lunes, 13 de julio de 2009

Ongoing projects

Geographical expansion of Acromyrmex lobicornis (finished project)

After defending my PhD at the Autonomous University of Barcelona we (my husband and I) returned to Argentina on 2007. Here, I got involved in the research project of Dr Alejandro Farji-Brener who investigates which factors favour the increase of the geographic range of Acromyrmex lobicornis. This leaf cutting ant is moving toward the south of Argentina and had already been found in the east limit of the National Park Nahuel Huapi, 15 km from the city of Bariloche (41º S, 72º W). In order to investigate if plasticity of nest arquitecture, diet choice and foraging activity allow this ant species to colonize new areas, I compared two populations, one located in the north of Argentina (Cafayate, Salta, 26º S, 65º W) and the other in the center of Argentina (San Cristóbal, Santa Fe, 30º S, 61º W).

Very happy after finding the first nest of Acromyrmex lobicornis at El Moyar an area 12km close to Cafayate a very nice village from the north of Argentina. I should follow the activity of the same ten nests for one year.
As part of my curiosity I excaveted an Acromyrmex lobicornis nest. I reached the first fungi chamber and here you can see a piece of fungi garden with some larvae in gaps and a A. lobicornis big worker at the left. If you enlarge the photo you can see the lobule at the base of the antenna (this is a taxonomic trait for Acromyrmex sp)

I love filming ant activities. When you see on a large TV screen what you had filmed you discover nice details of ant behaviour.

A. lobicornis nest are really different depending on the site. At Santa Fe this ant species built domes. Here I was sampling damp material.

It is really nice to share the field with the ants. Here I was at my camp where I lived for 12 days to invest less time in travelling from the village to the field. In my opinion organization is very important to do your field work properlly.

As part of my postdoctoral training, I was encouraged by Dr Farji-Brener to develop my own research projects. So, I did. One of them concerns the control of the invasive ant Linepithema humile in vineyards from north of Argentina and their effect on leaf cutting ants. The aim of the other project is to estimate the biodiversity of ground dwelling ants in the National Park of Iguazú (Misiones, Argentina).

Leaf cutting ants vs. Linepithema humile

In vineyards, leaf cutting ants are a serious problem, not only through direct economic loss but also because their control implies the use of pesticides which are not always desirable, particularly for organic wines. Some years ago (apparently 18 years ago), an ant species of Linephitema arrived in a timber load from the northeast of Argentina to San Pedro de Yacochuya an area 8km away from Cafayate, Salta, north of Argentina. At the beginning nobody noticed its presence. But, as time goes on, this ant species spread and it was noticed that tends insects in vineyards and it was seen actively attacking leaf cutting ants (see the video at: Now, in the area there is a supercolony that covers 293 ha. Local workers said “she took out from the nest some tiny-white things, like little worms”. This species of Linepithema seems able to steal larvae from leaf cutting ants in spite of their smaller size. As a consequence, the attacked leaf cutting ant species are apparently declining in the area. The owners of the vineyards, though that may be this ant species can be used as a biological control of leaf cutting ants. However, I think that other outcomes may arise due to aphid and coccid attention by ants. See research interest for a detalied explanation of this point. 
First of all it was necessary to confirm the species identification. So, I sent some workers to Dr Alex Wild from Illinois University who has reviewed this genus recently. He confirmed it is Linepithema humile. “Ups! we have a problem”, I though. The native distribution of this ant specie is the Paraná River drainage basin area of subtropical Argentina, Brazil, Paraguay, and Uruguay not the north of Argentina. At San Pedro de Yacochuya area, L. humile tends the mealybug Planococcus ficus, a pest of vineyards. So, the situation in this area matches with that showed in the right part of figure 2. Our aim in this project is to stop L. humile spread, to control it by combining poisoned baits and the modification of cuticular hydrocarbons (ants use them to recognize individuals belonging to the same colony) and finally to evaluate the net outcome for the vines.  The results of our first sampling are in the poster (only in Spanish) presented in the last meeting of the Ecological Society of Agentina in Buenos Aires.

Diversity of ground dwelling antsMore and more, ant taxonomy is becoming a great tool to evaluate the stage of conservation or restoration of an area. Ants seem to be good bioindicators because their taxonomy is described quite well; they are ubiquitous and relatively easy to sample.

      I chose the National Park of Iguazú for our research project because this area has been identified as a biodiversity hotspot at global scale. We are applying the ALL protocol to sample ants (pitfall, winklers and subterranean baited probes). In this way our data will be comparable to the information of other rainforest areas. This will be the first step of a bigger project trying to sample the ant community along the green corridor of Misiones Province. This corridor links some natural areas, protected areas and private areas in a good stage of conservation. Our big goal is to relate the composition of the ground-dwelling ant community to historical land use. We also hope to add some new records for myrmecology and to encourage students to become enthusiast ant taxonomists.

The red line shows the limit of the areas included in the green corridor of Misiones province. Light green represent protected areas occupying 412.259 ha.
    In this project it is involved Priscila Hanish, one of my undergraduate student, who is also working at the Museum of Natural Science of Buenos Aires at the Department of Entomology. Now, she is identifying ants at morphospecies and species level when possible. Go ahead Priscila! Other person that was involved in this project was my husband Pablo. He always participates in the logistic of the field travels i.e. making some equipment we need (he made very nice Berlesse extractors), transporting the heavy stuff, opening trails in the rain forest with the machete, doing the shopping, etc.

From the left to right. Pablo, my husband, me and Priscila an undergraduate student. We were going to work at the rain forest. January 2009

That me, shifting litter at rain forest

Having luch and doing a break. Mosquitos, bees and butterfly were really interested in our blood and sweatHanging winklers at the laboratory in the CIES, the research tropical center at the National Park of Iguazú

Research interest

Research interest

Ants interact with many other organisms through their feeding preferences, nesting and foraging activities: with plants, with honeydew-producing insects (aphids, whiteflies, scales, some butterfly larvae and mealybugs), with other insects and with microorganisms. In particular, ant species that tend honeydew-producing insects may change the abundance, diversity and fitness of those organisms involved in the interaction. My main interests are: how does the mutualism between ant species and honeydew-producing insects vary on time and space? How does the outcome of this mutualism change according to the particular species of tending ant and honeydew-producer involved? There are costs and benefits for each organism related, directly or indirectly, with the mutualistic interaction between tending ants and honeydew-producers (Fig 1). 

Fig. 1. This is a general overview of the mutualism between tending ants and honeydew producing insects (tended insects). Red arrows represent negative interactions towards the target organism, green arrows represent a positive interaction, and black arrows represent interactions that can be negative or neutral. The dotted violet arrow asks about the net effect (outcome) of ants on plants due their mutualism with tended insects. For detailed explanation see the text bellow.

       Usually, ants have a positive effect on honeydew producers’ abundance by protecting them against predators, parasitoids and providing them with hygienic services i.e. collecting honeydew stuck to its bodies. Although sometimes there is a cost of the fitness for the tended insect or even the ants prey them tended insects. As a consequence of this mutualism, sap consumption increases and fitness plant may be negatively affected. In some particular systems, ants may deter or prey herbibores from plants where they tend insects. This leads to a positive effect of ants on plants in spite they tend insects. The balance, between positives and negatives effects, of this mutualism will determinate the outcome for plants. This nest effect for plant is context- and species-dependant, and changes with time. Plant defences against tended insect and/or herbivores are costly and its production depends also on the net effect that tending ants have on plants.

      An extra question arises when a leaf cutting ant is the main herbivore of the arthropod community, because the two ant species would indirectly compete for their resource (i.e., the plant). Leaf cutting ants need the leaves to cultivate the fungi from which they feed, while tending ants need a healthy plant from which honeydew-producing insects can produce enough honeydew. So, what happens at the same plant species when leaf cutting ants meet an aggressive tending ant? Two general situations may appear when the main herbivore in the system is a leaf cutting ant and there are also tending ants (Fig 2).

The figure shows the two general situations that may appear when the main herbivores in the system are a leaf cutting ants. Red arrows represent negative interactions towards the target organism and green arrows represent positive interactions (dotted arrows represent indirect effect). For figure explanation please see text bellow.

   Both, ant species have positive and negative effects on plants. Leaf cutting ants indirectly increase soil nutrient content but, this effect occurs at a small-scale (in external o internal refused damp material). It had been demonstrated that plants growing close to nest or on external dump use these nutrients to increase its biomass and leaf quality compared with plants far away of the nest. On other hand, leaf cutting ants have a negative effect if we consider the herbivory of these ants. But, when the tending ant displaces leaf cutting ants the situation could become as the one showed in figure 1. The outcome for the herbivored plant will depend on the net effect of the mutualism between tending ants and honeydew producing insects and the net effect of the herbivory of leaf cutting ants.

     Additionally, I am strongly interested in ant taxonomy as a tool to put research of mutualism in a broader context by considering the composition of the whole ant community where these mutualisms develop. Taxonomy is also interesting because ants are good candidates for bioindicators of conservation stage in natural areas and of several processes such as soil restoration.