A role for genetic accommodation in evolution?

Whether evolutionary change can occur by genetic assimilation, or more generally by genetic accommodation, remains controversial. Here we examine some of the experimental evidence for both phenomena. Several experiments in Drosophila suggest that assimilation is possible, and a new paper shows that a color polyphenism in the tobacco hornworm, Manduca sexta, can evolve by genetic accommodation. We argue that genetic accommodation, including assimilation, is a plausible mechanism in evolution; however, more work is required to test how this mechanism acts and how often it is involved in evolutionary change.     

Investigation of the effects of sulfonylurea exposure on pancreatic beta cell metabolism

Prolonged exposure of pancreatic beta cells to the sulfonylureas glibencamide and tolbutamide induces subsequent desensitization to the actions of these drugs. The precise mechanisms underlying this desensitization remain unknown, prompting the present study, which investigated the impact of prolonged sulfonylurea exposure on glucose and energy metabolism using clonal pancreatic BRIN-BD11 beta cells. Following prolonged exposure to tolbutamide, BRIN-BD11 beta cells were incubated in the presence of [U-(13)C]glucose, and isotopomer analysis revealed that there was a change in the ratio of flux through pyruvate carboxylase (EC 6.4.1.1) and pyruvate dehydrogenase (EC 1.2.4.1, EC 2.3.1.12, EC 1.8.1.4). Energy status in intact BRIN-BD11 cells was determined using (31)P-NMR spectroscopy. Exposure to tolbutamide did not alter the nucleotide triphosphate levels. Collectively, data from the present study demonstrate that prolonged exposure of beta cells to tolbutamide results in changes in flux through key enzymes involved in glucose metabolism that, in turn, may impact on glucose-induced insulin secretion.     

What is metamorphosis?

Metamorphosis (Gr. meta- "change" + morphe "form") as a biologicalprocess is generally attributed to a subset of animals: mostfamously insects and amphibians, but some fish and many marineinvertebrates as well. We held a symposium at the 2006 Societyfor Integrative and Comparative Biology (SICB) annual meetingin Orlando, FL (USA) to discuss metamorphosis in a comparativecontext. Specifically, we considered the possibility that theterm "metamorphosis" could be rightly applied to non-animalsas well, including fungi, flowering plants, and some marinealgae. Clearly, the answer depends upon how metamorphosis isdefined. As we participants differed (sometimes quite substantially)in how we defined the term, we decided to present each of ourconceptions of metamorphosis in 1 place, rather than attemptingto agree on a single consensus definition. Herein we have gatheredtogether our various definitions of metamorphosis, and offeran analysis that highlights some of the main similarities anddifferences among them. We present this article not only asan introduction to this symposium volume, but also as a referencetool that can be used by others interested in metamorphosis.Ultimately, we hope that this article—and the volume asa whole—will represent a springboard for further investigationsinto the surprisingly deep mechanistic similarities among independentlyevolved life cycle transitions across kingdoms.     

Comparing thyroid and insect hormone signaling

Transitions between different states of development, physiology,and life history are typically mediated by hormones. In insects,metamorphosis and reproductive maturation are regulated by aninteraction between the sesquiterpenoid juvenile hormone (JH)and the steroid 20-hydroxy-ecdysone (20E). In vertebrates andsome marine invertebrates, the lipophilic thyroid hormones (THs)affect metamorphosis and other life history transitions. Interestingly,when applied to insects, THs can physiologically mimic manyfacets of JH action, suggesting that the molecular actions ofTHs and JH/20E might be similar. Here we discuss functionalparallels between TH and JH/20E signaling in insects, with aparticular focus on the fruit fly, Drosophila melanogaster,a genetically and physiologically tractable model system. Comparingthe effects of THs with the well defined physiological rolesof insect hormones such as JH and 20E in Drosophila might provideimportant insights into hormone function and the evolution ofendocrine signaling.     

A novel neurotensin/xenin fusion peptide enhances β-cell function and exhibits antidiabetic efficacy in high-fat fed mice

Neurotensin and xenin possess antidiabetic potential, mediated in part through augmentation of incretin hormone, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), action. In the present study, fragment peptides of neurotensin and xenin, acetyl-neurotensin and xenin-8-Gln, were fused together to create Ac-NT/XN-8-Gln. Following assessment of enzymatic stability, effects of Ac-NT/XN-8-Gln on in vitro β-cell function were studied. Subchronic antidiabetic efficacy of Ac-NT/XN-8-Gln alone, and in combination with the clinically approved GLP-1 receptor agonist exendin-4, was assessed in high-fat fed (HFF) mice. Ac-NT/XN-8-Gln was highly resistant to plasma enzyme degradation and induced dose-dependent insulin-releasing actions (P<0.05 to P<0.01) in BRIN-BD11 β-cells and isolated mouse islets. Ac-NT/XN-8-Gln augmented (P<0.001) the insulinotropic actions of GIP, while possessing independent β-cell proliferative (P<0.001) and anti-apoptotic (P<0.01) actions. Twice daily treatment of HFF mice with Ac-NT/XN-8-Gln for 32 days improved glycaemic control and circulating insulin, with benefits significantly enhanced by combined exendin-4 treatment. This was reflected by reduced body fat mass (P<0.001), improved circulating lipid profile (P<0.01) and reduced HbA1c concentrations (P<0.01) in the combined treatment group. Following an oral glucose challenge, glucose levels were markedly decreased (P<0.05) only in combination treatment group and superior to exendin-4 alone, with similar observations made in response to glucose plus GIP injection. The combined treatment group also presented with improved insulin sensitivity, decreased pancreatic insulin content as well as increased islet and β-cell areas. These data reveal that Ac-NT/XN-8-Gln is a biologically active neurotensin/xenin fusion peptide that displays prominent antidiabetic efficacy when administered together with exendin-4.     

Anorectic effect of fenfluramine, cholecystokinin and neurotensin in genetically obese (ob/ob) mice

To investigate the satiety defect of hyperphagic genetically obese (ob/ob) mice, acute feeding responses to three differently acting anorectic agents were determined in 7-9 weeks old lean (+/+) and ob/ob mice habituated to a restricted (0900-1230 hr) daily feeding routine. Fenfluramine (10 mg/kg), cholecystokinin (100 U/kg) and neurotensin (500 micrograms/kg), administered intraperitoneally 15 min before feeding, each produced a rapid but transient suppression of food consumption in ob/ob mice, similar to lean controls. The results suggest that neural satiety mechanisms triggered via serotoninergic pathways (fenfluramine), vagal afferents (cholecystokinin) and the hypothalamic paraventricular nucleus (neurotensin) are functional in ob/ob mice, supporting the view that the satiety defect of ob/ob mice resides outside of the nervous system.     

Hyperketonaemia markedly modulates the metabolic activation of chemical carcinogens

Male Wistar albino rats were rendered hyperketonaemic by oral administration of medium chain triacylglycerols or by a single intraperitoneal injection of the diabetogenic agent streptozotocin. Hepatic post-mitochondrial preparations from these animals were employed as activation systems in the Ames mutagenicity test. Activation systems from both groups of hyperketonaemic rats were more efficient than those of control rats in metabolically converting the precarcinogens Glu-P-1, Trp-P-1, Trp-P-2, N-nitrosopiperidine and N-nitrosopyrrolidine to mutagens. In contrast, when 2-aminofluorene was used as the precarcinogen, the preparations from the hyperketonaemic animals were less efficient than controls in activating this carcinogen. In all cases, the preparations from streptozotocin-treated rats displayed a more pronounced effect than those from triacylglycerol-treated rats, possibly reflecting the greater extent of hyperketonaemia in the former group. It is concluded that hyperketonaemia modulates the bioactivation of chemical carcinogens.     

Inference of chromosomal inversion dynamics from Pool‐Seq data in natural and laboratory populations of Drosophila melanogaster

Sequencing of pools of individuals (Pool‐Seq) represents a reliable and cost‐effective approach for estimating genome‐wide SNP and transposable element insertion frequencies. However, Pool‐Seq does not provide direct information on haplotypes so that, for example, obtaining inversion frequencies has not been possible until now. Here, we have developed a new set of diagnostic marker SNPs for seven cosmopolitan inversions in Drosophila melanogaster that can be used to infer inversion frequencies from Pool‐Seq data. We applied our novel marker set to Pool‐Seq data from an experimental evolution study and from North American and Australian latitudinal clines. In the experimental evolution data, we find evidence that positive selection has driven the frequencies of In(3R)C and In(3R)Mo to increase over time. In the clinal data, we confirm the existence of frequency clines for In(2L)t, In(3L)P and In(3R)Payne in both North America and Australia and detect a previously unknown latitudinal cline for In(3R)Mo in North America. The inversion markers developed here provide a versatile and robust tool for characterizing inversion frequencies and their dynamics in Pool‐Seq data from diverse D. melanogaster populations.     

Winter weather affects asp viper Vipera aspis population dynamics through susceptible juveniles

Detailed studies on mammals and birds have shown that the effects of climate variation on population dynamics often depend on population composition, because weather affects different subsets of a population differently. It is presently unknown whether this is also true for ectothermic animals such as reptiles. Here we show such an interaction between weather and demography for an ectothermic vertebrate by examining patterns of survival and reproduction in six populations of a threatened European snake, the asp viper ( Vipera aspis ), over six to 17 years. Survival was lowest among juvenile and highest among adult snakes. The estimated annual probability for females to become gravid ranged from 26% to 60%, and was independent of whether females had reproduced in the year before or not. Variation in juvenile survival was strongly affected by winter temperature, whereas adult survival was unaffected by winter harshness. A matrix population model showed that winter weather affected population dynamics predominantly through variation in juvenile survival, although the sensitivity of the population growth rate to juvenile survival was lower than to adult survival. This study on ectothermic vipers revealed very similar patterns to those found in long-lived endothermic birds and mammals. Our results thus show that climate and life history can interact in similar ways across biologically very different vertebrate species, and suggest that these patterns may be very general.