Using Environmental DNA to assess the endangered golden tree frog populations in Trinidad

Methods

Summary

Our goal is to develop a non-destructive sampling method for the golden treefrog. We have two methods to develop: Environmental DNA (eDNA) sampling and vocalization surveys.

We have already obtained and sequenced sample DNA so that we will be able to recognize Phylodytes’ signature when we see it.

A. Testing of Genetic Methodology

We have obtained a set of eDNA samples from El Tucuche and El Cerro Del Aripo. These samples are from habitats where we visually recorded the presence of the golden treefrog. These samples were used to confirm the accuracy of our test and sampling methods. This means we know how to handle samples in the laboratory and identify the “needle in the haystack” of diverse DNA’s that will appear in the collection.

B. Mapping of habitat

It is believed the distribution of the frog is strictly limited to the presence of giant tank bromeliad (Glomeropitcarinia erectiflora). This is an epiphytic plant, meaning it lives on another plant and derives its nutrients from the air, rain, and accumulation of falling debris. The bromeliad is far easier to see and census than the frog, and serves as an indicator of where the frog might be. However, it must be appreciated that these mountains are a vertiginous, trackless wilderness, so the accumulation of knowledge is challenging and time-consuming. Historically, the golden tree frog had only been recorded on Trinidad's second highest peak, El Tucuche. In the 1980's, Morley Read discovered the frog on El Cerro del Aripo, leading us to believe that undocumented populations may still exist.

One of our team has surveyed widely in the Northern Range Mountains and is creating a range map for the bromeliad. He has identified four other mountain peaks crowned by cloud forest with populations of the host bromeliad species as extensive as those on El Tucuche and Cerro Del Aripo. We are not aware of any prior effort to survey for golden tree frogs on these peaks. Each is a viable candidate for a new population. We have also identified additional, smaller populations of bromeliads elsewhere in the Northern Range Mountains.

C. Sample Collection

As funding permits, we will sample each of these montane populations with the same methods as employed on El Tucuche and Cerro Del Aripo to see if whether other populations exist in the Northern Range. Starting with the aforementioned sites, we will survey for new golden tree frog populations at lower elevations. From there, all additional populations of bromeliads will be assessed by population size, elevation, slope aspect (e.g. north or south facing) and patterns of cloud cover. Our ultimate goal is to expand sampling to these other habitat islands and, if some are occupied, to develop mathematical models for predicting what is required for a sustaining population of frog.

D. Developing new methods of population sampling

Morley Read, who discovered the golden tree frog on Cerro del Aripo in the 1980’s, also recorded what we think to be the call of the male golden tree frog. This recording creates an opportunity to develop new, non-invasive methods of assessing frog populations. First, we can record and map out wherever we hear a similar song. Second, we will use the recording to try to elicit calls by resident frogs and even draw them into view. Male frogs often follow the lead of other calling males by singing in response to their songs. We are developing the equivalent of a frog periscope (viewing-camera) to peer into the heart of bromeliads that appear to host calling males. With the development of new methods for finding frogs, we may discover that it is more widely distributed than previously thought.

E. Creation of a monitoring plan

I am working with Trinidad & Tobago's Wildlife Division of Forestry to develop a monitoring program based on my results. The habitat maps will be used as a guide for future explorations and surveys. If we are successful in developing our genetic methods, or in eliciting male vocalizations, we will create a field procedure for the continued monitoring of the species. The goal is for Trinidad & Tobago to develop its own long-term monitoring program, and ensure the continued presence of its endemic tree frog.