1. This study examined the interaction between western fence lizards and western black-legged ticks across different habitats at the Landels-Hill Big Creek Reserve in California. 2. The researchers found the highest numbers of lizards in human-inhabited and chaparral habitats, which provide good structures for basking and sheltering. Beach lizards had significantly more ticks than other habitats. 3. Habitat type was found to influence tick loads on lizards, with beach lizards having the most ticks, but gender and size of the lizard did not affect tick numbers. Understanding these lizard-tick dynamics can help reduce the risk of Lyme disease transmission.

1. 1
The Effects of Habitat on the Interaction Between Western Fence Lizards (Sceloporus
occidentalis) and Western Black-legged Ticks (Ixodes pacificus)
Ellie Alexander, Andray Cardoza, Nancy Franco, Wei Liu, Nicholas Parker, Stephanie Tang
Introduction:
In the western United States Ixodes pacificus, the western black-legged tick, is the primary
vector of Borrelia burgdorferi, the bacterium that causes Lyme disease (Burgdorfer et al. 1985;
Lane and Lavoie 1988; Clover and Lane 1995). Lyme disease can be fatal to humans, causing
fever, headaches, fatigue, and erythema migrans; if left untreated, the disease may impair the
skeletal, circulatory, and nervous system (Centers for Disease Control and Prevention 2015). The
potential lethality of Lyme disease therefore demands an understanding of its vector. We know
that black-legged ticks have a two year life cycle with four growth stages: egg, larva, nymph, and
adult (Anderson 1989). As a three-host species, these ticks feed on a different host for each of
their post-egg stages (Anderson 1989). If tick larvae feed on a mammal infected with B.
burgdorferi, then the tick becomes a vector for Lyme disease in the ensuing nymph stage
(Centers for Disease Control and Prevention 2011). This is an issue as approximately 80
mammals, including birds, lizards, rodents, lagomorphs, deer, and humans serve as hosts to I.
pacificus, and all are at risk of contracting Lyme disease (Anderson 1989). However, among
these hosts is a notable exception: the western fence lizard.
Nymphal black-legged ticks prefer to parasitize the western fence lizard (Sceloporus
occidentalis) over other available hosts, yet the lizards never contract Lyme disease (Casher et
al. 2001). This is because of a “borreliacidal factor” protein in their blood, which kills the B.
burgdorferi spirochetes that infected ticks transmit (Lane and Loye 1989). This means that S.
occidentalis effectively prevents ticks from infecting mammals. Then, as a byproduct of reducing
the pool of infected mammals in the ecosystem, the next generation of tick larvae will be less
likely to be infected by B. burgdorferi when they feed on their host. As a result, western fence
lizards disrupt the life cycle of B. burgdorferi and inhibit the spread of Lyme disease, providing
an invaluable ecosystem service as well as protecting human health.
Interestingly, there is a disparity between Lyme disease incidence on the east and west coasts of
the United States. The east coast has many more cases of Lyme disease despite the presence of
eastern fence lizards (S. undulatus) (Centers for Disease Control and Prevention 2016). One
possible explanation is that east coast climates are simply too cold to support a healthy lizard
population. However, on the west coast we can further study the effect of each environmental
variable so we may ensure that this lizard-tick relationship remains intact. Previous studies
explore spatial and temporal variables and their effects on lizard-tick interactions (Eisen et al.
2001; Eisen et al. 2003).
In this study, we investigated how the interaction between ticks and lizards varies across
different aspects of their environment, such as microhabitat and elevation. A previous study
compared lizard-tick loads based on size, gender, habitat, and color (Heimbach et al. 2016).
However, no significant correlative results were found on lizards across habitats, so we decided
to follow up on this study with an emphasis on increasing the sample size to see if lizard and tick

2. 2
loads vary with habitat. We scouted both natural and human-inhabited areas to compare tick
load. We anticipated to find more lizards and ticks in human-inhabited areas, as they provide
food, shelter, and areas where lizards can thermoregulate. We also predicted that there would be
a higher tick load on lizards from the chaparral and forest habitats and a lower tick load on
lizards from the grassland. It seemed likely that habitat type would have a strong effect on lizard-
tick load.
Methods:
Natural History of the Study Site
This study took place during the summer of 2016 at the Landels-Hill Big Creek Reserve
(36.0699° N, 121.5990° W) located in the Santa Lucia Mountains along the Big Sur Coast in
California (Fig. 1). The reserve experiences moderate temperatures year-round, with winter
rainfall and summer drought. It contains many different microclimates resulting from summer
fog belts and dynamic aspect differences. The geography of Big Creek is complex, consisting of
freshwater creeks originating from springs in the Santa Lucia Mountains and flow year-round
even during droughts (University of California Natural Reserve System). The combination of
climate and microclimates supports a diversity of wildlife including rattlesnakes, salmonids,
white-tailed deer, bobcats, and mountain lions.
Redwood forests occur on cooler north-facing slopes within fog reach while grasslands and
chaparral occur on drier, sunny south-facing slopes (Henson and Usner 1996). Other diverse
habitats include streams, bay, willow, alder, and oak forests, and coastal cliffs and scrubs.
In addition to these natural features, the presence of manmade structures also influences the
western fence lizard’s habitat and tick load.

3. 3
Figure 1. A map of Landels-Hill Big Creek Reserve within Big Sur (right). Lizards were
caught on the trails marked in yellow. On the left is a map of California with the reserve marked
by a yellow star.
Research Design
We captured lizards from five habitat types: grassland, beach, chaparral, forest, and human-
inhabited areas. Forest habitat was cumulative, consisting of mixed oak, bay and pine forests.
Our beach habitat consisted of a rocky shoreline surrounded by scrub and chaparral, as well as a
small riparian zone. Human areas consisted primarily of the Whale Point research station, a small
collection of cabins on a point overlooking the ocean, as well as the office alongside the road at
the entrance of the reserve. We searched for lizards from 11am-5pm from July 18-24 and used
slip nooses to capture each lizard we encountered. A slip noose is a long thin pole with a slip
knot made from surgical thread attached to one end. When a lizard was spotted, we carefully
approached it, lowered the noose over its head, and lifted it towards us. Escaped and uncaptured
lizards were recorded as “observed.” Lizards were found primarily along roads and trails in the
reserve (Fig. 1), as well as several other accessible sites. We captured lizards on Interpretive
Loop, Lower and Upper Dolan, Boronda Trail, Eagle Trail, Dairy Canyon, Whale Point, and
Highlands Camp.
We numbered each captured lizard and recorded the elevation of capture, its gender, length, tick
count and the habitat type. Lizards were marked upon capture to avoid recapture upon
subsequent visits to the site. Upon noticing more lizards at Whale Point than any other habitat,
we decided to conduct a mark and recapture study to estimate population size at this site. They

4. 4
were marked with nail polish based on gender--yellow for males and purple for females (Fig. 2).
Male western fence lizards have blue patches on their throats, black stripes along the blue
patches of their abdomen, and pronounced postanal scales and femoral pores on the bottom of
their hind legs; females lack these markings. After marking them, we measured in centimeters
with a ruler from their neck to their vent. We checked their nuchal (neck) pockets and armpits for
ticks (Fig. 3). Lastly, we used a Garmin GPS device to note down the elevation.
Figure 2. Lizards are marked with nail polish. The male is on the
left with a yellow mark and the female is on the right with a
purple mark.
Figure 3. Ticks are primarily found in the armpits and nuchal
pockets on lizards.

5. 5
After marking lizards for two days at Whale Point, we returned for the recapture three days later
on July 24 to determine the population size. We divided ourselves into separate areas (Fig. 4) to
avoid double counting and then we counted lizards for twenty minutes.
Figure 4: Diagram of the five separate counting sites at Whale Point.
We recorded male and female marked and unmarked lizards and used the following equation to
determine their total population size:
Total population = (# captured on second visit)(# marked on first visit)# recaptured that were
marked
Statistical Analyses
To determine habitat type, gender, and elevational effects on the lizards’ tick load, we conducted
statistical analyses using JMP statistical software. Habitat type and gender influences on tick
load were tested using one-way ANOVA tests, followed by Tukey tests. Elevation and length
effects on tick abundance were examined through bivariate test of fit and linear regression.
Results:
We caught a total of 105 lizards in the five habitat types within Big Creek Reserve. The majority
of lizards were found in the human (44 lizards) and chaparral (30 lizards) habitats, and the fewest
were found in grassland (3 lizards) (Figure 5). From our mark and recapture study we were able
to estimate a total population of 59 lizards at Whale Point. The bivariate fit test showed that there
is a negative trend between elevation and tick number (n = 105, r2
= 0.092, P < 0.01; Fig. 6).
However upon removal of beach data, any significant correlation between elevation and tick load
disappears (n = 88, r2
= 0.009, P > 0.1). One-way ANOVA tests revealed a significant variation
between tick load and habitat type (df = 4, F = 4.6525, P < 0.01; Fig. 7), but no significant
difference in tick loads between genders (df = 1, 102, F = 0.76, P > 0.1). Bivariate fit and linear
regression showed no correlation between lizard length and tick load (n = 101, r2
= 0.0004, P >
0.1).

6. 6
Figure 5. A pie chart showing the total number of lizards found in each of the five
habitats. Note that human and chaparral have the most lizards, while grassland has the fewest.
Figure 6. Graph of ticks by elevation. Note the significant regression disappears
when beach is removed (beach has highest tick load and lowest elevation).

7. 7
Figure 7. Tick load as a function of habitat type. Note that beach is more
significant than all other habitat types except for grassland, due to the small sample size
in grassland.
Discussion:
Whale Point, a human-inhabited area, showed the highest concentration of lizards. This is likely
due to the fallen logs, stumps, woodpiles, sheds, and decks that provide a structure for the
lizards. These microhabitats are suitable for the lizards, as the lizards can bask in the sun or
shade and also hide from predators. Chaparral was the next most concentrated habitat as the thick
bush clumps provide plenty of basking space and shelter. Although the beach and forest provide
the necessary structures, there were fewer lizards in those habitats. However, in the beach the
suitable habitat was limited, as none were found on the open rocks or sand near the water. Most
lizards were found in scrub and chaparral surrounding the beach, which was a smaller area and
rather difficult to access. Forest areas were generally quite cool and shady, helping to explain
why we found fewer lizards there. However, ticks are known to prefer these types of habitats, so
gaining a better understanding of lizard dynamics in forests is essential. Lastly, the low number
of lizards caught in grasslands was likely due to high sun exposure and lack of structure for
shelter. The few lizards seen and caught in grassland were on rocks or logs where they could
easily hide, and only one was actually seen in the grass and not on a structure. From this we can
infer that overall habitat type does influence the lizard populations, but further studies may
reveal that microhabitats and the availability of structures for the lizards could also be important.
For example, wood and stone structures could be set up in each habitat to see how they affect
lizard populations, as well as lizard-tick dynamics.
In comparing habitat type with tick abundance on lizards, we see that lizards inhabiting the beach
had significantly more ticks than in any other habitat, except grassland. We did not find any ticks
in grassland but our small sample size is not enough for us to make a conclusion about tick loads
in grasslands. The higher tick loads on the beach could be attributed to the population being
limited to a small area, thus increasing the spread of ticks between the lizards. However, the
relatively low number of lizards found there and the lower concentration of ticks in the dense

8. 8
Whale Point population suggests that this is likely not the case. It is also possible that the beach
is less suitable for other tick hosts, increasing the ticks’ reliance on the lizards. Interestingly, the
rest of the habitats showed no significant difference in their tick loads even though ticks are
predicted to be more abundant in woodland or forest habitats (Eisen et al. 2003). We also
expected to find more ticks at Whale Point because the population is so large, providing a wealth
of hosts for the ticks and opportunities for them to spread and thrive.
We initially found a negative correlation between tick load and elevation, suggesting that tick
abundance decreased with increasing elevation. To test if elevation was in fact influencing tick
load, the beach samples, which had the highest tick abundance and lowest elevation, were
removed. The relationship disappeared, indicating that elevation does not influence the amount
of ticks found on lizards. Therefore, we can conclude that habitat is the determining factor
affecting tick loads, although elevation may play a role at larger scales. Further studies would
need to examine a wider range of elevations and obtain a variety of lower elevation sites across
habitats.
Interestingly, gender and length were found to have no effect on tick load, whereas a previous
study found that gender and size were the main factors influencing tick abundance (Heimbach et
al. 2016). They found that the number of ticks increased with the length of the lizard. Our
contradictory data could be due to our different sampling techniques, because we measured neck
to vent length instead of the conventional snout-ventral length (SVL). This lowered the overall
size of each lizard we measured and also decreased accuracy because it was difficult to measure
from the same spot each time. Heimbach et al. 2016 also found that males had far more ticks
than females, which is to be expected, as higher testosterone levels are known to increase the
susceptibility of lizards to infection (Eisen et al. 2001). Our sample was biased because we found
far more males than females. In addition, the lizards were collected post-breeding season, when
lizards are less active, potentially lowering tick loads. Moreover, this study was conducted
during the late summer when tick activity decreases and parasitization is less common.
Additional studies could be carried out during different seasons to account for differences in
lizard occurrence and tick abundance.
It is important to understand all aspects of Lyme disease, especially ticks, the main vector of the
disease. Scientists have done this with other diseases such as malaria, where they studied the
feeding behavior of Anopheles gambiae mosquitoes. By observing mosquito feeding behavior,
preventative measures were put into place such as mosquito nets around beds and DDT infused
into the house walls, resulting in a reduced rate of malarial infections. A more drastic measure
that is currently underway is genetically modifying a population of A. gambiae where they
cannot support Plasmodium falciparum, the protozoan that causes the disease, and release this
population into the wild. Within a couple of generations none of the mosquitoes will be able to
support P. falciparum and Africa can be free of one of the main malaria vectors (Lanzaro 2016).
A similar attempt could be made with ticks, by modifying them to be inhospitable to B.
burgdorferi or working to prevent them from acquiring the bacterium in the first place. Genetic
modification regarding the borreliacidal factor protein from lizard blood could also be applied to
prevent ticks from acquiring Lyme disease or for human and animal medicinal purposes. Further
understanding of both tick and lizard biology could provide new ways to reduce the risk of Lyme
disease.

9. 9
Understanding tick and lizard interactions within their environment is only one small part of a
complex problem, but provides the potential for a major breakthrough in Lyme disease
prevention. The relatively low occurrence of Lyme disease on the west coast is partially due to
the widespread abundance of the western fence lizard, and ensuring that this relationship
continues to thrive is essential. While we do not yet know everything about this interaction,
habitat is a key factor that needs to be further examined and understood. It is encouraging that
our study shows a high population of lizards in human areas, because humans are constantly
reshaping and altering the natural landscape. However, our human study sites were fairly
pristine, as they were on a natural reserve with a relatively small human presence. Whereas
urbanization is not likely to have a positive effect on lizard populations, minimal human
disturbance may be beneficial. Woodpiles, decks, and other human structures provide excellent
areas for lizards to thrive, benefiting both parties. Striking a delicate balance between
disturbance and conservation is crucial to maintaining healthy lizard populations and regulating
Lyme disease. Working to protect areas where lizards are populous is important, as well as close
monitoring of lizard and tick populations to better understand and limit the spread of Lyme
disease. In areas where lizards have been extirpated from their natural habitat, reintroduction and
restoration may help to create a healthy ecosystem beneficial to all.

10. 10
Literature Cited
Anderson, J.F. 1989. Ecology of Lyme disease. Connecticut Medicine, 53(6), 343-346.
Casher, L., R. Lane, R. Barrett, L. Eisen. 2002. Relative importance of lizards and mammals as
hosts for ixodid ticks in northern California. Experimental and Applied Acarology.
26(127), 127-143.
Center for Disease Control and Prevention. 2015. Lyme Disease. Online. Available:
https://www.cdc.gov/lyme/. [accessed 7/29/2016]
Eisen, R.J., Eisen, L., Lane, R.J. 2001. Prevalence and abundance of Ixodes pacificus immatures
(Acari: Ixodidae) infesting western fence lizards (Sceloporus occidentalis) in northern
California: Temporal trends and environmental correlates. Journal of Parasitology, 87(6),
1301-1307.
Eisen, R.J., L. Eisen, M.B. Castro, and R.S. Lane. 2003. Environmentally Related Variability in
Risk of Exposure to Lyme Disease Spirochetes in Northern California: Effect of Climatic
Conditions and Habitat Type. Environmental Entomology, 32(5), 1010-1018.
Henson, P. and Donald J.U. 1996. The Natural History of Big Sur. University of California
Press, Berkeley and Los Angeles.
Lane, R.S. and J.E. Loye. 1989. Lyme Disease in California: Interrelationship of Ixodes pacificus
(Acari: Ixodidae), the Western Fence Lizard (Sceloporus occidentalis), and Borrelia
burgdorferi. Journal of Medical Entomology. 26(4), 272-278.
Lane, R.S., and Quistad G. B. 1998. Borreliacidal Factor in the Blood of the Western Fence
Lizard (Sceloporus Occidentalis). The Journal of Parasitology. 84(1), 29-34.
Lanzaro, G.C. “The Malaria Case: Introduction to the Topic”. Animal Biology 50C. UC-Davis.
Wellman Hall. April 2016.

11. 11
LoGiudice, K., Ostfeld, R.S., Schmidt, K.A., Keesing, F. 2003. The ecology of infectious
disease: Effects of host diversity and community composition on Lyme disease risk.
National Academy of Science, 100(2), 567-571.
Padgett, K.A. and R.S Lane. 1995. Life cycle of Ixodes pacificus (Acari: Ixodidae): timing of
developmental processes under field and laboratory conditions. J. Med. Entomol. 38, 684-
693.
Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin
Harcourt, New York.
Talleklint-Eisen, L., R.J. Eisen. 1999. Abundance of ticks (Acari: Ixodidae) infesting the western
fence lizard, Sceloporus occidentalis, in relation to environmental factors. Experimental
and Applied Acarology, 23, 731-740.
University of California Natural Reserve System. Landels-Hill Big Creek Reserve. Online.
Available: http://www.ucnrs.org/reserves/landels-hill-big-creek-reserve.html. [accessed
8/1/16]