CHLORPYRIFOS EFFECT ON ANTIPREDATORY AND FEEDING
BEHAVIOR IN THE AXOLTL Ambystoma mexicanum JUVENILES
C. Robles-Mendoza*1, M. A. Balleza-García2, D.G. Valencia-Segura2, S.R. ZúñigaLagunes3, R.C. Vanegas-Pérez3.
1
Unidad Multidisciplinaria de Docencia e Investigación Sisal, 2 Unidad de Análisis
Ambiental, 3Laboratorio de Ecofisiología.
Faculty of Sciences, National Autonomus University of Mexico. Mexico.
*rmc@ciencias.unam.mx
The axolotl Ambystoma mexicanum is endemic of Xochimilco, a wetland of the basin of
Mexico valley, nowadays an impacted lacustrine area at southern Mexico City. Severe
reduction of A. mexicanum wild population is related mainly with habitat reduction and
fragmentation, pathogens, introduction of non-native species (competitors and
depredators as the fish Oreochromis niloticus and Cyprinus carpio) and organicinorganic contaminants inputs due urban discharges and agricultural activities. In
Xochimilco, the use of organophosphate pesticides (OPPs) is a common practice in
cropping activities. Recent studies demonstrate the inhibition of esterases
(acetylcholinesterase and carbolylesterase) and motor activity alteration in A.
mexicanum exposed to environmental concentrations of the OPP chlorpyrifos (CPF).
However, the consequences of these alterations upon the ecological performance of the
species as prey-predator interactions are unknown. Thus, this study was conducted to
elucidate the perception cues in A. mexicanum juveniles of the predator Oreochromis
niloticus and the effect of CPF sublethal exposure in the axoltl-fish interactions.
Additionally, the effect of the interaction of CPF exposure and the predator pressure on
the feeding behavior of A. mexicanum was analyzed. Groups of axolotls and O. niloticus
were separately exposed for 48 h to 0.05 y 0.1 mg CPF L-1, realistic environmental
pesticide concentrations; un-exposed groups to CPF of both axolotl and fish were
considered as control groups. During the exposure period, organism remained un-feed.
For the testing phase (predator-prey interactions), after CPF exposure organisms were
transfer to four type of aquaria (pesticide-free water) designed to allow different
interactions within species: chemical, visual and direct contact; an aquaria avoiding any
type of interaction was considered as negative control. Each aquarium was divided in
five compartments; in four of them an axolotl was placed and in the fifth one an adult fish
was introduced. Additionally, ten small fishes (Chirostoma sp.) were introduced in each
axolotl compartment, as feeding source; several plastic pipes were also placed as axolotl
refugees. Three replicates were conducted for each axolotl-fish interaction condition.
Video recordings were conducted during 24 hours. Data analysis of axolotl-predator and
axolotl-prey interactions included frequency of contacts, axolotl swimming speed,
frequency of scape and erratic movements, time spend in activity and refugee use.
Additionally, frequency of axolotl prey attacks and feeding efficiency was analyzed.
Obtained results demonstrated that CPF exposure exerted and adverse effect on the
axolotl antipredatory responses and compromise the feeding activity of the organisms.
Also, predatory fish presence limited axolotl motor activity and in consequence, the
axolotl attack frequency to their prey was diminished as well as the feeding efficiency. It
is concluded that CPF exposure at environmental realistic concentrations, could
compromise the axolotl performance in their habitat due the adverse effects on feeding
behavior and antipredatory responses.