Drought stress drives intraspecific choice of food plants by Atta leaf‐cutting ants

Leaf‐cutting ants (LCA) are polyphagous and dominant herbivores throughout the Neotropics that carefully select plant individuals or plant parts to feed their symbiotic fungus. Although many species‐specific leaf traits have been identified as criteria for the choice of food plants, the factors driving intraspecific herbivory patterns in LCA are less well studied. Herein, we evaluate whether or not drought‐stressed native plants are a preferred food source using free‐living colonies of two leaf‐cutting ants, Atta sexdens L. (Hymenoptera: Formicidae: Attini), in combination with five plant species, Ocotea glomerata Nees (Lauraceae), Lecythis lurida S. A. Mori (Lecythidaceae), Miconia prasina DC (Melastomataceae), Tovomita brevistaminea Engl. (Clusiaceae), and Tapirira guianensis Aubl. (Anacardiaceae), and Atta cephalotes L., in combination with two plant species, O. glomerata and Licania tomentosa Benth. (Chrysobalanaceae). In dual‐choice bioassays, ants removed about three times more leaf area from drought‐stressed plants compared to control plants. Both leaf‐cutting ant species consistently preferred drought‐stressed plants for all species tested, except T. guianensis. The mean acceptability index – expressing the preference for one of two options on a scale of 0 to 1 – of drought‐stressed plants ranged from 0.65 to 0.86 across plant species, and the preference did not differ significantly among the tested plant species. Our results suggest that selection of drought‐stressed individuals is a general feature of food plant choice by leaf‐cutting ants irrespective of ant or plant species. As human‐modified forest assemblages across the Neotropics are increasingly prone to drought stress, the documented preference of Atta for drought‐stressed plants may have tangible ecological implications.     

<Emphasis Type="Italic">Xenopus laevis</Emphasis> (Daudin, 1802), a new exotic amphibian in Portugal

The African clawed frog Xenopus laevis has been introduced at several locations, including Mediterranean climate-type regions. In 2006, several individuals of this species were found inhabiting a stream at Oeiras, about 20 km W of Lisbon, Portugal. Although the place and time of introduction are not clearly identified, there are reasons to believe that this population may be the result of an almost 30-year-old introduction proceeding from research laboratories located nearby. Field surveys were conducted in 2007 and 2008 on the distribution and abundance of this species in the region. The species was found in two streams, about 5 km from each other. While being locally abundant, the adults of X. laevis are smaller than those from South Africa and California. In spite of an abundant production of eggs and tadpoles at one of the streams, no tadpoles were found in advanced developmental stages. Until now, most individuals were found in heavily urbanized areas that should constrain their ability to cross overland to other water bodies. An eradication program may be feasible, but the presence of adults on two streams indicates that the species may be expanding, in spite of the urban landscape.