Climate change and sex determination of Galapagos tortoises

Enjoy this blog on Sex ratios, climate change, and giant tortoises by Dr. Patrick Moldowan. Patrick provides a great review of the paper by Deem et al (2023) published earlier this year. In the paper, we investigated the roles of nest location and temperature in influencing the sex of hatchling tortoises. The findings from this study offer important information for the conservation of giant tortoises, among other species with temperature sex determination (TSD), in our changing world.

We All Live on an Island

If you are anything like me, when someone starts talking about an island, you are whisked away visually to a tropical paradise with sand and surf.  Possibly you are holding a fancy drink with a little umbrella.  But, over the years when I hear anyone talk about islands, I now see much more than this.   

The world from the eyes of an island boy

The first time I truly appreciated that “we all live on an island” is when my 4 ½ year old son, Charlie and I were heading east on highway 64 and into Saint Louis, Missouri.  In front of us was the famous Saint Louis Arch—the Gateway to the West.  Charlie was riding in the back, safely in his car seat.   As I drove we were having one of those priceless mother – son bonding discussions, easily switching between topics as I was invited in to see the world from the eyes of a child.  Then Charlie asked, “Mom, can you see the whole island from the top of the arch?” 

To better understand where this question may have originated, you must know where we had just been.  The day before Charlie asked this question, we had landed in the States after 6 months of living on a small island in the Galapagos, Ecuador.  In Charlie’s mind it only made sense that the whole island could be seen from the top of such a high structure.     

Lessons from Geographical Islands

Since that car ride, I have increasingly come to appreciate that we do all live on an island.  In the intervening years I have lived and worked in the Galapagos Islands, traveled often to work on the island nation of Madagascar, and have provided veterinary care to wildlife populations on “islands of remaining habitats” across the globe.  These life and work experiences have opened my eyes to appreciating how islands—both geographical and human created—share a growing number of conservation and health challenges. 

My years living in Galapagos probably brought this understanding most to light.  The Galapagos Islands—known as the world’s laboratory for the study of the theory of evolution by natural selection, may increasingly be a place of unnatural selection.  As tourists flock to the islands to see the endemic life forms, including marine iguanas, Darwin finches and Galapagos tortoises, change too has arrived on the islands.  Once protected from humans by the geographical isolation provided by the Pacific Ocean these species evolved naturally.  However, in this new age of the Anthropocene, we know that where people travel, human induced changes are inevitable.  These changes include land development, fragmentation and degradation, pollution, invasive species, and emerging infectious diseases.  For the creatures of Galapagos these changes have led to a new form of evolution by “unnatural selection” (https://www.stlzoo.org/files/4513/5058/8698/ICM_unnaturalselection2010.pdf).  This in the land of Charles Darwin!     

We all Live on an Island

Whether islands are geographical islands surrounded by an ocean or island habitats created by human modified landscapes, we all live on an island. One only needs to look at the fate of the inhabitants of Easter Island as a foreshadow of what occurs when natural resources, and space, are limited.  Threats for island species are related to population isolation, genetic bottlenecks, and smaller population sizes being at risk of random events, such as extreme weather patterns (think climate weirding!) or the introduction of novel disease causing pathogens.  Unfortunately, these threats are not limited to oceanic islands.

So how did I answer my son?  I stated with all the authority of a mom, “No honey you can’t see the whole island from the top of the arch.  The United States is a little too big for that”.  But, even then I knew that the question was not so outrageous.  Almost 10 years later I have sat down to write these thoughts while on another well-known island, Great Britain.  During the intervening years since my island boy asked me the question, I have had the privilege to work with wildlife populations on islands surrounded by watery oceans and island habitats surrounded by oceans of human modified land.  These experiences have made me increasingly aware that we do in fact all live on an island. Maybe the ultimate island is Earth: the only planet we know that harbors life as it moves through the solar system, surrounded by an ocean of space.  More importantly it has become evident that the lessons of island living should serve as a warning to how we may continue to live on this one island home that supports us all.