Organic matter and nitrogen accumulation and nitrogen fixation during early ecosystem development in Hawaii

We used a chronosequence comprised of 10 y, 52 y and 142 yold `a'a lava flows on Mauna Loa, Hawaii, to determine theaccumulation of organic matter and nitrogen and rates of nitrogenfixation through time. The mass of organic matter (live and deadbiomass and soil organic matter) on the 1984, 1942 and 1852 lavaflows was 0.6, 2.2 and 7.6 kg m^{– 2}, respectively, while total N was 4.8, 10.9 and 85.7 g m^{– 2}.We estimated the total rates of nitrogen fixation for thethree different aged ecosystems using an acetylene reduction assaycalibrated with ¹⁵N incubations. While mean rates of total N fixation remained largely constant across the three sites – between2.0 and 3.1 kg ha^{– 1} y^{– 1} – the most important sources of N fixation changed. On the 10 y flow, the most important fixer was the pioneering cyanolichen, Stereocaulon vulcani. After 52 years ofecosystem development, the most important N fixer was a cyanoalga,while after 142 years, the predominant N fixers were heterotrophicbacteria associated with leaf litter, twigs and detritus. The totalamount of N accumulated after 52 years of ecosystem development wasequivalent to cumulative inputs through biological N fixation. After 142 years, however, cumulative inputs from N fixation couldonly account for between 27–59% of the total nitrogen accrued.We used fertilizer additions of all essential nutrients otherthan N to test whether the availability of lithophilic nutrientsregulated rates of N fixation in early ecosystem development. Ratesof nitrogen fixation by the lichen, S. vulcani, approximately doubled when fertilized on the 1984 and 1942 flows. Rates of N-fixation by heterotrophic nitrogen fixing bacteria on leaf litter ofMetrosideros polymorpha also increased significantly when fertilized with lithophilic nutrients. These findings suggest that weathering rates of lava in part regulate rates of nitrogen fixation in these young ecosystems.     

Adolescent,but Not Adult,Binge Ethanol Exposure Leads to Persistent Global Reductions of Choline Acetyltransferase Expressing Neurons in Brain

During the adolescent transition from childhood to adulthood, notable maturational changes occur in brain neurotransmitter systems. The cholinergic system is composed of several distinct nuclei that exert neuromodulatory control over cognition, arousal, and reward. Binge drinking and alcohol abuse are common during this stage, which might alter the developmental trajectory of this system leading to long-term changes in adult neurobiology. In Experiment 1, adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2-day on/2-day off from postnatal day [P] 25 to P55) treatment led to persistent, global reductions of choline acetyltransferase (ChAT) expression. Administration of the Toll-like receptor 4 agonist lipopolysaccharide to young adult rats (P70) produced a reduction in ChAT+IR that mimicked AIE. To determine if the binge ethanol-induced ChAT decline was unique to the adolescent, Experiment 2 examined ChAT+IR in the basal forebrain following adolescent (P28–P48) and adult (P70–P90) binge ethanol exposure. Twenty-five days later, ChAT expression was reduced in adolescent, but not adult, binge ethanol-exposed animals. In Experiment 3, expression of ChAT and vesicular acetylcholine transporter expression was found to be significantly reduced in the alcoholic basal forebrain relative to moderate drinking controls. Together, these data suggest that adolescent binge ethanol decreases adult ChAT expression, possibly through neuroimmune mechanisms, which might impact adult cognition, arousal, or reward sensitivity.     

Livelihood Dynamics Across a Variable Flooding Regime

Variability in environmental phenomena such as fire, flooding, and weather-related events can have significant impacts for social and environmental systems and their coupled interactions. Livelihoods systems reliant on the natural environment can be disrupted or eliminated, while associated governance regimes require negotiation to ensure equitable and sustainable management responses. These patterns can be particularly pronounced within areas prone to flooding, as these sites can experience variability in the location, timing, amount, and duration of flooding events. While research within the social and natural sciences has evaluated these dynamics within flooding regimes, the coupled interactions can be underemphasized even though they are integral in producing livelihood systems and possibilities for environmental management. This paper details research conducted from 2011 to 2016 in five villages located in different locations within the Okavango Delta of Botswana. We report the findings from qualitative interviewing and livelihood mapping activities that are integrated with remote sensing analysis to provide concrete empirical detail on the variability of flooding and resulting variations in perception and livelihood responses. The paper demonstrates that flooding dynamics vary at discrete locations and produce diverse perceptions that are tied to livelihood adjustments in place-specific ways. These patterns are also embedded in regional and global processes that have significant implications for household vulnerability within socio-ecological systems strongly impacted by local and distant climatic and hydrological drivers of change.     

Behavioral and physiological control of yolk synthesis and deposition in the female red-sided garter snake (Thamnophis sirtalis parietalis)

Ovarian recrudescence in female garter snakes, Thamnophis sirtalis parietalis, follows spring emergence from hibernation and mating. In the laboratory, courtship and mating stimuli significantly increased the proportion of female garter snakes becoming pregnant, although some noncourted nonmated controls also became pregnant. Females given artificial mating stimuli under anesthetic, without courtship stimuli, were no more likely than either noncourted, nonmated or anesthetized controls to become pregnant. Hormonal changes and yolk synthesis rapidly followed mating in both laboratory and field females; serum estradiol increased more than 10-fold in 2 days and serum calcium, a measure of yolk precursor lipoprotein (vitellogenin) concentration, increased more than two times in 10 days. Administration of exogenous estradiol stimulated yolk synthesis, but did not result in yolk deposition into ovarian follicles. However, administration of ovine follicle-stimulating hormone induced both hepatic yolk synthesis and yolk deposition. Our results are consistent with the hypotheses that courtship and copulation are facilitatory to ovarian recrudescence but neither alone nor in combination is necessary nor sufficient, and in this species yolk synthesis and yolk deposition are separately regulated.     

Sex-determining potencies vary among female incubation temperatures in a turtle

Reptiles whose sex is determined by incubation temperature typically exhibit all-male or all-female sex ratios over a wide range of incubation temperatures. The question arises as to whether the various all-female temperatures (or the various all-male temperatures) are equivalent in their "potency", or capacity to effect female determination. In map turtles, warm incubation temperatures produce all females and cool ones produce all males. We compared sex determining potencies of two all-female temperatures, 31 degrees C and 32.5 degrees C, by incubating eggs first at a male-producing temperature (26 degrees C) and then shifting them to the warm temperatures. The resulting sex ratio was significantly more male biased in the 26 degrees C----31 degrees C shift than in the 26 degrees C----32.5 degrees C shift, indicating that 32.5 degrees C has the greater female potency. These results point to the possibility that sex determination depends on a quantitative rather than qualitative level of gene expression.     

Steroid hormone-induced male sex determination in an amniotic vertebrate.

In many reptiles, sex is determined by the temperature at which the eggs are incubated (i.e., temperature-dependent sex determination, or TSD). Past studies have shown that exogenous steroid hormones can override the effects of temperature and induce female sex determination. However, past attempts to induce male sex determination have consistently failed. In the present study, sex determination was studied in a turtle with TSD. By utilizing an incubation temperature regimen that resulted in approximately a 1:1 sex ratio in the control group, sex determination was shown to be sensitive to both exogenous androgen and estrogen treatments: androgen induced the production of male hatchlings, whereas estrogen induced the production of female hatchlings. This is the first report of an amniotic vertebrate in which an exogenous steroid hormone induces male sex determination.