Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

Background  

Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact.     

Benzene and the risk of non-Hodgkin lymphoma: A review and meta-analysis of the literature

Benzene, an accepted leukemogen, has been suggested to cause other hemato- and lymphopoietic cancers. Here we review the published literature for non-Hodgkin lymphoma (NHL) and occupational exposure to benzene. Six cohorts, sixteen case–control studies and two studies of other designs were identified through keyword searches of bibliographic databases. Twenty-two of twenty-four studies found no association between NHL and ever exposed to benzene compared to never; a random-effects meta-analysis gave a pooled risk estimate of 1.11 (95% confidence interval 0.94–1.30). Our finding of no effect agrees with one of two previous meta-analyses. The other meta-analysis examined if high benzene exposure increased NHL risk but a lack of consistent exposure categories within the same metric should have precluded pooling risks by exposure level. Instead, we reviewed whether dose–response relationships existed. The best available data came from six studies where exposure was estimated from historical measurements and on the whole, no trends in risks of NHL with rising cumulative, average, peak, or duration of benzene exposure were found. NHL is a heterogeneous group of malignancies and although less well-studied, benzene was not associated with any NHL subtype. In conclusion, benzene at either low or high doses does not increase the risk of NHL.     

New records for prehistoric introduction of Neotropical mammals to the West Indies: evidence from Carriacou,Lesser Antilles

Aim This paper investigates the prehistoric introduction of five mammalian taxa to Carriacou (Lesser Antilles) and refines the known anthropogenic ranges for these fauna in the pre‐Columbian West Indies. The importance of such records for understanding the region’s historical biogeography and ecology is considered. Location Carriacou Island, Grenada (12°28′ N, 61°26′ W). Methods Zooarchaeological assemblages from Carriacou’s earliest documented prehistoric sites, Grand Bay and Sabazan, were analysed, and exotic taxa were identified and quantified. The timing of introductions was established based on multiple radiocarbon assays, including three new accelerator mass spectrometry (AMS) direct dates obtained on the bone of exotic taxa. Source species and location(s) are considered and compared with known prehistoric records for the Caribbean to synthesize anthropogenic distributions for the pre‐Columbian period. The contexts of the zooarchaeological remains are evaluated to better understand the nature and purpose of introductions. Results Zooarchaeological investigation on Carriacou reveals the occurrence of multiple mammal introductions from South American between c. ad 700 and ad 1400. This paper presents the first records for guinea pig (Cavia sp.), armadillo (Dasypus sp.), peccary (Tayassu/Pecari sp.), opossum (Didelphis sp.) and agouti (Dasyprocta sp.) from the island. Human‐mediated transport of these taxa is indicated by their absence from the record prior to human settlement of Carriacou. Several translocated species are either rare or entirely unknown for the region, and overall West Indian distributions are temporally and spatially discontinuous. Archaeological contexts indicate that mammalian introductions arose from human subsistence needs, but other social factors may have shaped the dispersal of these fauna. Main conclusions The taxonomic combination and richness of Carriacou’s introduced fauna are unusual within the region. Importantly, the new records significantly improve the known pre‐Columbian geographic range for peccary, guinea pig and armadillo. Integrated with regional records, these data augment our understanding of the Caribbean’s historical biogeography, and have the potential to improve our understanding of human mobility and anthropogenic environmental impacts in the West Indies prior to the arrival of Europeans.     

Statistical methods for model comparison in parameter estimation problems for distributed systems

In this note we outline some recent results on the development of a statistical testing methodology for inverse problems involving partial differential equation models. Applications to several problems from biology are presented. The statistical tests, which are in the spirit of analysis of variance (ANOVA), are based on asymptotic distributional results for estimators and residuals in a least squares approach.Research supported in part under grants NSF MCS 8504316, NASA NAG-1-517, and AFOSRF-49620-86-C-0111. Part of this research was carried out while the first author was a visiting scientist at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA, which is operated under NASA contracts NASI-18107 and NASI-18605     

Differential expression of TGF beta isoforms in murine palatogenesis

We have studied the expression of genes encoding transforming growth factors (TGFs) beta 1, beta 2 and beta 3 during development of the secondary palate in the mouse from 11.5 to 15.5 days postcoitum using in situ hybridisation. The RNA detected at the earliest developmental stage is TGF beta 3, which is localised in the epithelial component of the vertical palatal shelf. This expression continues in the horizontal palatal shelf, predominantly in the medial edge epithelium, and is lost as the epithelial seam disrupts, soon after palatal shelf fusion. TGF beta 1 RNA is expressed with the same epithelial pattern as TGF beta 3, but is not detectable until the horizontal palatal shelf stage. TGF beta 2 RNA is localised to the palatal mesenchyme underlying the medial edge epithelia in the horizontal shelves and in the early postfusion palate. The temporal and spatial distribution of TGF beta 1, beta 2 and beta 3 RNAs in the developing palate, together with a knowledge of in vitro TGF beta biological activities, suggests an important role for TGF beta isoforms in this developmental process.     

Tegumental glucose permeability in male and female Schistosoma mansoni

Tegumental hexose transporters have been kinetically characterized in mated and separated male and female Schistosoma mansoni 8-12 wk postinfection. Significant gender-specific differences in Km and Vmax were observed. In mated males, the estimated constants (mean +/- SE) were: Km = 0.63 +/- 0.31 mM, Vmax = 0.93 +/- 0.44 nmol/mg worm water/min, and the Kd = 0.25 +/- 0.09 microliter/mg worm water/min. In mated females the kinetics were: Km = 0.99 +/- 0.40 mM, Vmax = 1.22 +/- 0.42 nmol/mg worm water/min, and Kd = 0.60 +/- 0.14 microliter/mg worm water/min. The influx of 2-deoxy-D-glucose and 3-O-methylglucose has been similarly characterized; these analogs share the same glucose transporter in male and female schistosomes. 2-Deoxy-D-glucose has a higher affinity, and 3-O-methylglucose a lower affinity, than does glucose. Because mated male schistosomes supply glucose to female partners, similarities between the free glucose concentration of the male and the affinity of the transporter determined for mated female schistosomes suggest that male-to-female transfer may be a potentially rate-limiting step in glucose utilization by the female. Permeability x surface are (PS) products and Vmax/Km ratios were significantly elevated in mated schistosomes, suggesting that the transporter is primarily localized to the dorsal surface of the male. Gender- and mating-specific analyses of PS products indicate that tegumental permeability to glucose is significantly increased in mated schistosomes, and compares very favorably to that of the host liver.