Research Article |
Corresponding author: Julio A. Lemos-Espinal ( lemosj44@yahoo.com.mx ) Academic editor: Lukas Landler
© 2023 Renato Sánchez-Sánchez, Olga Méndez-Méndez, Jazmín Hernández-Luría, Geoffrey R. Smith, Julio A. Lemos-Espinal.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sánchez-Sánchez R, Méndez-Méndez O, Hernández-Luría J, Smith GR, Lemos-Espinal JA (2023) Selection of substrate type, substrate color, and vegetation by tadpoles of Dryophytes plicatus. Herpetozoa 36: 153-157. https://doi.org/10.3897/herpetozoa.36.e105332
|
The characteristics of microhabitats in streams can drive the distribution of tadpoles. We experimentally examined microhabitat selection of tadpoles of Dryophytes plicatus. We used a series of choice experiments to test if tadpoles had preferences for particular substrate types, substrate colors, and vegetation. Tadpoles of D. plicatus had a strong preference for mud substrates over sand, gravel, and rock substrates and preferred darker substrates over lighter substrates. Dryophytes plicatus tadpoles used the non-vegetated side of an aquarium more than the vegetated side. Our experimental results matched previous field observations in the case of the preference for mud substrates but differed from the field observations for substrate color and vegetation, suggesting that basic underlying preferences may be modified by various factors in nature or by learning or conditioning.
Arroyo los Axolotes, behavior, Mexico, microhabitat selection, stream, tadpoles
In order to assess the consequences of potential degradation of stream habitats (
Several studies have examined a selection of substrates based on color in tadpoles. Some tadpoles show no preference among differently colored substrates (
Dryophytes plicatus
(formerly Hyla plicata;
We examined microhabitat selection of D. plicatus tadpoles using a series of laboratory choice experiments to determine if they prefer specific types of substrates (mud, sand, gravel, and rock), substrate color (dark brown, brown, light brown, and gray), and the presence and absence of vegetation. These experiments were informed by previous field observations of habitat and microhabitat use by D. plicatus tadpoles in nature. Visual surveys supplemented by physical probing of substrates (i.e., with a snake hook) indicated that D. plicatus tadpoles are often found in sites with mud (
We collected 135 tadpoles of D. plicatus from the Arroyo del Axolotes, mpio. Isidro Fabela, Mexico using a dipnet from December 2021 through November 2022. We transported tadpoles to a nearby facility for the experiments. We obtained the tadpoles from a variety of microhabitats; including pools, stream edges, shallows, and at the base of vegetation; along a 1 km stretch of the Arroyo los Axolotes. We pooled individuals into the wet (June to October; N = 100) and dry seasons (November to May; N = 35). Water temperatures are warmer and dissolved oxygen levels higher in the wet season than the dry season (
We conducted three choice experiments: substrate type, substrate color, and vegetation. Experiments were begun at around 1400 h, approximately one-four hours after capture. Prior to the experiments tadpoles were temporarily housed in plastic containers. For each experiment, we established multiple test arenas using 36 L glass aquaria (40 cm length × 30 cm width × 30 cm height) with each aquarium divided into sections as described below. We used water from the Arroyo los Axolotes to fill the aquaria. Experiments were run at a water temperature of between 7.3 °C and 8.1 °C; which was similar to water temperatures in the stream. At the start of each trial we placed tadpoles in the center of the aquarium and allowed to acclimate for 5 minutes prior to data collection. We recorded the location of the tadpole every minute for 15 minutes. To minimize the number of tadpoles used in the experiments, we ran each tadpole through all three experiments in the same order for all tadpoles (substrate color, substrate type, and vegetation), with 5–10 minutes between experiments.
For the substrate type experiment, we created four sections on the bottom of the aquaria: mud, sand, gravel, and solid rock, using material collected from the stream. The mud substrate was dark brown in color, the sand brown, the gravel gray, and the solid rock light brown or light gray. We used small rectangular plastic trays to contain the various substrate types and keep them separate. Since our goal was to assess potential preferences for substrate types we used actual natural substrates from the Arroyo Los Axolotes without attempting to control for their color or other aspects, such as the availability of food. For the substrate color experiment, we placed four equal-sized rectangular pieces of colored paper under the clear bottom. We chose colors to approximate the four most common colors of substrates in the Arroyo Los Axolotes using the COMEX color palette (brown color family): dark-brown, brown, light-brown, and gray (
For each tadpole we determined which substrate type or color they used the most. In the case of a tie, we excluded those individuals from the analyses (N = 0 excluded for substrate type; N = 2 excluded for substrate color; N = 0 excluded for vegetation). We used chi-square tests to determine if the numbers of individuals using each substrate type or color the most were different from that expected if the individuals chose substrate types or colors at random (i.e., 25% for each substrate type or color) or vegetated and non-vegetated sides at random (i.e., 50% on each side). We also used chi-square tests (or Fisher’s exact test if expected values were < 5 in > 20% of cells) to determine if substrate type and color preferences differed between the wet and dry seasons.
Tadpoles overwhelmingly chose mud substrates over the other substrates (Fig.
Tadpoles chose dark brown and brown more than light brown and gray (Fig.
Tadpoles used the non-vegetated side of the aquarium much more than the vegetated side (Fig.
Our experimental results suggest that tadpoles of D. plicatus had a strong preference for mud substrates over sand, gravel, and rock substrates. Our experimental results are similar to those from previous field studies that found mud to be the most used substrate for D. plicatus in the Arroyo Los Axolotes (
Tadpoles of D. plicatus preferred dark brown and brown substrates over light brown or gray substrates (i.e., they preferred the darker substrates), which is what we might expect given that the tadpoles of D. plicatus used in our experiment were jet black. For example, tadpoles of some species have been shown to select substrates that allow them to be more cryptic when disturbed (
In our experiments, D. plicatus tadpoles showed a strong preference for using the non-vegetated side of the aquarium over the vegetated side of the aquarium. In nature, D. plicatus tadpoles used sites with different types of vegetation, including no vegetation, in the same frequency as their availability along the Arroyo los Axolotes (
The series of experiments we conducted to examine the elements of microhabitat use in tadpoles of D. plicatus suggest that these tadpoles may have preferences for some characteristics of their environment (e.g., mud and darker substrates), but avoid others (e.g., vegetation). In addition, the difference between some of the results we obtained in our experiments for substrate color and vegetation and those from field studies emphasize that basic underlying preferences may be modified by various factors in nature or by learning or conditioning (see
Support for this study was provided by Dirección General de Asuntos del Personal Académico, Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (DGAPA-PAPIIT), through the Project IN202021. Tadpoles were handled under permit SGPA/SGVS/03662/20 and SGPA/DGVS/06608/21 from Secretaria del Medio Ambiente y Recursos Naturales of Mexico (SEMARNAT).