher within-colony sample sizes, find that Atta are more polyandrous than previously thought (approximately six to seven matings). The results show that high polyandry and a genetic influence on worker caste are present in both genera of leaf-cutting ants and add weight to the hypothesis that division of labour is a potential driver of the evolution of polyandry in this clade of ants.     

Foraging ants trade off further for faster: use of natural bridges and trunk trail permanency in carpenter ants

Trail-making ants lay pheromones on the substrate to define paths between foraging areas and the nest. Combined with the chemistry of these pheromone trails and the physics of evaporation, trail-laying and trail-following behaviours provide ant colonies with the quickest routes to food. In relatively uniform environments, such as that provided in many laboratory studies of trail-making ants, the quickest route is also often the shortest route. Here, we show that carpenter ants (Camponotus rufipes), in natural conditions, are able to make use of apparent obstacles in their environment to assist in finding the fastest routes to food. These ants make extensive use of fallen branches, twigs and lianas as bridges to build their trails. These bridges make trails significantly longer than their straight line equivalents across the forest floor, but we estimate that ants spend less than half the time to reach the same point, due to increased carriage speed across the bridges. We also found that these trails, mainly composed of bridges, are maintained for months, so they can be characterized as trunk trails. We suggest that pheromone-based foraging trail networks in field conditions are likely to be structured by a range of potentially complex factors but that even then, speed remains the most important consideration.     

Red legs and golden gasters: Batesian mimicry in australian ants

 There are numerous reports of invertebrates that are visual mimics of ants, but no formal reports of mimicry of an ant, by an ant. Two endemic Australian ants, Myrmecia fulvipes and Camponotus bendigensis are remarkably similar in colour and size; both are generally black but have red legs and golden gasters. The density and hue of the pubescence of each ant's gaster are relatively uncommon in ants, but are very rare when combined with the black forebody and red legs. The ants are similarly sized but are smaller than other species closely related to M. fulvipes. The range of C. bendigensis lies entirely within that of M. fulvipes, and both species excavate ground nests in open woodland. Finally, workers of both species are crepuscular and forage solitarily. These data suggest that the relatively benign formicine C. bendigensis is a Batesian mimic of the formidable myrmeciine M. fulvipes. Received: 9 August 1999 / Accepted in revised form: 22 December 1999     

Communal peeing: a new mode of flood control in ants

 The behavioral response of the obligate bamboo-nesting ant Cataulacus muticus to nest flooding was studied in a perhumid tropical rainforest in Malaysia and in the laboratory. The hollow internodes of giant bamboo, in which C. muticus exclusively nests, are prone to flooding by heavy rains. The ants showed a two-graded response to flooding. During heavy rain workers block the nest entrances with their heads to reduce water influx. However, rainwater may still intrude into the nest chamber. The ants respond by drinking the water, leaving the nest and excreting water droplets on the outer stem surface. This cooperative 'peeing' behavior is a new survival mechanism adaptive to the ants' nesting ecology. Laboratory experiments conducted with two other Cataulacus species, C. catuvolcus colonizing small dead twigs and C. horridus inhabiting rotten wood, did not reveal any form of water-bailing behavior. Received: 3 August 2000 / Accepted in revised form: 6 November 2000     

Nest excavation in ants: group size effects on the size and structure of tunneling networks

Collective digging activity was studied in the ant Messor sancta Forel in laboratory conditions and with a two dimensional set-up. We analyzed the digging dynamics and topology of tunneling networks excavated by groups of workers ranging from 50 to 200 individuals over 3 days. In all conditions, the dynamics of excavated sand volume were clearly non-linear. Excavation began with an exponential growth and after 3 days reached a saturation phase in which activity was almost totally stopped. The final volume of sand excavated was positively correlated with the number of workers. At the end of the experiments, the two-dimensional tunneling networks were mapped onto planar graphs where the vertices represent small chambers or intersections between tunnels and the edges represent tunnels. We found that all the networks belonged to a same topological family and exhibited several striking invariants such as the distribution of vertex degree that follows a power law. When increasing the number of ants, some changes occurred in the network structure, mainly an increase in the number of edges and vertices, and the progressive emergence of enlarged and highly connected vertices.     

科学理性与决策机制：“双评价”与国土空间规划的思考

“双评价”是国土空间规划体系具有前置和基础性作用的制度设定与技术基础。结合实践案例对“试行指南”进行理论思考,结果发现：“双评价”的技术、逻辑路径内含有科学问题和假设;同时,对制度建构具有约束和纠偏作用。“双评价”发挥有效作用需兼顾科学性和政策性,也因此难以两全齐美。技术方法和数据方面存在“加合困境”“分解困境”和“排序困境”。合理有效的“双评价”需要提高两个评价内容的技术合理性,并通过两者耦合进一步提升合理性。也要充分适应决策机制与主体目标,认识科学研究与决策支持研究之间的差异,根据不同层级地方政府事权层级和分工关系优化分析评价方法。结论对“双评价”定位优化与技术逻辑改进有实践指导意义。     

Predation and aggressiveness in host plant protection: a generalization using ants from the genus Azteca

In studying the ant genus Azteca, a Neotropical group of arboreal species, we aimed to determine the extent to which the ants use predation and/or aggressiveness to protect their host plants from defoliating insects. We compared a territorially dominant, carton-nester, Azteca chartifex, and three plant-ant species. Azteca alfari and Azteca ovaticeps are associated with the myrmecophyte Cecropia (Cecropiaceae) and their colonies shelter in its hollow branches; whereas Azteca bequaerti is associated with Tococa guianensis (Melastomataceae) and its colonies shelter in leaf pouches situated at the base of the laminas. Whereas A. bequaerti workers react to the vibrations transmitted by the lamina when an alien insect lands on a leaf making it unnecessary for them to patrol their plant, the workers of the three other species rather discover prey by contact. The workers of all four species use a predatory behaviour involving spread-eagling alien insects after recruiting nestmates at short range, and, in some cases, at long range. Because A. alfari and A. ovaticeps discard part of the insects they kill, we deduced that the workers' predatory behaviour and territorial aggressiveness combine in the biotic defence of their host tree.     

Effect of tunnel inclination on digging energetics in the tuco-tuco, Ctenomys talarum (Rodentia: Ctenomyidae)

Burrows play an important role for many species, providing them with shelter and access to food resources. For subterranean rodents, living underground imposes constraints on morphology and physiology. The convergence in burrow architecture among subterranean rodents has been related to the energy demands imposed by the cost of constructing an entire system. The low frequency of tunnels with downward angles steeper than 40° appears to be a common feature in burrow design. In the subterranean habitat, movements through the soil are expensive and gravity can exert important restrictions on digging energetics when individuals push out the soil removed in steeper digging angles. The aim of this study was to determine the effect of digging angle on digging energetics in Ctenomys talarum. The mass of the removed soil and burrowing speed were similar while digging metabolic rate and net cost of transport were higher in individuals digging in tunnels with angles >40° than in those digging tunnels with angles <40°. The cost of constructing a burrow in the horizontal plane differed by 20% from others in which the natural representation of tunnels >40° was considered. Even given that tunnels >40° represented only 6% of the total burrow length, burrow architecture appears to be constrained by the high energetic cost of constructing in steeper angles.     

Degeneration of sperm reservoir and the loss of mating ability in worker ants

Workers never mate in the large majority of ants, and they have usually lost the spermatheca, an organ specialized for long-term storage of sperm. Such ‘non-sexual’ workers are restricted to laying unfertilized eggs that give rise to males, and they cannot compete with the queens for the production of female offspring. In sharp contrast, workers in 200–300 species from phylogenetically basal subfamilies can reproduce sexually (‘gamergates’) because they retain a functional spermatheca like the queens. Importantly, ‘non-sexual’ workers in closely related species have a vestigial spermatheca. In this study, we compared the reservoir epithelium of ‘sexual’ workers to that of congeneric queens and ‘non-sexual’ workers using 21 species of Amblyoponinae, Ponerinae and Ectatomminae. We show that a pronounced thickening of the epithelium near the opening of the sperm duct is strictly associated with sexual reproduction in both castes. This is unlike ‘non-sexual’ workers in which this epithelium is always very thin, with few organelles; but all other structures remain intact. We discuss this evolutionary degeneration of the spermatheca and how it relates to behavioural or physiological modifications linked to mating. Our results help understand the loss of sexual reproduction by ant workers, a critical step in the extreme specialization of their phenotype.     

New exocrine glands in ants: the hypostomal gland and basitarsal gland in the genus Melissotarsus (Hymenoptera: Formicidae)

Fisher and Robertson (Insect Soc 46: 78–83, 1999) discovered the production of silk-like secretions emerging from slit-shaped openings along the anterior margin of the ventral hypostoma of Melissotarsus ant workers. The current histological study describes a hitherto unknown hypostomal gland from which this silk-like substance originates. In addition, this study describes a new basitarsal gland in the three pairs of legs of Melissotarsus workers.     

岩溶地下河水文地球化学对降雨的响应：以重庆雪玉洞地下河系统为例

通过对降雨条件下重庆雪玉洞地下河水文地球化学指标的监测,发现各种指标对降雨响应迅速,且存在相关性.采用主成分分析对各指标数据进行处理,提取能代表82.761%信息量的3个主成分,来分析降雨条件下岩溶地下河水文地球化学的特征及其成因.结果表明,以全Fe、全Mn、Al3+等浓度升高为代表的土壤淋失和以K+、Na+、Sr2+浓度降低、EC下降为代表的稀释效应,对水文地球化学特征变化的贡献率为41.718%,降雨加剧了岩溶区土壤的侵蚀,同时危及饮用水的安全,应引起相关部门的足够重视;岩溶水对白云岩的溶解和补给区农业活动、洞穴生物对水文地球化学特征变化的贡献率为29.958%;以Ca2+浓度升高为代表的岩溶水对灰岩的溶蚀作用对水文地球化学特征的贡献率为11.084%.     

Runoff and soil erosion in arable Britain: changes in perception and policy since 1945

The realisation that runoff and soil erosion was a problem came late to Britain and policies to tackle the problem have evolved slowly and may well have a taken a different route to that in other countries. The perception of soil erosion and runoff in Britain by three interest groups (researchers, policy makers and farmers) has changed over time since the 1940s. Prior to 1970 none of the groups considered erosion and runoff were problems. From then to 1985 researchers found that erosion was widespread. Between 1985 and 2005 researchers not only confirmed that erosion was a problem, but that runoff and its impacts (muddy floods and pollution of water courses by sediment, phosphate and pesticides) were also problems. These widespread and costly economic and environmental impacts led policy makers to tackle the problems of erosion and runoff. From 2005 farmers have had to keep their land in ‘Good Agricultural and Environmental Condition’ by, amongst other things, attempting to curtail erosion and runoff, to comply with regulation in order to receive subsidy. Policy change was also stimulated by changes in the European Union's Common Agricultural Policy and the passing by the EU of the ‘Water Framework Directive’. Policy, if it is to be evidence based, will always lag behind research. There is a continuing need for field-based monitoring to assess if regulation is working, to ensure compliance, and as a basis for future policy.     

Nest- and colony-mate recognition in polydomous colonies of meat ants (Iridomyrmex purpureus)

Workers of polydomous colonies of social insects must recognize not only colony-mates residing in the same nest but also those living in other nests. We investigated the impact of a decentralized colony structure on colony- and nestmate recognition in the polydomous Australian meat ant (Iridomyrmex purpureus). Field experiments showed that ants of colonies with many nests were less aggressive toward alien conspecifics than those of colonies with few nests. In addition, while meat ants were almost never aggressive toward nestmates, they were frequently aggressive when confronted with an individual from a different nest within the same colony. Our chemical analysis of the cuticular hydrocarbons of workers using a novel comprehensive two-dimensional gas chromatography technique that increases the number of quantifiable compounds revealed both colony- and nest-specific patterns. Combined, these data indicate an incomplete transfer of colony odor between the nests of polydomous meat ant colonies.