Heritability and genetic correlation of abdominal versus caudal vertebral number in the medaka (Actinopterygii: Adrianichthyidae): genetic constraints on evolution of axial patterning?

Variation in the number of abdominal vs. caudal vertebrae is an important source of morphological diversification of fish. It is not clear, however, whether abdominal and caudal regions evolve independently. Regressions of offspring on parents demonstrated substantial additive genetic variation within populations, i.e. heritability, in both abdominal and caudal vertebral numbers of the medaka ( Oryzias latipes ). However, the heritability of caudal vertebrae tended to be smaller than that of abdominal vertebrae in some estimations, suggesting that abdominal and caudal regions are controlled by separate developmental modules. Furthermore, genetic correlation between abdominal and caudal vertebral numbers, estimated using full-sib family means, was negative but weak, supporting independent evolution. In addition, substantial genetic differentiation among populations was demonstrated in abdominal vertebral numbers, but not in caudal numbers. These results support our view that Jordan's rule, a geographical tendency for fish from higher latitudes to have more vertebrae, in this fish reflects local adaptations of abdominal vertebral numbers. In contrast, the low heritability of caudal vertebrae may reflect the intrinsic invariability of genes associated with a change in caudal vertebral numbers. This genetic constraint may have restricted morphological diversification of not only the medaka, but also the Order Beloniformes as a whole.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 867–874.     

记中国首次发现的"真古兽类" (eupantotherian)化石

记述了在中国首次发现的采自辽宁黑山县八道壕矿区早白垩世晚期沙海组的一件“eu- pantotherian”(“真古兽类”)下颌骨化石。标本保存了最后两个前臼齿和4个臼齿,它以抬高的下颌角突,半臼齿化的最后一枚前臼齿,臼齿上面积增大但未发育成完整盆形的跟座,尚未形成的facet-5,及加长的最后臼齿等特点有别于所有已知的“eupantotherian”和具有雏形磨楔式臼齿的Kielantherium,被命名为一新属新种,Mozomus shikamai gen.et sp.nov.(鹿间明镇古兽),并由它而创建了一新科,Mozomuridae fam.nov. “Eupantotherian”是早期哺乳动物演化中的一个重要环节,是从无跟座的对齿兽(sym- metrodont)到具有磨楔式(tribosphenic)臼齿兽类的中间类型。早期兽类进化的成功模式是发育成具有磨楔式的臼齿,即在上臼齿上发育出原尖,而下臼齿的跟座形成由3个齿尖围成的盆状。这种结构扩大了牙齿的面积,使咀嚼切割能力更趋完善,今天的有袋类和真兽类均是如此。但在哺乳动物系统发育史上,“eupantotherian”类的化石发现不多,这给探讨具有磨楔式臼齿构造的两大门类(后兽类和真兽类)的起源带来不少困难和疑惑。而传统上的真古兽类形态分异又很大,并不是一个单系类群。其中有跟座发育较好者,如peramurans有可能更接近具有磨楔式臼齿兽类的基部位置,本文记述的Mozomus shikamai也应属于这一类型。具有雏形的被认为处于基干上的磨楔式臼齿类化石,迄今只有两种,即发现在英国早白垩世地层中的滨齿兽(Aegialodon)和蒙古早白垩世晚期Hoobor层的Kielantherium,前者仅有一颗下臼齿,后者由一枚下臼齿和一具有4颗臼齿的下牙床为代表。两种化石在分类上被归入单一的滨齿兽目(Order Aegialodontia Butler,1978),视为Boreosphenidans的基干(stem)。本文记述的Mozomus,其时代与Kielantherium的大体相当,在大小、齿式及臼齿形态上与后者也多有相近之处,但前者以其臼齿的facet-5尚未出现和跟盆发育不全等特点表明它较Kielantherium更为原始,不具备磨楔式臼齿的模式,因之不能归人Aegialodontia,而只能纳入”eupantotheri- ans”。但在后一类的组合中,Mozomus以它半臼齿化的最后前臼齿和面积增大但未发育成盆形的跟座等特点,又是组合中相当进步的类型。无论如何Mozomus的发现是在为数极少的向磨楔式臼齿模式进化的中间环节上增添了一件重要的化石标本,也增加了不少新的信息。它必会引起学者对这一进化过程的更加深入的反思和新的启示。     

Genetic Regulation of Melanocyte Differentiation

Melanocytes originate from the neural crest in vertebrates and migrate to the body surface where they differentiate into functional cells. Genes involved in melanocyte differentiation can be classified into two groups. One of them consists of the functional genes that control proteins specific to the function of the melanocyte. As the representative gene of this category, albino (c) locus in the mouse is considered to control tyrosinase, the key enzyme in melanogenesis. cDNA for mouse tyrosinase has been cloned and sequenced. The cDNA can be used to detect tyrosinase mRNA synthesized during melanocyte differentiation. On the other hand, genes such as brown (b) or pink-eyed dilution (p) have been assumed to control melanosome proteins. The other category consists of genes that regulate the expression of these functional genes directly or indirectly. In the mouse, so-called white-spotting genes and genes of the agouti series are considered to fall into this category. Based on the fact that mutations at the white-spotting loci result in the absence of melanocytes in a particular area of skin, it is assumed that some of these loci control the factors that promote either differentiation or migration of melanoblasts and are candidates for the classic regulator genes Genes at the agouti (a) locus in the mouse determine the type of melanin synthesized in hair follicle melanocytes, that is eumelanin or pheomelanin. An interesting feature of this locus is that the site of gene action is not within the melanocytes but in the cells surrounding them. The results of our study indicate that the gene product of the a-locus interacts with α-MSH at the α-MSH receptor site, regulates the cellular cAMP level via a signal transduction system and, in turn, determines the type of melanin synthesized in the cells.     

Distinct geographical structure across species units evidenced by chloroplast DNA haplotypes and nuclear ribosomal ITS genotypes of Corylopsis (Hamamelidaceae) in the Japanese islands

The geographical distribution of chloroplast DNA (cpDNA) haplotypes and nuclear ribosomal internal transcribed spacer (nrITS) genotypes of Japanese Corylopsis (Hamamelidaceae), which consists of four species, was investigated. Two hundred and five individuals belonging to four species from 30 populations, covering the entire geographical range, were studied. Based on approximately 1108 bp of the three non-coding regions of cpDNA, nine haplotypes were detected, and each was distinguished from adjacent haplotypes by one substitution. Based on approximately 507-bp nrITS sequences, 47 genotypes were detected, for which three clades were identified in the phylogenetic analysis. There was inconsistency between the cpDNA haplotypes, nrITS genotypes, and classification of Corylopsis taxa, possibly because of incomplete lineage sorting or introgressive hybridization. The distribution of the haplotypes was highly structured geographically, and N _ST (0.893) was significantly greater than G _ST (0.819), implying that the current distribution of Corylopsis species was structured phylogeographically during Quaternary climatic oscillations. The haplotype composition and results of analysis of molecular variance showed that the populations in Hokuriku were highly divergent, suggesting that they are long-term persistent populations arising from refugia during the Quaternary climatic oscillations. Refugial populations in Chugoku and Shikoku may have lost genetic diversity because of a bottleneck resulting from a small population size, followed by post-glacial range expansion. Pre-existing refugia may have been so small that the subsequent range expansion replaced the pre-existing genetic structure.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 501–518.     

A new species of Stegodon (Mammalia,Proboscidea) from the Kazusa Group (lower Pleistocene), Hachioji City,Tokyo, Japan and its evolutionary morphodynamics

Abstract: Stegodon protoaurorae sp. nov. (Proboscidea) from the lower Pleistocene Terada Formation of the Kazusa Group in Japan is proposed as a new species based on characteristic features of plate formula, molar size, tooth enamel and plate frequency, and is described herein. The specimen of the new species was transported by autumn storms and buried. The new species fills an evolutionary gap between S. miensis and S. aurorae. Speciation in the lineage from S. miensis through S. protoaurorae to S. aurorae is inferred to have been caused by reduction of terrestrial space during marine transgression. The biostratigraphic distribution of S. protoaurorae suggests intercalation of a new S. protoaurorae Zone between the S. miensis Zone and the S. aurorae Zone. The S. protoaurorae Zone can be defined in the Nakatsu Group and the Terada Formation of the Kazusa Group, and can be assigned an age of 2.9–2.1 Ma.     

Evolutionary trade-offs between thermal tolerance and locomotor and developmental performance in drosophilid flies

Cold-tolerant ectothermal animals are generally absent from warmer regions, suggesting that the acquisition of cold tolerance is associated with the loss of adaptation to warmer environments. In the present study, we compared thermal tolerance, walking speed (WS) and pupal development (PD) for 28 drosophilid species from cool-temperate, warm-temperate, and subtropical regions by the phylogenetically-based method and the conventional regression to understand trade-offs between these traits. A significant negative relationship was observed between cold tolerance and the rate of PD in both sexes and between cold tolerance and WS in the male in the phylogenetically-based analysis. Similar results were obtained in the conventional regression analysis, although the level of significance somewhat differed. Thus, cold tolerant species are assumed to have lost abilities to develop and walk fast. Subsequently, they may become more vulnerable to predators, parasitoids or infectious microorganisms and may have become extinct in warmer regions through enemy-mediated interactions and/or resource competition with cold susceptible species with faster development and quicker locomotion. In the present study, no significant relationship was observed between heat tolerance and WS or the rate of PD in the phylogenetically-based analysis, although heat tolerance was significantly related with the rate of PD in the conventional regression analysis. Thus, trade-offs associated with heat tolerance were not apparent.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 375–380.     

The land–atmosphere water flux in the tropics

Tropical vegetation is a major source of global land surface evapotranspiration, and can thus play a major role in global hydrological cycles and global atmospheric circulation. Accurate prediction of tropical evapotranspiration is critical to our understanding of these processes under changing climate. We examined the controls on evapotranspiration in tropical vegetation at 21 pan-tropical eddy covariance sites, conducted a comprehensive and systematic evaluation of 13 evapotranspiration models at these sites, and assessed the ability to scale up model estimates of evapotranspiration for the test region of Amazonia. Net radiation was the strongest determinant of evapotranspiration (mean evaporative fraction was 0.72) and explained 87% of the variance in monthly evapotranspiration across the sites. Vapor pressure deficit was the strongest residual predictor (14%), followed by normalized difference vegetation index (9%), precipitation (6%) and wind speed (4%). The radiation-based evapotranspiration models performed best overall for three reasons: (1) the vegetation was largely decoupled from atmospheric turbulent transfer (calculated from Ω decoupling factor), especially at the wetter sites; (2) the resistance-based models were hindered by difficulty in consistently characterizing canopy (and stomatal) resistance in the highly diverse vegetation; (3) the temperature-based models inadequately captured the variability in tropical evapotranspiration. We evaluated the potential to predict regional evapotranspiration for one test region: Amazonia. We estimated an Amazonia-wide evapotranspiration of 1370 mm yr⁻¹, but this value is dependent on assumptions about energy balance closure for the tropical eddy covariance sites; a lower value (1096 mm yr⁻¹) is considered in discussion on the use of flux data to validate and interpolate models.