Transmission ratio distortion in Arabidopsis lyrata: effects of population divergence and the S-locus

We investigated transmission ratio distortion within an Icelandic population of Arabidopsis lyrata using 16 molecular markers unlinked to the S-locus. Transmission ratio distortion was found more often than expected by chance at the gametic level, but not at the genotypic or zygotic level. The gametic effect may be due to meiotic drive or selection acting postmeiotically. At the gametic level, 10.9% of the tests were significant, which is substantially lower than earlier observed in an interpopulation cross (allowing for differences in power)-suggesting that the high level of transmission ratio distortion in the interpopulation cross is due to population divergence. It is also substantially lower than previously observed in intrapopulation crosses at the self-incompatibility locus, suggesting inherent fitness differences of the self-incompatibility alleles. We discuss the possible role of deleterious alleles accumulating at loci under balancing selection. Zygotic effects play a larger role in the interpopulation cross than in the intrapopulation crosses suggesting that Dobzhansky-Muller incompatibilities may be accumulating between the widely diverged populations.     

The ice cover on small and large lakes: scaling analysis and mathematical modelling

Lake ice cover is described by its thickness, temperature, stratigraphy and overlying snow layer. When the ratio of ice thickness to lake size is above ～10^?5, the ice cover is stable; otherwise, mechanical forcing breaks the ice cover, and ice drifting takes place with lead-opening and ridging. This transition enables a convenient distinction to be made between small and large lakes. The evolution of the ice cover on small lakes is solved by a wholly thermodynamic model, but a coupled mechanical–thermodynamic model is needed for large lakes. The latter indicates a wide distribution of ice thickness, and frazil ice may be formed in openings. Ecological conditions in large lakes differ markedly from those in small lakes because vertical mixing and oxygen renewal may take place during the ice season, and the euphotic zone penetrates well into the water column in thin ice regions. Mesoscale sea ice models are applicable to large lakes with only minor tuning of the key parameters. These model systems are presented and analysed using Lake Peipsi as an example. As the climate changes, the transition size between small and large lake ice cover will change.     

When fecundity does not equal fitness: evidence of an offspring quantity versus quality trade-off in pre-industrial humans

Maternal fitness should be maximized by the optimal division of reproductive investment between offspring number and offspring quality. While evidence for this is abundant in many taxa, there have been fewer tests in mammals, and in particular, humans. We used a dataset of humans spanning three generations from pre-industrial Finland to test how increases in maternal fecundity affect offspring quality and maternal fitness in contrasting socio-economic conditions. For 'resource-poor' landless families, but not 'resource-rich' landowning families, maternal fitness returns diminished with increased maternal fecundity. This was because the average offspring contribution to maternal fitness declined with increased maternal fecundity for landless but not landowning families. This decline was due to reduced offspring recruitment with increased maternal fecundity. However, in landowning families, recruited offspring fecundity increased with increased maternal fecundity. This suggests that despite decreased offspring recruitment, maternal fitness is not reduced in favourable socio-economic conditions due to an increase in subsequent offspring fecundity. These results provide evidence consistent with an offspring quantity-quality trade-off in the lifetime reproduction of humans from poor socio-economic conditions. The results also highlight the importance of measuring offspring quality across their whole lifespan to estimate reliably the fitness consequences of increased maternal fecundity.     

Quantitative-Trait-Locus Analysis of Body-Mass Index and of Stature, by Combined Analysis of Genome Scans of Five Finnish Study Groups

In recent years, many genomewide screens have been performed, to identify novel loci predisposing to various complex diseases. Often, only a portion of the collected clinical data from the study subjects is used in the actual analysis of the trait, and much of the phenotypic data is ignored. With proper consent, these data could subsequently be used in studies of common quantitative traits influencing human biology, and such a reanalysis method would be further justified by the nonbiased ascertainment of study individuals. To make our point, we report here a quantitative-trait-locus (QTL) analysis of body-mass index (BMI) and stature (i.e., height), with genotypic data from genome scans of five Finnish study groups. The combined study group was composed of 614 individuals from 247 families. Five study groups were originally ascertained in genetic studies on hypertension, obesity, osteoarthritis, migraine, and familial combined hyperlipidemia. Most of the families are from the Finnish Twin Cohort, which represents a population-wide sample. In each of the five genome scans, approximately 350 evenly spaced markers were genotyped on 22 autosomes. In analyzing the genotype data by a variance-component method, we found, on chromosome 7pter (maximum multipoint LOD score of 2.91), evidence for QTLs affecting stature, and a second locus, with suggestive evidence for linkage to stature, was detected on chromosome 9q (maximum multipoint LOD score of 2.61). Encouragingly, the locus on chromosome 7 is supported by the data reported by Hirschhorn et al. (in this issue), who used a similar method. We found no evidence for QTLs affecting BMI.     

Genetic divergence between the sympatric queen morphs of the ant Myrmica rubra

Pairs of obligate social parasites and their hosts, where some of the parasites have recently diverged from their host through intraspecific social parasitism, provide intriguing systems for studying the modes and processes of speciation. Such speciation, probably in sympatry, has also been propounded in the ant Myrmica rubra and its intraspecific social parasite. In this species, parasitism is associated with queen size dimorphism, and the small microgyne has become a social parasite of the large macrogyne. Here, we investigated the genetic divergence of the host and the parasite queen morphs in 11 localities in southern Finland, using nuclear and mitochondrial markers of queens and workers. We formulated and tested four speciation‐related hypotheses that differed in the degree of genetic divergence between the morphs. The queen morphs were genetically distinct from each other with little hybridization. In the nuclear data, when localities were nested within queen morphs in the hierarchical amova , 39% of the genetic variation was explained by the queen morph (standardized F'_CT = 0.63, uncorrected F_CT = 0.39), whereas 18% was explained by the locality (F'_SC = 0.39, F_SC = 0.29). This result corroborated the hypothesis of advanced sympatric speciation. In contrast, the mitochondrial DNA could not settle between the hierarchical levels of locality and queen morph, thus substantiating equally the hypotheses of incipient and advanced sympatric speciation. Together, our results support the view that the microgynous parasite has genetically diverged from its macrogynous host to the level of a nascent species.     

Chondrogenic differentiation of human bone marrow-derived mesenchymal stromal cells in a three-dimensional environment

Cell therapy combined with biomaterial scaffolds is used to treat cartilage defects. We hypothesized that chondrogenic differentiation bone marrow-derived mesenchymal stem cells (BM-MSCs) in three-dimensional biomaterial scaffolds would initiate cartilaginous matrix deposition and prepare the construct for cartilage regeneration in situ. The chondrogenic capability of human BM-MSCs was first verified in a pellet culture. The BM-MSCs were then either seeded onto a composite scaffold rhCo-PLA combining polylactide and collagen type II (C2) or type III (C3), or commercial collagen type I/III membrane (CG). The BM-MSCs were either cultured in a proliferation medium or chondrogenic culture medium. Adult human chondrocytes (ACs) served as controls. After 3, 14, and 28 days, the constructs were analyzed with quantitative polymerase chain reaction and confocal microscopy and sulfated glycosaminoglycans (GAGs) were measured. The differentiated BM-MSCs entered a hypertrophic state by Day 14 of culture. The ACs showed dedifferentiation with no expression of chondrogenic genes and low amount of GAG. The CG membrane induced the highest expression levels of hypertrophic genes. The two different collagen types in composite scaffolds yielded similar results. Regardless of the biomaterial scaffold, culturing BM-MSCs in chondrogenic differentiation medium resulted in chondrocyte hypertrophy. Thus, caution for cell fate is required when designing cell-biomaterial constructs for cartilage regeneration.     

Oligo-N-acetyllactosaminoglycans bearing Galβ1-4(Fucα1-3)GlcNAc sequences reveal lower affinities than their nonfucosylated,or α(1-2) fucosylated counterparts for immobilized wheat germ agglutinin

Relative affinities of several fucosylated and nonfucosylated oligo-N-acetyllactosaminoglycans for immobilized wheat germ agglutinin (WGA) were studied using a chromatographic technique. (1-3) Fucosylation of theN-acetylglucosamine unit(s) in mono- and biantennary saccharides of the Gal1-4GlcNAc-R type strongly reduced the WGA-affinity. In contrast, (1-2) fucosylation of the nonreducing galactose unit(s) of the saccharides did not reduce the affinity.