超声彩色血流成像的计算机快速仿真方法

研究超声彩色血流成像的快速仿真方法,克服原先仿真方法非常耗时的缺点。方法超声彩色血流成像计算机仿真中,血流信号是对成像区间内所有点散射体的回波信号累加而得到的。通过引入新的等效散射体模型,可以大大降低散射体的密度,从而减少计算回波信号所需时间。在计算机上用Matlab编程来进行仿真实验,对以往仿真方法和基于等效散射体模型方法的性能进行比较。结果实验表明:基于等效散射体模型的仿真,在保证相同流速精度的前提下,仿真速度比传统方法提高了10倍以上。结论基于等效散射体模型的仿真方法能极大地提高超声彩色血流成像的仿真速度,可以为超声彩色血流成像的方法研究提供便利。     

No sympatric speciation here: multiple data sources show that the ant Myrmica microrubra is not a separate species but an alternate reproductive morph of Myrmica rubra

No aspect of speciation is as controversial as the view that new species can evolve sympatrically, among populations in close physical contact. Social parasitism has been suggested to yield necessary disruptive selection for sympatric speciation. Recently, mitochondrial DNA phylogeography has shown that the ant Myrmica microrubra is closely related to its host, Myrmica rubra, leading to the suggestion that sympatric speciation has occurred. We investigated the relationships between the two ant forms using mitochondrial and nuclear DNA sequences, microsatellite genotyping and morphometrics. Molecular phylogenetic and population structure analyses showed that M. microrubra does not evolve separately to its host but rather shares a gene pool with it. Probability analysis showed that mitochondrial DNA data previously adduced in favour of sympatric speciation do not in fact do so. Morphometrically, M. microrubra is most readily interpreted as a miniature queen form of M. rubra, not a separate species. Myrmica microrubra is not an example of speciation. The large (typical M. rubra) and small (M. microrubra) queen forms are alternative reproductive strategies of the same species. Myrmica microrubraSeifert 1993 is consequently synonymized here with M. rubra Linnaeus, 1758.     

Dispersal and rapid evolution in brown trout colonizing virgin Subantarctic ecosystems

Two brown trout Salmo trutta stocks of different origin (wild Polish, domestic commercial) came into secondary contact after deliberate releases conducted in virgin rivers systems of the Subantarctic Kerguelen Islands (70 degrees E 49 degrees S). Samples obtained in 2001-2003 and a historical sample from 1993 were analysed for genetic variation at seven microsatellite loci and one allozyme locus (LDH-C1*). Bayesian clustering analysis demonstrated that rapid genetic differentiation formed separate genetic units in neighbouring rivers in less than 20 years. These genetic units were characterized by a large proportion of Polish genotypes mixed with some genomes of domestic origin (up to 30%). A different colonization strategy of the naturalized stocks, likely related with differential performance, was identified as a cause of rapid population differentiation in this area.     

The impacts of flow on chemical communication strategies and fight dynamics of crayfish

Signal transmission is influenced by the physics of an environment. Consequently, a physical effect on sensory signals can influence how animals send or sample sensory information. Habitat-specific physics may constrain or enhance signal transmission (e.g. sound transmission in a flowing river versus a still pond) and provide a mechanism for the evolution of sensory biases. This study investigated how the transmission of chemically mediated social signals in crayfish is influenced by two different aquatic environments. Agonistic bouts between crayfish were performed under lotic (flowing water) and lentic (nonflowing, still water) conditions. When crayfish (Orconectes rusticus) collected from a lotic system (river) interacted under lotic conditions, we noted that dominant O. rusticus spent more time upstream than subordinate O. rusticus. Orconectes rusticus positioned themselves randomly and spent equal amounts of time with respect to upstream and downstream in the nonflowing environment. We tested another species, Orconectes virilis, collected from a nonflowing environment (lake) and they showed no positional preference when tested in flow. Additionally, both O. rusticus and O. virilis took longer to reach high fight intensities under flow conditions. It was possible to visualize O. rusticus urine release, and they released urine more often when upstream of an opponent in a flow environment during these agonistic bouts. These results suggest that O. rusticus collected from lotic environments release urine to maximize the transmission of chemical cues to a fight opponent. It appears that crayfish may adapt their signalling processes based upon their long-term ambient environments.     

Stable genetic polymorphism in heterogeneous environments: balance between asymmetrical dispersal and selection in the acorn barnacle

Elucidating the processes responsible for maintaining polymorphism at ecologically relevant genes is intimately related to understanding the interplay between selection imposed by habitat heterogeneity and a species' capacity for dispersal in the face of environmental constraints. In this paper, we used a model-based approach to solve equilibria of balanced polymorphism, given values of fitness and larval dispersal among different habitats in the acorn barnacle Semibalanus balanoides from the Gulf of St Lawrence. Our results showed that allele frequencies observed at both MPI* and GPI* loci represented stable equilibria, given empirical estimates of fitness values, and that considerably more larvae dispersed from one region (north) to the other (south) than vice versa. Dispersal conditions were predicted to be similar for the maintenance of polymorphism at both loci. Moreover, the values of asymmetrical dispersal required by the model to reach stable equilibria were compatible with empirical estimates of larval dispersal and oceanic circulation documented in this system. Overall, this study illustrated the usefulness of a modified and computable version of Bulmer's model (1972) in order to test hypotheses of balanced polymorphism resulting from interactions between spatial selection and asymmetrical dispersal.     

Genetic identification of immigrants to the Scandinavian wolf population

Continued gene flow is fundamental to the survival of small, isolated populations. However, geography and human intervention can often act contrary to this requirement. The Scandinavian wolf population is threatened with a loss of genetic variation yet limited in the accessibility to new immigrants by the geographical distance of this peninsular population from its nearest neighbouring population and by human reluctance to allow wolves in the northern reindeer-breeding areas. In this study, we describe the identification of immigrants into this population using autosomal microsatellites, and maternally inherited mtDNA. Samples of 14 wolves collected in the “dispersal corridor” in northern Sweden in 2002–2005 were compared with 185 resident Scandinavian wolves and 79 wolves from the neighbouring Finnish population. We identified four immigrant wolves, suggesting some westward migration, although only one of these is likely to still survive. The integration of such immigrants into the breeding population is necessary to assure the long-term survival of this isolated and inbred population and highlights the importance of genetics techniques to the management of threatened populations.     

Significant patterns of population genetic structure and limited gene flow in a threatened macropodid marsupial despite continuous habitat in southeast Queensland, Australia

Many endangered species worldwide are found in remnant populations, often within fragmented landscapes. However, when possible, an understanding of the natural extent of population structure and dispersal behaviour of threatened species would assist in their conservation and management. The brush-tailed rock-wallaby (Petrogale penicillata), a once abundant and widespread rock-wallaby species across southeastern Australia, has become nearly extinct across much of the southern part of its range. However, the northern part of the species’ range still sustains many small colonies closely distributed across suitable habitat, providing a rare opportunity to investigate the natural population dynamics of a listed threatened species. We used 12 microsatellite markers to investigate genetic diversity, population structure and gene flow among brush-tailed rock-wallaby colonies within and among two valley regions with continuous habitat in southeast Queensland. We documented high and significant levels of population genetic structure between rock-wallaby colonies embedded in continuous escarpment habitat and forest. We found a strong and significant pattern of isolation-by-distance among colonies indicating restricted gene flow over a small geographic scale ( <10 km) and conclude that gene flow is more likely limited by intrinsic factors rather than environmental factors. In addition, we provide evidence that genetic diversity was significantly lower in colonies located in a more isolated valley region compared to colonies located in a valley region surrounded by continuous habitat. These findings shed light on the processes that have resulted in the endangered status of rock-wallaby species in Australia and they have strong implications for the conservation and management of both the remaining ‘connected’8 brush-tailed rock-wallaby colonies in the northern parts of the species’8 range and the remnant endangered populations in the south.     

Mutual reproductive dependence of distylic Cordia leucocephala (Cordiaceae) and oligolectic Ceblurgus longipalpis (Halictidae, Rophitinae) in the Caatinga

Background and Aims

The close relationship between distylic Cordia leucocephala and the bee Ceblurgus longipalpis, both endemic to the Caatinga, north-east Brazil, was investigated, emphasizing reproductive dependence, morphological adaptations of the partners, and pollen flow.

Methods

In the municipality of Pedra, in the Caatinga of Pernambuco, the breeding system and reproductive success of C. leucocephala, its interaction with flower visitors and inter- and intramorph pollen flow were determined.

Key Results

The bee Ceblurgus longipalpis, the unique flower visitor and effective pollinator of self-incompatible Cordia leucocephala, presents morphological features adapted to exploit hidden pollen and nectar in the long and narrow corolla tubes. Pollen of low-level anthers is collected with hairs on prolonged mouthparts and pollen of high-level anthers with clypeus, mandibles, and labrum, showing pollen removal from both levels with the same effectiveness. In both morphs, this results in similar legitimate, i.e. intermorph cross-pollen flow. Illegitimate pollen flow to stigmas of pin flowers, however, was much higher than to stigmas of thrum flowers. Moreover, more illegitimate pollen was transported to stigmas of pin and less to those of thrum flowers when compared with legitimate pollen flow.

Conclusions

The study reveals a one-to-one reproductive inter-dependence between both partners. Data indicate that this relationship between bee species and plant species is one of the rare cases of monolecty among bees. Monotypic Ceblurgus longipalpis, the only rophitine species of Brazil, evolved prolonged mouthparts rare among short-tongued bees that enable them to access pollen from flowers with short-level anthers hidden for bees of other species, and nectar at the base of the flower tube.     

塔玛亚历山大藻遗传多样性的微卫星分析

应用12个微卫星标记对9株来自欧洲和中国等不同海域的塔玛亚历山大藻(Alexandrium tamarense)进行了遗传多样性分析,探讨了不同地理藻株之间的遗传分化程度和基因流水平,分析了我国沿海塔玛亚历山大藻的遗传多样性。结果表明：9株塔玛亚历山大藻共检测出26个等位基因,其中9个位点具有多态性,多态比率75%。有效等位基因数1.3243～3.2667,平均为1.8774。塔玛亚历山大藻种内基因多样性为0.3630。9株塔玛亚历山大藻大致可以分为3个进化支,进化支与藻株的地理位置相关联。其中,中国海域的塔玛亚历山大藻至少可分为2个进化支。不同地理分布的塔玛亚历山大藻的遗传分化水平较高,达0.7522。种群间的基因流估算水平较低,提示3个种群间可能不存在基因交流。     

Does character displacement initiate speciation? Evidence of reduced gene flow between populations experiencing divergent selection

Character displacement – trait evolution stemming from selection to lessen resource competition or reproductive interactions between species – has long been regarded as important in finalizing speciation. By contrast, its role in initiating speciation has received less attention. Yet because selection for character displacement should act only where species co‐occur, individuals in sympatry will experience a different pattern of selection than conspecifics in allopatry. Such divergent selection might favour reduced gene flow between conspecific populations that have undergone character displacement and those that have not, thereby potentially triggering speciation. Here, we explore these ideas empirically by focusing on spadefoot toads, Spea multiplicata, which have undergone character displacement, and for which character displacement appears to cause post‐mating isolation between populations that are in sympatry with a heterospecific and those that are in allopatry. Using mitochondrial sequence data and nuclear microsatellite genotypes, we specifically asked whether gene flow is reduced between populations in different selective environments relative to that between populations in the same selective environment. We found a slight, but statistically significant, reduction in gene flow between selective environments, suggesting that reproductive isolation, and potentially ecological speciation, might indeed evolve as an indirect consequence of character displacement. Generally, character displacement may play a largely underappreciated role in instigating speciation.