Response to Comment on “Evidence of humans in North America during the Last Glacial Maximum”

Madsen et al . question the reliability of calibrated radiocarbon ages associated with human footprints discovered recently in White Sands National Park, New Mexico, USA. On the basis of the geologic, hydrologic, stratigraphic, and chronologic evidence, we maintain that the ages are robust and conclude that the footprints date to between ~23,000 and 21,000 years ago. Madsen et al . ( 1 ) question the veracity of calibrated radiocarbon ages used to constrain the antiquity of human trackways discovered recently at White Sands National Park (WHSA) Locality 2, New Mexico, USA ( 2 ). The ages were derived from seeds of the aquatic plant Ruppia cirrhosa , which they suggest may suffer from hard-water (or reservoir) effects, making them too old, potentially by thousands of years. We were well aware of this possibility, investigated it, and presented several lines of evidence that argued against such a problem. Here we respond to each of their four primary points.

A profound view and discourse on the typification and status of three confused taxa: Ruppia maritima, R. spiralis and R. cirrhosa

Taxonomic difficulties have persisted within the genus Ruppia for a long time. We first unravel misconceptions as perceived on different continents and subsequently present a revised interpretation of the identity and typification of three European taxa at species level: Ruppia maritima L., Ruppia spiralis L. ex Dumortier, and Ruppia cirrhosa (Petagna) Grande. To do this, historical specimens, illustrations and original descriptions were studied. We supersede a previous choice of the figure of Buccaferrea maritima, foliis minus acutis Micheli (1729) as the lectotype of R. maritima and type species of the genus Ruppia owing to a serious conflict with the protologue. Based on a meticulous interpretation of protologues and figures in a historical context, we reject the recent view of assigning R. cirrhosa and its proposed lectotype (iconotype) as a homotypic synonym of R. maritima. We agree with an earlier lectotypification of R. spiralis, though for another reason than the above-mentioned abused homotypy. Consequently, R. cirrhosa is a synonym of neither R. maritima or R. spiralis, based on material from Petagna in the Herbarium of Naples designated as the holotype of R. cirrhosa. We argue for three species to be considered as fully independent taxa: R. maritima, R. spiralis and R. cirrhosa.

Is the zooplankton of mesosaline lakes in protected areas in the semiarid Pampa of Argentina different from those in lakes with high anthropic influence?

Most of the mesosaline lakes in the semiarid central Pampas have a high anthropic influence. The objective was to determine the limnological and zooplankton parameters of a mesosaline lake with little human impact, the West Lake of the Parque Luro Reserve, and compare it with previously studied aquatic ecosystems. Monthly samples were taken (2014–2015). The mean depth and salinity were 0.66 m and 29.33 g/L, respectively. The transparency was high and favored the growth of the macrophyte Ruppia cirrhosa. Zooplankton diversity was low, with autochthonous halophilic crustaceans (Daphnia menucoensis and Boeckella poopoensis). Zooplankton density was 20 to 100 times lower than that of other pampean lakes, probably due to the presence of the macrophyte, which distinguishes this lake from others in the region.

Effects of salinity and temperature on the performance of Cymodocea nodosa and Ruppia cirrhosa: a medium-term laboratory study

The effects of salinity and temperature on the photosynthetic and growth performance of the seagrasses Cymodocea nodosa and Ruppia cirrhosa were studied to understand their local seasonality and distribution. Cymodocea nodosa shoots were collected from Cape Vrasidas, and R. cirrhosa shoots from the coastal lagoon Fanari, all from the Eastern Macedonian and Thrace Region, Greece. Effective quantum yield (ΔF/Fm′), leaf chlorophyll-a content (mg g−1 wet mass) and growth (% of maximum) were tested at different temperatures (10–40°C) and salinities (5–60). The results showed that: (a) R. cirrhosa was more euryhaline (5–55/60) than C. nodosa (10–50), (b) the upper thermal tolerance of C. nodosa (34–35°C) was higher than that of R. cirrhosa (32–34°C), (c) C. nodosa could not tolerate 10°C, whereas R. cirrhosa could, and (d) the growth optimum of C. nodosa was 30°C and that of R. cirrhosa 20–30°C. The thermal optima and tolerances of growth and photosynthesis confirm the seasonal patterns of R. cirrhosa but not of C. nodosa. However, the sensitivity of C. nodosa to low salinities and temperatures may explain its absence from shallow coastal lagoons. Ruppia cirrhosa could be vulnerable to future climate change.

New highly polymorphic microsatellite markers for the aquatic angiosperm Ruppia cirrhosa reveal population diversity and differentiation

Ruppia cirrhosa is a clonal monoecious plant phylogenetically associated to seagrass families such as Posidoniaceae and Cymodoceaceae. It inhabits shallow waters that are important for productivity and as a biodiversity reservoir. In this study, we developed 10 polymorphic microsatellite loci for R. cirrhosa. Additionally, we obtained cross-amplification for two microsatellites previously described for Ruppia maritima. These 12 markers were tested in four R. cirrhosa populations from the southwest of Europe. The number of alleles per locus was high for most of the markers, ranging from 4 to 13. Two populations (Sicily and Cádiz) showed heterozygote deficit (p < 0.001). The four populations (Sicily, Murcia, Cádiz, and Tavira) were significantly differentiated (FST ≠ 0; p < 0.001), corroborating the usefulness of these microsatellites on R. cirrhosa population genetics.