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Tracking past human impact on islands by improving palaeoecological reconstructions with PalEnDNA analysis

Periodic Reporting for period 2 - ISLANDPALECO (Tracking past human impact on islands by improving palaeoecological reconstructions with PalEnDNA analysis)

Periodo di rendicontazione: 2018-10-01 al 2019-09-30

Island ecosystems host a significant proportion of global biodiversity, but their rich biotas are more vulnerable to pressures than continental ones. Human colonization has been a recent event on most islands, and has nearly always resulted in losses of biodiversity. The Canary Islands were no exception; colonized by aborigines at least 2000 years ago and later by Europeans, they have been transformed since that time. Despite being one of the most biodiverse regions within Europe and a target for EU biodiversity policies, there is a knowledge gap about the pre-human state and natural variability of Canarian ecosystems. This makes the Canaries the perfect place to reconstruct baselines and the long-term impact of human activities. One of the main difficulties in the implementation of palaeoecological tools in the Canaries is to detect fossils. This is due to poor conditions for preservation at certain sites, i.e. “silent sites”, and under-representation of key taxa in the fossil record, i.e. “ghost taxa”. The analysis of ancient DNA from palaeoenvironmental samples (PalEnDNA), provides a complementary tool to traditional proxies. The main aims addressed by ISLANDPALECO are: 1) to improve the reconstruction of past environments by revealing the past occurrence of “ghost taxa” and unlocking past records from “silent sites”; 2) to assess the timing and extent of human impact on Canarian ecosystems, providing pre-human vegetation baselines, and related post-(aboriginal) and post-(European) vegetation responses; and 3) to communicate the results to scientists and managers so that palaeoecological information can be easily incorporated into ecological restoration and conservation, and disseminated to the society. PalEnDNA has been successfully retrieved from “silent sites” providing a first insight into the long-term dynamics and early human impact of lowland ecosystems in the Canary Islands. PalEnDNA from “ghost taxa” has also been detected improving the knowledge on the long-term ecology of key species for Canarian ecosystems. The results obtained are improving environmental reconstructions and are significantly valuable for managers targeting effective restoration programs. This is the first time that PalEnDNA analysis is implemented in the Canaries and probably one of the few cases on islands, being a valuable example for other island regions.
WP1) Accessing “silent sites”. Sampling at lowland sites yielded sediments spanning the last 3000 to 12000 years. Although technically challenging, PalEnDNA was isolated, amplified and sequenced at all sites. To improve its recovery, a set of extraction protocols, amplification and sequencing methods was tested and implemented. Reconstruction of vegetation was also addressed by pollen analysis. Combining both proxies a dominance of coastal vegetation plants was detected, suggesting little transformation of coastal ecosystems until the arrival of Europeans. A signal of pollen and PalEnDNA from tree species was spotted, pointing to their past occurrence in the nearby mountains. Those trees are no longer present in the surrounding areas, indicating a higher transformation of forested vegetation by human activities as compared to coastal areas. Both taxonomic resolution and detection of taxa were significantly improved by PalEnDNA analysis.

WP2) Detecting “ghost taxa”. Sediments from mid-elevation sites were retrieved for detection of Lauraceae PalEnDNA. A set of specific primers to target Lauraceae DNA were designed. In general, the amount and quality of PalEnDNA sequences retrieved from mid-elevations sites was scarce, probably due to humid conditions favoring DNA degradation. Lauraceae DNA was detected at several sites but only in few samples, indicating its presence in very scattered moments in time, thus preventing further conclusions about the significance of these trees in the past. The performance of specific Lauraceae primers was good on environmental modern samples but failed when used on ancient sediment samples. Lauraceae detection was higher when using universal plant metabarcode primers. The effectiveness of other methods to recover PalEnDNA at mid-elevation sites, such as BEST 2.0 and shotgun sequencing, is being explored.

WP3) Preparing a reference sequence database. A reference database for a subset of the Canarian flora was prepared to complement the DNA barcode sequences and data from GenBank already available, with additional markers and taxa that were missing. DNA from the species that lacked information was searched in the DNA bank at the Jardín Botánico Canario Viera y Clavijo – CSIC, then amplified, and sequenced. A more complete reference database for the Canarian flora is now available to be used for barcode identification of PalEnDNA sequences.

WP4) Tracking human impact on islands. Literature available on human impact in the Canaries has been thoroughly reviewed. Data and results obtained from PalEnDNA and pollen fossil analysis are used to compare ecological variables within different scenarios of human colonization. An inter-archipelago comparison between the Canaries and New Zealand, has been the basis for an article showing how islands with contrasting natural histories result in a very similar outcome in terms of the consequences of human impact on nature.

WP5) Communicating and disseminating palaeoecological data to ensure an effective transference of the results. A workshop on the application of palaeodata into nature management and conservation was organized. Managers expressed their interest in the application of palaeoecological information and proposed media for the transference of results. The project has been introduced to the scientific community and communicated to the general public though presentations on scientific and outreach activities, news in the local press and radio, and updates via websites and social media (i.e. twitter @LCR_LTEL, @ISLANDPALECO, @FdezPalaciosLab).
Results from ISLANDPALECO have shown how the analysis of PalEnDNA can be implemented outside cold regions, being one of the few examples of its applicability on islands. This is completely novel for oceanic islands and regions alike, were long-term records are difficult to find and study. Technical challenges posed by unfavorable environmental conditions in the Canaries, have led to the trial of the latest methods in PalEnDNA analysis and their efficacy on these difficult samples. Results deriving from the project are improving the knowledge on Canarian nature and biodiversity, its history and the long-term effect of human impact. The dissemination of ISLANDPALECO result has generated interest among the scientific community and several lines of collaboration stablished with other teams. Managers have started to consider the application of palaeo-data in conservation and management, essential for the restoration schemes. For instance, a research project at EL Teide National Park will be using palaeoecological information to guide restoration and conservations strategies. The originality of the research and results is also appealing to the general public and the media, leading to greater public understanding of pre-human baselines and how current ecosystems are threatened by human land use and managed, but also how historical uses have shaped them and the role of pre-historic inhabitants in their transformation, an aspect of Canarian history virtually unknown.
Laurel forest in the Canary Islands
Coastal vegetation at lowland sites in the Canary Islands