The Mutation Process in Colored Coalescent Theory

The mutation process is introduced into the colored coalescent theory. The mutation process can be viewed as an independent Poisson process running on the colored genealogical random tree generated by the colored coalescent process, with the edge lengths of the random tree serving as the time scale for the mutation process. Moving backward along the colored genealogical tree, the color of vertices may change in two ways, when two vertices coalesce, or when a mutation happens. The rule that governs the coalescent change of color involves a parameter x; the rule that governs the mutation involves a parameter μ. Explicit computations of the expectation of the coalescent time (the first hitting time), and the coalescent probabilities (the first hitting probabilities) are carried out. For example, our calculation shows that when x=1/2, for a sample of n colored individuals, the expected time for the colored coalescent process with the mutation process superimposed to first reach a black MRCA or a white MRCA, respectively, is 3−2/n with probability 1/2 for any value of the parameter μ. On the other hand, the expected time for the colored coalescent process with mutation to first reach a MRCA, either black or white, is 2−2/n for any values of the parameters μ and x, which is the same as that for the standard Kingman coalescent process.     

The First Peopling of South America: New Evidence from Y-Chromosome Haplogroup Q

Recent progress in the phylogenetic resolution of the Y-chromosome phylogeny permits the male demographic dynamics and migratory events that occurred in Central and Southern America after the initial human spread into the Americas to be investigated at the regional level. To delve further into this issue, we examined more than 400 Native American Y chromosomes (collected in the region ranging from Mexico to South America) belonging to haplogroup Q – virtually the only branch of the Y phylogeny observed in modern-day Amerindians of Central and South America – together with 27 from Mongolia and Kamchatka. Two main founding lineages, Q1a3a1a-M3 and {"type":"entrez-protein","attrs":{"text":"Q1a3a1","term_id":"123949938","term_text":"Q1A3A1"}}Q1a3a1-L54(xM3), were detected along with novel sub-clades of younger age and more restricted geographic distributions. The first was also observed in Far East Asia while no {"type":"entrez-protein","attrs":{"text":"Q1a3a1","term_id":"123949938","term_text":"Q1A3A1"}}Q1a3a1-L54(xM3) Y chromosome was found in Asia except the southern Siberian-specific sub-clade Q1a3a1c-L330. Our data not only confirm a southern Siberian origin of ancestral populations that gave rise to Paleo-Indians and the differentiation of both Native American Q founding lineages in Beringia, but support their concomitant arrival in Mesoamerica, where Mexico acted as recipient for the first wave of migration, followed by a rapid southward migration, along the Pacific coast, into the Andean region. Although Q1a3a1a-M3 and {"type":"entrez-protein","attrs":{"text":"Q1a3a1","term_id":"123949938","term_text":"Q1A3A1"}}Q1a3a1-L54(xM3) display overlapping general distributions, they show different patterns of evolution in the Mexican plateau and the Andean area, which can be explained by local differentiations due to demographic events triggered by the introduction of agriculture and associated with the flourishing of the Great Empires.     

A New Type of Rhythmic Plant Movement: Mocronutation

A low amplitude oscillatory movement, distinct from the nutationalmovements occuring in the same plant, has been found to occurin seedling plants of runner bean. The frequency of the oscillationis between two and five cycles per hour, and appears to havea temperature coefficient of 2.24 in the range 15–25°C.The theoretical implication of this oscillation on the ‘geotropichunting’ theory of nutation is discussed.     

A New Case of Consensual Decision: Collective Movement in Earthworms

Collective movements are reported for many species from microorganisms to humans. But except for a few soil‐inhabiting species, intra‐specific interactions in soil are poorly studied. Some intra‐specific interactions occur in earthworms. Most of them are negative, concerning parameters like the rate of survival, maturation, food ingestion or growth. Virtually nothing is known about collective movement in earthworms that represent the dominant biomass of the soil. This study, the first one on annelids, highlights a consensual decision phenomenon based only on contact between followers. Using an olfactometer set‐up and modelling, we show that earthworms Eisenia fetida influence each other to select a common direction during their migration. Experiments in a binary choice test showed that contacts between individuals are responsible for collective movement. This coordination in movement could allow earthworms to benefit from forming clusters. The resulting local higher densities, enhancing individual survival and favouring the cooperation, may be at the origin of Allee effects reported for these species.     

New observations on Erioderma in North America

For the three species of Erioderma occurring in North America ( E . mollissimum (Samp.) Du Rietz, E. pedicellatum (Hue) P. M. Jørg. and E. sorediatun D. Gall. & P. M. Jørg), considerable range extensions are being reported together with ecological information that will help to understand the distribution of these lichens. Erioderma sorediatum has been recently discovered in North America by Sherwood and Pike (unpubl.), while E. mollissimum and E. pedicellatum are reported as new to Nova Scotia herein along with a number of new localities for the latter species in Newfoundland. Ongoing work on E. pedicellatum and its symbionts has been summarized and an attempt has been made to outline its possible postglacial history. It is postulated that the presently known ranges have been occupied by the lichen only within the past few thousand years (more recently in Europe than in North America), and that considerable migrations must have taken place prior to that. This is NRCC publication No. 20463.     

正畸牙移动中的潜在新角色:牙周膜肌成纤维细胞

肌成纤维细胞(myofibroblasts,MFb)是一种具有出色的应力敏感性和基质合成功能的细胞,在纤维性疾病和瘢痕挛缩中发挥重要作用。在口腔医学领域,MFb同样存在于牙周膜中,且在牙移动过程中显著增多并可能发挥一定作用。现对MFb的特征、功能及分化来源进行介绍,并在此基础上综述肌成纤维细胞发挥功能的生物学基础和应力刺激下可能影响其分化形成的相关信号通路及串话,分析MFb在传递正畸力、促进牙周组织改建中的潜在作用及牙移动过程中可能影响牙周膜肌成纤维细胞分化形成的机制,以期为探索牙周膜肌成纤维细胞的功能、研究正畸牙移动提供新思路。