Detection and use of foraging trails of the leaf-cutting ant Atta laevigata (Hymenoptera: Formicidae) by Amphisbaena alba (Reptilia: Squamata)

Detección y uso de senderos de la hormiga cortadora de hojas Atta laevigata (Hymenoptera: Formicidae) por Amphisbaena alba (Reptilia: Squamata)

Vitor Azarias Campos,¹ Wesley Dáttilo,²* Fabricio Hiroiuki Oda,³ Luis Eduardo Piroseli ⁴ & Aline Dartora⁴

¹ Universidade Federal de Mato Grosso, 78060-900. Cuiabá, Mato Grosso, Brazil.

³ Universidade Estadual de Maringá, 87020-900. Maringá, Paraná, Brazil.

⁴ Universidade do Estado de Mato Grosso, 78300-000, Tangará da Serra, Mato Grosso, Brazil.

Recibido: 16/05/2013;
Aceptado: 24/03/2014.

RESUMEN

Se provee información sobre un individuo de Amphisbaena alba (Reptilia: Squamata) que reconoce y usa un sendero de la hormiga cortadora de hojas Atta laevigata (Hymenoptera: Formicidae) en la sabana neotropical de Brasil. También registramos y describimos movimientos de desviación de obstáculos y el comportamiento de A. alba para reconocer el sendero de hormigas. Adicionalmente, discutimos cómo el mimetismo químico de A. alba pudiera estar involucrado en nuestra observación y sugerimos que esta relación va más allá de un simple inquilinismo, donde A. alba puede usar el nido como un sitio de reposo y alimentación para otros organismos asociados con nidos de hormigas cortadoras.

Palabras clave: Inquilinismo, nidos de hormiga, mimetismo químico, estrategia no agresiva, interacciones interespecíficas.

Amphisbaenians, or worm lizards, constitute a monophyletic group of highly specialized fossorial squamates with approximately 200 species (Pinna et al. 2010). Six families are recognized in the suborder Amphisbaenia, of which only Amphisbaenidae is present in Brazil with 68 known species (Pinna et al. 2010). The life cycle of amphisbaenians is almost entirely restricted to the interior soil of tropical and temperate environments (Kearney 2003), and their diet consisted mainly of small invertebrate prey (e.g., beetles, ants and spiders) (Colli & Zamboni 1999). Because they live underground, the natural history of amphisbaenians remains poorly understood (Andrade 2006). This is applicable to Amphisbaena alba Linnaeus 1758, one of the most common and widely distributed amphisbaenids in South America east of the Andes (see Pinna et al. 2010). This species does not exhibit sexual dimorphism and its reproduction occurs apparently in the dry season (Colli & Zamboni 1999).

Associations of A. alba with leaf-cutting ants of the genus Atta is long-standing known (Riley et al. 1986). Some studies indicate that A. alba can be considered a facultative inquiline of leaf-cutting ant nests, such as Atta cephalotes (Stahel & Geijskes 1939, Riley et al. 1986), Atta sexdens (Stahel & Geijskes 1939) and some species ofAcromyrmex (Della Lucia et al. 1993). Within the nests, individuals of A. alba feed primarily on small invertebrates, which are inquilines of ant nests (Riley et al. 1986). The present study adds new information on the association of A. alba with leaf-cutting ants after an observation made under natural circumstances in the Neotropical Savanna.

During a field expedition to the "Garimpo do Araes", municipality of Nova Xavantina, Mato Grosso State, Brazil (14°52'59" S; 52°48'96" W, 334 m above sea level), an adult specimen of A. alba was observed following a foraging trail of the leaf-cutting ant Atta laevigata F. Smith 1858. During the observation, we employed the focal animal method to record all occurrences of specific behaviors of interest exhibited by the amphisbaenid. Ant workers were collected as vouchers and identified according to Della Lucia (1993), and subsequently deposited in the Entomological Collection of Universidade Federal de Mato Grosso (CEMT).

On April 23^th 2009, at 08:50 h, after a rainy night, an individual of A. alba was found in activity on the soil surface in an area covered by Cerrado sensu stricto vegetation (Neotropical Savanna). Constantly tongue-flicking, the animal crawled for about 18 minutes, without going in any particular direction. At 09:08 h, it apparently detected a foraging trail of the leaf-cutting ant A. laevigata, which was not in activity at the time of observation. Tongue-flicking rate increased as soon as the animal entered the trail (Fig. 1A). The amphisbaenian deviated from obstacles (small stones with mean diameter of approximately 20 mm) on two occasions while moving along the trail, after which it soon returned to the trail and continued to move forward (Fig. 1B). With the head always near the ground while continuously tongue-flicking, the individual moved strictly forward along the trail for 53 meters until it reached and entered the main entrance hole of the ant nest, at 09:25 h (Fig. 1C). During the whole time, the distance between the observer and the individual of A. alba was approximately three meters. Additionally, we observed another individual of A. alba recognizing and using a foraging trail of A. laevigata in the same area in November 2011. However, we do not have detailed information about this behavior.

Although scarce, our observations suggest that individuals of A. alba in nature could use chemical cues along trails to locate and reach nests of leaf-cutting ants of the genus Atta. Riley et al. (1986) experimentally demonstrated that A. alba can follow ant trails and suggested that the orientation cue used is predominantly olfactory, and methyl 4-methylpyrrole-2-carboxylate could be the major trail pheromone, although there could be a complex of pheromonal factors (Robertson et al. 1980). Additionally, the same authors also observed that individuals of A. alba maintained the head near to the ground surface and increased tongue-flicking rate while following trails of A. cephalotes.

Chemoreception is an advantageous adaptation component to fossorial habit organisms (López & Martín 2001), which could help A. alba to locate nests of the leaf-cutting ants from the genus Atta. It is possible that when A. alba moves along the trail, ants pheromone particles could adhere to the amphisbaenian body, thus enabling it to chemically mimetize leaf-cutting ants of the genus Atta, in order to get a kind of "passport entry" into the nest. We already know that pheromones found on the trail of leaf-cutting ants can last up to 96 hours (four days) (Moreira & Della Lucia 1993). Therefore, regardless of the presence or absence of ants on the trails, if a trail is active, individuals of A. alba could acquire the ants pheromone. In fact, organisms entering the nests of ants developed elaborate morphophysiological and behavioral adaptations, otherwise they would be recognized by the ants and attacked (Della Lucia et al. 1993).

Although this report does not provides enough information to conclude the actual relationship between A. alba and leaf-cutting ants, if chemoreception is involved this relationship may go beyond a simple inquilinism. Worm lizards use nests of A. laevigata as refuge after heavy rains (see Stahel & Geijskes 1939). A. alba can use leaf-cutting ants nests as sites for egg laying and feeding on other organisms associated with nests. Thus, the ability to recognize chemical trails of A. laevigatta, added with experiments performed by Riley et al. (1986) suggest that chemosensory adaptation helps in the recognition of Atta nests.

ACKNOWLEDGMENTS

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