The extra-limital spread of an invasive species via 'stowaway' dispersal: toad to nowhere?

The mechanisms by which invasive species spread through new areas can influence the spatial scale of their impact. Although previous research has focused on 'natural' dispersal rates following initial introductions, human-aided inadvertent dispersal by 'stowaways' on commercial and domestic transport is thought to be a major contributor to long-distance dispersal. Few data exist to support this assumption. Cane toads Bufo marinus were introduced to north-eastern Australia in 1935, and have since dispersed rapidly through the tropics. Based on information accumulated by community groups in Sydney, 400 km south of the cane toads' current Australian distribution, we document high rates of translocation (at least 50 toads arriving in Sydney per year). Most toads were translocated on commercial truck transport carrying landscaping and building materials from the current range of the cane toads in New South Wales and Queensland, and resulted in highly clumped locations of toad arrival reflecting primary truck transport destinations. Most introductions involved single toads (68 of 102 translocation events), but some introductions involved two to 19 animals. Adults of both sexes were represented equally but juveniles were rarely detected. High rates of translocation of adult toads of both sexes suggest that the eventual distribution of cane toads in Australia may be limited by the animals' bioclimatic tolerances rather than by an inability to reach suitable habitats, even in areas far distant from the toads' current range.     

Stimulation of ammonium ion excretion in the toad urinary bladder by an extract of human urine

It is well known that ammonium ion excretion is increased during metabolic acidosis in mammals. The purpose of this study was to determine whether we could isolate from human urine during metabolic acidosis a factor that would stimulate NH₄⁺ and/or H⁺ excretion in toad urinary bladder. Extracts of urine from six human subjects collected during NH₄Cl-induced acidosis were prepared. These extracts were tested for their effect on NH₄⁺ excretion in hemibladders mounted between plastic chambers. The extracts significantly increased NH₄⁺ excretion in the toad urinary bladder. We found no effect on H⁺ excretion by these extracts. This ammoniuretic activity was not present in the urine when the same individuals were in metabolic alkalosis. We conclude that during metabolic acidosis a humoral factor is present which stimulates the excretion of NH₄⁺. The factor could act as a permease in the bladder cell or as a stimulator of an NH₄⁺ transport system.     

温度对中华大蟾蜍和中华鳖冬眠前离体红细胞免疫功能及其大小的影响

为了探讨温度变化对中华大蟾蜍(Bufo gargarizans)和中华鳖(Trionyx sinensis)离体红细胞免疫功能及细胞大小的影响,我们设计了10℃、20℃、30℃、37℃ 4个温度组,通过红细胞C3b受体花环试验和红细胞免疫复合物花环试验检测红细胞免疫活性,同时测量其红细胞大小.结果表明,温度对中华大蟾蜍离体红细胞C3b受体花环率影响显著,随着温度的升高,中华大蟾蜍离体红细胞C3b受体花环率逐渐降低,在30℃和37℃时,其红细胞C3b受体花环率明显比10℃时低;而温度对其离体红细胞免疫复合物花环率和红细胞大小却没有显著影响.温度对中华鳖离体红细胞C3b受体花环率、免疫复合物花环率及其大小亦没有显著影响.除了10℃时中华鳖离体红细胞免疫复合物花环率与中华大蟾蜍没有明显差别外,其余各温度下中华鳖离体红细胞C3b受体花环率和免疫复合物花环率均明显比中华大蟾蜍的高,而其红细胞的长径和短径却明显比中华大蟾蜍红细胞的小.这说明,温度能明显影响中华大蟾蜍离体红细胞免疫功能,而对中华鳖离体红细胞的免疫活性影响不明显,随着动物进化程度的提高,中华鳖红细胞对温度变化的适应能力和免疫活性比中华大蟾蜍明显增强.     

Comparative multi-locus phylogeography confirms multiple vicariance events in co-distributed rainforest frogs

Though Pleistocene refugia are frequently cited as drivers of species diversification, comparisons of molecular divergence among sister species typically indicate a continuum of divergence times from the Late Miocene, rather than a clear pulse of speciation events at the Last Glacial Maximum. Community-scale inference methods that explicitly test for multiple vicariance events, and account for differences in ancestral effective population size and gene flow, are well suited for detecting heterogeneity of species' responses to past climate fluctuations. We apply this approach to multi-locus sequence data from five co-distributed frog species endemic to the Wet Tropics rainforests of northeast Australia. Our results demonstrate at least two episodes of vicariance owing to climate-driven forest contractions: one in the Early Pleistocene and the other considerably older. Understanding how repeated cycles of rainforest contraction and expansion differentially affected lineage divergence among co-distributed species provides a framework for identifying evolutionary processes that underlie population divergence and speciation.     

Decomposition of Avicennia marina on an iron‐smelting slag substrate

The present study, conducted near Newcastle, Australia, used a blocked analysis of variance experimental design to compare initial nutrient concentrations and decomposition rates of Avicennia marina (grey mangrove) grown on sand and rock blast furnace slag. There were no significant differences ( ANOVA ; P > 0.05) in mean initial nutrient concentrations of total C, N and P for plants grown on the sand and slag substrates. A litterbag technique was used to estimate decomposition rates. After 360 days of incubation, repeated measures analysis did not identify significant differences between the substrates for the interaction term ‘substrate × time’ or the term ‘substrate’ for percentage weight loss or for C, N and P remaining. Avicennia marina on both substrates had nutrient characteristics and decomposition rates comparable to those found in the literature. Results suggest that initial nutrient concentration and decomposition rates are not dramatically influenced by the presence of slag.     

蟾蜍血清梭曼水解酶（somanase）的纯化及性质的研究

从蟾蜍血清中发现并纯化出了一种与血清载脂蛋白有关的可催化神经性军用毒剂梭曼（０－１,２,２－ｔｒｉｍｅｔｈｙｌｐｒｏｐｙｌｍｅｔｈｙｌｐｈｏｓｐｈｏｆｌｕｏｒｉｄａｔｅ,ｓｏｍａｎ）的水解酶,此酶全部与高密度脂蛋白（ＨＤＬ）以复合形式存在于血清中。我们经过多种纯化手段,从ＨＤＬ中分离纯化出了酯酶的最小分子量组分,得到了高活性、高纯度的酶蛋白,在ＳＤＳ－聚丙烯酰胺凝胶电泳及等电聚焦电泳中呈单一区带,分子量４２ｋＤ,等电点ｐＨ５．２,并证明此酶不是ＨＤＬ中的任何一种已知载脂蛋白,也不是磷脂酶Ａ_２和磷脂酶Ｃ以及存在于ＨＤＬ中的卵磷脂胆固醇酰基转移酶（ＬＣＡＴ）。它是与ＨＤＬ中的主要载脂蛋白ａｐｏＡ_１比较牢固地连接在一起并含量甚微的一种酶蛋白,水解梭曼的Ｋｍ值ｐＨ７．２、３７℃时为３．１３ｍｍｏｌ／Ｌ。可被对氯汞苯甲酸、ＨＣｌ－胍和ＥＤＴＡ－Ｎａ_２所抑制,二硫苏糖醇对酶活性有恢复作用。     

Transient phosphorylation by ATP of a 160 000 dalton protein in rod outer segments of Bufo marinus

Radioactive phosphate was incorporated from [γ-³²P]ATP into a 160 000 dalton protein from preparations of highly purified toad retinal rod outer segment membranes. Maximal incorporation occurred at 1μM ATP, and turnover in the presence of nonradioactive substrate was rapid, showing that the 160 kdalton protein catalyzes ATP hydrolysis. The 160 kdalton intermediate was sensitive to hydroxylamine, suggesting an acyl linkage between the protein and phosphate. Ionic requirements for phosphorylation showed the ATPase is different from other membrane-bound ionic pumps. The phosphorylated intermediate was almost completely suppressed by 20 μM vanadate, and partial suppression occurred at lower concentrations. About one 160 kdalton protein was labelled per 30 000 molecules of rhodopsin. Although [γ-³²P]GTP labeled the protein, the ATPase was far more specific for adenine than guanine nucleotides. The specificity for ATP and sensitivity to vanadate of the intermediate suggest a relation to an ATP-dependent structural change which occurs in stacks of outer segment discs (Thacher, S.M.; (1980) Fed. Proc. 39, 2066).     

Amphibian larvae and zinc sulphate: a suitable model to study the role of brain-derived neurotrophic factor (BDNF) in the neuronal turnover of the olfactory epithelium

The vertebrate olfactory system has fascinated neurobiologists over the last six decades because of its ability to replace its neurons and synaptic connections continuously throughout adult life, under both physiological and pathological conditions. Among the factors that are proposed to be involved in this regenerative potential, brain-derived neurotrophic factor (BDNF) is a candidate for having an important role in the neuronal turnover in the olfactory epithelium (OE) because of its well-documented neurogenic and trophic effects throughout the nervous system. The aim of the present study was to generate a suitable model to study the participation of BDNF in the recovery of the OE after injury in vivo. We developed an experimental design in which the OE of Rhinella arenarum tadpoles could be easily and selectively damaged by immersing the animals in ZnSO₄ solutions of various concentrations for differing time periods. Image analysis of histological sections showed that different combinations of each of these conditions produced statistically different degrees of injury to the olfactory tissue. We also observed that the morphology of the OE was restored within a few days of recovery after ZnSO₄ treatment. Immunohistochemical analysis of BDNF was performed with an antiserum whose specificity was confirmed by Western blotting, and which showed drastic changes in the abundance and distribution pattern of this neurotrophin in the damaged olfactory system. Our results thus suggest that BDNF is involved in the regeneration of the OE of amphibian larvae, and that our approach is suitable for further investigations of this topic. This work was supported by grants from CONICET (PIP 5842), Universidad de Buenos Aires (UBACYT X131) and ANPCYT (PICT 32219).     

海七鳃鳗(Petromyzon marinus)anoctaimin-1蛋白的生物信息学分析

七鳃鳗是现存的最原始的无颌类脊椎动物之一,也是连接无脊椎动物与脊椎动物的重要环节,对生物的起源与进化有很高的研究价值。anoctamin-1蛋白(ANO1)是一种重要的跨膜蛋白,与细胞内阴离子的跨膜运输相关。以海七鳃鳗为例,利用不同软件对海七鳃鳗ANO1蛋白的理化性质、结构域、蛋白结构特征、物种进化保守性以及系统进化关系进行生物信息学分析表明:海七鳃鳗ANO1的开放阅读框为2 373 bp,编码791个氨基酸,属于anoctamin蛋白家族,具有7个跨膜区;二级结构含有无规则卷曲、α螺旋和β折叠。将海七鳃鳗与其他物种的ANO1氨基酸序列进行同源比对,并构建系统进化树,以确认海七鳃鳗ANO1基因的保守性和进化地位。对ANO1基因及蛋白的生物信息学分析为ANO1基因及蛋白的相关研究提供了重要的信息基础。     

Induction from posterior hypothalamus is essential for the development of the pituitary proopiomelacortin (POMC) cells of the toad (Bufo japonicus)

The role of the posterior hypothalamus in the development of the epithelial hypophysis was studied in Bufo embryos. In animals from which the central part of the neural plate (NP) had been surgically removed at the open neurula stage, the infundibulum did not develop, and the epithelial hypophysis was formed away from the normal site without morphological connection with the brain. Immunoreactive MSH cells and ACTH cells, i.e, the pituitary POMC cells, were not detected in any of the surgically treated animals while other types of secretory cells (PRL, GH, TSH and GTH cells) were invariably present. In view of the fact that POMC cells originate in the anterior neural ridge, and not in the neural plate, the embryonic brain seems to exert an inductive influence upon the primordial pituitary POMC cells. Since these cells differentiate in a tail graft, isolated from the brain at a later stage (tail-bud stage), the inductive stimuli must be conveyed from/via the posterior hypothalamus to the pituitary anlage between the open neurula and the tail-bud stages.Abbreviations ACTH Adrenocorticotropic hormone - ANR anterior neural ridge - GH growth hormone - GTH gonadotropic hormone - MSH metanocyte stimulating hormone - NP central part of anterior neural plate - POMC proopiomelanocortin - PRL prolactin - TSH thyroid-stimulating hormone     

Tissue kinetics,ion transport,and recruitment of mitochondria-rich cells in the skin of the toad (Bufo bufo) in response to exposure to distilled water

Mitochondria-rich cells (MRC) of the amphibian epidermis are responsible for active chloride uptake at low external salinity, and new MRCs are recruited in response to exposure to distilled (deionized) water. The time-course of this recruitment, the tissue kinetics and ion transport have been studied in toads (Bufo bufo) immediately before, and after 2,7, and 14 days exposure to distilled water. General epidermal structure was not affected. However, the numbers of MRCs per mm² (D_MRC) increased throughout the experiment as revealed by staining of epidermal sheets with AgNO₃ (Ag) or methylene blue (MB). Part of the increased D_MRC was accounted for by an increase in MRC subpopulation(s) that stained neither with Ag nor MB. The cell birth rate (K_b) decreased and cell loss by moulting (K_d) increased without any significant change in epidermal cell pool size, indicating a reduced apoptotic rate. The increase in D_MRC was accompanied by a 3-fold increase in Cl^- current (I_Cl). At day-2 there was a transient reduction in the I_Cl per MRC. H⁺ secretion was progressively reduced during prolonged exposure to distilled water. Thus, at day-2 MRCs appeared incompletely differentiated as indicated by decreased I_Cl and H⁺ flux per MRC, and by the increased proportion of MRCs unstained by Ag or MB. Full Cl^- (but not H⁺) transport capacity, was restored at day-7. We conclude that increased D_MRC following exposure to low external Cl^-, rather than being due to an increased K_b, is the combined effect of a decreased apoptotic rate and an increased rate of differentiation, where morphological differentiation precedes functional differentiation.Parts of this study have been presented at the 32th International Congress of Physiological Sciences, 1–6 August, 1993, Glasgow, Scotland, and the 19th meeting of the European Study Group for Cell Proliferation, 5–9 October, 1993, Bruges, Belgium