A morphological and genetic analysis of the European bitterling species complex

Bitterling fishes lay their eggs on the gills of living freshwater mussels and are valuable models in behavioural and evolutionary ecology. We used morphological and genetic data to resolve the taxonomic relationships of bitterling in Europe. Previous studies have suggested the European bitterling is either a single species with a wide but discontinuous geographic distribution, or a complex of species. Morphometric and meristic data identified differences between three putative species; with a clear distinction between the eastern Asian Rhodeus sericeus, western European bitterling Rhodeus amarus, and colchian bitterling, Rhodeus colchicus. Polymorphism in the mitochondrial DNA control region was predominantly due to insertion/deletion events, making phylogenetic inference difficult, but the single haplotype found in R. sericeus populations was detected at low frequency (one of 24 individuals) in R. amarus and R. colchicus populations. Eight control region haplotypes were found in R. amarus populations, which were distinct from the two haplotypes in a R. colchicus population. Cytochrome b data produced a phylogeny with strongly‐supported differentiation between a clade of two R. sericeus haplotypes and a clade of six R. amarus/colchicus haplotypes. The star‐like topology of the R. amarus/colchicus haplotypes in a minimum spanning network suggested a rapid radiation in this clade. Our results are consistent with an hypothesis of relatively ancient divergence of R. sericeus from R. amarus/colchicus and more recent and rapid differentiation between R. amarus and R. colchicus. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 337–347.     

Intertidal mesograzers in field microcosms: linking laboratory feeding rates to community dynamics

Mesograzers (herbivores <2.5 cm) are both diverse and abundant, but their relative effects on intertidal communities have rarely been quantified. Here I examine the effects of crustacean and polychaete mesograzers on two intertidal resources, the red alga Odonthalia floccosa Esp. (Falkenb.) and the epiphytic diatom Isthmia nervosa Kütz. The mesograzers were hermit crabs (Pagurus hirsutiusculus (Dana) and P. granosimanus (Benedict)), amphipods (Hyale frequens Stout and H. pugettensis (Dana)), isopod (Idotea wosnesenskii (Brandt)), juvenile kelp crab (Pugettia producta (Randall)), and polychaete worm (Platynereis bicanaliculata (Baird)). Feeding rates on Isthmia, measured in the laboratory for different consumer species and size classes, scaled allometrically with body mass. Consumption rates were 2-23% of body mass daily on a fresh weight basis. However, feeding rates on Odonthalia did not scale, suggesting that size will not always indicate per capita effect. Mesograzer densities were measured on Tatoosh Island, Washington, USA. The mesograzer predicted to have the largest total effect (P. hirsutiusculus), based on densityxfeeding rate, was neither the most abundant nor the most voracious. The validity of these sorts of predictions depends on how well feeding rates measured in the laboratory approximate per capita effects under field conditions. Predictions were compared to observed effects in field microcosms. Given known numbers of mesograzers, predictions were made about the amount of Isthmia biomass that should disappear over 2 weeks from microcosms (9x9x12 cm) anchored in tidepools. Average per capita effects in field microcosms were correlated with laboratory feeding rates, but, for three species with significant feeding on Isthmia, effects were lower than feeding rates predicted. Feeding trials may overestimate community impact because they fail to account for alternative food, search times, resource productivity and stimulation of growth, or interference from other consumers. Nevertheless, densities of mesograzers can reach sufficiently high levels so that even feeble per capita effects combine to alter biomass of epiphytes and perhaps other small algae.     

Pathologies of non‐marine bivalve shells from the Late Triassic of Poland

Gorzelak, P., Nied?wiedzki, G. & Skawina, A. 2010: Pathologies of non‐marine bivalve shells from the Late Triassic of Poland. Lethaia, Vol. 43, pp. 285–289. Shells of Late Triassic non‐marine bivalves from Lisowice (Lipie ?l?skie clay pit, southern Poland), which co‐occur with remains of several vertebrate taxa (mammal‐like reptiles, carnivorous dinosaurs, pterosaurs, temnospondyl amphibians, hybodont sharks, dipnoan and ganoid fish), bear evidence of pathologies. Distribution, dimension and shape of some of these injuries (radiate tooth marks) closely match the dental morphology of lungfish (here probably represented by the genus Ceratodus). Thus, we interpret these pathologies as evidence of unsuccessful predatory attack on bivalves by this fish. This interpretation is also consistent with modern examples of such behaviour among lungfish. The feasibility that other culprits caused other pathologies (shell scarring and wedges) on the bivalves analysed is also discussed. Discovery of these traces constitutes important evidence of predator–prey interaction, which provides ‘fingerprints’ of trophic structure within this Late Triassic freshwater ecosystem. □Freshwater bivalves, lungfish, pathologies, predation, Triassic.     

Modeling the Increase and Control of Caulerpa taxifolia, an Invasive Marine Macroalga

Population modeling based on species’ demography makes it possible to predict the pace of an invasion and evaluate the likelihood of success of different control strategies. We modeled the initial (density-independent) rate of increase of Caulerpa taxifolia (Vahl) C. Agardh (aquarium strain), a green alga that has markedly altered marine communities where it has invaded in the Mediterranean Sea. Parameter values for patch growth (from stolon extension) and reproduction (by asexual fragmentation and reattachment) were gleaned from published studies. Only the most conservative model, invoking field growth rates and low levels of fragment reattachment (2.5 m⁻² of existing patch each summer), closely matched observed increases (4–14 × annually). The most effective times for control (greatest reduction in rate of increase) were removal of established patches before summer and removal of fragments after summer. These times correspond to just before maximum growth and just after maximum reproduction, respectively. Only a combined strategy, incorporating 99% removal of all fragments and annual removal of 99% of established patches, was predicted to eliminate C. taxifolia entirely (λ < 1). This level of effort is only likely to be possible during the first few years of an invasion, arguing strongly for careful monitoring and rapid response to potential high-impact invaders.     

To sink or float: the fate of dormant offspring is determined by maternal behaviour in Daphnia

• 1 As the ephippia (chitinous shells enclosing diapausing eggs) of pelagic crustaceans of the genus Daphnia have been occasionally reported to float at the water surface, we considered that this might be an adaptation promoting their passive dispersal. We investigated the mechanisms by which ephippia appear at the water surface.
• 2 While field surveys revealed that floating Daphnia ephippia are often numerous in various freshwater habitats, laboratory tests showed that newly formed ephippia are not buoyant initially. Once transferred to the surface by whatever means, however, they may remain there due either to surface tension or gas absorption.
• 3 Video recordings showed that all ephippia at the water surface in laboratory vessels were shed there by ephippial females when moulting (despite the attendant risk of exposure to UV radiation). This implies that the moulting behaviour of female Daphnia may determine the fate of their dormant offspring, predetermining whether they remain in the natal environment (when the ephippium is released into the water column) or disperse (when it is deposited at the water surface).
• 4 Our findings reveal a potential mechanism underlying the high dispersal capacity of freshwater cladocerans inhabiting island‐like aquatic habitats.

     

Characterization of a purified chromatin acceptor protein (receptor binding factor 1) for the avian oviduct progesterone receptor

The specific, high-affinity binding of the avian oviduct progesterone receptor (PR) with target-cell nuclei and chromatin has been shown to involve DNA complexed with specific chromatin acceptor proteins. One of these chromatin acceptor proteins has been partially purified and found to be a small hydrophobic protein with a broad pI of 5.0-6.0 [Goldberger, A., & Spelsberg, T. C., (1988) Biochemistry 27, 2103-2109]. This paper describes the final purification over 100,000-fold to apparent homogeneity of this candidate PR acceptor protein, termed the receptor binding factor 1 (RBF-1). When the avian genomic DNA is bound by RBF-1, saturable, high-affinity (KD approximately 2 x 10(-9) M) binding sites for PR are generated. RBF-1 has a unique, hydrophobic N-terminal sequence. The PR binding to the RBF-1-DNA complexes is shown to be dependent on an intact activated PR with which excess nonradiolabeled PR can compete. By use of a new, highly specific monoclonal antibody (mAb) to the RBF-1 with Western immunoblotting, RBF-1 was shown to be localized in the nucleus and to be tissue and species specific. Selective removal of the chromatin proteins containing RBF-1 results in the loss of the highest affinity class of PR binding sites. A second class of residual PR binding sites remains in the nucleoacidic protein (NAP), a complex of proteins more tightly bound to the DNA. This class of PR binding activity has been classified as the RBF-2. The RBF-1 is estimated to be 0.03% of the total chromatin protein with about 1.2 x 10(5) molecules/diploid cell.     

Light acclimation,retrograde signalling,cell death and immune defences in plants

This review confronts the classical view of plant immune defence and light acclimation with recently published data. Earlier findings have linked plant immune defences to nucleotide‐binding site leucine‐rich repeat (NBS‐LRR)‐dependent recognition of pathogen effectors and to the role of plasma membrane‐localized NADPH‐dependent oxidoreductase (AtRbohD), reactive oxygen species (ROS) and salicylic acid (SA). However, recent results suggest that plant immune defence also depends on the absorption of excessive light energy and photorespiration. Rapid changes in light intensity and quality often cause the absorption of energy, which is in excess of that required for photosynthesis. Such excessive light energy is considered to be a factor triggering photoinhibition and disturbance in ROS/hormonal homeostasis, which leads to cell death in foliar tissues. We highlight here the tight crosstalk between ROS‐ and SA‐dependent pathways leading to light acclimation, and defence responses leading to pathogen resistance. We also show that LESION SIMULATING DISEASE 1 (LSD1) regulates and integrates these processes. Moreover, we discuss the role of plastid–nucleus signal transduction, photorespiration, photoelectrochemical signalling and ‘light memory’ in the regulation of acclimation and immune defence responses. All of these results suggest that plants have evolved a genetic system that simultaneously regulates systemic acquired resistance (SAR), cell death and systemic acquired acclimation (SAA).     

Biodiversity mediates top–down control in eelgrass ecosystems: a global comparative‐experimental approach

Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom–up and top–down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top–down and bottom–up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top–down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross‐site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large‐scale patterns corresponded strikingly with prior small‐scale experiments. Our results link global and local evidence that biodiversity and top–down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.