Composite interval mapping reveals a major locus influencing embryonic development rate in rainbow trout (Oncorhynchus mykiss)

Little is known about the genetics controlling the rate of embryonic development in salmonids, despite the fact that this trait plays an important role in the life history of wild and cultured stocks. We investigated the genetics of embryonic development rate by performing an analysis of quantitative trait loci (QTL) on two families of androgenetically derived doubled haploid rainbow trout produced from a hybrid of two clonal lines with divergent embryonic development rates. A total of 170 doubled haploid individuals were genotyped at 222 marker loci [219 amplified fragment length polymorphism (AFLP) markers, 2 microsatellites, and p53]. A genetic linkage analysis resulted in a map consisting of 27 linkage groups with 21 of the markers remaining unlinked at a minimum LOD of 3.0 and maximum theta of 0.40. Eight of these linkage groups were matched to published rainbow trout linkage groups. Composite interval mapping (CIM) revealed evidence for two QTL influencing time to hatch, and suggestive evidence for a third. These QTL accounted for a total of 24.6% of the variation in time to hatch. One of these QTL had a large effect on development rate, especially in one family of doubled haploids, in which it explained 25.6% of the variance in time to hatch. QTL influencing embryonic length and weight at the commencement of exogenous feeding were also identified. The QTL with the strongest effect on embryonic length (lenR13) mapped to the same position as the QTL with the strongest effect on time to hatch (tthR13), suggesting a single QTL may have a pleiotropic effect on both these traits. These results suggest that the use of clonal lines with a doubled haploid crossing design is an effective way of analyzing the genetic basis of complex traits in salmonids.     

Complex organization of the mitochondrial genome of petaloid CMS carrot

The petaloid trait in carrot is a mitochondrially associated homeotic-like conversion of stamens into petals which results in cytoplasmic male sterility (cms), but little is understood about the phenomenon at the molecular level. Identification of region(s) of the mitochndrial (mt) genome that are causally implicated in cms may be aided by a physical map of cms-associated mtDNA. The mt genome of petaloid cms carrot is 255 kb in length and contains three pairs of repeated sequences, two in direct orientation and one in inverted orientation. All regions of the genome are present in equal stoichiometries, but the arrangement of the repeated sequences prevented the representation of the entire genome as a single master circle or multiple subgenomes. An alternative model of mtDNA replication that accounts for our data is discussed.     

A temperature-sensitive mutation of Crygs in the murine Opj cataract

In Opj, an inherited cataract in mice, opacity is associated with a mutation in Crygs, the gene for gammaS-crystallin, the first mutation to be associated with this gene. A single base change causes replacement of Phe-9, a key hydrophobic residue in the core of the N-terminal domain, by serine. Despite this highly non-conservative change, mutant protein folds normally at low temperature. However, it exhibits a marked, concentration-dependent decrease in solubility, associated with loss of secondary structure, at close to physiological temperatures. This is reminiscent of processes thought to occur in human senile cataracts in which normal proteins become altered and aggregate. The Opj cataract is progressive and more severe in Opj/Opj than in Opj/+. Lens histology shows that whereas fiber cell morphology in Opj/+ mice is essentially normal, in Opj/Opj, cortical fiber cell morphology and the loss of maturing fiber cell nuclei are both severely disrupted from early stages. This may indicate a loss of function of gammaS-crystallin which would be consistent with ideas that members of the betagamma-crystallin superfamily may have roles associated with maintenance of cytoarchitecture.     

Genotypic effects of fertilization on seedling sweetgum biomass allocation,N uptake,and N use efficiency

Screening and selecting tree genotypes that are responsive to N additions and that have high nutrient use efficiencies can provide better genetic material for short-rotation plantation establishment. A pot experiment was conducted to test the hypotheses that (1) sweetgum ( Liquidambar styraciflua L.) families have different patterns in biomass production and allocation, N uptake, and N use efficiency (NUE), because of their differences in growth strategies, and (2) sweetgum families that are more responsive to N additions will also have greater nutrient use efficiencies. Seedlings from two half-sib families (F10022 and F10023) that were known to have contrasting responses to fertility and other stress treatments were used for an experiment with two levels of N (0 vs. 100 kg N/ha equivalent) and two levels of P (0 vs. 50 kg P/ha equivalent) in a split-plot design. Sweetgum seedlings responded to N and P treatments rapidly, with increases in both size and biomass production, and those responses were greater with F10023 than with F10022. Growth response to N application was particularly strong. N and P application increased the proportional allocation of biomass to leaves. Under increased N supply, P application increased foliar N concentration and content, as well as total N uptake by the seedlings. However, NUE was decreased by N addition and was higher in F10023 than in F10022 when P was not limiting. A better understanding of genotype by fertility interactions is important in selecting genotypes for specific site conditions and for optimizing nutrient use in forestry production.     

Effects of temperature on the development and survival of Nanomia bijuga (Hydrozoa, Siphonophora)

Abstract. The effects of temperature on the development of marine invertebrates have been studied primarily in benthic species. For this study, gametes were collected from Nanomia bijuga , a mesopelagic siphonophore, and were self-crossed. Fertilized eggs kept at 8 and 12°C developed more slowly at the lower temperature. Developing stages were preserved after 2, 4, 6, and 9 days of development for comparative analysis with SEM. Concurrent experiments compared survival. Eggs collected from two additional colonies were placed in four temperature treatments: 4, 8, 12, and 18°C. The young developed normally in all treatments, but survived longer at lower temperatures. Young of N. bijuga will develop to siphonulae possessing tentacles, nematocysts, and a functional gastrozooid without being fed. Nonetheless, it is likely that food constraints, rather than temperature, limited survival in this study.