Monday, December 27, 2004

The latest in Argentine ant research, brought to you by the Ant News Department of Shameless Self-Promotion:

N Roura-Pascual, AV Suarez, C Gomez, P Pons, Y Touyama, AL Wild and AT Peterson. 2004. Geographical potential of Argentine ants (Linepithema humile Mayr) in the face of global climate change. Proceedings of the Royal Society of London, Series B 271: 2527-2535.

Summary. We examined the potential worldwide distribution of the Argentine ant (Linepithema humile) based on current climate models and also in the face of projected future climate change. Native to South America, Argentine ants have invaded broad areas around the world. Our results suggest that Argentine ants still have the potential to spread into areas not currently known to be occupied, particularly in regions of Africa and Asia. Higher latitudes appear to become more suitable for the Argentine ant under global climate change scenarios. Because invasion processes have the potential to alter global biodiversity considerably, this improved knowledge of the potential geography of the Argentine ant should be considered in preventive efforts.

Roura-Pascual et al's study makes use of the native range distribution contained in this recent paper:

Wild, A. L. 2004. Taxonomy and Distribution of the Argentine Ant, Linepithema humile (Hymenoptera: Formicidae). Annals of the Entomological Society of America 97: 1204 - 1215.

Abstract. The taxonomy of an invasive pest species, the Argentine ant, is reviewed. Linepithema humile (Mayr) 1868 is confirmed as the valid name for the Argentine ant. Morphological variation and species boundaries of L. humile are examined, with emphasis on populations from the ant's native range in southern South America. Diagnoses and illustrations are provided for male, queen, and worker castes. Collection records of L. humile in South America support the idea of a native distribution closely associated with major waterways in lowland areas of the ParanĂ¡ River drainage, with recent introductions into parts of Argentina, Brazil, Chile, Colombia, Ecuador, and Peru.

If you're curious, but in too much of a hurry to download the pdf, the distribution of the Argentine Ant in it's native range looks like this:

Saturday, December 11, 2004

Is unicoloniality not as important as we thought in the invasive success of Argentine ants?

Heller, N. E. (2004) Colony structure in introduced and native populations of the invasive Argentine ant, Linepithema humile. Insectes Sociaux 51(4): 378 - 386.

Summary. The Argentine ant, Linepithema humile, severely decreases the abundance and diversity of native ant fauna in areas where it invades, but coexists with a more diverse assemblage of ants in its native range. The greater ecological dominance of L. humile in the introduced range may be associated with differences in colony structure and population density in the introduced range relative to the native range. In this study, I compared aspects of L. humile colony structure, including density, the spatial pattern of nests and trails, and patterns of intraspecific aggression in parts of the introduced and native ranges. I also compared the number of ant species coexisting with L. humile. Introduced and native populations did not differ significantly in nest density, ant density, nest size, and nearest-neighbor distances. In three of the four study populations in the native range and all of the study populations in the introduced range, colonies were organized into supercolonies: they consisted of multiple, interconnected nests that were dense and spatially clumped, and aggression among conspecifics was rare. In one population in the native range, colonies were organized differently: they occupied single nest sites, nests were sparse and randomly dispersed, and ants from neighboring nests were aggressive toward each other. Species richness was significantly higher in the native range than in the introduced range, even in areas where L. humile formed dense supercolonies. The results suggest that differences in species coexistence between ranges may due to factors other than L. humile colony structure. One likely factor is the superior competitive ability of other ant species in the native range.

After the series of astute papers a few years ago by Tsustui, Suarez, Giraud, Keller, and others documenting a genetic bottleneck at introduction correllating with a decrease in intraspecific aggression and an increase in the extent of unicoloniality in the Argentine ant's introduced range, the idea spread that the enormous success of the Argentine ant in eliminating native species was due to this change in colony structure. So, the Argentine ant in its native range must not be unicolonial, right?

Apparently the story is more complicated. Heller's central finding- that Argentine ants can frequently be unicolonial in the native range and that nests can be just as dense while coexisting with numerous other ant species- shows that there is something beyond mere Argentine ant unicoloniality in the spread of the species around the world. Heller thinks that native species in Argentina are simply tougher than native species in California. I am sympathetic to this idea, but what we need to flesh this out is some careful ecological experimentation in the native range.

(disclaimer: I helped collect some of the data in Heller's study, so I am not an entirely unbiased observer...)

Thursday, December 09, 2004

Ant Excrement: More Important Than You Think

SOLANO, PASCAL JEAN & DEJEAN, ALAIN (2004) Ant-fed plants: comparison between three geophytic myrmecophytes. Biological Journal of the Linnean Society 83 (4), 433-439.

ABSTRACT: In their association with myrmecophytes (i.e. plants that shelter a limited number of ant species in hollow structures), ants sometimes provide only poor biotic protection for their host plants, but may supply them with nutrients (myrmecotrophy). We studied three geophytic myrmecophytes growing in the understorey of Guianian rain forests. Allomerus ants build spongy-looking galleries rich in detritus and insect debris over the stems of their host plants [Cordia nodosa Lamark (Boraginaceae) and Hirtella physophora Martius & Zuccharini (Chrysobalanaceae)], while Pheidole minutula Mayr colonies deposit their waste in the leaf pouches of their host plant [Maieta guianensis Aublet (Melastomataceae)]. This waste is more nitrogen-rich than that found in the Allomerus galleries, themselves containing more nitrogen than the plant leaves. Using stable isotope analysis we noted a significant difference in 15N between ant-occupied and unoccupied plants only for Maieta, for which 80% of the host plant nitrogen is derived from Pheidole waste. Experiments on all three plants using a 15N-supplemented solution of NH4Cl confirmed these results, with an increase in this isotope noted between control and experimental plants only for Maieta. The internal surfaces of Maieta leaf pouches bear protuberances whose likely role is to absorb nutrients from the Pheidole waste. The alternative hypothesis, that these protuberances play a role in provisioning ants, was rejected after comparing their structure with those of extrafloral nectaries and food bodies in a histological study.

Monday, December 06, 2004

Busy, busy, busy...

The past month has seen the usual flurry of articles on ant research. There's more out there than I can possibly blog. The latest Insectes Sociaux is out, chock-full of ant goodies. For sheer drama, I recommend Powell and Clark's study on combat between Atta and Nomamyrmex.

There are several ant/social insect articles in December's Naturwissenschaften. This month's Evolution contains an article on genetic population structure in European Formica. If microsatellites are your thing, the latest issue of Molecular Ecology Notes reports microsatellites in Oecophylla, Pachycondyla, and Cataglyphis. Neotropical ant taxonomy buffs should see Lacau et al's new Typhlomyrmex species in Zootaxa. Ipser et al document the ground-dwelling ants of Georgia in The Florida Entomologist.

If your brain hurts from poring over research reports, you can always take a break to look at the new pretty ant pictures I've posted at Like this lovely Formica oreas from the Sierra Nevada:

More research to come. I'll be posting several new Argentine ant articles shortly, and some findings from European Formica that don't bode well for those trendy mtDNA "barcoding" projects.