A genetic linkage map for Arctic char (Salvelinus alpinus): evidence for higher recombination rates and segregation distortion in hybrid versus pure strain mapping parents.

We constructed a genetic linkage map for Arctic char (Salvelinus alpinus) using two backcrosses between genetically divergent strains. Forty-six linkage groups (expected = 39-41) and 19 homeologous affinities (expected = 25) were identified using 184 microsatellites, 129 amplified fragment length polymorphisms (AFLPs), 13 type I gene markers, and one phenotypic marker, SEX. Twenty-six markers remain unlinked. Female map distance (9.92 Morgans) was substantially higher than male map distance (3.90 Morgans) based on the most complete parental information (i.e., the F1 hybrids). Female recombination rates were often significantly higher than those of males across all pairwise comparisons within homologous chromosomal segments (average female to male ratios within families was 1.69:1). The female hybrid parent had significantly higher recombination rates than the pure strain female parent. Segregation distortion was detected in four linkage groups (4, 8, 13, 20) for both families. In family 3, only the largest fish were sampled for genotyping, suggesting that segregation distortion may represent regions possessing influences on growth. In family 2, almost all cases showing segregation distortion involved markers in the female hybrid parent.     

Aminopeptidase N1 (EtAPN1), an M1 Metalloprotease of the Apicomplexan Parasite Eimeria tenella,Participates in Parasite Development

Aminopeptidases N are metalloproteases of the M1 family that have been reported in numerous apicomplexan parasites, including Plasmodium, Toxoplasma, Cryptosporidium, and Eimeria. While investigating the potency of aminopeptidases as therapeutic targets against coccidiosis, one of the most important avian diseases caused by the genus Eimeria, we identified and characterized Eimeria tenella aminopeptidase N1 (EtAPN1). Its inhibition by bestatin and amastatin, as well as its reactivation by divalent ions, is typical of zinc-dependent metalloproteases. EtAPN1 shared a similar sequence, three-dimensional structure, and substrate specificity and similar kinetic parameters with A-M1 from Plasmodium falciparum (PfA-M1), a validated target in the treatment of malaria. EtAPN1 is synthesized as a 120-kDa precursor and cleaved into 96-, 68-, and 38-kDa forms during sporulation. Further, immunolocalization assays revealed that, similar to PfA-M1, EtAPN1 is present during the intracellular life cycle stages in both the parasite cytoplasm and the parasite nucleus. The present results support the hypothesis of a conserved role between the two aminopeptidases, and we suggest that EtAPN1 might be a valuable target for anticoccidiosis drugs.     

Changes in the chemistry of sedimentary organic matter within the Coorong over space and time

Like many other coastal systems across the world, the Coorong lagoonal ecosystem (South Australia) has degraded over the last 100 years; in this case as a result of extensive regulation and diversions of water across the Murray-Darling Basin following European settlement. To evaluate whether the sources of organic matter (OM) supporting its food-web have changed since the inception of water management and barrage construction, sedimentary OM was characterised in cores spanning the Coorong’s salinity gradient at depths representative of the last 100 years over which the management alterations to river and estuarine flow were most marked. Detailed ²¹⁰Pb, ¹³⁷Cs and Pu dating in conjunction with palaeolimnological data (Pinus pollen) allowed for the reconstruction of the timing of substantial changes observed in the composition of the OM, most of which occur during the early 1950s, concurrent with management-related variations in water flow and salinity. Negative shifts in δ¹³C of up to 8.3‰ in the 2–10 and <2 μm fractions after the 1950s suggest a pronounced alteration in biogeochemical cycling or in the origin of OM. Elemental ratios and δ¹³C values of potential sources are inconclusive as to the cause of these biogeochemical changes. However, ¹³C-NMR spectra of the sediments suggest that degraded phytoplankton constitutes a large proportion of today’s OM and also reveal that an OM source rich in lignin was present prior to the 1950s. The high δ¹³C (?18.3‰) and low C/N (7.5) signatures of the lignin-bearing sediments are inconsistent with a C3 terrestrial OM source and instead suggest that the lignin-bearing seagrass Ruppia megacarpa (δ¹³C of ?13‰) contributed to a large degree to the sediment of the North Lagoon. R. megacarpa once was abundant in the North Lagoon but today has all but vanished from the system. Thus, only through a combination of isotopic and spectroscopic techniques was it possible to effectively decipher the changes in the composition of OM deposited throughout the Coorong over space and time. These results have important implications for research in estuarine OM dynamics in other geographic locations. Specifically, utilising complementary analytical techniques may sometimes be essential in reliably determining OM sources and processes in estuaries and lagoons.     

Climate Versus In-Lake Processes as Controls on the Development of Community Structure in a Low-Arctic Lake (South-West Greenland)

The dominant processes determining biological structure in lakes at millennial timescales are complex. In this study, we used a multi-proxy approach to determine the relative importance of in-lake versus indirect processes on the Holocene development of an oligotrophic lake in SW Greenland (66.99°N, 50.97°W). A ¹⁴C and ²¹⁰Pb-dated sediment core covering approximately 8500 years BP was analyzed for organic–inorganic carbon content, pigments, diatoms, chironomids, cladocerans, and stable isotopes (δ¹³C, δ¹⁸O). Relationships among the different proxies and a number of independent controlling variables (Holocene temperature, an isotope-inferred cooling period, and immigration of Betula nana into the catchment) were explored using redundancy analysis (RDA) independent of time. The main ecological trajectories in the lake biota were captured by ordination first axis sample scores (18–32% variance explained). The importance of the arrival of Betula (ca. 6500 years BP) into the catchment was indicated by a series of partial-constrained ordinations, uniquely explaining 12–17% of the variance in chironomids and up to 9% in pigments. Climate influences on lake biota were strongest during a short-lived cooling period (identified by altered stable isotopes) early in the development of the lake when all proxies changed rapidly, although only chironomids had a unique component (8% in a partial-RDA) explained by the cooling event. Holocene climate explained less variance than either catchment changes or biotic relationships. The sediment record at this site indicates the importance of catchment factors for lake development, the complexity of community trends even in relatively simple systems (invertebrates are the top predators in the lake) and the challenges of deriving palaeoclimate inferences from sediment records in low-Arctic freshwater lakes.