Molecular Ecology Resources最新文献

Few processes are as decisive as predation in shaping the structure and dynamics of ecological communities. For most predator species, however, the number of prey items killed by a predator in a day (predation rate) remains impossible to assess because direct observations are scarce or impossible to acquire. For such species, molecular gut content analyses are routinely used to test for the presence of a prey in the predator's gut. Specifically, our model uses a novel mechanistic representation of predation and digestion to integrate field data on prey detection and laboratory data on prey molecular signal decay in the predator's gut. Model fit provides an estimate of the slope and intercept of the digestion curve (molecular signal decay) and an estimate of the predation rate. In a case study targeting 25 carabid beetle species and 5 types of prey in agricultural fields (winter wheat), we use our model to estimate predation rates for each predator–prey pair. Based on predation rate estimates, we introduce a new biocontrol indicator at community scale and explore its potential for advanced agroecological research. We discuss the performance of our model on the basis of the scant information available in the literature and detail its conditions of application to highlight its advantages over existing predation models.

Genetic data, including environmental DNA (eDNA), are regularly used to monitor escalating biodiversity concerns globally. In Aotearoa New Zealand, biodiversity is unique and cherished—many species are taonga (treasured) and cared for by kaitiaki (guardians with customary responsibilities), specifically mana whenua with custodial rights (Māori; the Indigenous people of New Zealand). Discussions are currently underway regarding the development of a reference DNA barcode database for biodiversity in Aotearoa New Zealand to improve outcomes for biosecurity surveillance and biodiversity assessment. A priority of these discussions is that the database development and eventual implementation accords with Te Tiriti o Waitangi (The Treaty of Waitangi). Here, we evaluate current practices for storing genetic data from samples collected in Aotearoa New Zealand by examining two major public data repositories—the National Centre for Biotechnology Information (NCBI) GenBank and the Barcode of Life Data System (BOLD). We find that current database practices limit opportunities for Māori data sovereignty, with DNA from many taonga species uploaded to public repositories with no associated restrictions or guidelines over use. This is an important finding that will help shape the development of a future DNA reference database for Aotearoa New Zealand that integrates the rights and interests of Indigenous communities.

Understanding diet composition is essential for unravelling trophic interactions in aquatic ecosystems. DNA metabarcoding, utilising various variable regions of the 18S rRNA gene, is increasingly employed to investigate zooplankton diet composition. However, accurate results depend on rapid inactivation of digestive enzymes and DNA nucleases through proper sample processing and preservation. In this study, we compare the prey communities of Antarctic krill retrieved from the 18S variable regions V4 and V7 and assess how different processing treatments affect the detected prey composition of both krill and salps. Our findings highlight the critical importance of prompt sample processing for species with highly efficient digestive enzymes, such as krill, to preserve rapidly digested prey, including gelatinous plankton. Comparative analyses of the V4 and V7 regions revealed significantly different prey communities within the same krill samples, indicating that these regions may not be suitable for direct comparisons within or across studies. To complement molecular approaches, we also analyse fatty acids (FA) as trophic markers which provide insights into dietary habits over both short and long time scales. By comparing FA signals from stomach and tissue samples of the same krill and salp individuals, we identified significant differences in trophic markers representing different plankton groups. These findings emphasise the necessity of separating digestive tract from tissue to distinguish between short- and long-term diet signals. Furthermore, integrating FA analysis with metabarcoding offers valuable insights into zooplankton digestion efficiency across taxonomic levels. This combined approach enhances our understanding of zooplankton feeding ecology and trophic interactions in marine ecosystems.

Efficient use of environmental nucleic acids (eNAs) in freshwater biodiversity monitoring requires understanding their degradation and detectability in interconnected ecosystems. We employed a novel field-scale assay to compare environmental DNA (eDNA) and environmental RNA (eRNA) decay rates and detectability across four genetic markers (16S, 18S, COI and LDHA) in connected and isolated 1000-L mesocosms containing natural planktonic assemblages. This design provides ecologically relevant and complex settings to assess how connectivity influences the detectability of eNA over time. Isolated and head mesocosms were spiked with eNAs from cultured Daphnia pulex, absent from the water source, while downstream mesocosms received eNAs via unidirectional water transfers. Using digital PCR (dPCR), we captured fine-scale temporal patterns across mitochondrial and nuclear markers and transcript types (mRNA and rRNA), an approach rarely combined in previous research. eRNA degraded significantly faster than eDNA across markers and mesocosm types. Among RNA types, mRNA (COI, LDHA) degraded faster than rRNA (16S, 18S). eRNA followed a uniform monophasic decay pattern, whereas eDNA displayed biphasic decay for nuclear markers and monophasic decay for mitochondrial markers. eNA decay rates in this field-relevant mesocosm network exceeded those from laboratory scale. While decay rates remained consistent across networks, detectability declined with dilution. Even after a 10,000-fold dilution, both eNAs were detected in terminal mesocosms, demonstrating effective transport across the network. Although RNA degrades rapidly, high detectability was achieved across diverse dilutions using dPCR, highlighting eRNA's potential for detecting active biological communities in freshwater systems.

Genotype imputation, the inference of missing genotypes using a reference set of population haplotypes, is a cost-effective tool for improving the quality and quantity of genetic datasets. Imputation is usually applied to large and well-characterised datasets of humans and livestock, even though it could also benefit smaller natural populations. This study aims to understand the best practices and effectiveness of imputation with a small reference panel for species with low genetic diversity, using a case study of a population of the hihi/stitchbird (Notiomystis cincta). We used a leave-one-out method to test imputation on 30 high-coverage hihi individuals where SNPs were masked before being imputed with Beagle v5.4. Imputation accuracy was measured using r², the correlation between imputed and ground truth genotype dosages. We tested combinations of five imputation parameters, the inclusion of two linkage maps, reference panels of different sizes and compositions and targets of various SNP densities and sporadic missingness. We achieved mean r² exceeding 0.95 in most tests from a small reference panel of high-fecundity individuals. Imputation accuracy was not improved by including a linkage map and decreased at very low SNP densities. Imputed SNPs were filtered using r² to assess downstream heterozygosity calculations, the site frequency spectrum (SFS) and inference of runs of homozygosity (ROHs). We found that filtering and SNP density greatly affected heterozygosity and SFS at low SNP densities but that ROH inference was relatively robust to both. We provide a template for testing and optimising imputation in other wild populations.

DNA barcoding traditionally relies on Sanger sequencing but faces limitations with degraded samples. High-throughput sequencing (HTS) offers a cost-effective alternative, enabling rapid barcode generation for extensive datasets. The advantage of HTS is its ability to employ multiplexing strategies, allowing thousands of samples to be processed simultaneously in a single sequencing run. This study presents the CODEX approach, a double-indexed HTS method designed to sequence overlapping cox-1 barcode fragments, suitable for samples with degraded DNA. The approach was applied to neogastropods, a diverse lineage of marine molluscs, using specimens (both recently collected and relatively older) from the Muséum national d'Histoire naturelle (MNHN) collections. The pipeline was used to process 15,076 samples, yielding 10,905 cleaned and assembled sequences, achieving a success rate of 72.33%. The CODEX method demonstrated advantages over Sanger sequencing by enabling the recovery of barcodes from samples previously deemed unsuitable, with significantly reduced costs (€0.5 per sequence vs. €4.5). Notably, DNA quality and sequencing success were strongly correlated with collection date, emphasising the impact of preservation methods and storage conditions. Sequencing success rates varied among families but were not correlated with phylogenetic relationships or specimen size, indicating the robustness of the primers designed for neogastropods. This study highlights the efficiency of the CODEX approach for large-scale DNA barcoding projects, especially when handling degraded samples. The CODEX pipeline and associated resources are publicly accessible, offering a scalable solution for molecular systematics and beyond.