Short Communication |
Corresponding author: Verónica Neves ( veronica.rc.neves@uac.pt ) Academic editor: Günter Gollmann
© 2022 Verónica Neves, Dorothee Rund, Catarina J. Pinho, Raquel Vasconcelos, Paco Bustamante, Petra Quillfeldt.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Neves V, Rund D, Pinho CJ, Vasconcelos R, Bustamante P, Quillfeldt P (2022) Diet of the exotic Madeiran wall lizard: first insights into trophic interactions in an Atlantic seabird sanctuary. Herpetozoa 35: 107-113. https://doi.org/10.3897/herpetozoa.35.e82096
|
The Madeiran wall lizard Teira dugesii is a relatively new species to the Azores Archipelago, where it was accidentally introduced about 150 to 200 years ago. This lacertid quickly became naturalised and now occurs in all the nine main islands of the Azores. At Praia Islet, off Graciosa Island, the Madeiran wall lizard was recently observed preying on chicks of the threatened Monteiro’s storm-petrel Hydrobates monteiroi. To characterise the lizards’ trophic niche, we conducted a study of the diet of the Madeiran wall lizard at Praia using stable isotope analysis and next-generation sequencing. Our results indicate that the Madeiran wall lizard has a varied diet, consisting of at least 23 invertebrate taxa, 17 plant species, and occasionally, birds (two species detected, including storm-petrels). Marine derived food items were present in few samples, and it is vital to monitor the trophic interactions at Praia Islet to ensure the conservation of this threatened storm-petrel.
Azores, conservation, Macaronesia, next-generation sequencing, Praia Islet, stable isotopes
Invasive species can pose a risk to local wildlife as predators (
Even though lizards and other reptiles are frequently the only terrestrial vertebrates on oceanic islands, there are few studies documenting interactions between reptiles and seabirds. The interactions between the endemic tuatara Sphenodon punctatus and the fairy prion Pachyptila turtur in Stephens Island, New Zealand, are perhaps the most studied case (e.g.,
Ground-breeding seabirds often nest exclusively on small islands, which are probably selected because of a lack of predators (
This study aims to investigate the diet of Madeiran wall lizards at Praia Islet as a first step towards effectively protecting the endemic Monteiro’s storm-petrel. To assess the lizards’ trophic niche, we studied their diet using Stable Isotopes (SI) in blood and next-generation sequencing in faeces. Stable isotopes analyses provide information on the trophic position and diet (Kartizinel and Pringle 2015) and next-generation sequencing identifies the prey items (
Praia Islet is located about 1.2 km off Graciosa Island, one of the nine main islands of the Azores Archipelago (Fig.
A. Location of Praia Islet in the Azores Archipelago. Squares marked in the east and north-east of the islet indicate the location of artificial nests of Monteiro’s storm-petrel, Hydrobates monteiroi; the diamond symbol in the west of the islet indicates the location of the house. Adapted from
Caught lizards were brought to the support house, measured (snout–vent length, SVL) and weighed. Faecal samples were collected by gentle palpation of the abdomen and stored in 70% ethanol. A blood sample (5–10 μL) was drawn with a sterile insulin syringe (0.33 × 12.7 mm, 29G) from the caudal vein (see
To provide an isotopic baseline of the food resources, we also sampled 18 food items for SI analysis: six arthropods and two plant species as terrestrial food, as well as blood from 10 Monteiro’s storm-petrel chicks as marine-derived food. Blood samples were briefly centrifuged, supernatant (i.e., plasma) was discarded, and the Eppendorf tubes were put into a drying chamber to evaporate the water content of the blood cells. The dried samples were then pulverized using a mortar and pestle to obtain a fine powder, and a subsample of 0.35–0.45 mg was weighed into tin capsules. Some samples were slightly lighter if there was not sufficient blood, but no less than 0.12 mg. Stable isotope ratio for carbon and nitrogen was determined with an Isotope Ratio Mass Spectrometer at the University of La Rochelle, LIENSs SI Facility. Carbon and nitrogen ratios were determined with a continuous-flow mass spectrometer (Delta V Advantage or Delta V Plus with a Conflo IV interface, Thermo Scientific, Bremen, Germany) coupled with an elemental analyser (Flash EA 1112 or Flash 2000, Thermo Scientific, Milan, Italy). Measurements of internal laboratory standards were conducted using acetanilide (Thermo Scientific) and peptone (Sigma-Aldrich) and indicated an experimental precision of ± 0.15‰ for both elements. Results are expressed in parts per thousand (‰), in the usual δ notation relative to Vienna Pee-Dee Belemnite for δ13C and atmospheric N2 for δ15N, following the formula: δ13C or δ15N = [(Rsample/Rstandard) – 1] × 1000, where R is 13C /12C or 15N/14N, respectively. Differences in the mean δ13C in the different habitats before and after the hatching of the chicks were analysed using Wilcoxon rank sum test with continuity correction because the data were not normally distributed (R v3.3.2,
Faecal samples were dried in an incubator at 50 °C to remove the ethanol. The DNA was extracted using the Stool DNA Isolation Kit (Norgen Biotek Corp., Canada), following the manufacturer’s instructions. In the end, two DNA elutions were obtained with a final volume of 50 μL each, but only the first elution was used for the next steps. To correctly identify the different prey types (vertebrates, invertebrates, and plants) three different DNA fragments were selected for amplification. For vertebrates, the V5-loop fragment of the mitochondrial 12S gene (Suppl. material
Library preparation was carried out following Illumina MiSeq protocol “16S Metagenomic Sequencing Library Preparation” (Illumina 2013) according to the method described in
We collected and analysed for SIs 57 Madeiran wall lizard blood samples; mean values and standard deviation for carbon and nitrogen isotopes for the different sampling locations and times are given in Table
Results of the isotopic analyses from lizard blood samples. Sample size (n), stable carbon (δ13C) and nitrogen (δ15N) isotope ratios (mean ± standard error in permillage, ‰) for the different sampling locations and periods. Check Fig.
Location_period | n | δ13C (‰) | δ15N (‰) |
---|---|---|---|
House_incubation | 16 | -24.53 ± 0.12 | 12.63 ± 0.12 |
House_chick-rearing | 13 | -24.27 ± 0.07 | 12.90 ± 0.23 |
Nests_incubation | 12 | -24.14 ± 0.27 | 11.46 ± 0.25 |
Nests_chick-rearing | 16 | -23.11 ± 0.41 | 12.03 ± 0.17 |
Out of the nine faecal samples analysed, only seven worked for most markers used and two samples failed to be sequenced. In total, 43 molecular operational taxonomic units (MOTU) were identified: 17 plants, 23 invertebrates and 3 vertebrates (Suppl. material
Results of the isotopic analyses from reference food items samples. Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios (mean ± standard error in permillage, ‰) for reference food resources. Terrestrial items include two plant and six arthropod species, and the marine items consist of blood samples from Monteiro’s storm-petrel chicks.
Food items | δ13C (‰) | δ15N (‰) |
---|---|---|
Terrestrial | -24.71 ± 0.63 | 9.62 ± 1.19 |
Plants | -26.94 ± 0.42 | 12.74 ± 2.92 |
Arthropods | -23.97 ± 0.53 | 8.58 ± 1.09 |
Marine | -20.23 ± 0.06 | 11.08 ± 0.07 |
Our study indicates that the values for stable carbon isotopes are higher in lizards caught around nest sites than in those caught around the support house, suggesting a possible higher reliance on marine-derived items in the diet of lizards caught in proximity to breeding seabirds. The marine-derived items on the lizards’ diet can include remains of hatched eggs (eggshell or membrane), prey dropped in the colony by terns and/ or seabirds (resulting from either scavenging or predation). There was also a higher marker for marine items after the hatching of the chicks than during incubation around the nests, as indicated by the higher carbon isotope levels. Although not significant, this difference is higher than the difference between the two study areas. However, this analysis does not allow distinguishing between marine items consumed and that could have been seabirds in the form of eggs (either whole or remains of eggshell and membrane after hatching), chicks, dead birds, faeces or dropped fish and regurgitate.
The SI analysis also revealed one individual with a stable carbon isotope ratio almost as high as was found in the chicks a month before the hatching started, an indication that marine food sources, other than Monteiro’s storm-petrel chicks, are available. These can probably be attributed to Macaronesian shearwater and band-rumped storm-petrel, species that breed during the winter period. In general, there was a wider variance in the stable carbon ratios for the lizards at the nests which indicates that some individuals specialise more in terrestrial food and some more in marine food. Previous studies on lizards and SIs have shown that soil lithology may affect the values of stable carbon isotopes (Martín et al. 2017), but in our case the study islet is small and there is no variation in soil type.
The faecal sample analysis using metabarcoding indicated that these lizards are highly reliant on invertebrates and plants as was found for this species at Selvagens Islands (
It is important to consider that Praia Islet only holds an estimated 150–183 pairs of Monteiro’s storm-petrel (
This study provides a first step towards understanding the trophic links at one of the main seabird sanctuaries in the Azores. Our results also confirm the potential of next-generation sequencing to further our understanding of the lizard/ storm-petrel trophic interactions. Marine-derived food items are not ubiquitous in a lizard’s diet and to assess lizards’ impact on the breeding success of Monteiro’s storm-petrel it would be necessary to increase the sample size and to sample in different seasons. Further studies should also attempt to use wildlife cameras on the nests to study the interactions between lizards and storm-petrels and clarify if the presence of marine items in the diet of the Madeiran wall lizard result from direct predation of viable eggs and nestlings or from scavenging of chicks that died for other reasons or remains of the membrane from hatched eggs.
This study was conducted under permit from the Azores Government – Regional Environmental Directorate #27/2016/DRA. Funding came from the Portuguese “Fundação para a Ciência e a Tecnologia”, I.P. (FCT) and FRCT through grants to VN (SFRH/BPD/88914/2912 and FRCT/M3.1.a/F/072/2016) and national funds under the scope of ‘norma transitória’ to RV (DL57/2016/CP1440/CT0002). VN was co-financed by the Operational Program AZORES 2020, through the Fund 01-0145-FEDER-000140 “MarAZ Researchers: consolidate a body of researchers in Marine Sciences in the Azores” of the European Union. CJP (SFRH/BD/145851/2019) was supported by a PhD grant funded by FCT, financed by the European Social Fund and the Human Potential Operational Programme, POPH/FSE. This work received national funds through the FCT under the project UIDB/05634/2020 and UIDP/05634/2020 and through the Azores Government through the initiative to support the Research Centers of the University of the Azores and the project M1.1.A/REEQ.CIENTÍFICO UI&D/2021/010. The IUF (France) is acknowledged for its support to PB. We are grateful to G. Guillou from the “Plateforme Analyses Isotopiques” of LIENSs for running SI analysis. We thank Stefanie Klemm for help with the fieldwork and the team of Graciosa Natural Park for transport to the islet and logistic support. Finally, we express our gratitude to R. Medeiros for help with Fig.
Table S1: Forward and reverse primers used in this study. The amplified region, the fragment length (in base pairs, bp), the sequences, and the reference for each primer set is given
Data type: Word file
Explanation note: This table is referred to in the Methods section and specifies the DNA markers selected for amplification to identify prey types.
Table S2: Results of the metabarcoding analyses. List of Operational Taxonomic Units (OTUs) sequenced from the faecal pellets of Madeiran wall lizard for the different taxonomic groups and the incidence (n) of the identified taxa
Data type: Word file
Explanation note: This table is referred to in the results section and lists all the prey items identified through next-generation sequencing of Madeiran wall lizard faeces.
Dataset S1: Taxonomic identification of the haplotypes sequenced for the three taxonomic groups (plants, invertebrates and vertebrates). Code, sequence, length, amplification primer, number of reads, incidence, taxonomic identification (final, at species, family, order and class level), and percentage of match in blast is given for each haplotype
Data type: Excel file
Explanation note: This table is referred to in the Results section and contains the taxonomic identification of the haplotypes sequenced for the three taxonomic groups (plants, invertebrates and vertebrates), namely: ID, code, sequence, sequence length, amplification primer, incidence (number of reads, number of samples), taxonomic identification (final, at species, family, order and class level), and percentage of match in blast is given for each haplotype.