The effects of nitrate on three species of male tree frogs Hyla regilla, H. cadaverina, and H. chrysoscelis Megan Tracey, Becky Talyn & Erik Melchiorre, California State University, San Bernardino. Abstract - PowerPoint PPT Presentation
Citation preview
The effects of nitrate on three species of male tree frogs Hyla
regilla, H. cadaverina, and H. chrysoscelisMegan Tracey, Becky
Talyn & Erik Melchiorre, California State University, San
Bernardino AbstractAmphibians are good bioindicator species for
aquatic environments. Nitrate is a known contaminant, but based on
previous fieldwork does not affect frog distribution. However, high
levels of nitrate have been shown to negatively affect tadpoles. In
this experiment we observed tree frogs behavioral response to
nitrate contamination under controlled laboratory conditions to
better understand the implications of nitrate contamination on
amphibian populations. We tested the effects of nitrate on three
species of tree frogs (Fig. 1): Hyla regilla (N=7), H. chrysoscelis
(N=6) and H. cadaverina (N=8). We used 7, 10, 20, and 50 ppm, and
control (0 ppm) treatments in blind trials. A small habitat cage
was placed upon wooden supports, with a mirror for observation
underneath. A Kim wipe was placed randomly on the right or left
side of the habitat cage, with 5ml of one of the test solutions.
Frogs were observed for up to 15 minutes or until they left the
treatment. We noted whether or not they were absorbing the
treatment, and how much time they spent squatting. Results show no
relationship between time spent on treatment, absorbing or
squatting and the level of nitrate used. Thus none of the three
species responded to the presence or absence of nitrate in the lab,
corroborating earlier field results. As studies have shown that
exposure to nitrate puts tadpoles at risk for decreased growth rate
and likelihood of survival, this lack of behavioral response to
nitrate contamination may contribute to population decline,
particularly in heavily farmed areas. Introduction This behavioral
experiment was done to determine the implications of sub-lethal
nitrate contamination on amphibian populations. The experiment
follows on a pond study in which water samples were collected to
determine whether frogs choose which ponds to use for reproduction
based on chemical contamination of the water. Nitrate is a known
local contaminant, especially in agricultural areas, but based on
previous fieldwork does not affect frog distribution (Talyn et al.
2003). However, high levels of nitrate have been shown to
negatively affect tadpoles, and their development (Rouse et al.
1999). This experiment was designed to observe tree frogs
behavioral response to nitrate contamination under controlled
laboratory conditions to better understand the implications of
nitrate contamination on amphibian populations. Specifically, we
assessed the behavioral response of adult male tree frogs to
nitrate in water. MethodsThe experiment was performed using the
male tree frogs Hyla regilla (Fig. 1 top; N=6) and H. cadaverina
(Fig. 1 bottom right; N=7) found locally in areas surrounding
California State University San Bernardino, and H. chrysoscelis
(Fig. 1 bottom left; N=5) from Indiana. Frogs were exposed to 5 ml
of nitrate-contaminated isosmotic solutions at 0, 7, 10, 20, and 50
ppm. Each trial was conducted in a half gallon aquarium placed on
wooden supports above with a mirror. Each frog was carefully voided
using gentle abdominal pressure, and weighed to 0.1 grams. We then
placed the frog onto the solution with a small weigh boat for
restraint. Approximately 20 seconds later the weigh boat was lifted
off and observations started. Frogs were observed continuously for
up to 15 minutes, recording absorption and squatting behavior.
Absorbing occurred when the whole abdomen of the frog was fully
pressed onto the solution. Squatting behavior accompanied increased
breathing rate with just the pelvic region actively absorbing the
treatment. If the frog was squatting he was absorbing, but the
reverse is not true. When a frog left the treatment the trial was
stopped. Results were analyzed separately for each behavior (length
of trial, time absorbing, time squatting) using a two way ANOVA
with species and nitrate concentration as factors. Figure 2:
Nitrate concentration does not alter behavior of treefrogs.Figure
3: Three species of treefrogs do not respond differently to nitrate
contamination. A) Time spent on solution, B) Time
squatting.ABResultsOur data show no relationship between time spent
on treatment, absorbing or squatting and the level of nitrate used
(Fig. 2; MANOVA: overall F=1.304, P=0.219; on treatment F=0.767,
P=0.550; absorbing F=0.943, P=0.444; squatting F=1.391, P=0.246).
While the three species differed in some of the behaviors (MANOVA:
Species: overall F=6.424, P