Molecular phylogenies reveal host-specific divergence of Ophiocordyceps unilateralis sensu lato following its host ants

Ophiocordyceps unilateralis (Hypocreales, Ascomycetes) is an entomopathogenic fungus specific to formicine ants (Formicinae, Hymenoptera). Previous works have shown that the carpenter ant Camponotus leonardi acts as the principal host with occasional infections of ants from the genus Polyrhachis (sister genus of Camponotus). Observations were made on the permanent plots of Mo Singto, Khao Yai National Park of Thailand according to which O. unilateralis was found to occur predominantly on three host species: C. leonardi, C. saundersi and P. furcata. Molecular phylogenies of the elongation factor 1-α and β-Tubulin genes indicate a separation of O. unilateralis samples into three clades, reflecting specificity to each of the three different ant species. Samples collected from P. furcata and from C. leonardi were found to form sister groups with samples from C. saundersi forming an outgroup to the latter. Additional samples collected from unidentified ant species of Camponotus and Polyrhachis were positioned as outgroups to those samples on identified species. These results demonstrate that O. unilateralis is clearly not a single phylogenetic species and comprises at least three species that are specific to different host ant species. These cryptic species may arise through recent events of speciation driven by their specificity to host ant species.     

Supplementing Seed Banks to Rehabilitate Disturbed Mojave Desert Shrublands: Where Do All the Seeds Go?

Revegetation of degraded arid lands often involves supplementing impoverished seed banks and improving the seedbed, yet these approaches frequently fail. To understand these failures, we tracked the fates of seeds for six shrub species that were broadcast across two contrasting surface disturbances common to the Mojave Desert—sites compacted by concentrated vehicle use and trenched sites where topsoil and subsurface soils were mixed. We evaluated seedbed treatments that enhance soil‐seed contact (tackifier) and create surface roughness while reducing soil bulk density (harrowing). We also explored whether seed harvesting by granivores and seedling suppression by non‐native annuals influence the success of broadcast seeding in revegetating degraded shrublands. Ten weeks after treatments, seeds readily moved off of experimental plots in untreated compacted sites, but seed movements were reduced 32% by tackifier and 55% through harrowing. Harrowing promoted seedling emergence in compacted sites, particularly for the early‐colonizing species Encelia farinosa, but tackifier was largely ineffective. The inherent surface roughness of trenched sites retained three times the number of seeds than compacted sites, but soil mixing during trench development likely altered the suitability of the seedbed thus resulting in poor seedling emergence. Non‐native annuals had little influence on seed fates during our study. In contrast, the prevalence of harvester ants increased seed removal on compacted sites, whereas rodent activity influenced removal on trenched sites. Future success of broadcast seeding in arid lands depends on evaluating disturbance characteristics prior to seeding and selecting appropriate species and seasons for application.     

Review of the Southeast Asian species of the Aenictus javanus and Aenictus philippinensis species groups (Hymenoptera, Formicidae, Aenictinae)

The Southeast Asian species of the Aenictus javanus and Aenictus philippinensis groups are revised. Six species (four named and two new species) of the Aenictus javanus group occurring in this area are: Aenictus doydeei Jaitrong & Yamane, 2011, Aenictus duengkaei Jaitrong & Yamane, sp. n., Aenictus javanus Emery, 1896, Aenictus longinodus Jaitrong & Yamane, sp. n., Aenictus nishimurai Terayama & Kubota, 1993, and Aenictus piercei Wheeler & Chapman, 1930. Four species (three named and one new species) are recognized in the Aenictus philippinensis group: Aenictus pangantihoni Zettel & Sorger, 2010, Aenictus philippinensis Chapman, 1963, Aenictus punctatus Jaitrong & Yamane, sp. n., and Aenictus rabori Chapman, 1963. Aenictus piercei is removed from the members of the Aenictus piercei group sensu Jaitrong and Yamane (2011) and transferred to the Aenictus javanus group. Lectotypes and paralectotypes are designated for Aenictus piercei and Aenictus rabori. Size variation occurs among individuals from single colonies of the Aenictus javanus group, while the workers in the Aenictus philippinensis group are clearly monomorphic.     

Ants under crowded conditions consume more energy

Social insects live in colonies consisting of many workers, where worker interactions play an important role in regulating colony activities. Workers interact within the social space of the nest; therefore, constraints on nest space may alter worker behaviour and affect colony activities and energetics. Here we show in the ant Temnothorax rugatulus that changes in nest space have a significant effect on colony energetics. Colonies with restricted nest space showed a 14.2 per cent increase in metabolic rate when compared with the same colonies in large uncrowded nests. Our study highlights the importance of social space and shows that constraints on social space can significantly affect colony behaviour and energy use in ants. We discuss the implications of our findings regarding social insects in general.     

Limiting Spread of a Unicolonial Invasive Insect and Characterization of Seasonal Patterns of Range Expansion

Limiting dispersal is a fundamental strategy in the control of invasive species, and in certain situations containment of incipient populations may be an important management technique. To test the feasibility of slowing the rapid spread of two Argentine ant (Linepithema humile) supercolonies in Haleakala National Park, Hawaii, we applied ant bait and toxicant within an experimental plot situated along a supercolony boundary. The 120×260 m plot simulated a small section of what could potentially be a 120 m wide treatment encompassing the entire expanding boundaries of both supercolonies. Foraging ant numbers at baited monitoring stations decreased sharply within two weeks after treatment, and ant spread was completely halted within the plot for at least one year. In contrast, an adjacent untreated colony boundary advanced an average of 65.2 m over the course of 1 year. Most of this spread took place in the summer and fall, at the time of highest ant abundance at bait monitoring stations, while no outward dispersal occurred during the spring and early summer. These patterns are consistent with the hypothesis that local budding dispersal in this unicolonial species stems from density dependent pressure rather than inherent founding behavior associated with mating. Based on results from this experiment, we are investigating the effectiveness of annual boundary treatments in slowing the Argentine ant invasion at Haleakala National Park. The goals of this program are to protect populations of native arthropods and to keep options open for eventual attempts at eradication. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Basis for Spatial and Social Patterns in Ant Species: Dynamics and Mechanisms of Aggregation

Aggregation is usually studied in functional terms, forgetting mechanisms. In this paper, experimental results on the ant Lasius niger, complemented by a model, allow us to understand the mechanisms responsible for aggregation and to study the influence of the population density on this phenomenon. The results show (1) a high level of aggregation and the emergence of a large cluster; (2) that aggregation results from an amplification mechanism—the greater the number of ants inside a cluster, the greater the time spent by one ant in this cluster; and (3) that population density has only a weak influence on the aggregation process. This method of analysis and these results can certainly be extended not only in social insects but also in other species, like subsocial arthropods.     

The relative availabilities of complementary resources affect the feeding preferences of ant colonies

Theory predicts that consumers selecting among complementaryresources will show stronger preferences for items that becomerelatively less available. I tested this hypothesis in a fieldstudy that compared the preferences of ant colonies given simultaneousaccess to experimental foods differing in carbohydrate and proteincontent. In the first part of the study, I examined the effectof nutrient supplementation on colony-level preference in theant Dorymyrmex smithi. Colonies that had received a proteinsolution for 24 h consumed proportionally more carbohydratesthan control colonies that had been given access to water, suggestingthat colonies preferred nutrients when they became relativelyrare. In the second part of the study, I compared colony-levelpreference among eight species of ants that differ in theirrelative access to carbohydrates and protein in the field. Ifound that species with relatively easy access to carbohydratespreferred protein, whereas species with greater access to proteinpreferred carbohydrates. These results suggest that the benefitsof a nutritionally mixed diet coupled with differences in therelative availability of nutrients may explain variation infeeding decisions both within and among ant species.     

Male reproductive investment and queen mating-frequency in fungus-growing ants

Sperm number and male accessory gland compounds are often importantdeterminants of male mating success but have been little studiedin social insects. This is because mating in social insectsis often difficult to manipulate experimentally, and first evidencefor an explicit influence of accessory gland secretions on malemating success in social insects was obtained only recently.Here we perform a comparative analysis of male sexual organsacross 11 species of attine fungus-growing ants, representingboth genera with single- and multiple-queen mating. We foundthat the general morphology of the male sexual organs was verysimilar across all species, but the relative sizes of the accessoryglands and the sperm-containing accessory testes vary significantlyacross species. Small testes and large accessory glands characterizespecies with singly mated queens, whereas the opposite is foundin species with multiply mated queens. However, in the socialparasite Acromyrmex insinuator, in which queens have secondarilyreverted to single mating, males have accessory gland characteristicsreminiscent of the lower attine ants, but without having significantlyreduced their investment in sperm production. We hypothesizethat the main function of accessory gland compounds in attineants is to monopolize male paternity in similar ways as knownfrom other social insects. This would imply that the evolutionof polyandry in the terminal clade of the fungus-growing ants(the leafcutter ants) has resulted in selection for decreasedinvestment by males in accessory gland secretions and increasedinvestment in sperm number, in response to sperm competitionfor sperm storage.