棕色田鼠性别决定研究进展

哺乳动物性别决定方式属于雄性异配型性别决定, 依赖于Y染色体, SRY基因是性别决定中最重要的基因。文章报道了棕色田鼠指名亚种有Y染色体, 但是Y染色体上没有SRY基因, 性别决定不依赖于SRY基因, 排除了R-spondin 1基因是性别决定基因, 同时讨论了棕色田鼠指名亚种SRY基因缺失后可能的性别决定 机制。     

长苞铁杉种群个体年龄与胸径的多维时间序列模型研究

 利用多维时间序列分析方法,建立长苞铁杉(Tsuga longibracteata)种群胸径生长的多维时间序列模型,即Yt=1.7870785Yt-1-0.8950167Yt-2+0.4509997Ut-0.8036035Ut-1+0.3950577Ut-2,其中Yt、Yt-1、Yt-2分别为t年、t-5年、t-10年长苞铁杉胸径值(cm),Ut、Ut-1、Ut-2分别为t年、t-5年、t-10年长苞铁杉种群个体年龄（a）,模型相关系数为0.9998。以年轮确定种群个体年龄法与多维时间序列模型相结合,建立能     

Biostratigraphy of the Pleistocene Fossiliferous Deposits of the Southern Brazilian Coastal Area

Fossils of Pleistocene mammals have been discovered in the southern Brazilian coastal area since the late XIX century, in two main places: the continental shelf and the Chuí Creek. Although the taxonomic composition of fossil assemblages from these areas has been the focus of most studies during the late XX century, research concerning the ages, stratigraphic position, and biostratigraphy of such assemblages remains scarce. This is due to the lack of suitable materials for age determination and the reworked nature of the fossiliferous deposits in the continental shelf. Only in recent years have new data shed light on these subjects. Taxonomic revisions, ESR ages, and biostratigraphic correlations confirm a late Pleistocene age for the fossil assemblages, although those from the shelf represent a significant time averaging, while fossils from the Chuí Creek exhibit a narrower age range. The fossil mammals found in southern Brazil represent a mixture of Brazilian and Pampean taxa, including forms that disappeared much earlier from the Argentinean pampas. Gaining an understanding of the biostratigraphic context of such assemblages in comparison to similar assemblages from Argentina and Uruguay, in conjunction with stratigraphic, geomorphological, and paleoclimatic data should provide additional tools with which to reconstruct the environmental and climatic dynamics of this portion of South America during the late Pleistocene—early Holocene and its effects on the fauna, and possibly to help address the problem of the disappearance of megamammals in the area.     

Historical biogeography of Drosophila simulans based on Y-chromosomal sequences

Y-chromosomal sequences have been used for phylogeographic studies in humans and other mammals, but so far have been ignored as a source of historical information in Drosophila and other insects with X/Y sex determination. Here, we present the first phylogeographic study of Drosophila simulans based on the Y chromosome. Geographic distribution of Y-chromosomal haplotypes suggests a high degree of population subdivision within Africa, as well as between the African and cosmopolitan groups of populations. Consistent with earlier studies based on autosomal and X-linked loci, our results suggest that D. simulans originated in Madagascar or East Africa, and that the South and West African populations of this species are derived.     

Age determination of the African buffalo, Syncerus caffer Sparrman

Age criteria for the African buffalo are described. These are based on the tooth eruption sequence and on wear of the first molar. Assignment of absolute ages to the tooth eruption and wear classes has been made by reference to known-age animals and to numbers of cementum lines in tooth sections. For ageing animals to the nearest year, the normal degree of accuracy of the methods is assumed to be about ± 1/2year (1–5 years of age); about ± 1 year (5–15 years of age); and about ±2 years (15-20years of age). A field method of age determination is presented based on horn characteristics and relative body size.     

EYE LENS WEIGHT AND AGE IN AFRICAN ELEPHANTS

Eye lens dry-weights have been determined for 543 African elephants from three populations in East Africa. When plotted against estimated ages based on tooth replacement and wear criteria they indicate growth curves with rapid initial growth in lens weight, succeeded by a phase of rectilinear growth which apparently persists throughout life.
Parameters for the regressions of lens dry weight on age have been calculated by sex and locality. Confidence limits are fitted and no significant difference in the growth rates can be demonstrated, except for a sex difference in the values for the α intercept.
Variability at age is slightly greater in males than females, but is little greater than i3 indicated by studies on other species using known-age animals. This is taken to confirm the accuracy of the age criteria adopted and leads to conclusions on their precision.
It is suggested that this method might provide an objective check on the accuracy and precision of age estimates in other species.     

Foetal age determination and development in elephants

Elephants have the longest pregnancy of all mammals, with an average gestation of around 660 days, so their embryonic and foetal development have always been of special interest. Hitherto, it has only been possible to estimate foetal ages from theoretical calculations based on foetal mass. The recent development of sophisticated ultrasound procedures for elephants has now made it possible to monitor the growth and development of foetuses of known gestational age conceived in captivity from natural matings or artificial insemination. We have studied the early stages of pregnancy in 10 captive Asian and 9 African elephants by transrectal ultrasound. Measurements of foetal crown-rump lengths have provided the first accurate growth curves, which differ significantly from the previous theoretical estimates based on the cube root of foetal mass. We have used these to age 22 African elephant foetuses collected during culling operations. Pregnancy can be first recognized ultrasonographically by day 50, the presumptive yolk sac by about day 75 and the zonary placenta by about day 85. The trunk is first recognizable by days 85-90 and is distinct by day 104, while the first heartbeats are evident from around day 80. By combining ultrasonography and morphology, we have been able to produce the first reliable criteria for estimating gestational age and ontological development of Asian and African elephant foetuses during the first third of gestation.     

Bloodlines: mammals,leeches, and conservation in southern Asia

Southern Asia is a biodiversity hotspot both for terrestrial mammals and for leeches. Many small-mammal groups are under-studied in this region, while other mammals are of known conservation concern. In addition to standard methods for surveying mammals, it has recently been demonstrated that residual bloodmeals within leeches can be sequenced to find mammals in a given area. While these invertebrate-parasite-derived DNA (iDNA) methods are promising, most of the leech species utilized for this type of survey remain unevaluated, notwithstanding that their diversity varies substantially. Here we examine approximately 750 individual leech specimens in the genus Haemadipsa across a large range in southern Asia (Bangladesh, Cambodia, and China), specifically reviewing the diversity of mammals they feed on and their own genetic structuring. Leeches were found to feed on a considerable variety of mammals, corroborating prior studies. Additionally, leeches were found to have fed both on bats and on birds, neither of which has previously been recorded with this method. The genetic structuring of the leeches themselves revealed 15 distinct clades of which only two precisely corresponded to previously characterized species, indicating that much work is needed to finalize classifications in this genus. Most importantly, with regards to mammal conservation, leeches in these clades appear to feed on a broad range of mammals.     

Test of histological methods of determining chronology of accentuated striae in deciduous teeth

One of the difficulties that has prevented Wilson bands, internal defects of enamel growth, from achieving maximum usefulness as indicators of stress in bioarchaeological studies is the inaccuracy of the methods for determining ages of defect occurrence. This study tests a technique that uses microstructural growth markers of enamel to establish the chronology of Wilson bands in deciduous teeth. A sample of 274 teeth from 127 subadults from an Imperial Roman necropolis was sectioned and examined under a microscope. The sample ranged in age at death from birth to 13 years. Sixty-four teeth from 50 individuals were found to have 447 Wilson bands in total. Of those contributing multiple teeth to the sample, 13 individuals had at least one Wilson band in each of two teeth that could be identified as having been formed coevally. These provided the basis for testing the methodology. Paired t-tests found no significant differences between the chronologies of matched pairs in the two teeth, with mean ages from each differing by less than 1 day. The authors propose a hypothesis that explains the development of Wilson bands, and classifies them within the context of other features of enamel. The most important implications arising from this paper are: 1) aging methods using microstructural growth markers can be applied to deciduous teeth; 2) physiological stressors leave different traces in enamel, depending on severity and time of occurrence relative to total crown development; 3) no threshold level exists; all physiological stress will leave a record; 4) therefore, no minimal definition of a Wilson band can be delineated that recognizes all such events; 5) implying that studies using them will only identify minimum rates of occurrence.     

Using otolith weight to age fish

The problem of determining and verifying ages of fish, from populations having a considerable variation in size at age, has been investigated using the relationship between otolith size and fish size, which has been shown by several authors to be influenced by growth rate. In such a population of Sardinella aurita Val. an index of age can be obtained for individual fish by calculating the equivalent otolith weight at a particular fish length, using the otolith weight–fish length relationship determined for each age group. This statistic not only permits a much greater proportion of fish to be assigned ages than is possible with otolith reading alone, but also enables the age groups to be verified as year classes. However, it is concluded that, although appropriate models based on otolith-fish size relationships can predict age for groups of fish in which growth rates are known or can be assumed to be consistent, such techniques have a limited application in ageing fish from wild populations with highly variable growth rates.     

Use of the frontal bone in age determination of Labeo horie (Pisces,Cyprinidae) in Jebel Aulia Reservoir,Sudan

In spite of the exuberance of recent approaches to age determination of fish, many ecologists are convinced that the most valid method is age reading from permanent marks or growth rings laid on skeletal parts. Of the known structures used, only the vertebrae are suitable and readable for a large variety of species and sizes. Examination of different skeletal structures of Labeo horie, a Cyprinid collected from Jebel Aulia reservoir, revealed that the frontal bone carried well-defined growth rings. The validity of these rings was checked against other direct and indirect methods of age determination. Results proved to be statistically valid, and the frontal bone offers an additional device of age determination of L. horie.     

Brief communication: Comparison of methods for estimating chronological age at linear enamel formation on anterior dentition

Linear enamel hypoplasia (LEH) is an enamel defect that records the effects of physiological stress on tooth formation. Estimating the age at which LEH defects form is integral to the reconstruction of population health in bioarcheological studies. Two principal methods for aging LEH defects have been introduced in the literature. The conventional approach employs regression equations based on a linear model of tooth growth. The newer, Reid and Dean [Am J Phys Anthropol 113 (2000) 135-139] approach, is based upon a histologically derived curvilinear model of enamel development and therefore likely provides more accurate age estimates. However, the extent to which the Reid and Dean method produces estimated ages at defect formation differing from those of the regression equations has not, until now, been determined. This study quantifies the differences between these two methods. Evaluating the degree to which these methods differ is essential for interpreting the accuracy of LEH age estimates given in previous bioarcheological studies. Age estimates of LEH defects on 338 anterior teeth from the Hamann-Todd osteological sample were calculated using both methods. The resulting estimated ages were compared through a randomized block ANOVA. However, the mean differences between the estimated ages yielded by both methods range from 4 months or less depending on the tooth type with an overall average of 2.63 months. The discussion focuses on the degree to which this difference affects answers to bioarcheological questions.     

Termites, Large Herbivores, and Herbaceous Plant Dominance Structure Small Mammal Communities in Savannahs

Large herbivores and termites are important functional groups in African savannahs. Both groups affect small mammals, which are also important determinants for savannah structure and function. Because vegetation on Macrotermes mounds are preferentially grazed by large herbivores, and mounds represent resource-rich distinct habitat patches for small mammals in relatively resource-poor savannahs, termite mounds are ideal sites for studies of how grazing by large mammals and productivity affect communities of small mammals. We conducted an experiment in Lake Mburo National Park, Uganda, with four treatments: large vegetated Macrotermes mounds (with and without large herbivores) and adjacent savannah areas (with and without large herbivores). We replicated the treatment blocks nine times and trapped small mammals regularly over a period of almost 2 years. Small mammal species assemblages differed considerably between mounds and savannah areas. Grazing had a substantial effect on small mammal species assemblages in the resource-poor savannah, but not in the relatively resource-rich termitaria. Small mammal species abundance, biomass, and richness were higher on termite mounds than adjacent savannah areas. Excluding large herbivores caused a major increase in species abundance, biomass, and richness both on savannah and termitaria. Herbaceous plant species evenness was an important determinant of the small mammal community. Small mammal biomass increased with high plant dominance, indicating that a few dominant plant species are important for biomass production of small mammals. Small mammal diversity was not related to any of the treatments, but increased with plant species evenness as well as richness. Fencing increased species dominance in the small mammal community on both savannah and termitaria, probably because competitive patterns shift from inter-guild (that is, between large and small mammals) to intra-guild (that is, between small mammals) when large mammals are excluded. The study highlights the complex interactions among large herbivores, termites, herbaceous plants, and small mammals in African savannahs. When studying the structure and function of small mammal communities it is therefore important to consider several coexisting functional groups.     

A fine line: a comparison of methods for estimating ages of linear enamel hypoplasia formation

It is accepted that linear enamel hypoplasias (LEHs), a specific type of enamel thickness deficiency, are related to periodic physiological disruptions to enamel matrix secretion during times that teeth are developing. Thus, LEHs are treated as general indicators of metabolic stress. Because the disruptions that cause LEHs affect only the portion of the crown that is in the process of forming, determining their locations allows researchers to reconstruct chronologies of stressful events. It is widely held that the many of the commonly used macroscopic methods for estimating the timing of LEHs are imprecise and do not conform to our current understanding of the process of enamel formation. The goal of the present study is to compare estimated ages of LEH formation produced by two of the most commonly used macroscopic methods to those derived from data in recent histological studies that include more precise information about the timing of crown formation across diverse human populations. These approaches are compared in two ways: 1) by creating a theoretical model using simulated LEHs and 2) empirically, by analyzing data collected on a sample of ancient Nubians from Semna South (present-day Sudan). Results indicate that the approach derived from histological studies provides significantly higher age estimates than the commonly used methods and this difference is particularly marked in early forming LEHs. The magnitude of this difference is large enough to produce divergent interpretation of bioarchaeological datasets and suggests that reevaluation of the methods used to estimate ages of LEH formation may be justified.     

Estimating age and growth in long‐lived temperate freshwater crayfish using lipofuscin

1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method.
2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short‐lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer‐lived, temperate species, the signal crayfish, Pacifastacus leniusculus .
3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P. leniusculus from several known year‐classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age ( r² = 92.4%) and produced much more accurate age estimates than conventional body size‐based procedures.
4. A model derived from the crayfish of known‐age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin‐estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P. leniusculus to approximately 16 years.
5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish, with probable further potential both within and outside the Crustacea.     

Segmented Bayesian calibration approach for estimating age in forensic science

Forensic age estimation is receiving growing attention from researchers in the last few years. Accurate estimates of age are needed both for identifying real age in individuals without any identity document and assessing it for human remains. The methods applied in such context are mostly based on radiological analysis of some anatomical districts and entail the use of a regression model. However, estimating chronological age by regression models leads to overestimated ages in younger subjects and underestimated ages in older ones. We introduced a full Bayesian calibration method combined with a segmented function for age estimation that relied on a Normal distribution as a density model to mitigate this bias. In this way, we were also able to model the decreasing growth rate in juveniles. We compared our new Bayesian‐segmented model with other existing approaches. The proposed method helped producing more robust and precise forecasts of age than compared models while exhibited comparable accuracy in terms of forecasting measures. Our method seemed to overcome the estimation bias also when applied to a real data set of South‐African juvenile subjects.     

Comparable ages for the independent origins of electrogenesis in African and South American weakly electric fishes

One of the most remarkable examples of convergent evolution among vertebrates is illustrated by the independent origins of an active electric sense in South American and African weakly electric fishes, the Gymnotiformes and Mormyroidea, respectively. These groups independently evolved similar complex systems for object localization and communication via the generation and reception of weak electric fields. While good estimates of divergence times are critical to understanding the temporal context for the evolution and diversification of these two groups, their respective ages have been difficult to estimate due to the absence of an informative fossil record, use of strict molecular clock models in previous studies, and/or incomplete taxonomic sampling. Here, we examine the timing of the origins of the Gymnotiformes and the Mormyroidea using complete mitogenome sequences and a parametric bayesian method for divergence time reconstruction. Under two different fossil-based calibration methods, we estimated similar ages for the independent origins of the Mormyroidea and Gymnotiformes. Our absolute estimates for the origins of these groups either slightly postdate, or just predate, the final separation of Africa and South America by continental drift. The most recent common ancestor of the Mormyroidea and Gymnotiformes was found to be a non-electrogenic basal teleost living more than 85 millions years earlier. For both electric fish lineages, we also estimated similar intervals (16-19 or 22-26 million years, depending on calibration method) between the appearance of electroreception and the origin of myogenic electric organs, providing rough upper estimates for the time periods during which these complex electric organs evolved de novo from skeletal muscle precursors. The fact that the Gymnotiformes and Mormyroidea are of similar age enhances the comparative value of the weakly electric fish system for investigating pathways to evolutionary novelty, as well as the influences of key innovations in communication on the process of species radiation.     

The applicability of metapopulation theory to large mammals

Metapopulation theory has become a common framework in conservation biology and it is sometimes suggested that a metapopulation approach should be used for management of large mammals. However, it has also been suggested that metapopulation theory would not be applicable to species with long generations compared to those with short ones. In this paper, we review how and on what empirical ground metapopulation terminology has been applied to insects, small mammals and large mammals. The review showed that the metapopulation term sometimes was used for population networks which only fulfilled the broadest possible definition of a metapopulation, i.e. they were subpopulations connected by migrating individuals. We argue that the metapopulation concept should be reserved for networks that also show some kind of metapopulation dynamics. Otherwise it applies to almost all populations and loses its substance. We found much empirical support for metapopulation dynamics in both insects and small mammals, but not in large mammals. A possible reason is the methods used to confirm the existence of metapopulation dynamics. For insects and small mammals, the common approach is to study population turnover through patch occupancy data. Such data is difficult to obtain for large mammals, since longer temporal scales need to be covered to record extinctions and colonizations. Still, many populations of large mammals are exposed to habitat fragmentation and the resulting subpopulations sometimes have high risks of extinction. If there is migration between the subpopulations, the metapopulation framework could provide valuable information on their population dynamics. We suggest that a metapopulation approach can be interesting for populations of large mammals, when there are discrete breeding subpopulations and when these subpopulations have different growth rates and demographic fates. Thus, a comparison of the subpopulations’ demographic fates, rather than subpopulation turnover, can be a feasible alternative for studies of metapopulation dynamics in large mammals.     

Proteomic analysis of glycosylation: structural determination of N- and O-linked glycans by mass spectrometry

This review summarizes the methods, mainly based on mass spectrometry, for the structural determination of N- and O-linked carbohydrates that are post-translationally attached to a large number of proteins and which play a key role in determining the function and biophysical properties of these compounds. Analysis of these carbohydrates has proved difficult in the past due to their structural complexity. However, modern analytical methods such as mass spectrometry have the ability to elucidate most structural details at the concentration levels required for proteomics. This review describes methods for direct examination of glycoproteins by mass spectrometry, the release of N- and O-linked glycans from glycoproteins separated in sodium dodecyl sulfate polyacrylamide electrophoresis gels, and the analysis of these compounds by techniques such as matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. Matrix-assisted laser desorption/ionization mass spectrometry provides the most rapid method for comparing glycan profiles and is probably most appropriate for clinical studies. One of the most promising techniques for determining the structures of N-glycans in proteomic studies is negative ion fragmentation of electrosprayed ions. This technique combines high throughput with ease of structural interpretation and provides structural details that are difficult to obtain by classical methods.