The Effect of Variant Elevations on the Dorsal Scale Banding Patterns of The
Western Fence Lizard, Sceloporus occidentalis
Andrew Favor, Patrick Stumps, David Atta, and Ishav Singh
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
In nature, species undergo adaptive changes in both form and physiology in
order to facilitate survivability in a given environment. Elevation gradients present
variance in climates that stimulate adaptive divergence among species through
induced changes in both temperature and exposure to ultraviolet radiation. These
factors strongly influence the physiological nature of ectotherms, due to their
dependence on environmental temperature sources for thermoregulation. In this
project, lizards were gathered from various locations around southern Orange
County, which spanned three different elevation-groups. Group 1: less than 100
meters above sea level. Group 2: 100-149 meters above sea level. Group 3: 150
meters above sea level and higher. The percentages of lizards found possessing
white scales in groups 1, 2, and 3 were: 62.5%, 64.3%, and 84.6%, respectively (p =
0.0007). The percentages of lizards found possessing blue scales in groups 1, 2, and 3
were: 62.5%, 57.1%, and 53.8%, respectively (p = 0.4561). These results suggest
that lizards at higher elevations in the coastal regions of desert climates are subject
to hotter conditions, and thus develop white scales to prevent excessive heat
absorption. Additionally, lizards in lower elevations of coastal regions are exposed
to cold air from the nearby sea, and develop blue scales in order to promote
thermoregulation via heat absorption.
Introduction
In nature, species undergo adaptive changes in both form and physiology as a response to
environmental pressures, in a manner facilitative of survivability in a given environment. Elevation
gradients present variance in climates and habitats, thus providing an abundance of sources to stimulate
adaptive divergence among species. Previous experiments in this field have found a range of interesting
patterns in morphological variation correlating with changes in elevation. For instance, despite its distinct
phenotype, Sceloporus occidentalis taylori has evolved multiple times, independently, due to variant
elevations (Leache, et al., 2010).
Changes in altitude can influence organisms through induced changes in both temperature and
exposure to ultraviolet radiation. These factors influence the physiological nature of ectotherms, due to
their dependence on environmental temperature sources for thermoregulation. Examination of the color
patterns of the lizard Psammodromus algirus have found a darker scale coloring to be present on specimens
found at higher elevations. This pattern in evolution is assumed to have taken place in order to promote
hastened warming at higher elevations, as well as to protect against the increased exposure to UV radiation
at higher altitudes (Reguera et al., 2014).
Additionally, climate gradients tend to present variation in the size of dorsal scales in lizards, as
those found in warmer regions display larger scales, presumptively for the purpose of regulating the heat
load that they are exposed to (Oufiero et al., 2011).
Furthermore, in analyzing patterns of relation between geographic variations and the differential
morphology of lizards within experimentally controlled environments, the degree of difference in multivariate morphology has been found to correlate with the degree of difference between ecological conditions
of experimentation sites (Malhotra and Thorpe, 1991).
The previous research in this field suggests that there will be a significant difference in the dorsal
scale colors of Sceloporus occidentalis found at different altitudes along costal elevation gradients. By
examination of the variations in both coloring and scale size of Sceloporus occidentalis, this project seeks
to shed light upon the relationship between morphological variation and environmental differences
manifested along elevation gradients. With the information gained through this research, perhaps a greater
understanding may be reached of the complex interplay between environmental factors and exterior
morphology in the achieved metabolic regulation of ectotherms.
Methods
Lizards were gathered from various locations around cities located in southern Orange County,
which spanned three different elevation-groups (<100, 100-150, and >150 meters above sea-level). Once
caught, the lizards were measured with a ruler, and photographs were taken of their dorsal and ventral
sides. For each lizard, the presence of white and blue dorsal scales was noted. Once the photographs were
taken and a sufficient group had been collected, statistical analysis of the dorsal scale colorations were
performed. Researchers used contingency tables in order to determine whether or not patterns of
phenotypic variation occurred with respect to changes in elevation.
Results
Among the lizards found in elevations below 100 meters above sea level, 62.5% had white scales.
Among the lizards found between 100 and 150 meters (100 ≤ x < 150) above sea level 64.3% had white
scales. Among the lizards found at 150 meters above sea level and higher, 84.6% had white scales. There
is a significant difference in the number of lizards possessing white scales between the three elevation
groups (contingency table, p = 0.0007). The percentages of lizards that were found possessing white dorsal
scales increased as elevation increased, rejecting the null hypothesis (Figure 1).
Among the lizards found in elevations below 100 meters above sea level, 62.5% had blue scales.
Among the lizards found between 100 and 150 meters (100 ≤ x < 150) above sea level 57.1% had blue
scales. Among the lizards found at 150 meters above sea level and higher, 53.8% had blue scales. There is
no significant difference in the number of lizards possessing blue scales between the three elevation groups
(contingency table, p = 0.4561). The percentages of lizards that were found possessing blue dorsal scales
increased as elevation increased, but the difference was not great enough to reject the null hypothesis
(Figure 2).
<100 m
[100 m, 150 m)
>150 m
White scales
62.50%
64.29%
84.62%
No white scales
37.50%
35.71%
15.38%
Blue Scales
62.50%
57.14%
53.85%
No blue scales
37.50%
42.86%
46.15%
Table 1. Percentage of lizards found possessing white and blue scales per elevation category (m = meters
above sea-level).
% of Lizards With Scale-Type
90%
80%
70%
60%
50%
40%
30%
White Scales Yes
20%
White Scales No
10%
0%
<100
[100,150)
>150
Elevation (meters above sea level)
Lizards Possessing White Dorsal Scales
% of Lizards With Scale-Type
Figure 1. Frequency of lizards with white dorsal scales increases as elevation increases. Contingency
table (p = 0.0007).
70%
60%
50%
40%
30%
Blue Scales Yes
20%
Blue Scales No
10%
0%
<100
[100,150)
>150
Elevation (meters above sea level)
Lizards Possessing Blue Dorsal Scales
Figure 2. Frequency of lizards with blue dorsal scales increases as elevation increases. Contingency
table (p = 0.4561).
Discussion
As seen in the results of this study, there was an increase in the abundance of lizards with white
dorsal scales as elevations increased, with a significant difference being found. Additionally, there was a
decrease in lizards found with blue dorsal scales as elevations increased. Although the blue scale data did
not have a significant difference, a subtle trend is visible, and it is possible that a significant difference
might be found with a larger sample size.
These phenotypic variations are likely the product of adaptations to better provide
thermoregulation along elevation gradients in coastal regions. In coastal regions, sea wind can often bring
immerse lower elevation regions in cold air, and the higher elevation coastal regions of southern California
are often subject to high temperatures, which are characteristic of a desert climate. The blue scales in
Sceloporus lizards are produced by iridiophores (light reflecting cells), positioned above a melanin layer
that absorbs the non-reflected light (Quinn & Hews, 2003), thus, the blue scales are indicative of a greater
degree of melanin in these lizards. A higher degree of melanin possession would likely provide assistance
to the lizards in lower coastal elevations with thermoregulation by allowing them to take in more heat from
light amidst the colder temperatures they would experience there.
Furthermore, lizards at higher elevations in coastal regions might not be quite as challenged in
terms of heat maintenance due to less cold sea-air pervading their habitats. Rather, they would likely need
a way to avoid excessive heat exposure within the hot desert climate of southern California, and thus,
would instead possess more white scales which would help them minimize heat absorption in the far
warmer high-elevation coastal regions by reflecting a broader range of radiation from the visible light
spectrum.
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