On the 13C/12C isotopic signal of day and night respiration at the mesocosm level

While there is currently intense effort to examine the ¹³C signal of CO₂ evolved in the dark, less is known on the isotope composition of day‐respired CO₂. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure c_i/c_a effect) from respiratory effect (production of CO₂ with a different δ¹³C value from that of net‐fixed CO₂) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO₂]. We show that whole mesocosm‐respired CO₂ is slightly ¹³C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly ¹³C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the ¹³C abundance in day‐ and night‐evolved CO₂. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO₂ production may change, thereby explaining the different ¹²C/¹³C respiratory fractionations in the light and in the dark.     

Host kairomone learning and foraging success in an egg parasitoid: a simulation model

Abstract 1. Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) is an egg parasitoid that recognises chemical residues left by its host the green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) as kairomone signals, enabling it to find egg masses in which to lay eggs. 2. Kairomones are usually present as patches deposited by N. viridula females, and recent results (Peri et al., Journal of Experimental Biology, 209 , 3629–3635, 2006) indicated that females of T. basalis are able to learn the features of their foraging environment and to adjust accordingly the amount of time spent on the patches of kairomones they are visiting, depending on whether or not host eggs are found. 3. In order to assess the impact of this learning ability, a Monte Carlo, spatially explicit and individual‐based simulation model was built to quantify the foraging efficiency of T. basalis females in environments with different levels of host abundance and distribution. In all cases, the present study compared the foraging efficiency of simulated T. basalis females having the ability to learn with those lacking this ability. 4. Learning females always visited a higher number of kairomone patches and attacked a higher number of hosts than non‐learning females, especially when there was a high density of kairomone patches in the environment. 5. Learning ability globally appears to allow the maintenance of efficient foraging success, especially when there is a low probability for the kairomone patches to contain discoverable hosts. 6. The increase in foraging efficiency for learning females appears to depend on the characteristics of the habitat in which they are foraging. Results thus suggest that significant variation in learning ability is likely to occur in natural wasp populations facing different environments with different host spatial distributions.     

A longirostrine Temnodontosaurus (Ichthyosauria) with comments on Early Jurassic ichthyosaur niche partitioning and disparity

Abstract: We describe an almost complete ichthyosaur skeleton from the middle Toarcian (Lower Jurassic) of the Beaujolais foothills near Lyon, France, and assign it to Temnodontosaurus azerguensis sp. nov. This new species exhibits cranial peculiarities such as a thin, elongated and possibly edentulous rostrum, as well as a reduced quadrate. These characters indicate dietary preferences that markedly differ from other species referred to Temnodontosaurus, a genus previously considered as the top predator of the Early Jurassic seas. Despite a conservative postcranial skeleton, we propose that Temnodontosaurus is one of the most ecologically disparate genera of ichthyosaurs, including apex predators and now a soft prey longirostrine hunter. Ammonites collected from the same stratigraphic level as the described specimen indicate that the new species is somewhat younger (bifrons ammonite zone) than the most known Toarcian ichthyosaurs and therefore slightly postdates the interval of severe environmental changes and marine invertebrate extinctions known as the Toarcian Oceanic Anoxic Event. The present study therefore raises the question of whether postcrisis recovery of vertebrate faunas, including the radiation of Temnodontosaurus into a new ecological niche, may have been a consequence of marine ecosystem reorganization across this event.     

A NEW PCR METHOD OF CHARACTERIZING SEAFISH FRESHNESS

Objective criteria used to assess the fish freshness in the laboratory are currently inadequate. During contamination of muscle tissue, bacteria reduce trimethylamine oxide (TMAO) to trimethylamine (TMA) in the absence of oxygen. Based on this reaction, we envisaged a new approach and have developed and optimized a PCR method which targets the tor A gene sequence that encodes TMAO reductase. We applied this method to two fish species (Whiting (Merlangus merlangus) and Pouting (Gadus luscus)) during monitoring of spoilage, in parallel with assay of TVBN and enumeration of total aerobic flora. The PCR results tally with the chemical and microbiological findings. Used in quantitative PCR, this method could characterize fish freshness.     

Multiple origins of viviparity,or reversal from viviparity to oviparity? The European common lizard (Zootoca vivipara,Lacertidae) and the evolution of parity

The evolution of viviparity in squamates has been the focus of much scientific attention in previous years. In particular, the possibility of the transition from viviparity back to oviparity has been the subject of a vigorous debate. Some studies have suggested this reversal is more frequent than previously thought. However, none of them provide conclusive evidence. We investigated this problem by studying the phylogenetic relationships between oviparous and viviparous lineages of the reproductively bimodal lizard species Zootoca vivipara . Our results show that viviparous populations are not monophyletic, and that several evolutionary transitions in parity mode have occurred. The most parsimonious scenario involves a single origin of viviparity followed by a reversal back to oviparity. This is the first study with a strongly supported phylogenetic framework supporting a transition from viviparity to oviparity.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 1–11.