How many is enough? Determining optimal count totals for ecological and palaeoecological studies of testate amoebae

Testate amoebae are increasingly used in ecological and palaeoecological studies of wetlands. To characterise the amoeba community a certain number of individuals need to be counted under the microscope. To date, most studies have aimed for 150 individuals, but that sample size is not based on adequate evidence. When testate amoeba concentrations are low, it can be difficult or impossible to reach this total. The impacts of lower count totals have never been seriously scrutinised. We investigated the impact of count size on number of taxa identified, quantitative inferences of environmental variables and the strength of the links between amoebae and environmental data in the context of predicting depth to water table. Low counts were simulated by random selection of individuals from four existing datasets. Results show progressively diminishing returns by all criteria as count size increases from low numbers to counts of 150. A higher count is required to identify all taxa than to adequately characterise the community for transfer function inference. We suggest that in most cases, it will be a more efficient use of time to count a greater number of samples to a lower count. While a count of 50 individuals may be sufficient for some samples from some sites we recommend that counts of 100 individuals should be sufficient for most samples. Counts need only be increased to 150 or more where the aim is to identify relatively minor, but still potentially ecologically relevant community changes. This approach will help reduce lack of replication and low resolution, which are common limitations in testate amoeba-based palaeoecological and ecological studies

Molecular phylogenetic and biogeographical analysis of Nitraria based on nuclear and chloroplast DNA sequences

Based upon DNA sequences from six plastid regions (rbcL, psbB-psbH, trnL-trnF, rpS16, psbA-trnH, rpS16-trnK) and the internal transcribed spacer (ITS) region of nuclear ribosomal DNA, the phylogenetic relationships in the genus Nitraria and family Nitrariaceae are investigated by using methods of maximum parsimony, maximum likelihood, and Bayesian inference. Our study strongly supports the monophyly of Nitraria. Nitraria can be divided into four parts, namely, the N. sphaerocarpa group, N. retusa group, the N. roborowskii and N. tangutorum group, and a group consisting of N. schoberi, N. komarovii, N. sibirica, and N. billardieri. Ancestral area reconstruction using S-Diva shows that eastern Central Asia is most likely the place of origin, and then dispersals occurred to western Central Asia, Africa, and Australia

Supernumerary (B) chromosomes in populations of Picea abies (L.) H. Karst. from Western Rhodopes (Bulgaria)

Investigations on B chromosomes found for the first time for Picea abies (L.) H. Karst. have been conducted. Seeds of Picea abies from two populations of Western Rhodopes (Bulgaria) located at the southern border of species range, and protected according to Bern Convention and EC Habitat Directive were collected for this study. Mixoploidy was detected in some germinating seeds of Picea abies. It was found that metaphase cells of germinating seeds contain 0–4 B chromosomes of both metacentric and submetacentric types. The variability of B chromosomes number and their occurrence was observed. Along with B chromosomes, some chromosome aberrations such as fragments and ring chromosomes were revealed in metaphase cells of Picea abies from studied populations. The possible adaptive role of B chromosomes presence for Picea spp. is discussed.Проведено исследование В-хромосом, обнаруженных впервые у вида Picea abies (L.) H. Karst. Для настоящего исследования семена собраны из двух популяций Picea abies в Западных Родопах (Болгария), расположенных на южной границе видового ареала и охраняемых в соответствии с Бернской конвенцией и Директивой ЕС о местообитаниях. В отдельных проростках семян Picea abies найдена миксоплоидия. Обнаружено, что метафазные клетки проростков семян из изученных популяций Picea abies содержат 0–4 В-хромосомы как метацентрического, так и субметацентрического типов. Наблюдается изменчивость числа В-хромосом и их появления. Наряду с В-хромосомами в метафазных клетках Picea abies выявлены хромосомные мутации – фрагменты и кольцевые хромосомы. Обсуждается возможная адаптивная роль присутствия В-хромосом у видов Picea.Проведено дослідження В-хромосом, виявлених вперше у виду Picea abies (L.) H. Karst. Для даного дослідження насіння зібране з двох популяцій Picea abies в Західних Родопах (Болгария), що розташовані на південному кордоні видового ареалу та охороняються відповідно до Бернської конвенції та Директивою ЄС про місце розповсюдження. В окремих проростках насіння Picea abies знайдено міксоплоїдію. Виявлено, що метафазні клітини проростків насіння з вивчених популяцій Picea abies містять 0–4 В-хромосоми як метацентричного, так і субметацентричного типів. Спостерігається мінливість числа В-хромосом. Поряд з В-хромосомами у метафазних клітинах Picea abies виявлено хромосомні мутації – фрагменти та кільцеві хромосоми. Обговорюється можлива адаптивна роль присутності В-хромосом у видів Picea

Young dispersal of xerophil Nitraria lineages in intercontinental disjunctions of the Old World

Many cases of intercontinental disjunct distributions of seed plants have been investigated, however few have concerned the continents of Eurasia (mainly Central Asia), Africa, and Australia, especially the xerophytic lineages are lacking. Nitraria (Nitrariaceae) is just one of these xerophytic lineages. Previous Nitraria studies have hypothesized either Africa as the ancient center, with dispersals to Australia and Eurasia, or alternatively Central Asia, due to a concentration of endemism and diversity there. Our findings show eastern Central Asia, i.e. the eastern Tethys, to be the correct place of origin. Dispersal westward to Africa occurred during the late Oligocene to Pliocene, whereas dispersal to Australia from western Central Asia was young since Pliocene 2.61 Ma. Two related tetraploids are indicated to have diversified in eastern Central Asia at approximately 5.89 Ma, while the Australian tetraploid N. billardieri, is an independently derived, recent dispersal from western Central Asia

Lack of the PGA exopolysaccharide in Salmonella as an adaptive trait for survival in the host

Many bacteria build biofilm matrices using a conserved exopolysaccharide named PGA or PNAG (poly-β-1,6-N-acetyl-D-glucosamine). Interestingly, while E. coli and other members of the family Enterobacteriaceae encode the pgaABCD operon responsible for PGA synthesis, Salmonella lacks it. The evolutionary force driving this difference remains to be determined. Here, we report that Salmonella lost the pgaABCD operon after the divergence of Salmonella and Citrobacter clades, and previous to the diversification of the currently sequenced Salmonella strains. Reconstitution of the PGA machinery endows Salmonella with the capacity to produce PGA in a cyclic dimeric GMP (c-di-GMP) dependent manner. Outside the host, the PGA polysaccharide does not seem to provide any significant benefit to Salmonella: resistance against chlorine treatment, ultraviolet light irradiation, heavy metal stress and phage infection remained the same as in a strain producing cellulose, the main biofilm exopolysaccharide naturally produced by Salmonella. In contrast, PGA production proved to be deleterious to Salmonella survival inside the host, since it increased susceptibility to bile salts and oxidative stress, and hindered the capacity of S. Enteritidis to survive inside macrophages and to colonize extraintestinal organs, including the gallbladder. Altogether, our observations indicate that PGA is an antivirulence factor whose loss may have been a necessary event during Salmonella speciation to permit survival inside the host.This work was supported by the Spanish Ministry of Economy and Competitiveness grants BIO2014-53530-R and SAF2014-56716-REDT (http://www.mineco.gob.es/portal/site/mineco/?lang_choosen=en). JV was supported by Ramon y Cajal (RYC-2009-03948) contract from the Spanish Ministry of Economy and Competitiveness