Pushing north one bottleneck at a time: site frequency spectra tell the history of Sitka spruce

Reconstructing the history of populations is a longstanding goal of molecular ecologists. In addition to a better understanding of the past, it is hoped that this knowledge would also facilitate predictions regarding species’ responses to future events such as climate change. The traditional way of doing this is through the fossil record, but these historical records are often incomplete. Inferring historical demography from patterns of nucleotide variability can help to fill these gaps. In this issue of Molecular Ecology, Holliday et al. (2010) glimpse into the demographic past of Sitka spruce, Picea sitchensis, an economically and ecologically important species native to northwestern United States and Canada, by examining the site frequency spectrum (SFS) of 153 loci in six populations covering the species entire range.     

The genetics of adaptation to novel environments: selection on germination timing in Arabidopsis thaliana

When studying selection during adaptation to novel environments, researchers have often paid little attention to an organism’s earliest developmental stages. Despite this lack of attention, early life history traits may be under strong selection during colonization, as the expression of adaptive phenotypes at later points is contingent upon early survival. Moreover, the timing of early developmental transitions can constrain the timing of later transitions, with potentially large effects on fitness. In this issue, Huang et al. (2010) underscore the importance of early life history traits in the adaptation of Arabidopsis thaliana to old‐field sites in North America. Using a new population of mapped recombinant inbred lines, the authors examined germination timing and total lifetime fitness of A. thaliana while varying site latitude, dispersal season, and maternal photoperiod. Huang et al. (2010) discovered several Quantitative Trait Loci (QTL) with large effects on fitness that colocalized with QTL for field germination timing and seed dormancy—demonstrating that fitness is genetically associated with these early life history traits, and that these loci are likely under strong selection during adaptation to novel environments. In the epistatic interactions of some loci, recombinant genotypes outperformed parental genotypes, supporting the potentially adaptive role of recombination. This study provides elegant evidence that traits expressed early in an organism’s development can play an important role during adaptive evolution.     

Incursion and range expansion in the bluetongue vector Culicoides imicola in the Mediterranean basin: a phylogeographic analysis

Abstract.  The bluetongue (BT) vector Culicoides imicola Kieffer (Diptera: Ceratopogonidae) has undergone widespread range expansion across most of the Mediterranean basin, concomitant with the largest BT epizootic outbreaks on record. Knowledge of the substructure of this vector expansion would be useful for identifying specific source−expansion systems. To this end we analysed the haplotype diversity of the mitochondrial cytochrome oxidase I gene in 273 C. imicola from 88 Mediterranean sites and outgroups. All the C. imicola haplotypes ( n  = 26) formed a single, distinct clade in comparison with haplotypes of four other species of the Imicola group from southern Africa, confirming C.   imicola as a single phylospecies. Haplotype distribution showed extreme differentiation across the Mediterranean basin, with four common haplotypes each predominating in different areas. Eastern and western areas characterized by distinct BT incursions accounted for most of the molecular variance in haplotype composition. Shared common haplotypes identified one area of incursion and expansion encompassing the western half of the Mediterranean basin, with evidence of population growth, and another system encompassing Anatolian Turkey, the Aegean Islands and mainland Greece. A third area of range expansion was identified in the central Mediterranean, with a possible source in Algeria and unsampled parts of central North Africa. We conclude that the expansion of C.   imicola in the Mediterranean basin consists of at least three incursions followed by expansions and that the western system experiences conditions promoting high population growth.     

Carbon Source and Micronutrient Requirements of the Aquatic Phycomycete, Catenaria anguillulae Sorokin

The requirements of the aquatic Phycomycete, Catenaria anguillulaewere analysed in liquid, shake cultures using a standardizedzoospore inoculum. Growth was determined by measuring mycelialdry weight and rate of production of titratable acid. D-glucose was the best carbon source and had an optimum concentrationof 166 mM of carbon for the medium used. When other carbon sourceswere supplied, only those related to glucose (fructose and mannose)or composed of glucose units with an alpha-linkage (maltose,glycogen, and starch) were readily utilized. Lactic acid wasdetermined qualitatively as an end-product of carbon metabolism. The optimum level of phosphate was 1.0 mM. The optimum concentrationof EDTA was 0.032 mM. Of the chelated cations included in themedium only the omission of iron, zinc, calcium, or magnesiumreduced growth. Concentrations of calcium below 0.4 mM and ofmagnesium below 0.2 mM were limiting; whereas, concentrationsof both ions up to 1 mM were non-toxic.