Effects of Predation by Invasive Western Mosquitofish(Gambusia affinis) on Survival of Eggs,Embryos and Tadpoles of Pelophylax nigromaculatus and Duttaphrynus melanostictus in South China

Alien species are one of the most serious threats to the decline and extinction of native amphibian populations. In this study, we examined the predation of invasive Western Mosquitofish Gambusia affinis on the eggs, embryos, and tadpoles of Duttaphrynus melanostictus and Pelophylax nigromaculatus in south China. Our results suggested that the survival of eggs and embryos remaining in the egg capsules of P. nigromaculatus and D. melanostictus was significantly higher than those removed from the egg capsule at 12-h intervals within 72 h in the presence of G. affinis. The survival of P. nigromaculatus eggs and embryos without egg capsules was significantly lower than those of D. melanostictus without egg capsules. The survival of P. nigromaculatus eggs and embryos with egg capsules was significantly higher than those of D. melanostictus with egg capsules from 24 h to 72 h except for 12 h. The survival of D. melanostictus tadpoles was significantly higher than that of P. nigromaculatus tadpoles in the presence of G. affinis. The survival of Gosner stage 26 tadpoles of P. nigromaculatus was significantly higher than that of Gosner stage 30 tadpoles from 12 h to 60 h, but there were no significant differences at 72 h. In contrast, the survival of Gosner stage 26 tadpoles of D. melanostictus was significantly lower than that of Gosner stage 30 tadpoles within 72 h, recording every 12 h. The increasing temperature caused a significant increase in predation by G. affinis on P. nigromaculatus eggs and embryos. The outer jelly capsule surrounding anurans eggs might serve as a mechanical defense against predation by G. affinis due to its large diameter, relatively stationary state and unpalatability. The differences in the vulnerability of P. nigromaculatus and D. melanostictus embryos and tadpoles to G. affinis probably due to differences in the unpalatability, black skin and activity. Based on the magnitude of predation by G. affinis on the eggs, embryos and tadpoles of these two species and the combined impact of temperature, we might speculate that invasive G. affinis and global warming would have more detrimental impacts on population viability of P. nigromaculatus than D. melanostictus in China.     

中华大蟾蜍蝌蚪变态过程中脊椎骨化次序

两栖动物在幼体变态即由水栖到陆栖的环境转变中,骨骼系统会发生重塑。本文采用茜素红和阿利新蓝的双染色技术对不同发育阶段中华大蟾蜍(Bufo gargarizans)蝌蚪变态过程中(Gosner 38~46)脊椎骨的发育进程进行了形态学研究。结果显示,在中华大蟾蜍蝌蚪Gosner 39期,椎板中线处发生融合;荐前椎Ⅱ-Ⅷ和荐椎的椎体、椎弓起始骨化发生在Gosner 42期;其次荐前椎Ⅱ-Ⅷ和荐椎的横突、底索和荐后椎Ⅰ开始骨化;荐后椎Ⅱ骨化最晚;在Gosner 46期,尾杆骨最终形成。荐后椎愈合形成尾杆骨反映无尾类幼体由水栖环境转变为陆生环境中骨骼系统的机能适应。     

Distribution and reproductive strategies of Gyrinicola batrachiensis (Oxyuroidea: Pharyngodonidae) in larvae of eight species of amphibians from Nebraska

In total, 462 tadpoles and salamander larvae of 8 species were examined for the presence of Gyrinicola batrachiensis from 5 locations in Nebraska. Infection by G. batrachiensis occurred in tadpoles of Rana blairi , Rana catesbeiana, Rana pipiens, and Bufo woodhousii. Tadpoles of Hyla chrysoscelis , Spea bombifrons, and Pseudacris maculata and larvae of Ambystoma mavortium were not infected with G. batrachiensis. Population structure, defined as prevalence, mean abundance, and mean intensity of G. batrachiensis, varied among tadpoles of different amphibian species and was determined by collection locality, developmental period of tadpole hosts, amphibian species co-occurrence, and different reproductive strategies of G. batrachiensis , or a combination. Gyrinicola batrachiensis observed in all ranid tadpoles and B. woodhousii tadpoles from where bufonids were the only anuran species present, confirmed to the didelphic haplodiploidy and monodelphic parthenogenetic reproductive strategies, respectively. However, tadpoles of B. woodhousii that co-occurred with tadpoles of R. pipiens at Cedar Creek were inconsistent with these predictions and contained both male and didelphic female nematodes, but at a low mean intensity (1.61 ± 0.70). Didelphic female nematodes from B. woodhousii tadpoles at Cedar Creek only produced thick-shelled eggs, whereas nematodes in R. pipiens tadpoles had a high mean intensity (14.88 ± 23.83) from this location and contained both thick-shelled and thin-shelled eggs in their respective uteri. More importantly, adult female nematodes from tadpoles of R. pipiens and B. woodhousii from Cedar Creek were morphologically more similar to each other than to female nematodes recovered from tadpoles of other anuran species, other locations, or both. These data suggest that when strains of G. batrachiensis are shared by tadpoles of different amphibian species that differ in developmental period, the nematodes have an intermediate reproductive strategy in amphibian species, with tadpoles having short development.     

Tadpoles of three common anuran species from Thailand do not prey on mosquito larvae

Tadpoles are often considered to be predators of mosquito larvae and are therefore beneficial for the control of certain disease vectors. Nevertheless, only a few species have actually been recorded to prey on mosquito larvae. The mosquito larvae predation rates of tadpoles of three common Thai anuran species (Bufo melanostictus, Kaloula pulchra and Hylarana raniceps) were experimentally tested. Tadpoles in varying developmental stages were used to assess a size/age effect on the predation rate. In addition, different instars of Culex quinquefasciatus were used in order to assess a prey size effect on the predation rates. All three species failed to show any evidence of mosquito larvae predation. Neither small nor large tadpoles fed on mosquito larvae. Prey size also did not affect predation. Although tadpoles do not feed on mosquito larvae, there may be other direct or indirect inter‐specific interactions that adversely impact the development of larvae in shared habitats with tadpoles.     

外来捕食者克氏原螯虾对黑斑侧褶蛙不同发育阶段幼体表型与运动能力的影响

外来物种入侵是造成本土无尾两栖类种群下降和灭绝的最严重威胁之一。在中国南部丽水地区,克氏原螯虾(Procambarus clarkiion)是一种捕食本土无尾类蝌蚪的入侵物种。在实验室条件下,通过对黑斑侧褶蛙(Pelophylax nigromaculatus)受精卵和蝌蚪先后进行克氏原螯虾捕食风险的不同处理,检测孵出蝌蚪的形态特征、中期蝌蚪的形态特征、游泳表现及活动水平、变态时间与大小以及幼蛙跳跃表现,评估克氏原螯虾的捕食风险对黑斑侧褶蛙不同生长阶段幼体生长发育、运动能力及行为的综合影响。单因素方差分析表明,捕食者长期存在条件下黑斑侧褶蛙孵出蝌蚪的体长、尾长和尾肌宽均显著短于无捕食者的空白对照组和捕食者仅存在2 d的实验组,后两者处理下的蝌蚪体长差异显著,但尾长和尾肌宽差异不显著。长期捕食者存在条件下黑斑侧褶蛙蝌蚪的游泳总路程和平均游速均显著小于无捕食者和捕食者存在2 d的实验组,而蝌蚪体长、尾长、尾鳍高和尾肌高的组间差异均不显著。有捕食者存在下黑斑侧褶幼蛙的体长和体重均显著大于无捕食者和捕食者存在2 d的实验组的情况,而变态时间和幼蛙跳跃距离组间差异不显著。两因素方差分析表明,测试时间、捕食者设置和两因素的相互作用均显著影响蝌蚪的活动频次。不同实验时间,长期捕食者存在实验组蝌蚪活动频次均小于无捕食者和捕食者存在2 d的实验组。无捕食者实验组蝌蚪的活动频次前期高于捕食者存在2 d的实验组,后期低于捕食者存在2 d的实验组。线性回归分析结果显示,捕食者存在2 d实验组蝌蚪相对活动频次与检测时间相关不显著,长期捕食者存在实验组相对蝌蚪活动频次与检测时间呈显著的正相关。本研究表明了黑斑侧褶蛙蝌蚪能够感知来自入侵捕食者克氏原螯虾的捕食风险,诱导产生较小的孵出个体、蝌蚪较低的活动水平,但这种不足可通过后期补偿生长,不影响进入陆地生境的变态个体的表型与运动能力。     

单独隔离孵化对镇海林蛙蝌蚪生长发育、社交行为和运动表现的影响

两栖类胚胎呈卵群一起孵化在反捕食、维持胚胎间的温度平衡和促进胚胎的同步发育等方面具有重要作用。在实验条件下探究孵化条件(单独隔离孵化和卵群一起孵化)对镇海林蛙(Rana zhenhaiensis)蝌蚪的生长发育、社交行为及其运动表现能力的影响。结果表明,孵出2天后,单独隔离孵化组蝌蚪的体长和发育历期均显著大于卵群一起孵化组。以体长为协变量的协方差分析表明,特定体长的单独隔离孵化组蝌蚪的体宽和体重均显著大于卵群一起孵化组的个体。在蝌蚪的活动行为中,单独隔离孵化组蝌蚪在水体上层和中层出现的频次显著小于卵群一起孵化组,而在水体底层的出现频次显著大于卵群一起孵化组。单独隔离孵化组蝌蚪个体的分布面积率、最近邻个体的距离、个体间的距离均显著大于卵群一起孵化组,但个体间的接触频次显著小于卵群一起孵化组。在运动表现方面,单独隔离孵化组胚胎的摆尾搏动频次显著小于卵群一起孵化组。单独隔离孵化组蝌蚪的运动时长和运动频次均显著小于卵群一起孵化组。本研究结果将为无尾两栖类幼期的生长发育规律提供参考数据。     

不同程度的尾损伤对镇海林蛙(Rana zhenhaiensis)蝌蚪游泳速度的影响

无尾两栖类蝌蚪的尾巴通过产生强大的游泳速度在反捕食中起到了重要的作用。以镇海林蛙(Rana zhenhaiensis)蝌蚪为实验动物来评估断尾的运动代价。以74尾具有完整尾蝌蚪作为实验组,通过截去不同尾长片段,人为分成轻微尾损伤组(30%)和严重尾损伤组(30%)并测定两组蝌蚪在断尾前后的游泳速度。以16尾完整尾蝌蚪作为对照组在实验组断尾前后同时进行游泳速度的测定。实验结果显示断尾影响蝌蚪的游泳速度,但仅在尾损伤程度达到尾长的30%以上时才产生不利的影响。这表明轻微尾损伤并不对镇海林蛙蝌蚪的游泳速度产生严重影响。在断尾前后实验组蝌蚪的游泳速度均与尾长呈正相关。在相同尾长状态下,尾损伤蝌蚪的相对游泳速度明显快于完整尾蝌蚪。因此,尾损伤的镇海林蛙蝌蚪有可能通过改变尾和身体的摆动频次等方式在断尾后对游泳速度进行了一定的补偿。尾损伤在野外频繁发生于蝌蚪的尾远端,据此推测镇海林蛙蝌蚪在自然条件下的尾损伤并不会产生严重运动代价。     

除草剂草甘膦对中华大蟾蜍的慢性毒性

为揭示除草剂对农林生态系统中脊椎动物天敌潜在的、长期的慢性毒性,测定了草甘膦对中华大蟾蜍（Bufo gargarizans Cantor）蝌蚪生长发育和运动频率的影响以及对中华大蟾蜍成体空胃率的影响。结果表明,亚致死剂量的草甘膦溶液对中华大蟾蜍蝌蚪的生长发育和运动频率具有明显的抑制作用,蝌蚪体长、体宽、尾长、尾宽和体质量的增长率均与草甘膦浓度呈极显著负相关;蝌蚪的运动频率亦与草甘膦浓度显著负相关。同时,草甘膦的喷施对中华大蟾蜍成体的捕食造成负面影响,其空胃率与草甘膦浓度呈极显著正相关,即使在草甘膦的推荐使用浓度范围之内．中华大蟾蜍（成体）处理组亦出现30％～60％的空胃率。     

Thyroid hormone-dependent gene expression as a biomarker of short-term 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) exposure in European common frog (Rana temporaria) tadpoles

The effects on thyroid hormone-dependent gene biomarker responses of the persistent organochlorine pesticide metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) were investigated after exposure of 4-week-old European common frog (Rana temporaria) (stage 36) tadpoles to two (0.001 and 0.01 ppm) DDE concentrations. Total body weight, total length, and tail length and width increased after 3-day exposure to DDE. Expression patterns of genes encoding for growth hormone, thyroid-stimulating hormone (TSHβ) and thyroid hormone receptor (TRα and TRβ) isoforms were evaluated in the head, body and tail regions using a validated real-time polymerase chain reaction (PCR) method. The mRNA expression of growth hormone in the body, and TSHβ in the head showed significant DDE concentration-dependent decreases. While DDE caused variable effects on TRα mRNA steady-state, the expression of TRβ was significantly decreased in the tail by DDE in a concentration-specific manner. The effect of DDE exposure on TRβ mRNA expression showed a negative correlation with tail length and width during the exposure period. The unique pattern of a DDE-induced decrease of tail TRβ expression probably reflects the significant role of this thyroid hormone receptor isoform in tail re-absorption and overall metamorphosis in anuran species. Therefore, the present study shows that the evaluation of thyroid hormone-dependent genes may represent quantitative biomarkers of acute exposure to organochlorine pesticides in anuran species during critical developmental periods such as metamorphosis. Given the widespread environmental levels of DDT and its metabolites, these pollutants will remain a subject of concern and their effects on anuran species should be studied in more detail.     

西藏蟾蜍线粒体COI和Cyt b基因序列的分析研究

采用聚合酶链式反应克隆西藏蟾蜍Bufo tibetanus线粒体COI和cyt b基因,首次报道该物种这两个基因的全序列,利用分子生物学软件结合比较与其他7种两栖动物的同源序列.结果显示:西藏蟾蜍两个基因序列中碱基G含量明显低于其它三种碱基,密码子第三位碱基G含量在4种蟾蜍中是最低的;碱基替换主要发生在第三位,属内转换率大于颠换率;相比核苷酸数据,氨基酸序列显示的遗传距离表明氨基酸序列更加保守,遗传距离显示西藏蟾蜍与中华大蟾蜍B.gargarizans的遗传距离最小;构建系统进化树,显示西藏蟾蜍和中华大蟾蜍的亲缘关系最近.     

Cryptic anuran biodiversity in Bangladesh revealed by mitochondrial 16S rRNA gene sequences

To survey the diversity of anuran species in Bangladesh, we compared mitochondrial 16S rRNA gene sequences (approximately 1.4 kbp) from 107 Bangladesh frog specimens. The results of genetic divergence and phylogenetic analyses incorporating data from related species revealed the occurrence of at least eight cryptic species. Hoplobatrachus tigerinus from two districts diverged considerably, indicating the involvement of a cryptic species. Two Fejervarya sp. (large and medium types) and Hylarana cf. taipehensis formed lineages distinct from related species and are probably new species. Microhyla cf. ornata differed from M. ornata with respect to type locality area and involved two distinct species. In addition, we found that Hylarana sp. and Microhyla sp. did not match congeners examined to date in either morphology or 16S rRNA sequence. The occurrence of M. fissipes was tentatively suggested. Consequently, at least, 19 species were found from Bangladesh in this study. These findings revealed a rich anuran biodiversity in Bangladesh, which is unexpected considering the rather simple topographic features of the country.     

Thyroid hormone-dependent gene expression as a biomarker of short-term 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) exposure in European common frog (Rana temporaria) tadpoles.

The effects on thyroid hormone-dependent gene biomarker responses of the persistent organochlorine pesticide metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) were investigated after exposure of 4-week-old European common frog (Rana temporaria) (stage 36) tadpoles to two (0.001 and 0.01 ppm) DDE concentrations. Total body weight, total length, and tail length and width increased after 3-day exposure to DDE. Expression patterns of genes encoding for growth hormone, thyroid-stimulating hormone (TSHbeta) and thyroid hormone receptor (TRalpha and TRbeta) isoforms were evaluated in the head, body and tail regions using a validated real-time polymerase chain reaction (PCR) method. The mRNA expression of growth hormone in the body, and TSHbeta in the head showed significant DDE concentration-dependent decreases. While DDE caused variable effects on TRalpha mRNA steady-state, the expression of TRbeta was significantly decreased in the tail by DDE in a concentration-specific manner. The effect of DDE exposure on TRbeta mRNA expression showed a negative correlation with tail length and width during the exposure period. The unique pattern of a DDE-induced decrease of tail TRbeta expression probably reflects the significant role of this thyroid hormone receptor isoform in tail re-absorption and overall metamorphosis in anuran species. Therefore, the present study shows that the evaluation of thyroid hormone-dependent genes may represent quantitative biomarkers of acute exposure to organochlorine pesticides in anuran species during critical developmental periods such as metamorphosis. Given the widespread environmental levels of DDT and its metabolites, these pollutants will remain a subject of concern and their effects on anuran species should be studied in more detail.     

Helminth and leech community structure in tadpoles and caudatan larvae of two amphibian species from Western Nebraska

Currently no comparative studies exist on helminth and leech community structure among sympatric anuran tadpoles and salamander larvae. During June-August 2007-2009, we examined 50 bullfrog tadpoles, Rana catesbeiana , 50 barred tiger salamander larvae, Ambystoma mavortium , and 3 species of snails from Nevens Pond, Keith County, Nebraska for helminth and leech infections. The helminth and leech compound community of this larval amphibian assemblage consisted of at least 7 species, 4 in bullfrog tadpoles and 4 in barred tiger salamander larvae. Bullfrog tadpoles were infected with 2 species of nematodes ( Gyrinicola batrachiensis and Spiroxys sp.) and 2 types of metacercariae ( Telorchis sp. and echinostomatids), whereas barred tiger salamander larva were infected with 1 species of leech ( Placobdella picta ), 2 species of adult trematodes ( Telorchis corti and Halipegus sp.), and 1 species of an unidentified metacercaria. The component community of bullfrog tadpoles was dominated by helminths acquired through active penetration, or incidentally ingested through respiratory currents, or both, whereas the component community of larval salamanders was dominated by helminths acquired through ingestion of intermediate hosts (χ2 = 3,455.00, P < 0.00001). Differences in amphibian larval developmental time (2-3 yr for bullfrog tadpoles versus 2-5 mo for salamander larvae), the ephemeral nature of intermediate hosts in Nevens Pond, and the ability of bullfrog tadpole to eliminate echinostome infections had significant effects on mean helminth species richness among amphibian species and years (t = 12.31, P < 0.0001; t = 2.09, P = 0.04). Differences in herbivorous and carnivorous diet and time to metamorphosis among bullfrog tadpoles and barred tiger salamander larvae were important factors in structuring helminth communities among the larval stages of these 2 sympatric amphibian species, whereas size was important in structuring helminth and leech communities in larval salamanders, but not in bullfrog tadpoles.     

黑斑侧褶蛙蝌蚪断尾后的补偿生长和发育研究

动物在经历不利的生长条件或环境后往往出现补偿生长。研究了黑斑侧褶蛙(Pelophylax nigromaculatus)蝌蚪经历来自食蚊鱼(Gambusia affinis)捕食造成断尾损伤后的补偿生长模式、断尾损失对蝌蚪游泳能力以及变态时间与大小的影响。结果表明,经历捕食压力后,全尾组和1/3断尾组蝌蚪的体长显著大于1/2断尾组蝌蚪的体长,全尾组和1/3断尾组之间的蝌蚪体长差异不显著;第19天时,1/2断尾组蝌蚪经过补偿生长后体长显著大于全尾组蝌蚪,1/3断尾组与全尾组和1/2断尾组之间的蝌蚪体长差异均不显著;三个实验组之间蝌蚪尾长差异不显著;全尾组蝌蚪的疾游速显著大于1/2断尾组蝌蚪的疾游速,1/3断尾组蝌蚪的疾游速与全尾组和1/2断尾组之间差异不显著,表明严重断尾对蝌蚪疾游速产生了消极影响。三个实验组蝌蚪的变态时间和变态前后形态差异均不显著。黑斑侧褶蛙蝌蚪能够在变态前调整生长轨迹补偿早期捕食风险造成的生长损失,断尾损失并不影响变态时间与大小,断尾超过一半的蝌蚪经过补偿生长后仍要付出一定的运动代价。     

Vitamin A mediated limb deformities in the common Indian toad, Bufo melanostictus (Schneider)

Several types of limb deformities were induced by vitamin A in B. melanostictus. These ranged from total suppression of all the limbs (ectromelia) to partial development of either the forelimb or the hindlimb or both (mesomelia) to reduction or absence of digits in either the forelimbs or hindlimbs or both and absence of long bones in either the forelimbs or hindlimbs or both (phocomelia) or duplication of the hindlimbs (polymelia). All the limb abnormalities were induced in the developing limbs of the tail amputated tadpoles of B. melanostictus following vitamin A treatment, which is all the more interesting. The results suggest that vitamin A induces the above mentioned abnormalities by either switching on or over-expressing or disrupting the limb-specific hox genes by yet unknown mechanisms.     

泽陆蛙和饰纹姬蛙蝌蚪不同热驯化下选择体温和热耐受性

用泽陆蛙（Fejervarya limnocharis）蝌蚪和饰纹姬蛙（Microhyla ornata）蝌蚪做研究模型,检测热驯化（20 、25 和30 C）对选择体温（Tsel）、低温耐受性（CTMin）和高温耐受性（CTMax）的影响。结果显示,两种蝌蚪的Tsel既不受驯化温度的影响,也不存在种间差异;泽陆蛙蝌蚪的CTMin显著小于饰纹姬蛙蝌蚪,而CTMax和VTR则显著大于饰纹姬蛙蝌蚪;CTMin和CTMax随驯化温度的升高而升高,VTR则随驯化温度的升高而减小。研究结果表明,热驯化显著影响两种蝌蚪的CTMin、CTMax和VTR,而对两种蝌蚪的体温调定点无显著影响;这些热生物学特征对两种蝌蚪有效适应环境温度变化、利用资源、减少种间竞争具有重要的生态学意义。     

同水塘分布两种无尾两栖类蝌蚪的竞争策略

实验室条件下,通过活动性水平,变态时的体重、增长率和完成变态所需时间考察同水塘分布的中华蟾蜍(Bufo gargarizans)和高原林蛙蝌蚪(Rana kukunoris)的竞争策略。实验按照2×3因子设计,即:食物资源2个水平(高、低),组合方式3个水平(10只中华蟾蜍蝌蚪,记为B组;5只中华蟾蜍蝌蚪和5只高原林蛙蝌蚪,记为BR组;10只高原林蛙蝌蚪,记为R组)。中华蟾蜍蝌蚪的活动性在食物水平低时显著低于食物水平高时,而高原林蛙蝌蚪的活动性在不同食物水平下无显著差异;食物水平低时,混合组的高原林蛙蝌蚪变态时体重和体重增长率都显著高于R组,而混合组中华蟾蜍蝌蚪与B组相比无显著差异;在不同处理组中,食物水平低时混合组中华蟾蜍蝌蚪幼体期最短。这些结果表明:中华蟾蜍蝌蚪在不同食物资源条件下所选择的生存策略可能不同,即食物资源充足时,增加活动性获取更多食物;食物资源有限时,降低活动性且提前完成变态;与中华蟾蜍蝌蚪相比,在食物资源有限时高原林蛙蝌蚪获取食物能力更强。     

Alternative life cycle strategies of Megalodiscus temperatus in tadpoles and metamorphosed anurans

Megalodiscus temperatus (Stafford, 1905) is a common paramphistome trematode of North American amphibians with a two host life cycle and has been reported to infect frogs and rarely tadpoles. In this study we document the alternative life cycle strategy of M. temperatus in tadpoles and metamorphosed anurans. We show through field work and experimental infections that M. temperatus can establish in both anuran life stages and worms become gravid and release eggs in both tadpoles and metamorphosed frogs. However, worms exhibit differences in route of infection, development, egg production, and diet in tadpoles and metamorphosed anurans. These alternative life history strategies of M. temperatus suggest different selective pressures on the development and reproductive success of these worms in tadpoles and metamorphosed anurans, and we discuss the evolutionary avenues for and constraints on amphibian trematode life cycles presented by these two different anuran life stages.     

Direct and indirect effects of the introduced toad Bufo marinus (Anura: Bufonidae) on populations of native anuran larvae in Australia

Introduced species are frequently believed to have adverse effects on native biota and ecosystems. However, much of our knowledge of the ecological impacts of introduced species is anecdotal, and the mechanisms controlling these effects are often poorly understood. I used replicated artificial pond experiments to investigate the impact of eggs and hatchlings of the introduced toad Bufo marinus on populations of native anuran larvae (Limnodynastes ornatus and Litoria rubella) in Australia. Bufo marinus eggs and hatchlings are highly toxic to predatory native tadpoles. Under naturalistic conditions, populations of predatory L. ornatus tadpoles experienced significantly reduced survival when exposed to Bufo eggs and hatchlings. The impact of Bufo on L. ornatus survival was positively correlated with Bufo density. However, the toxic effects of Bufo on L. ornatus indirectly facilitated the survival of later-breeding L. rubella by altering predator-prey interactions between L. ornatus and L. rubella. Limnodynastes ornatus tadpoles are voracious predators of L. rubella eggs and hatchlings. Consequently, the negative impact of Bufo on populations of L. ornatus tadpoles reduced the intensity of predation by L. ornatus tadpoles on L. rubella eggs and hatchlings, thereby increasing L. rubella survival. The results demonstrate that B. marinus plays an important role in structuring native larval anuran communities via direct and indirect mechanisms, and that Bufo may have both negative and positive effects on populations of native anuran larvae. As far as I am aware, these are the first quantitative data to demonstrate that introduced fauna may affect populations of native biota via toxic effects.     

Phylogeographic analysis of the Bufo gargarizans species complex: a revisit

Using mtDNA sequencing and allozyme electrophoresis data, we tested the "vicariance followed by dispersal" hypothesis of the Bufo gargarizans species group and re-evaluated the species status in the general lineages species concept. A phylogenetic analysis suggested that dispersal, instead of vicariance, dominated the history of the species group. There was a general trend of west to east dispersal, while some lineages from the east subsequently returned to the west. The secondary admixture of those previously allopatric lineages produced substantial levels of sympatric genetic diversity, often as high as 7.0% pairwise difference within populations. The phylogenetic hypothesis does not support the current two species designation. Neither B. andrewsi nor B. gargarizans represents an independent evolutionary lineage, and monophyletic groups did not correspond to geographically discrete groups. Allozyme data also failed to reveal any fixed allelic difference among the populations. Therefore, we recommend regarding the complex as a single species, Bufo gargarizans, without subspecies division.