Another Horned Lizard Friday!

By Cameron Barrows, PhD. Associate Research Ecologist Center for Conservation Biology, UCR |

First, as the COVID-19 virus infections are spiking once again, it doesn’t appear that there is any trajectory that would allow us to get together this Fall in one place to celebrate the graduation of the California Naturalists of 2020. Therefore, we are going to mail you your diplomas and pins. We thought it would be fun to have the 2020 class take selfies with your diplomas and send them to us so we could put together a collage of our graduates.  I also wanted to congratulate Mary Ellen Herman and Lawrence Isaac for turning in their capstones within the last few weeks. There is still a small handful that could still turn in their capstones; its never too late.

 Second, we still hope to put together a “Desert Naturalist Showcase”, where any of you could update your capstones or present what new discoveries  you are making as Certified California Desert Naturalists. Again, given the COVID-19 situation, these will be Zoom presentations. So far we have two volunteers, but we need a lot more! To give you all a bit more time, we are shifting the “Showcase” to September 22nd.

 I wanted to start my weekly contribution with (another) celebration of horned lizards, especially desert horned lizards. I can’t think of any other local lizard that has demonstrated the power of natural selection to color match their environment and so provide that extra protection from predators. Jennifer Prado (CalNat 2018) sent me the attached picture of a hatching desert horned lizard she saw the week before from the edge of the La Quinta Cove. I’d wager if I didn’t tell you it was there, for many, like a “Where’s Waldo” picture book, it would be a challenge to find it. The color matching is just amazing. To be clear, while most lizards can change from lighter to darker skin color to maximize or minimize solar radiation absorption and so their thermoregulatory efficiency, they don’t perceive a patterned background and then try to match it. An often repeated misconception is that old world chameleons can change colors to match their environment. Rather they change their skin color (by opening or closing chromatophore cells imbedded in their skin) in response to both temperature and their mood.  A relaxed chameleon is one color, threatened is another, and “hey baby”…”or leave me alone” (messaging to a lizard of the opposite gender) are yet other color patterns. It should be no surprise that their relaxed color pattern does match their dominant environment because, through natural selection, that color provides them the greatest protection from predators – just like desert horned lizards. However, our desert horned lizard color patterns are fixed and don’t change with their moods. The amazing thing to me is how precise natural selection can be at producing lizards that blend with their environment and by doing so giving them the best chance at surviving to breed and pass along those same color pattern genes.

 Another aspect of Jennifer’s picture is that this little guy (3.5 cm, or about 1.5 inches) hatched maybe a month or more earlier than any other record I have. I also found a flat-tailed horned lizard hatchling on sand dune survey this week – another early season record.  These early hatchlings may be the result of warmer early spring temperatures allowing their parents and their hormones to get into breeding condition earlier. I can imagine that these early hatchlings might have a month or more jump on the more typical hatching dates, giving them more time to eat and grow before summer heat narrows possible foraging times into smaller and smaller windows of non-lethal temperatures. That then may give the early season hatchlings a better survival rate as temperatures rise.

 Understanding how desert species are adjusting (or maybe not adjusting) to increasing temperatures and aridity is a major theme of the research I do. Just this week we had a new paper published, titled  “Responding to increased aridity: evidence for range shifts in lizards across a 50-year time span in Joshua Tree National Park”.  In the paper we were able to acknowledge many of the California Naturalist graduates who had helped me collect data, including: Colin Barrows (2018), Tracy Bartlett (2018), Charles Bemis (2019), Therese Cochlin (2019), Jane - Spider - Fawke (2019), John Frazier (2019), Larry Heronema (2018), Lloyd and Sue Shigenaga (2018) and Cathy Wiley (2019). Without their help we would have never been able to document the current distribution of lizards and to use that as comparison to a 50 year old data set (before any measurable changes to temperatures and aridity in this region had occurred). Those historical data came from professors and students at California State University Long Beach (where I earned my Masters Degree back in 1980). As part of a natural history class, the students and professors camped out in what was then Joshua Tree National Monument between 1958 and 1972, caught lizards and recorded the locations as mileage from the nearest road intersections (this was way before GPS satellites had been launched). I received a call one day from a Long Beach alumni saying they found a box in the Biology Department’s basement labeled Joshua Tree data, and before tossing in the dumpster, wanted to know if I would like to look at it first. I said yes.

 Those data have been a treasure trove – like having a time machine to go back and see the world (of lizards) before climate change. Our comparisons revealed that all the lizard distributions appear to be leaning upslope compared to 50 years ago, and some like desert horned lizards appear to have leapt upslope about 200 meters (about 640 feet). Today desert horned lizard populations within the Park are densest at elevations around 1100-1400 meters (3,800-4,500 feet), elevations where the Long Beach crews never recorded them. We even have one observation of a desert horned lizard at Keys View, over 1500 m, or about 5,000 feet. Today desert horned lizards still occupy those lower elevations where the long Beach crew recorded them, albeit at much lower densities than those now occurring at higher elevation. Desert horned lizards appear to be survivors.

 The other horned lizard occurring in Joshua Tree National Park, the Blainville’s (or coast) horned lizard occupies just the higher elevations, from about 1230-1670 m, may not be doing as well. Notice the overlap with the desert horned lizards recent upslope climb. Wherever desert horned lizards have moved in, the Blainville’s are nowhere to be found. They are being squeezed into the top 200 m of the Park’s elevation, into an increasingly smaller space. Not too different from indigenous island dwellers whose home are shrinking due to rising sea levels.

 My next venture is to determine whether the same lizard species occupying the Santa Rosa and San Jacinto Mountains National Monument are doing the same thing. Unfortunately I don’t have that historical data set for comparison. These mountains are much higher and steeper than those in Joshua Tree National Park so I will have to analyze the data differently. One observation I have noticed is that desert horned lizards here occur all the way down to the Coachella Valley floor (at least where there is natural open space left for them) and occur as high as 950 m in elevation (again an observation from Jennifer Prado). Still that is quite a difference from the high elevations in Joshua Tree National Park. Why would there be that kind of difference?   Really, I’d like to hear your ideas.

 Take Care,

Stay safe, stay healthy, and go outside.