Revisiting Bergmann's rule for saguaros (Carnegiea gigantea (Engelm.) Britt. and Rose): stem diameter patterns over space

Aim The influence of winter temperatures and other climate variables are explored to determine which variables are associated with saguaro stem diameter and to determine if Bergmann's rule is applicable to saguaros. Location The northern Sonoran Desert in Arizona, USA. Methods Thirty saguaro populations were sampled (height, diameter, number of branches), and after adjustment for population height structure, mean relative thickness of saguaros was calculated for each plot (population). Fifty‐seven climate variables were calculated for the thirty populations. Regression was run to determine which variables (cold winter, hot summer and precipitation) best predict relative thickness. Previous studies have demonstrated a significant positive relationship between winter precipitation and saguaro branching ( Drezner, 2003 , Ecography, in press). To determine if relative thickness may be an artefact of branching (branches), partial correlation analysis was employed. Results Mean March precipitation best predicts relative thickness. When only winter temperature variables are considered, none are significantly related to relative thickness. Relative thickness is not an artefact of branches. Main conclusions (1) Rainfall, not temperature, best predicts saguaro stem thickness. In addition, despite the focus on summer rains in the literature, winter precipitation is the best predictor of thickness. (2) Bergmann's rule is not applicable to saguaro populations as has been previously suggested [e.g. Niering et al. (1963) Science 142 , 15], as thickness does not increase significantly with latitude. In addition, the suggested mechanism for Bergmann's rule, cold winter temperature, does not significantly predict saguaro stem diameters over the area studied. In some populations that experience high winter rainfall as well as cold temperatures, individuals likely derive thermal benefits from a larger stem diameter; however, the trend is not observed over the area studied and it does not appear to be adaptive.     

Circulating vitamin D3 and 25-hydroxyvitamin D in humans: An important tool to define adequate nutritional vitamin D status

Circulating 25-hydroxyvitamin D [25(OH)D] is generally considered the means by which we define nutritional vitamin D status. There is much debate, however, with respect to what a healthy minimum level of circulation 25(OH)D should be. Recent data using various biomarkers such as intact parathyroid hormone (PTH), intestinal calcium absorption, and skeletal density measurements suggest this minimum level to be 80 nmol (32 ng/mL). Surprisingly, the relationship between circulating vitamin D₃ and its metabolic product—25(OH)D₃ has not been studied. We investigated this relationship in two separate populations: the first, individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6400 IU vitamin D₃/day for 6 months.Results (1) the relationship between circulating vitamin D₃ and 25(OH)D in both groups was not linear, but appeared saturable and controlled; (2) optimal nutritional vitamin D status appeared to occur when molar ratios of circulating vitamin D₃ and 25(OH)D exceeded 0.3; at this point, the V_max of the 25-hydroxylase appeared to be achieved. This was achieved when circulating 25(OH)D exceeded 100 nmol.We hypothesize that as humans live today, the 25-hydroxylase operates well below its V_max because of chronic substrate deficiency, namely vitamin D₃. When humans are sun (or dietary) replete, the vitamin D endocrine system will function in a fashion as do these other steroid synthetic pathways, not limited by substrate. Thus, the relationship between circulating vitamin D and 25(OH)D may represent what “normal” vitamin D status should be.     

Sudden cardiac arrest on the field of play: turning tragedy into a survivable event

Sudden cardiac arrest remains the leading cause of death in exercising athletes, and recent studies have shown that it occurs more frequently than historical estimates. While out-of-hospital cardiac arrest often proves fatal, advance preparation can improve outcomes and the chance of survival. First responders to a collapsed athlete on the field of play may include team medical personnel, coaches, other athletes, officials, venue staff, emergency medical services personnel, or lay bystanders. Prompt and accurate recognition of sudden cardiac arrest, a comprehensive and rehearsed emergency action plan, early cardiopulmonary resuscitation, and immediate access to and use of an automated external defibrillator are each pivotal links in the chain of survival. This review summarises the components of an effective emergency action plan, highlights the critical role of automated external defibrillators, and reviews the diagnosis and management of sudden cardiac arrest on the field of play.     

Reduced renal cortical ribonucleoside triphosphate pools in three different hypophosphatemic animal models

Renal cortical metabolite quantitation in three different models of hypophosphatemia demonstrates that ribonucleoside triphosphate depletion is a common manifestation of reduced plasma phosphate concentration. Total tissue inorganic phosphate is not necessarily altered as the result of hypophosphatemia. Compensatory increases in mono- and diphosphate pools maintain the total ribonucleotide pool but cause reductions in the energy charge for the adenine, guanine, and uridine nucleotides. The coordinate regulation of all ribonucleoside triphosphate pools suggests cellular dysfunction accompanying hypophosphatemia may be the consequence of a generalized derangement in energy and nucleotide metabolism.     

ASARM peptides: PHEX-dependent and -independent regulation of serum phosphate

Increased acidic serine aspartate-rich MEPE-associated motif (ASARM) peptides cause mineralization defects in X-linked hypophosphatemic rickets mice (HYP) and "directly" inhibit renal phosphate uptake in vitro. However, ASARM peptides also bind to phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and are a physiological substrate for this bone-expressed, phosphate-regulating enzyme. We therefore tested the hypothesis that circulating ASARM peptides also "indirectly" contribute to a bone-renal PHEX-dependent hypophosphatemia in normal mice. Male mice (n = 5; 12 wk) were fed for 8 wk with a normal phosphorus and vitamin D(3) diet (1% P(i) diet) or a reduced phosphorus and vitamin D(3) diet (0.1% P(i) diet). For the final 4 wk, transplantation of mini-osmotic pumps supplied a continuous infusion of either ASARM peptide (5 mg·day(-1)·kg(-1)) or vehicle. HYP, autosomal recessive hypophosphatemic rickets (ARHR), and normal mice (no pumps or ASARM infusion; 0.4% P(i) diet) were used in a separate experiment designed to measure and compare circulating ASARM peptides in disease and health. ASARM treatment decreased serum phosphate concentration and renal phosphate cotransporter (NPT2A) mRNA with the 1% P(i) diet. This was accompanied by a twofold increase in serum ASARM and 1,25-dihydroxy vitamin D(3) [1,25 (OH)(2)D(3)] levels without changes in parathyroid hormone. For both diets, ASARM-treated mice showed significant increases in serum fibroblast growth factor 23 (FGF23; +50%) and reduced serum osteocalcin (-30%) and osteopontin (-25%). Circulating ASARM peptides showed a significant inverse correlation with serum P(i) and a significant positive correlation with fractional excretion of phosphate. We conclude that constitutive overexpression of ASARM peptides plays a "component" PHEX-independent part in the HYP and ARHR hypophosphatemia. In contrast, with wild-type mice, ASARM peptides likely play a bone PHEX-dependent role in renal phosphate regulation and FGF23 expression. They may also coordinate FGF23 expression by competitively modulating PHEX/DMP1 interactions and thus bone-renal mineral regulation.     

Effects of larval diet on development rates and reproductive maturation of male and female Mediterranean fruit flies

Abstract Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae) larvae are capable of developing in one of many hosts that may vary greatly in quality. We hypothesized that they will respond to the larval environment in a manner beneficial to their subsequent reproductive performance. Accordingly, we investigated the effects of various larval diets (varying in the amount of protein and sugar they contain) on the size, development time, nutritional status and reproductive maturation (ovarian development and onset of sexual behaviour) of females and males. We found that flies which undergo larval development in artificial host fruit that contain sugar and protein ('protein-fed') were larger, developed faster and emerged with more nutritional reserves than flies that were protein-deprived as larvae. Protein-fed males, regardless of their size, became sexually active before males that developed in hosts with no protein. Protein-fed females produced more mature eggs than protein-deprived ones. Moreover, protein-fed females tended to copulate sooner than females that developed in hosts with no protein. In addition, regardless of female larval diet, females with more mature eggs tended to copulate sooner than females with less mature eggs. In light of these results, the importance of the larval environment for adult reproductive success is discussed.     

Circulating vitamin D3 and 25-hydroxyvitamin D in humans: An important tool to define adequate nutritional vitamin D status

Circulating 25-hydroxyvitamin D [25(OH)D] is generally considered the means by which we define nutritional vitamin D status. There is much debate, however, with respect to what a healthy minimum level of circulation 25(OH)D should be. Recent data using various biomarkers such as intact parathyroid hormone (PTH), intestinal calcium absorption, and skeletal density measurements suggest this minimum level to be 80 nmol (32 ng/mL). Surprisingly, the relationship between circulating vitamin D₃ and its metabolic product—25(OH)D₃ has not been studied. We investigated this relationship in two separate populations: the first, individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6400 IU vitamin D₃/day for 6 months.

Results (1) the relationship between circulating vitamin D₃ and 25(OH)D in both groups was not linear, but appeared saturable and controlled; (2) optimal nutritional vitamin D status appeared to occur when molar ratios of circulating vitamin D₃ and 25(OH)D exceeded 0.3; at this point, the V_max of the 25-hydroxylase appeared to be achieved. This was achieved when circulating 25(OH)D exceeded 100 nmol.

We hypothesize that as humans live today, the 25-hydroxylase operates well below its V_max because of chronic substrate deficiency, namely vitamin D₃. When humans are sun (or dietary) replete, the vitamin D endocrine system will function in a fashion as do these other steroid synthetic pathways, not limited by substrate. Thus, the relationship between circulating vitamin D and 25(OH)D may represent what “normal” vitamin D status should be.