Such discoveries of large vertebrates are rare in the 21st century. And these animals are the largest tortoises in the world! So how is it possible that a new species would just now be discovered nearly 500 years after the Spanish explorers first visited the islands?
Turns out, this new species was hiding in plain sight! It is a cryptic species (not to be confused with crypsis – the ability of an organism to avoid detection – see my previous blog post. Cryptic species are genetically distinct in spite of their identical appearances. In other words, until recently Santa Cruz Island in the Galapagos was thought to have just one species of tortoise, Chelonoides porteri, that existed in two separate populations: Cerro Fatal on the east side of the island and Reserva on the west and southwest side. Now the larger Reserva population is considered to be the original species and the smaller Cerro Fatal population has a new species name Chelonoides donfastoi.
Populations on other islands in the volcanic island chain off the coast of Ecuador, are also being investigated to see if more cryptic species are “hiding” there. For more on the Galapagos Islands check out this Radiolab story.
The existence of such “hidden” species is quite common across all organismal groups, also known as taxa, and in all ecosystems2 (https://www.newscientist.com/article/dn12293-hidden-species-may-be-surprisingly-common/). And include some other giant organisms, elephants!
The existence of cryptic species has increased significantly in the past couple decades, born out of new molecular tools that compare genomes of different organisms and allow detection of differences that are not apparent morphologically3. And their discovery is not without controversy as even experts may be using different definitions of the word “species” known as species concepts. These concepts define species in different ways and therefore have different requirements for species differentiation (for more on this topic – see Dominic Evangelista’s posts here and here.
So who are these heroes on the front-line of species determination? And what exactly do they do?
These scientists are known as taxonomists. Taxonomists are scientists who describe and identify species. They don’t just give names to species; they also classify them as belonging (or not) to different biological groups. For example, the new tortoise species is still a part of the same biological group of giant tortoises (for a quick reminder of scientific names and binomial nomenclature see this link). Most taxonomists are also systematists, scientists who determine the evolutionary relationships among species (for a more detailed description of this field, see this link).
Taxonomy, like all science, depends upon the technology available, and in our modern era includes high tech imaging devices that allow more precise measures of morphological features as well as molecular techniques that can compare the genomes of organisms. These devices have allowed for a revolution in how organisms are defined.
However, some stand-bys from previous eras remain critical tools in the quest to define Earth’s biota. These include microscopes (which are now more powerful than ever), binoculars and most importantly, the observational skills of individual taxonomists.
Regardless of the species definition used, in order to officially name a species a detailed physical description of the organism is required. This detailed description is used to identify the species going forward and is the result of a painstaking process requiring numerous hours of comparing sometimes minute differences between specimens and then explaining all the characteristics in excruciating4 detail. The variation in physical characteristics between populations of the same species should also be noted as well as any existing behavioral or ecological information.
There are actually international scientific “rules” or conventions that govern how organisms are named, including the International Code of Nomenclature (ICN) for algae, fungi and plants, the Code of Zoological Nomenclature (ICZN) for all animals, and the International Code of Nomenclature of Bacteria (ICNB). These separate conventions are in part due to historical reasons, but also reflect the reality that naming different types of organisms requires different procedures.
These conventions all require that along with a written description there is a type specimen. This specimen is usually a preserved individual of the species upon which the description is based. A preserved individual is preferred because it allows for future generations (often with new technology or information unavailable at the time of the first description) to reanalyze the specimens (for more on the value – and controversy – of collecting specimens see here). It also allows for genetic comparisons as in the case of the new Galapagos tortoise species in which the genomes of the two subpopulations were compared to that of the preserved type specimen. However, for organisms that are rare or threatened, a photograph or illustration will sometimes suffice.
Taxonomy is a dynamic field, with names and species descriptions being updated as new information comes to light. Genomics have revolutionized the field of taxonomy, making it possible to detect cryptic species as well as species with polymorphisms, in other words, species that include organisms that look very different (poly = many; morph = type) but that are not genetically distinct.
Having accurate species descriptions is incredibly important! For one thing, it allows us to better account for global biodiversity.
Worldwide, conservation efforts use the species as the basic unit when describing biodiversity and when determining how precious and limited conservation resources are spent. Not properly identifying cryptic species may result in an underestimation of diversity, which has serious implications as habitats with high species richness (species richness being the total number of species in an area) are often prioritized for protection.
Although cryptic species may look the same, they may actually have very different roles in the ecosystem or even different evolutionary histories. Taxonomy then is the basis upon which many other scientists, ecologists and evolutionary biologists of all stripes, depend. One interesting example of this is a group of skipper butterflies found in the tropical forests of South America. Until recently, this group of butterflies was thought to be one polymorphic (at the caterpillar stage) species. Now that one species is now known as a group of ten (10!) cryptic species5. This discovery changes the understanding of the ecological community in which these butterflies live as well as their evolutionary history.
Accurate identification of cryptic species also allows for more effective conservation efforts. Conservation status at both the global and local levels, including the International Union for the Conservation of Nature (IUCN) and the U.S. Endangered Species Act use population estimates which require know what are populations of the same species and what are different species.
Once found to require some level of protection, the conservation plans for individual species’ require understanding their ecological roles and needs. For example the cryptic butterflies species described above are all specialists, requiring specific plants for their survival. This requires a very different conservation strategy than when they were considered one generalist species.
Another example is the African elephant species complex discussed earlier. Each species lives in very different habitats as indicated by their names. The African Bush Elephants live in the savannah, a very open habitat with different resources, competitors and natural enemies than those experienced by the African Forest Elephant. The same is likely true of the new Galapagos Tortoise species that live on different parts of the same island.
Finally, and possibly most importantly, from our anthropocentric point of view, cryptic species impact our ability to manage pest species as well as foster beneficial species.
Pest species are those species that carry disease and destroy our agricultural crops. In these cases, not resolving cryptic species identifications can have deadly consequences, for example, malaria and its vector Anopheles7 mosquitos. Malaria is spread by mosquitos and at the beginning of the 20th century, one mosquito species was thought to be responsible. Later it was determined that this one species was actually a group of six species with only half of them able to transmit malaria.
Recently cryptic genetic diversity was found within a species of mosquito in Cameroon8 where malaria kills several thousand people each year (3200 people in 2013 alone). This knowledge may help reduce the spread of malaria in this region more effectively through mosquito management plans that better fit the specifics of the actual species of interest. Similar benefits come from understanding that cryptic species may have different resistance to pesticides or vary in their response to other biological control methods.
On the flip side, cryptic species might have unique services and benefits for humans that would be missed if we didn’t properly identify them. For example, medicinal substances found in plants and other organisms vary by species and important discoveries might not happen if cryptic species remain hidden.
In spite of its critical importance to biology, taxonomy is often thought a “dying” profession9 (see here and here). In many western universities taxonomy is no longer offered, much less required and at many institutions new taxonomist hires are down even as the older generation retires in greater numbers. The good news is these changes may be more of a “range” shift than an outright extinction event with an increasing number of taxonomists found in South America, Asia and Africa10.
Regardless of the overall state of taxonomy, as a scientist, the loss of an eminent taxonomist in your taxa of interest is tragic. As discussed in previous posts, I study bees, and bee biologists everywhere are mourning the loss of Dr. Charles D. Michener.
Dr. Michener developed a classification system for bees three years after finishing his PhD that was adopted worldwide and used until he updated it nearly 50 years later. After retiring, he authored his magnum opus, the comprehensive The Bees of the World. His interest in science started as child when by the age of 10 he had sketched 120 wildflower species until he ran out of new ones and began working with insects. Over his 80 year career he developed and shared his expertise, naming and describing over 600 bee species, publishing over 500 scientific papers, and training dozens of other scientists, including several individuals who I have had the pleasure of studying under at the American Museum of Natural History’s beloved “Bee Course” (organized by another amazing bee taxonomist Dr. Jerry Rozen – thanks so much!). Although, I myself have never met Dr. Michener, all accounts indicate that beyond being an amazing scientist that he was an amazing human being and I am sure he has been so proud that so many of his students (and their colleagues) generously share their time and expertise with so many others.
So I would like to dedicate this blog post to the memory of Dr. Charles D. Michener and the other bee taxonomists upon whose work my work depends; and in honor of the amazing living taxonomists that I have encountered in my work, I am greatly in debt to their help in identifying – and training me to identify – my specimens.
1 Poulakakis et al. 2015. Description of a new Galapagos Giant Tortoise species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island. PLOS1. DOI: 10.1371/journal.pone.0138779 (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138779)
2 Pfenniger & Schwenk. 2007. Cryptic animal species are homogeneously distributed among taxa and biogeographical regions. BMC Evolutionary Biology. DOI: 10.1186/1471-2148-7-121. (https://www.biomedcentral.com/content/pdf/1471-2148-7-121.pdf
3 Bickford et al. 2006. Cryptic species as window on diversity and conservation. Trends in Ecology and Evolution 22: 148-155.
4 excruciating to a novice like myself at least
5 Herrera et al. 2015. Mixed signals? Morphological and molecular evidence suggest a color polymorphism in some neotropical Polythore damselflies. PLOS1. DOI: 10.1371/journal.pone.0125074. (https://www.plosone.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pone.0125074&representation=PDF)
6 Hebert et al. 2004. Ten species in one: DNA barcoding reveals cryptic species in the neotropical skipper butterfly Astraptes fulgerator. PNAS. DOI: 10.1073.pnas.0406166101 (https://www.pnas.org/content/101/41/14812.full.pdf)
7 Anopheles is Greek (anofelis) for “good for nothing”
8 Ndo et al. 2013. Cryptic genetic diversity within the Anopheles nili group of malaria vectors in the equatorial forest area of Cameroon (Central Africa). PLOS1. DOI: 10.1371/journal.pone.0058862 (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0058862)
9 Drew. 2011. Are we losing the science of taxonomy? BioScience 61: 942-946.
10 Costello et al. 2013. Can we name Earth’s species before they go extinct. Science 339: 413-416.