Promitosis and Rod Occurrence in the Limax Ameba Vahlkampfia lobospinosa*

SYNOPSIS. Nuclear division and trophozoite structure and function were investigated in Vahlkampfia lobospinosa. During karyokinesis the nucleolus remained present and divided to form polar masses. Chromatids separated and were directed to the polar masses by spindle fibers within an intact nuclear membrane. No interzonal body was formed. Trophozoites consistently contained and extruded a rod-like structure 10–15 × 1–2 μm. Although it was found in other areas of the cell within the cytoplasm, this rod most frequently protruded from the uroid.     

Updating the Trachelocercids (Ciliophora, Karyorelictea). I. A Detailed Description of the Infraciliature of Trachelolophos gigas N. G., N. Sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) N. Comb

ABSTRACT. Trachelolophos gigas n. g., n. sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) n. comb. (basionym: Tracheloraphis filum) were discovered in the mesopsammon of the French Atlantic coast at Roscoff. Their morphology and infraciliature were studied in live and protargol impregnated specimens. The new genus, Trachelolophos, belongs to the family Trachelocercidae and is unique in having a conspicuous ciliary tuft, which is very likely a highly modified brosse, in the oral cavity. The two species investigated have a very similar infraciliature, differing only in morphometric characteristics and in the nuclear configuration. The entire somatic and oral infraciliature consists of dikinetids which have both basal bodies ciliated or only the anterior or posterior ones, depending on the region of the cell. The right side is densely and uniformly ciliated. Its kineties extend onto the left side to the glabrous stripe, where an anterior and posterior secant system are formed, reducing the number of kineties in the narrowed neck and tail region. The left side bears a narrow glabrous stripe bordered by slightly irregularly arranged dikinetids having rather stiff cilia (bristles), possibly forming an uninterrupted, prolate ellipsoidal (bristle) kinety as indicated by their ciliation. The bristle kinety commences subapically at the right margin of the glabrous stripe, extends posteriorly, then anteriorly at the left, to end up at the right margin again. The dikinetids of the right posterior portion of the bristle kinety have the posterior basal bodies ciliated, whereas the anterior basal bodies are ciliated in its left and right anterior portion. The ends of the bristle kinety meet distinctly subapically at the right margin of the glabrous stripe, as indicated by the diametrically opposed ciliation of the dikinetids. The anterior region (head) of the cell bears a distinct circumoral kinety composed of very regularly arranged dikinetids, associated with nematodesmata forming an oral basket together with the nematodesmal bundles originating from the oralized somatic dikinetids at the anterior end of the somatic kineties. The systematics of trachelocercid ciliates are briefly reviewed and discussed.     

Intraclass Evolution and Classification of the Colpodea (Ciliophora)

ABSTRACT. Using nine new taxa and statistical inferences based on morphological and molecular data, we analyze the evolution within the class Colpodea. The molecular and cladistic analyses show four well‐supported clades: platyophryids, bursariomorphids, cyrtolophosidids, and colpodids. There is a widespread occurrence of homoplasies, affecting even conspicuous morphological characteristics, e.g. the inclusion of the micronucleus in the perinuclear space of the macronucleus. The most distinct changes in the morphological classification are the lack of a basal divergence into two subclasses and the split of the cyrtolophosidids into two main clades, differing mainly by the presence vs. absence of an oral cavity. The most complex clade is that of the colpodids. We partially reconcile the morphological and molecular data using evolutionary systematics, providing a scenario in which the colpodids evolved from a Bardeliella‐like ancestor and the genus Colpoda performed an intense adaptive radiation, giving rise to three main clades: Colpodina n. subord., Grossglockneriina, and Bryophryina. Three new taxa are established: Colpodina n. subord., Tillinidae n. fam., and Ottowphryidae n. fam. Colpodean evolution and classification are far from being understood because sequences are lacking for most species and half of their diversity is possibly undescribed.     

An energy balance from absorbed photons to new biomass for Chlamydomonas reinhardtii and Chlamydomonas acidophila under neutral and extremely acidic growth conditions

Chlamydomonas is one of the most well-studied photosynthetic organisms that had important biotechnological potential for future bioproductions of biofuels. However, an energy balance from incident photons to the energy stored in the new biomass is still lacking. In this study, we applied a recently developed system to measure the energy balance for steady state growth of Chlamydomonas reinhardtii grown at pH 6.5, and C. acidophila that was grown at pH 6.5 and 2.6. Energy use efficiency was quantified on the basis of light absorption, photosynthetic quantum yield, photosynthetic and respiratory quotient, and electron partitioning into proteins, carbohydrates and lipids. The results showed that lower growth rates of C. acidophila under both pH conditions were not caused by the differences in the photosynthetic quantum yield or in alternative electron cycling, but rather by differences in the efficiency of light absorption and increased dark respiration. Analysis of the macromolecular composition of the cells during the light phase showed that C. acidophila uses biosynthetic electrons preferentially for carbohydrate synthesis but not for synthesis of lipids. This led to a strong diurnal cycle of the C/N ratio and could explain the higher dark respiration of C. acidophila compared with C. reinhardtii .     

Diversification in flowering time due to tandem FT-like gene duplication, generating novel Mendelian factors in wild and cultivated rice

The complex structure of a single Mendelian factor widespread in the Asian cultivated rice ( Oryza sativa ) and its wild progenitor ( Oryza rufipogon ) that caused diverse phenotypes in the timing of flowering under natural field conditions was investigated in near isogenic lines. These near isogenic lines showed differences in flowering time despite all eight accessions collected from tropical regions possessing a recessive gene allelic to the se-pat gene. Fine mapping in two of these near-isogenic lines revealed that cultivated (Patpaku) and wild (W593) accessions had three and two linked quantitative trait loci (QTL) in the candidate regions, respectively, showing that Patpaku and W593 possessed linked QTLs with different effects in addition to the commonly-observed recessive gene ( se-pat ). Molecular dissection suggested that the tandemly duplicated FT-like genes ( Hd3a and RFT1 ) could be the candidate genes for these QTLs. Interestingly, the linked QTLs differed in their epistases, degree of dominance, and genotype × environment interactions. The nucleotide sequences showed that RFT1 has diverged more rapidly than Hd3a during rice evolution, suggesting phenotypic diversification of the two genes. Phylogenetic analysis implied that the se-pat ⁺ alleles might have emerged in different lineages within O. sativa . The present results strongly suggest that nucleotide divergence and shuffling of the linked QTLs by recombination might have created novel Mendelian factors that probably contribute to responding to local environments.     

Life-history traits of lake plankton species may govern their phenological response to climate warming

A prominent response of temperate aquatic ecosystems to climate warming is changes in phenology – advancements or delays in annually reoccurring events in an organism's life cycle. The exact seasonal timing of warming, in conjunction with species-specific life-history events such as emergence from resting stages, timing of spawning, generation times, or stage-specific prey requirements, may determine the nature of a species' response. We demonstrate that recent climate-induced shifts in the phenology of lake phytoplankton and zooplankton species in a temperate eutrophic lake (Müggelsee, Germany) differed according to differences in their characteristic life cycles. Fast-growing plankton in spring (diatoms, Daphnia ) showed significant and synchronous forward movements by about 1 month, induced by concurrent earlier ice break-up dates (diatoms) and higher spring water temperature ( Daphnia ). No such synchrony was observed for slow-growing summer zooplankton species with longer and more complex life cycles (copepods, larvae of the mussel Dreissena polymorpha ). Although coexisting, the summer plankton responded species specifically to seasonal warming trends, depending on whether the timing of warming matched their individual thermal requirements at decisive developmental stages such as emergence from diapause (copepods), or spawning ( Dreissena ). Others did not change their phenology significantly, but nevertheless, increased in abundances. We show that the detailed seasonal pattern of warming influences the response of phyto- and zooplankton species to climate change, and point to the diverse nature of responses for species exhibiting complex life-history traits.     

Influence of submergence on growth of seedlings of Scirpus lacustris and Phragmites australis

• 1 Seeds of Scirpus lacustris and Phragmites australis were germinated in early June, and twenty-four seedlings of each species were subsequently exposed to submerged conditions (eight seedlings at each of the water depths 0.2, 0.4 and 0.8m), in outdoor 500–1 tanks in southern Sweden. Weight and shoot length of the plants were measured in September.
• 2 The Phragmites seedlings did not show any significant growth when submerged. The Scirpus seedlings, however, developed submerged leaves and exhibited considerable submerged growth. One Scirpus plant, in shallow water (0.2m), had developed an aerial shoot by September. Shoot length of the remaining (submerged) Scirpus plants was positively related to plant weight within water depth treatments, and was higher, in relation to plant weight, in deeper water. Mean weight in September of the submerged Scirpus plants decreased with increased water depth.
• 3 In south Swedish lakes with a lowered water table, Scirpus often occupies large areas on the lakeward side of the reed belt, which is generally dominated by Phragmites. The differences between the two species, in performance of submerged seedlings, suggest that this zonation may be created through successful submerged seedling establishment of Scirpus on the lakeward side of Phragmites.

     

Predicted warming and browning affect timing and magnitude of plankton phenological events in lakes: a mesocosm study

1. Aquatic ecosystems in Northern Europe are expected to face increases in temperature and water colour (TB) in future. While effects of these factors have been studied separately, it is unknown whether and how a combination of them might affect phenological events and trophic interactions. 2. In a mesocosm study, we combined both factors to create conditions expected to arise during the coming century. We focused on quantifying effects on timing and magnitude of plankton spring phenological events and identifying possible mismatches between resources (phytoplankton) and consumers (zooplankton). 3. We found that the increases in TB had important effects on timing and abundance of different plankton groups. While increased temperature led to an earlier peak in phytoplankton and zooplankton and a change in the relative timing of different zooplankton groups, increased water colour reduced chlorophyll‐a concentrations. 4. Increased TB together benefitted cladocerans and calanoid copepods and led to stronger top‐down control of algae by zooplankton. There was no sign of a mismatch between primary producers and grazers as reported from other studies. 5. Our results point towards an earlier onset of plankton spring growth in shallow lakes in future with a stronger top‐down control of phytoplankton by zooplankton grazers.