Sunday, January 23, 2005

Pearcy, M., S. Aron, C. Doums, L. Keller. 2004. Conditional Use of Sex and Parthenogenesis for Worker and Queen Production in Ants. Science 306: 1780-1783.

Ward, Philip S. & Downie, Douglas A. (2004) The ant subfamily Pseudomyrmecinae (Hymenoptera: Formicidae): phylogeny and evolution of big-eyed arboreal ants. Systematic Entomology 0 (0), -. (Online Early).

Abstract. The ant subfamily Pseudomyrmecinae comprises three genera of hyperoptic, arboreal ants, widely distributed in tropical and subtropical regions: Pseudomyrmex (200 species, New World), Myrcidris (two species, South America) and Tetraponera (100 species, Palaeotropics). The phylogenetic relationships among these ants were investigated using DNA sequence data (5.2 kb from 18S rDNA, 28S rDNA, wingless, abdominal-A, and long-wavelength rhodopsin genes) and 144 morphological characters, both separately and in combination. Data were gathered from a representative set of forty-nine pseudomyrmecine species, plus eighteen species from various outgroups. There was substantial agreement among the results obtained from different datasets, and from different methods of phylogenetic inference (parsimony, Bayesian inference). The monophyly of the following groups is strongly supported (100% bootstrap support and 1.00 posterior probability in the molecular dataset): Pseudomyrmecinae, Pseudomyrmex, and Pseudomyrmex + Myrcidris. The status of the genus Tetraponera is less clear: the DNA sequence data indicate that the genus is paraphyletic, but morphological features and a unique insertion in the 28S gene support the monophyly of this taxon. Seven of nine Pseudomyrmex species groups, established previously on the basis of morphology alone, are strongly upheld, but monophyly is rejected for the P. pallens group and the P. viduus group. In the latter case, molecular evidence indicates the existence of two independent clades, associated with the ant-plants Triplaris and Tachigali, respectively, whose convergent morphological features had caused them to be placed erroneously in the same species group. The present results confirm an earlier assertion that obligate associations with domatia-bearing plants have arisen at least twelve times in the subfamily. Molecular and morphological data support the hypothesis of a sister-group relationship between Pseudomyrmecinae and Myrmeciinae (84% parsimony bootstrap, combined dataset), which implies a Cretaceous origin of the stem-group pseudomyrmecines in the southern hemisphere. Pseudomyrmecines appear to have arisen in the Palaeotropics and later dispersed from Africa to South America, where they experienced a pronounced burst of diversification.

Tuesday, January 11, 2005

I'm a bit behind in posting David Holway's latest Argentine ant article, but here it is:

David A. Holway. 2004. Edge effects of an invasive species across a natural ecological boundary. Biological Conservation 121(4 ): 561-567.

Natural habitats adjacent to human-modified areas often suffer edge
effects stemming from physical disturbance, elevated predator densities, or
invasive species. Although seldom documented, detrimental edge effects can also
occur at natural ecological boundaries. Here I examine the spatial pattern and
ecological effects of a biological invasion at well-delineated and abrupt edges
between riparian corridors and coastal sage scrub at 10 sites in southwestern
California. The invasive Argentine ant Linepithema humile thrives in moist
riparian corridors but decreases greatly in number with increasing distance into
adjacent dry scrub habitats. As L. humile numbers decrease, both the number of
native ant workers and the number of native ant species captured in pitfall
traps increase. Argentine ants appear to suppress native ants within at least 50
m of riparian corridors, but these effects diminish to undetectable levels by
200 m. At comparable uninvaded sites neither the number of native ant workers
nor the number of native ant species captured in pitfall traps varies
significantly across riparian-scrub edges. Areas subject to this edge effect may
be sinks both for native ants and for organisms that depend on them for food or
services. In general edge effects occurring at natural boundaries should receive
increased attention as they might disrupt ecosystems not greatly altered by
human activity.

Latest news from the Florida Harvester Ant

Tschinkel, W., 2004. The nest architecture of the Florida harvester ant, Pogonomyrmex badius. Journal of Insect Science, 4:21

The architecture of the subterranean nests of the Florida harvester ant, Pogonomyrmex badius, was studied through excavation and casting. Nests are composed of two basic units: descending shafts and horizontal chambers. Shafts form helices with diameters of 4 to 6 cm, and descend at an angle of about 15-20o near the surface, increasing to about 70o below about 50 cm in depth. Superficial chambers (< 15 cm deep) appear to be modified shafts with low angles of descent, and are distinct from deeper chambers. In larger nests, they have a looping, connected morphology. Chambers begin on the outside of the helix as horizontal-floored, circular indentations, becoming multi-lobed as they are enlarged. Chamber height is about 1 cm, and does not change with area. Chamber area is greatest in the upper reaches of the nest, and decreases with depth. Vertical spacing between chambers is least in the upper reaches and increases to a maximum at about 70 to 80% of the maximum depth of the nest. The distribution of chamber area is top-heavy, with about half the total area occurring in the top quarter of the nest. Each 10% depth increment of the nest contains 25 to 40% less area than the decile above it, no matter what the size of the nest.

Nests grow by simultaneous deepening, addition of new chambers and/or shafts and enlargement of existing chambers. As a result, the vertical spacing between chambers is similar at all nest sizes, and the relative distribution of chamber area with relative nest depth did not change during colony growth (that is, the size-free nest shape was the same at all colony sizes). Total chamber area increased somewhat more slowly than the population of workers excavating the nest. The branching of shafts was consistently shallow (< 40 cm), somewhat more so in large nests than small. Large colonies rarely had more than 4 shaft/chamber series. Each new series contributed less to the total chamber area because its chambers were smaller. Incipient colonies were usually 40 to 50 cm deep while mature colonies were commonly 2.5 to 3.0 m deep.

Workers captured near the top of a mature nest (and therefore older) and penned in escape proof enclosures, excavated larger nests than did young workers captured from the bottom of the nest. Most of this difference was due to a larger fraction of older workers engaging in digging, rather than an increase in their rate of work. All ages of workers produced similar top-heavy nests. When different ages of workers from different levels of a mature colony were allowed to re-assort themselves in a vertical test apparatus buried in the soil, older workers moved upward to assume positions in the upper parts of the nest, much as in the colonies from which they were taken. The vertical organization of workers based on age is therefore the product of active movement and choice. A possible template imparting information on depth is a carbon dioxide gradient. Carbon dioxide concentrations increased 5-fold between the surface and the depths of the nest. A preference of young workers for high carbon dioxide concentrations, and a tendency for workers to dig more under low carbon dioxide concentrations could explain both the vertical age-distribution of workers, and the top-heaviness of the nest’s architecture.

!!! Worth to take a look at the amazing pictures of "plaster-nests" :) !!!

Strehl, C.-P. and Gadau, J., 2004. Cladistic Analysis of Paleo-Island Populations of the Florida Harvester Ant (Hymenoptera: Formicidae) based upon divergence of Mitochondrial DNA Sequences, Florida Entomologist 87(4)

To examine the relationships of geographically isolated paleo-island populations of Pogonomyrmex badius (Latreille 1802) in Florida we generated a phylogeographic hypothesis based on mitochondrial DNA (mtDNA) sequences. We found at least three distinct mtDNA lineages and a positive correlation between genetic and geographic distances. The relationships between nowadays isolated P. badius populations might resemble a long lasting separation due to either restricted gene flow caused by inbreeding, paleo-climatic events or the impact of novel invasive species. The current depletion of the only representative of the ant genus Pogonomyrmex in the south-eastern USA makes a more fine-scaled mapping of the remaining, small P. badius populations necessary to identify evolutionary distinct units for conservation purposes.

Monday, January 10, 2005

Antoine Pezon, Damien Denis, Philippe Cerdan, et al. 2004. Queen movement during colony emigration in the facultatively polygynous ant Pachycondyla obscuricornis. Naturwissenschaften, Online First.

Virginie Cuvillier-Hot, Valérie Renault, Christian Peeters. 2004. Rapid modification in the olfactory signal of ants following a change in reproductive status. Naturwissenschaften, Online First.

Thursday, January 06, 2005

The big man speaks...

Wilson, E. O. 2005. Early ant plagues in the New World. Nature 433.
The identity and origin of the West Indian plague ants of the early sixteenth and late eighteenth centuries have long been a mystery. By reviewing historic accounts with an analysis of the present-day Caribbean ant fauna, I have narrowed the list of suspects to two species and their insect symbionts.

Tuesday, January 04, 2005

Wenseleers, T., A. G. Hart, & F. L. W. Ratnieks. 2004. When Resistance Is Useless: Policing and the Evolution of Reproductive Acquiescence in Insect Societies. American Naturalist 164: E154-E167.

Walsh, Peter D., Henschel, Phillipp, Abernethy, Kate A., Tutin, Caroline E. G., Telfer, Paul, Lahm, Sally A. 2004. Logging Speeds Little Red Fire Ant Invasion of Africa. BIOTROPICA 36: 637-641.

Fáveri, Sarita B., Vasconcelos, Heraldo L. 2004. The Azteca–Cecropia Association: Are Ants Always Necessary for Their Host Plants? BIOTROPICA 36: 641-646.