Liana abundance and diversity increase with rainfall seasonality along a precipitation gradient in Panama

In tropical regions, rainfall gradients often explain the abundance and distribution of plant species. For example, many tree and liana species adapted to seasonal drought are more abundant and diverse in seasonally-dry forests, characterized by long periods of seasonal water deficit. Mean annual precipitation (MAP) is commonly used to explain plant distributions across climate gradients. However, the relationship between MAP and plant distribution is often weak, raising the question of whether other seasonal precipitation patterns better explain plant distributions in seasonally-dry forests. In this study, we examine the relationship between liana abundance and multiple metrics of seasonal and annual rainfall distribution to test the hypothesis that liana density and diversity increase with increasing seasonal drought along a rainfall gradient across the isthmus of Panama. We found that a normalized seasonality index, which combines MAP and the variability of monthly rainfall throughout the year, was a significant predictor of both liana density and species richness, whereas MAP, rainfall seasonality and the mean dry season precipitation (MDP) were far weaker predictors. The strong response of lianas to the normalized seasonality index indicates that, in addition to the total annual amount of rainfall, how rainfall is distributed throughout the year is an important determinant of the hydrological conditions that favor liana proliferation. Our findings imply that changes in annual rainfall and rainfall seasonality will determine the future distribution and abundance of lianas. Models that aim to predict future plant diversity, distribution, and abundance may need to move beyond MAP to a more detailed understanding of rainfall variability at sub-annual timescales.     

Comparing temporal patterns in body condition of ringed seals living within their core geographic range with those living at the edge

Ecological theory suggests that demographic responses by populations to environmental change vary depending on whether individuals inhabit central or peripheral regions within the species’ geographic range. Here, we tested this prediction by comparing a population of ringed seals Pusa hispida located at high latitudes as part of their core range (core) with a population located at the southern extremity of their range (peripheral). First, we compared the two regions’ environmental trends in timing of sea-ice breakup and freeze-up, open-water duration and the North Atlantic Oscillation (NAO). We found that the core region shifted to progressively warmer conditions in the early 1990s; whereas, in the peripheral region, the warming trend shifted in 1999 to one with no warming trend but high inter-annual variability. Next, we examined how body condition, inferred from blubber depth, responded to temporal changes in sea-ice and climatic variables – variables that have been shown to influence ringed seal demography. Core seals displayed minimal seasonal changes in body condition; whereas peripheral seals displayed a 20–60% amplitude seasonal change in body condition with a phase shift to earlier initiation of fat accumulation and loss. Finally, we tested for interannual differences and found that both core and peripheral seals responded similarly with decreased body condition following more positive NAO. Environmental variables influenced body condition in opposite directions between the two regions with core seals declining in body condition with later spring breakup and shorter open-water duration, whereas peripheral seals showed opposite relationships. Seals living at the core likely benefit from an evolved match between adaptation and environmental variation resulting in dampened seasonal and interannual fluctuations in body condition. Knowledge of how different populations respond to environmental change depending on geographic location within a species range can assist in anticipating population specific responses to climate warming.     

Focus: Preventive Medicine: Undiagnosed Hypertension and Undiagnosed Type 2 Diabetes among Overweight and Obese Marshallese Participants in a Diabetes Prevention Program

Hypertension and type 2 diabetes (T2D) are major public health issues that disproportionately affect minority communities, including Native Hawaiians and Pacific Islanders (NHPI). Minority communities are also more likely to have undiagnosed hypertension and T2D. Marshallese Pacific Islanders have been shown to have high proportions of diagnosed and undiagnosed hypertension and T2D. Using survey and biometric data collected from 378 overweight/obese Marshallese Pacific Islander adults, this study documents the prevalence of hypertension and T2D, as well as the prevalence of undiagnosed hypertension and T2D. The study also examines associations between undiagnosed hypertension and undiagnosed T2D and age group, sex, health care access (defined by foregone care due to cost and health insurance status), and body mass index (BMI). Among participants with blood pressure readings indicative of hypertension, 68.4% were undiagnosed, and among participants with HbA1c indicative of T2D, 31.6% were undiagnosed. A quarter of participants (24.5%) had blood pressure and HbA1c measures indicative of both undiagnosed hypertension and undiagnosed T2D. Undiagnosed hypertension was significantly associated with age group (p’s<0.0001) and sex (p=0.028). Undiagnosed T2D was significantly associated with age group (p’s<0.05), forgone care due to cost (p=0.018), health insurance status (p=0.035), and BMI (p=0.001). Participants in this study had high proportions of undiagnosed hypertension and undiagnosed T2D. These findings will be immediately useful for those working to address hypertension and T2D disparities among Marshallese and other NHPI populations.     

The Role of Human LRRK2 in Acute Methylmercury Toxicity in Caenorhabditis elegans

Neurochemical Research - Methylmercury (MeHg) exposure and its harmful effects on the developing brain continue to be a global environmental health concern. Decline in mitochondrial function is...     

Hysteresis in poly‐2′‐deoxycytidine i‐motif folding is impacted by the method of analysis as well as loop and stem lengths

In DNA, i‐motif (iM) folds occur under slightly acidic conditions when sequences rich in 2′‐deoxycytidine (dC) nucleotides adopt consecutive dC self base pairs. The pH stability of an iM is defined by the midpoint in the pH transition (pH_T) between the folded and unfolded states. Two different experiments to determine pH_T values via circular dichroism (CD) spectroscopy were performed on poly‐dC iMs of length 15, 19, or 23 nucleotides. These experiments demonstrate two points: (1) pH_T values were dependent on the titration experiment performed, and (2) pH‐induced denaturing or annealing processes produced isothermal hysteresis in the pH_T values. These results in tandem with model iMs with judicious mutations of dC to thymidine to favor particular folds found the hysteresis was maximal for the shorter poly‐dC iMs and those with an even number of base pairs, while the hysteresis was minimal for longer poly‐dC iMs and those with an odd number of base pairs. Experiments to follow the iM folding via thermal changes identified thermal hysteresis between the denaturing and annealing cycles. Similar trends were found to those observed in the CD experiments. The results demonstrate that the method of iM analysis can impact the pH_T parameter measured, and hysteresis was observed in the pH_T and T_m values.