Influence of late Quaternary climate on the biogeography of Neotropical aquatic species as reflected by non-marine ostracodes

We evaluated how ranges of four endemic and non-endemic aquatic ostracode species changed in response to long-term (glacial–interglacial cycles) and abrupt climate fluctuations during the last 155 kyr in the northern Neotropical region. We employed two complementary approaches, fossil records and species distribution models (SDMs). Fossil assemblages were obtained from sediment cores PI-1, PI-2, PI-6 and Petén-Itzá 22-VIII-99 from the Petén Itzá Scientific Drilling Project, Lake Petén Itzá, Guatemala. To obtain a spatially resolved pattern of (past) species distribution, a downscaling cascade is employed. SDMs were reconstructed for the last interglacial (∼120 ka), the last glacial maximum (∼22 ka) and the middle Holocene (∼6 ka). During glacial and interglacial cycles and marine isotope stages (MISs), modelled paleo-distributions and paleo-records show the nearly continuous presence of endemic and non-endemic species in the region, suggesting negligible effects of long-term climate variations on aquatic niche stability. During periods of abrupt ecological disruption such as Heinrich Stadial 1 (HS1), endemic species were resilient, remaining within their current areas of distribution. Non-endemic species, however, proved to be more sensitive. Modelled paleo-distributions suggest that the geographic range of non-endemic species changed, moving southward into Central America. Due to the uncertainties involved in the downscaling from the global numerical to the highly resolved regional geospatial statistical modelling, results can be seen as a benchmark for future studies using similar approaches. Given relatively moderate temperature decreases in Lake Petén Itzá waters (∼5 ∘C) and the persistence of some aquatic ecosystems even during periods of severe drying in HS1, our data suggest (1) the existence of micro-refugia and/or (2) continuous interaction between central metapopulations and surrounding populations, enabling aquatic taxa to survive climate fluctuations in the northern Neotropical region

Tropical freshwater ostracodes as environmental indicators across an altitude gradient in Guatemala and Mexico

Ostracodes are bivalve microcrustaceans with calcium carbonate shells that preserve well in lake sediment. They are very sensitive to environmental variables and are therefore powerful tools in paleoclimate and paleoenvironmental studies that cover time periods from decades to millions of years. Detailed knowledge of species ecological preferences and robust taxonomy are prerequisites for such studies. Such information, however, is still lacking for many areas of the world, including the Neotropics. Previous studies in the northern Neotropics were conducted mainly in the karst lowlands of the Yucatán Peninsula, but higher-altitude areas remained relatively poorly investigated. This study was designed to expand our knowledge of the modern, Neotropical freshwater ostracode fauna, across an altitudinal gradient from the karst lakes in the lowlands of El Petén, Guatemala (~100 - 500 m asl), to the mid-elevation water bodies of the Lacandón forest (~500 - 1000 m asl), to the higher-altitude lakes of Montebello, Chiapas, México (~1000 - 1500 m asl). Eighteen ostracode species were identified in 24 lakes. Ostracodes were absent in Lakes Amarillo and Lacandón (mid-altitude), and San Diego (lowlands). Statistical analysis indicated that the most abundant species, Cypridopsis vidua, Cytheridella ilosvayi, Pseudocandona antillana, and Darwinula stevensoni have a continuous distribution along the entire altitudinal gradient. Other species display more restricted distributions, determined by temperature, precipitation and conductivity. For example, Eucypris sp. is restricted to the lowlands, Vestalenula sp. and Cypria sp. were found only at middle elevations, and a Cyprididae species was restricted to the highlands. Species diversity is slightly greater in warm lakes at middle altitudes (Haverage = 1.09) than in water bodies in the lowlands (Haverage = 0.94) and in cooler lakes in the highlands (Haverage = 0.94). LOESS regressions provided ecological preference information for the four most frequent and widely distributed species, with respect to temperature, conductivity, bicarbonate (HCO3-) concentration, precipitation, and pH. Cypria petenensis, Heterocypris punctata, and Paracythereis opesta display higher abundances in lowland lakes, whereas, Cytheridella ilosvayi, and Pseudocandona antillana prefer lowland and mid-elevation lakes. Environmental conditions in the higher-elevation lakes of Montebello favor the presence of Darwinula stevensoni. Such quantitative ecological information will improve ostracode-based paleoenvironmental reconstructions in southern México and northern Guatemala, and our approach serves as a model for future paleoecological studies that employ other aquatic bioindicators, such as testate amoebae, cladocerans, and chironomids

High‐throughput identification of non‐marine Ostracoda from the Tibetan Plateau: Evaluating the success of various primers on sedimentary DNA samples

Dwelling in a variety of aquatic habitats, one of the most abundant groups of microcrustaceans, ostracodes, are widely used indicator organisms in paleolimnological research. Typically, they are identified via traditional methods using morphological features but this may be excessively time-consuming and prone to inter-investigator variation. DNA barcoding and metabarcoding have become important tools for specimen identification, with a great impact in the field of taxonomy, (paleo-)ecology and evolution. Despite its potential, metabarcoding has been rarely used to analyze the community structure of ostracodes. Here, we evaluate the performance of a metabarcoding approach for ostracode identification in surface sediment samples collected from Lake Nam Co on the Tibetan Plateau. We tested six different primer pairs amplifying fragments of three different genes, and compared their success in inferring ostracode communities, coupled with morphological identification of ostracodes from the same sediment samples. In total, depending on the primer pair used, seven to nineteen ostracode amplicon sequence variants (ASVs) were identified. Via microscopy, eight morphospecies were identified. We found considerable differences between primer pairs in yielding ostracode sequences via metabarcoding. In general, the highest proportions of ostracode reads and ASVs were found with primers amplifying fragments of the 18S rRNA gene, whereas primers for COI gene had the highest in silico amplification success and highest sequencing depth per sample but only contained <1% of ostracode sequences. As a consequence, the metabarcoding results with 18S rRNA gene were more consistent with the morphological data compared to those obtained with COI or mitochondrial 16S rRNA primers. No significant effects of treatment with different sediment quantities for DNA extraction (10 g vs. 0.5 g) were found on ostracode ASVs community composition. These results indicate that DNA metabarcoding can serve as an efficient tool for ostracode-based environmental reconstructions but requires an informed decision on primers and target gene, as well as extending the barcoding database for improved accuracy