An article we wrote (with Leite, Milsom, Sanders, Andrade, Abe, and Cadena) has been recommended on @F1000Prime http://f1000.com/prime/730235759?key=6H8E8TOzD6P62gZ
I am writing this blog post to accompany a manuscript of ours that has just been accepted in Functional Ecology. The link to the article is here. The final proofs are not yet ready, as of Sept 24, 2017, but the accepted manuscript is available, so I think it is safe to blog about it.
Darwin’s finches have been the focus of much intense study demonstrating how climatic fluctuations coupled with resource competition drive the evolution of a variety of bill sizes and shapes. Darwin’s finches are only found on the Galápagos Islands, located ~1000 km west of Ecuador in the middle of the Pacific ocean, pretty much along the equator. Climatically, these islands are typically considered warm to hot throughout the year, but also experience a relatively dry climate (<300 mm/year).
Darwin’s finches have been well studied with regard to the role of the bill in resource acquisition (i.e., searching for food, acquiring and crushing seeds etc.). Here is a young Geospiza searching for seeds in the relatively barren ground surface:
Bird bills are not dead structures, however. Bird bills are well vascularized (i.e. blood vessels are right below the beak keratin), while their limbs have specialized vasculature that promote heat loss or heat conservation, depending on the ambient conditions. In other words, these body surfaces (bill and legs especially) are “thermoregulatory windows“, which is a term used to refer to the fact that they can be “opened” and “closed” accordingly to dump or save body heat.
With this in mind, we hypothesized that Darwin’s finch bills have evolved in part for their role in thermoregulation, possibly co-opted, following adaptation for other functions. We predicted that bills of Darwin’s finches are effective thermoregulatory windows, and that species differences in morphology, along with physiology and behavior, lead to differences in thermoregulatory function.
To shed light on these hypotheses, we conducted a field study to assess heat exchange and microclimate use differences in three ground finch species and sympatric cactus finch (Geospiza). We collected thermal images of free-living birds during a hot and dry season and recorded microclimate data for each observation. We used individual thermographic data to model the contribution of bills, legs, and bodies to overall heat balance and compared surface temperatures to those from dead birds to test physiological control of heat loss from these surfaces. We derived and compared species-specific threshold environmental temperatures, which are indicative of a species’ thermally neutral temperature.
We could not formally test the question of adaptation in this study, but what this study represents is our initial observations of surface temperatures in four species of birds living within the same habitat. Conceptually, then, if they truly experience the same heat load and thermal regime (a null hypothesis), we would not observe differences in surface temperatures of bills, limbs, or feathers.
In all species, the bill surface was an effective heat dissipater during naturally occurring warm temperatures. We found that finches controlled surface temperatures through physiology (i.e. body surfaces exhibited different responses to changing heat loads) and that young birds had higher surface temperatures than adults. Larger bills contributed proportionally more to overall heat loss than smaller bills.
We demonstrate here that related, sympatric species with different bill sizes exhibit different patterns in the use of these thermoregulatory structures, supporting a role for thermoregulation in the evolution and ecology of Darwin’s finch morphology.
More work is to come, however. This study is still very much scratching the surface, and we hope to publish more on this topic in the months and years to come.
Below, I have attached some photos from our field work, and some summary data on the microhabitat patterns observed in the study:
Summary of the observed microhabitat differences from our field thermography:
Field based thermography
In addition to the discoveries listed above, we think that this study will prove useful for others considering a non-invasive, but quantitative approach to assessing thermoregulatory responses in the field. Infrared thermography is a camera based approach to capturing surface temperatures of objects. Bird surface temperatures are a function of the bird’s own internal heat production as well as their balance with solar heat gain and environmental heat exchange. We have tried to provide a detailed materials and methods in this paper’s supplementary in order to assist others who might be considering this approach in their field work.
How did it all happen?
We really need to thank and acknowledge Dr. Russell Greenberg for initiating and facilitating many of the ideas presented in this study, and who sadly passed away before the manuscript was written. In 2009, following my publication in Science, and a follow-up review paper in American Naturalist, I received an email from Russ, asking for my opinion a study about bill size dimorphism he had recently published on. In his study, he observed bill size differences amongst subspecies of sparrows and had just read my paper and wondered if some of his observations could be based on thermoregulatory constraints and the role of the bill in heat exchange. This discussion eventually led to one of my students, Viviana Cadena, going to work with Russ Greenberg and Ray Danner at the Smithsonian Institute and led to publication in 2012 in PLoS.
During this time, Russ and I opined about going to Galápagos to test our hypotheses in Darwin’s Finches. We put together a proposal and submitted it to the National Geographic Society, and received news of the positive outcome of the funding in October 2012. This good news was met with sad news, however, as Russ had recently been diagnosed with pancreatic cancer. We did, however, get to work together in the field. In April/May of 2013, Russ, Ray, and myself travelled to Galápagos, where we met up with Jaime Chaves, and conducted the study now published in Functional Ecology. We might have been slower at writing up our work than you were, Russ, but we finally did it!
Tattersall, G. J., Chaves, J. A. and Danner, R. M. (2017/2018), Thermoregulatory windows in Darwin’s Finches. Funct Ecol. Accepted Author Manuscript. doi:10.1111/1365-2435.12990
Research funding for this study was kindly provided by the National Geographic Society, the Smithsonian Migratory Bird Center, the Galápagos Institute for the Arts and Sciences-Universidad San Francisco de Quito Grant, and the Natural Sciences and Engineering Research Council of Canada (RGPIN-2014-05814). Logistical support was kindly provided by the Charles Darwin Research Station and the Galápagos National Park. Permits to conduct research were provided by the Galápagos National Park Service (Authorization No. PC-05-13).
Data will be made available on Data Dryad: Dryad entry doi:10.5061/dryad.t4k41.
At long last, my former MSc student, Ian Black’s first paper has been published! (Citation below) Ian graduated last year and moved to Ottawa, but has been maintaining contact and working with me to write his work up (so far, we have a book chapter in review and a second manuscript being edited now).
To many that keep lizards as pets, the results of this study might not be so surprising, as articulated by this meme:
From a scientific perspective, however, these results might not have been predicted. So, what did we show? In a nutshell, we demonstrated that bearded dragons prefer to keep their heads facing toward the heat when given a choice.
To thermoregulatory biologists, this is intriguing. Why? It is often stated in the herpetology literature that lizards are either heliothermic (i.e. they bask in the sun) or thigmothermic (i.e. they warm up via contact with the substrate), and an implicit corollary is that if a species is known to be heliothermic, it cannot respond to contact based thermal cues (i.e. they cannot sense heat via the skin). Thus one might not expect them to orient toward or away from this kind of heat source or thermal gradient if they are heliothermic/baskers.
We conducted this study by creating an artificial thermal gradient to allow the lizards the chance to move and select different temperatures throughout the day.
Our paper clearly demonstrates that bearded dragons are very capable of orienting their body along a gradient of temperature, and thus are quite thermally “aware” of the environment around them. We also demonstrate that both adults and neonates show this behaviour. Finally, as the lizards choose warmer temperatures later in the day (i.e. move up the gradient), they orient less and less toward the heat, suggesting that they are capable of using their orientation to keep their heads from getting too warm. Therefore, orientation behaviour is used to fine-tune their thermoregulatory control. This is analogous to how Galapagos marine iguanas use sky-pointing orientation to maximise solar absorption int he early morning and maximise convective cooling later in the day to prevent overheating (Bartholomew, 1966. Copeia. p 241-250).
Please find links to the study below and consider sharing our findings.
Citation and Links
Black, IRG and Tattersall, GJ. 2017. Thermoregulatory behavior and orientation preference in bearded dragons. Journal of Thermal Biology. 69: 171-177. doi:doi:10.1016/j.jtherbio.2017.07.009
For a limited time (until Sept 13, 2017) the paper is available for free for anyone that does not have a subscription here:
Hats off to Environment Canada, the Department of Fisheries and Oceans, and the Canadian Coast Guard for putting on a great open house today at the Canadian Centre for Inland Waters (CCIW)! Most of my lab (see picture below) agreed to a “lab outing” to the CCIW. I had always wanted to see what research occurs at CCIW, which is a building nestled directly under the Burlington Skyway in southern Ontario:
With the yoke of information control (http://www.macleans.ca/news/canada/when-science-goes-silent/) lifted following the election of a new government in 2015 (http://www.macleans.ca/society/unmuzzled-government-scientists-ready-to-discuss-a-decade-of-work/), it was amazing to see the enthusiasm in the faces of the scientists working hard to assess environmental impacts of human influences on wildlife, plants, and the ecosystems around us. Why these scientists were ever bureaucratically muzzled is beyond me.
Here we are looking pleased with ourselves:
We even receive visitors badges that reminded me of a strange 1980s sci-fi show:
On the trip home, we even were stopped by the lift bridge, something I usually avoid when driving the QEW:
All told, I was extremely impressed with the open house put on by CCIW and wish to thank them for opening their doors to the public. Keep up the good work!
A couple of significant events occurred in the past couple of weeks in the lab, and I wanted to note them here.
My MSc student, Curtis Abney found out he is a recipient of an Ontario Graduate Scholarship for his research on the thermal biology of garter snakes. Congratulations, Curtis!
My MSc student, Justin Bridgeman, who is busy attending conferences this summer, received a travel support fellowship to attend the Fisheries Society of the British Isles annual meeting this July! Congratulations, Justin!
Last month, Canadian Nuclear Laboratories invited a number of researchers to witness the nightly roosting of chimney swifts in one of their ventilation stacks! They were kind enough to allow me to film using my thermal camera the gathering of over 1000 birds at ~8:45pm one evening. Now, if only I can find the time to help with writing code to help them count the birds entering the chimney! Here is a brief video and a link to CNL’s facebook site:
Congratulations to Susan Wang, MSc student working in my lab and co-supervised with Dr. Janet Koprivnikar (Ryerson University) for successfully defending her thesis on:
“Behavioural Thermoregulation and Energetics in Two Intermediate Hosts of Trematode Parasites”
Thank you for all members of the examining committee for their hard work and interesting defence discussions:
External Examiner: Dr. Carl Lowenberger, Simon Fraser University
Committee Members: Dr. Gaynor Spencer, Dr. Robert Carlone, Dr. Dorina Szuroczki
Her time in the lab was far too short, but we are proud of her accomplishments and for her hard work on an interesting project. Because of Susan, I can safely say that we can readily do interdisciplinary research! Ecological physiology of disease and host:parasite interactions is a fun topic and I’m glad to have had this project taking place in my lab and grateful for Janet Koprivnikar for funding, intellectual, and logistic support, collaboration, and supervision at every step.
Brock University’s Brock News has written up a great piece on Anne Yagi’s (an MSc student in my lab) research. Anne has worked for the Ministry of Natural Resources for a number of years and joined my lab to pursue questions into the overwintering physiology of snakes. The article below covers the Conservation Physiological approach she has been taking to understand neonatal rattlesnakes in a sensitive population. Hopefully we’ll be publishing on this soon. Congratulations Anne!
Following the CSZ meeting, a very kind graduate student from University of Winnipeg, Ana Breit, agreed to drive Justin and myself up to Narcisse, Manitoba on the last afternoon of the meeting. I brought the thermal camera with me, so I could document the spring emergence of garter snakes, and the writhing reproductive orgy that is customary at this field amazing site.
Here are some sample images in visual, thermal and thermal video:
Many thanks to the people at Nature north for maintaining this site: http://www.naturenorth.com/spring/creature/garter/Narcisse_Snake_Dens.html
My student, Justin Bridgeman and myself were the representatives from my lab this year. Unfortunately, I forgot to take photos of him speaking or of me defending my student, Katlyn Dundas’s poster.
For posterity, though, here are the clips from the CSZ program book:
Winnipeg was a great host city and the meeting was excellent. Always good to catch up with fellow Canadian scientists.