Unravelling the mystery of the snakes of Galapagos

May 8, 2018

By Luis Ortiz-Catedral, Lecturer in Environmental Science and Ecology at Massey University in New Zealand.

Animal taxonomy is complicated. Snake taxonomy, very complicated. Galapagos terrestrial snake taxonomy, well… it may be in a class of its own.

In September 1835, Charles Darwin collected a small, light brownish-grey snake on Floreana Island. Twenty-five years later, that single specimen (housed at the Natural History Museum in London, below) was the basis for the description of a new species, now known as the Galapagos (Floreana) racer, Pseudalsophis biserialis. Unfortunately, this species later disappeared from Floreana, although it can still be found on one of the satellite islands.

Floreana racer snake

Sixteen years passed before another Galapagos snake species was described. The description of the Santa Cruz Island racer (Pseudalsophis dorsalis) was based on a specimen collected in 1868. No other terrestrial snake species from Galapagos were described until the California Academy of Sciences expedition of 1905-1906. Based on their collections, four new species were presented to the scientific community.

With an increasing number of collections in the 20th century, several new species, subspecies, and “morphs” were described. Unfortunately, much of the knowledge about these snakes comes from preserved museum specimens, which are sometimes mislabelled, and often faded as a result of the method of preservation. The resulting descriptions and actual distinctions between species end up rather fuzzy.

Park staff with Galapagos snake

Danny Rueda, Andrea Loyola and Wilson Cabrera of the GNPD examine an adult specimen of Pseudalsophis dorsalis on North Seymour.

So, how many species of snakes are there in the Galapagos Islands? In 2015, working with colleagues from the Galapagos National Park Directorate (GNPD), I began to look into this matter to understand not only the diversity of the group, but also the evolutionary relationship between these species and snakes on the South American continent.

Unlike previous efforts to classify Galapagos snakes, we planned to obtain as much information as possible from live specimens in the wild, instead of from museum collections. This requires visiting numerous locations across most islands, finding snakes, photographing them, and obtaining valuable morphometric information as well as tissue samples for genetic analysis. 

The task of locating, surveying, measuring, and photographing Galapagos snakes throughout the Archipelago has been monumental in terms of personnel, logistics, time, and effort. Field trips included park rangers, volunteers, and students, all dedicated to getting the job done well. In 2017-2018, thanks to strategic funding from the Galapagos Conservancy, we sampled one of the most graceful and elusive snake species in Galapagos, the Banded Galapagos racer (Pseudalsophis slevini). This species was originally described from material collected on Pinzón Island, but field records remained sporadic. Last November, my team and I encountered 24 individuals. We now have a much better understanding of the species, its distribution, habits and morphology.

Banded Galapagos racer snake

The work on Pinzón has been added to our catalog of 25 locations and nine species and subspecies since the project began. The molecular analysis of the tissue samples will be directed by Dr. Danielle Edwards at the University of California, Merced. Her results, in combination with field data, will get us closer to answering not only the question of how many species are present in Galapagos, but also their relationship to other South American species. 

Our research has determined that most species and subspecies are restricted to a single island and its adjacent islets. However, the Striped Galapagos snake (Pseudalsophis steindachneri) was found on Santa Cruz, Baltra, North Seymour, and Santiago. These gentle snakes are often found in semi-shaded spots or climbing on trunks or rocks. Their preferred food appears to be geckos. The local residents of Santa Cruz often report seeing these snakes in their backyards, gardens, and living rooms. One resident told us of seeing a medium-sized individual hiding inside an air conditioning unit!

Striped Galapagos Snake

Our team has a busy few months ahead — analyzing the most comprehensive dataset on morphology of live snakes from Galapagos and completing the DNA analysis of the tissue samples. Our work goes beyond simply stating how many species of snakes exist in Galapagos. We will also update the conservation status of each species to assist the GNPD in its task of preserving the species and ecosystems of these wonderful islands.

Luis Ortiz-CatedralLuis Ortiz-Catedral is a Lecturer in Environmental Science and Ecology at Massey University in New Zealand. Since 2010 he has worked with the Galapagos National Park monitoring and researching threatened native species in Galapagos.

All photos © Luis Ortiz-Catedral except author photo © Yosimar Perez.

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  1. Super summary. Glad to have been able to act as a VERY small part of the field work, and looking forward to more.

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