Vibration attraction response is a plastic trait in blind Mexican tetra (Astyanax mexicanus), variable within subpopulations inhabiting the same cave

Animals evolve their sensory systems and foraging behaviours to adapt and colonize new and challenging habitats such as the dark cave environment. Vibration attraction behaviour (VAB) gives fish the ability to locate the source of a water disturbance in the darkness. VAB evolved in the blind Mexican cave tetra, Astyanax mexicanus. VAB is triggered in cavefish by vibration stimuli peaking at 35 Hz, which is within the main spectrum of water fluctuations produced by many prey crustaceans and insects. VAB has a genetic component and is correlated to an increased number of head mechanosensory neuromasts in the eye orbital region when compared to surface fish. Previous competitive prey capture assays have supported the advantage of VAB for foraging in the dark. Despite its putative adaptive function, VAB has been described as absent in some Astyanax cave populations (Tinaja and Molino) but present in others (Pachón, Piedras, Toro and Sabinos). Here we have tested the occurrence of VAB in the field and in multiple cave populations using a vibrating device in natural pools. Our results confirmed the presence of VAB in caves such as Pachón, Toro and Sabinos but showed that VAB is also present in the Tinaja and Molino cave populations, previously reported as VAB-negative in laboratory experiments. Thus, VAB is available throughout the range of hypogean A. mexicanus. However, and most notably, within a given cave the levels of VAB were highly variable among different pools. Fish at one pool may express no VAB, while fish at another nearby pool of the same cave may actively show VAB. While a variety of environmental conditions may foster this diversity, we found that individuals inhabiting pools with a high abundance of organic matter have reduced expression of VAB. In contrast, in pools with little organic debris where fish probably depend more on hunting than on scavenging, VAB is enhanced. Our results suggest that expression of VAB is a plastic trait whose variability can depend on local conditions. Such plasticity may be required within and among caves where high environmental variability between pools results in a diverse availability of food.     

Production of phytohormones by root-associated saprophytic actinomycetes isolated from the actinorhizal plant Ochetophila trinervis

The aim of the present study was to evaluate phytohormone production by symbiotic and saprophytic actinomycetes isolated from the actinorhizal plant Ochetophila trinervis which had previously proved to stimulate nodulation by Frankia. Three saprophytic strains out of 122, isolated from the rhizosphere of this plant with multiple enzymatic activities were selected for plant growth experiments in pots: Streptomyces sp. (BCRU-MM40), Actinoplanes sp. (BCRU-ME3) and Micromonospora sp. (BCRU-MM18). For experiments, the symbiotic N₂-fixing strain Frankia (BCU110501), isolated from nodules of the same actinorhizal plant was used. Phytohormone production was evaluated in supernatant of non-inoculated and inoculated culture media in exponential growth phase. Indole 3-acetic acid (IAA) and gibberellic acid (GA₃) were analyzed by gas chromatography-mass spectrometry (GC–MS), while zeatine (Z) production was determined by gas chromatography-flame ionization detector and high performance liquid chromatography (HPLC fluorescent and UV). The levels of the three phytohormones produced by the saprophytic rhizoactinomycetes were higher than that produced by the symbiotic Frankia strain. Zeatine biosynthesis was higher (μg ml⁻¹) than IAA and GA₃ (ng ml⁻¹), and Micromonospora strain produced the highest levels of these phytohormones. Although O. trinervis has been shown to be intercellularly infected by Frankia without mediation of root hair deformation, when plants were co-inoculated with actinomycetes’ culture, some root hair deformation was observed. This is the first report on identification of IAA, GA₃ and Z in saprophytic actinomycetes and their potential role in plant–microbe interaction.     

Bioturbation in matgrounds at Lake Bogoria in the Kenya Rift Valley: implications for interpreting the heterogeneous early Cambrian seafloor

Modern burrowing organisms feed on microbial organic matter in matgrounds near hot springs on the margins of Lake Bogoria, a saline alkaline lake in the Kenya Rift Valley. The burrowers produce a low-diversity trace assemblage similar to those produced by undermat miners during the Ediacaran–Cambrian transition. Despite obvious differences in body plans and phylogenetic affinities, these modern animals feed on microbes in similar ways to those inferred for primitive bilaterians. With increasing distance from hot-spring vents, outflow channels and adjacent matgrounds, the diversity and depth of the traces increase and mixgrounds become dominant. This modern extreme environment gives clues for interpreting the heterogeneous early Cambrian seafloor, with: (1) the restriction of ‘pre-agronomic revolution’ matground substrates; and (2) expansion of adjacent ‘post-agronomic revolution’ mixground areas.     

Stable carbon isotope ratios for the gray whale (<Emphasis Type="Italic">Eschrichtius robustus</Emphasis>) in the breeding grounds of Baja California Sur,Mexico

This work investigated the feeding ecology and behaviour of gray whales in Bahía Magdalena. Underwater observations of bottom feeding were made (n=4). Skin biopsies of the gray whale had a carbon isotope value of –16.5 ± 0.1 (range from –16.4 to –16.7, n=7). Prey in Bahía Magdalena had a carbon isotope value of –18.4. Dietary enrichment from prey in Bahía Magdalena would correspond to 2 ± 0.1, whereas previously published results for prey in Alaska would result in an enrichment of 3, which suggests that whales were more likely feeding on prey from Bahía Magdalena. Carbon isotopic oscillation along the baleen plate of a stranded 1-year-old whale showed a variation in diet during the year, which suggests continual feeding during this time and corresponding to dietary sample measurements from Bahía Magdalena in winter and Alaska in summer.     

Phylogeny, diversification rates and species boundaries of Mesoamerican firs (Abies, Pinaceae) in a genus-wide context

The genus Abies is distributed discontinuously in the temperate and subtropical montane forests of the northern hemisphere. In Mesoamerica (Mexico and northern Central America), modern firs originated from the divergence of isolated mountain populations of migrating North American taxa. However, the number of ancestral species, migratory waves and diversification speed of these taxa is unknown. Here, variation in repetitive (Pt30204, Pt63718, and Pt71936) and non-repetitive (rbcL, rps18-rpl20 and trnL-trnF) regions of the chloroplast genome was used to reconstruct the phylogenetic relationships of the Mesoamerican Abies in a genus-wide context. These phylogenies and two fossil-calibrated scenarios were further employed to estimate divergence dates and diversification rates within the genus, and to test the hypothesis that, as in many angiosperms, conifers may exhibit accelerated speciation rates in the subtropics. All phylogenies showed five main clusters that mostly agreed with the currently recognized sections of Abies and with the geographic distribution of species. The Mesoamerican taxa formed a single group with species from southwestern North America of sections Oiamel and Grandis. However, populations of the same species were not monophyletic within this group. Divergence of this whole group dated back to the late Paleocene and the early Miocene depending on the calibration used, which translated in very low diversification rates (r_0.0 = 0.026-0.054, r_0.9 = 0.009-0.019 sp/Ma). Such low rates were a constant along the entire genus, including both the subtropical and temperate taxa. An extended phylogeographic analysis on the Mesoamerican clade indicated that Abies flinckii and A. concolor were the most divergent taxa, while the remaining species (A. durangensis, A. guatemalensis, A. hickelii, A. religiosa and A. vejari) formed a single group. Altogether, these results show that divergence of Mesoamerican firs coincides with a model of environmental stasis and decreased extinction rate, being probably prompted by a series of range expansions and isolation-by-distance.     

Time of Progression to Osteopenia/Osteoporosis in Chronically HIV-Infected Patients: Screening DXA Scan

Background

Algorithms for bone mineral density (BMD) management in HIV-infected patients are lacking. Our objective was to assess how often a dual-energy x-ray absorptiometry (DXA) scan should be performed by assessing time of progression to osteopenia/osteoporosis.

Methods

All DXA scans performed between 2000 and 2009 from HIV-infected patients with at least two DXA were included. Time to an event (osteopenia and osteoporosis) was assessed using the Kaplan–Meier method. Strata (tertiles) were defined using baseline minimum T scores. Differences between strata in time to an event were compared with the log-rank test.

Results

Of 391 patients (1,639 DXAs), 49.6% had osteopenia and 21.7% osteoporosis at their first DXA scan. Of the 112 (28.6%) with normal BMD, 35.7% progressed to osteopenia; median progression time was 6.7 years. These patients were stratified: “low-risk" (baseline minimum T score >−0.2 SD), “middle-risk" (between −0.2 and −0.6 SD), and “high-risk" (from −0.6 to −1 SD); median progression time to osteopenia was 8.7, >7.2, and 1.7 years, respectively (p<0.0001). Of patients with osteopenia, 23.7% progressed to osteoporosis; median progression time was >8.5 years. Progression time was >8.2 years in “low-risk" tertile (T score between −1.1 and −1.6 SD), >8.5 years in “middle-risk" (between −1.6 and −2), and 3.2 years in “high-risk" (from −2 to −2.4) (p<0.0001).

Conclusions

Our results may help to define the BMD testing interval. The lowest T score tertiles would suggest recommending a subsequent DXA in 1–2 years; in the highest tertiles, ≥6 years. Early intervention in patients with bone demineralization could reduce fracture–related morbidity/mortality.     

Enhancing estimation methods for integrating probability and nonprobability survey samples with machine-learning techniques. An application to a Survey on the impact of the COVID-19 pandemic in Spain

Web surveys have replaced Face-to-Face and computer assisted telephone interviewing (CATI) as the main mode of data collection in most countries. This trend was reinforced as a consequence of COVID-19 pandemic-related restrictions. However, this mode still faces significant limitations in obtaining probability-based samples of the general population. For this reason, most web surveys rely on nonprobability survey designs. Whereas probability-based designs continue to be the gold standard in survey sampling, nonprobability web surveys may still prove useful in some situations. For instance, when small subpopulations are the group under study and probability sampling is unlikely to meet sample size requirements, complementing a small probability sample with a larger nonprobability one may improve the efficiency of the estimates. Nonprobability samples may also be designed as a mean for compensating for known biases in probability-based web survey samples by purposely targeting respondent profiles that tend to be underrepresented in these surveys. This is the case in the Survey on the impact of the COVID-19 pandemic in Spain (ESPACOV) that motivates this paper. In this paper, we propose a methodology for combining probability and nonprobability web-based survey samples with the help of machine-learning techniques. We then assess the efficiency of the resulting estimates by comparing them with other strategies that have been used before. Our simulation study and the application of the proposed estimation method to the second wave of the ESPACOV Survey allow us to conclude that this is the best option for reducing the biases observed in our data.