Shell features, main colonized environments, and fractal analysis of sutures in Late Jurassic ammonites

A precise approach to the quantification of relationships between suture complexity, as measured by fractal analysis (step-line procedure), the architecture of shells, and the main colonized environments, has been made in a set of Late Jurassic ammonites ( N =507). Statistically significant differences between fractal-dimension ( D _f) mean values of evolute and involute shells are interpreted as caused by differences in the surface:volume ( S:V ) ratio. Suture complexity is also related to the shape of whorl section. The lowest D _f values correspond to subcircular whorl sections (low S:V ratio) and the highest ones to acute sections (high S:V ratio). The shape of flanks shows correlation with suture complexity. The highest values of D _f are found in planulate shells and the lowest ones in whorl cross sections with convex flanks. Highly significant differences appear between D _f mean values from unsculptured shells and those from ammonites with ribs and/or tubercles of medium to large size. Multivariate analysis shows a combined variation of shell features and suture complexity, resulting in a heterogeneous distribution of D _f values within the ammonite morphospace, mainly according to structural (shell architecture) and ornamental (sculpture strength rather than density) factors. Finally, the data obtained on relationships between suture complexity and the colonized environments (epicontinental vs. epioceanic inhabitants) suggest that suture complexity is not primarily related to bathymetry, and/or that no major differences in habitat depths existed between epicontinental and epioceanic ammonites.     

Competition between the native and the introduced hornets Vespa crabro and Vespa velutina: a comparison of potentially relevant life‐history traits

1. Invasive alien species are a major threat to biodiversity. In addition to predation and parasitism, native species might suffer from competition when invasive alien species occupy a similar ecological niche. 2. This study focused on the potential interspecific interaction between two hornets: the Asian yellow‐legged hornet, Vespa velutina, a high‐concern invasive alien species recently arrived in Europe; and the native European hornet, Vespa crabro. The two species share a similar ecological niche and V. velutina is rapidly expanding across Europe, which suggests that V. crabro might suffer from competition. 3. Under laboratory‐controlled conditions, two life‐history traits that might cause the two species to compete were investigated: (i) the ability of workers to find food sources and their flexibility in exploiting them (through individual food item choice tests and exploration assays); and (ii) the worker resistance to pathogens (through immune challenge tests). 4. The results show that trophic preference of both species highly overlaps, with a marked dietary preference for honeybees compared with other insect prey and non‐prey protein items. No differences were observed in the exploratory behaviour of both species. Finally, constitutive antibacterial activity was greater in workers of the native species than in workers of the invasive hornet. 5. This laboratory study provides a first assessment under controlled conditions of the factors affecting competition between workers of two hornet species and proposes a framework to assess, in wild contexts, the magnitude of the competition and the impact of the introduced V. velutina on the native V. crabro.     

Sutural complexity and bathymetry in ammonites: fact or artifact?

The widespread assumption that sutural complexity in ammonites is mainly proportional to water depth is revisited. Fractal analysis has been used for the precise morphometric evaluation of sutural complexity in 131 Upper Jurassic ammonites. Suture lines belonging to twelve families have been analyzed, account being taken of shell structure (coiling, shape of whorl section), sculpture and paleoenvironments. Fractal dimensions obtained in epicontinental and epioceanic ammonites show the unlikelihood of precise relationships between suture complexity and depth, and/or the absence of major differences in habitat depth if bathymetry played any significant role in the configuration of intricate septa. Suture complexity appears to be better related to shell structural types. □ Fractal analysis, ammonite sutures, Upper Jurassic.     

Genetic relationships and population structure within taxa of the endemic Sideritis pusilla (Lamiaceae) assessed using RAPDs

RAPD analysis has been performed for 15 plant populations, covering eight different infraspecific taxa of Sideritis pusilla (Lange) Pau, member of the Lamiaceae endemic to southeastern Spain, and their putative parental species Sideritis hirsuta L. and Sideritis Uucantha Cav. Genetic distances, together with the presence of numerous fixed molecular markers differentiating S. pusilla from its putative ancestors, indicate that it should be considered as a true species. Cladistic and populational analysis led to the allocation of S. pusilla populations into three major groups– osteoxylla, jlavovirens and pusilla/almeriensis –which include taxa previously described as ranging from the varietal to the specific level. Low genetic differentiation among groups revealed by a reduced number of specific molecular markers justify their assignment under the infraspecific range. Moreover, the existence of both morphological and biogeographical differences, supports a status for these groups as subspecies of S. pusilla. Highly significant ( P <0.002) variance partitioning data (AMOVA) extracted from the analysis of individuals within S. pusilla populations show that, of the total genetic diversity, 68.8% was attributable to individual differences within populations, 19.9% to populational differences within groups, and only 11.3% to divergence between groups. This distribution is in agreement with the outcrossing nature of these plants. Comparative analysis of variance within populations reveals a reduced genetic variation for the osteoxylla group, thus supporting its previous consideration as an endangered taxon.     

The first humans travelling on ice: an energy‐saving strategy?

Economy of locomotion is a constant challenge for animals, particularly when related to migrations and travelling. The present study focuses on human locomotion and particularly on the development of ice skating. The aim of our research was to understand whether an environmental feature such as a strong presence of lakes (frozen in winter) could force humans to develop ice skates in order to limit the energy cost of travelling. We hypothesized that the energy-saving principle was a determinant factor in the development of human locomotion on ice. Five healthy adult participants took part in the experiments, during which we recorded the speed (1.2 ± 0.3 m s⁻¹) and metabolic energy cost (4.6 ± 0.9 J kg⁻¹ m⁻¹) associated with travelling on bone skates. Simulations were also performed to demonstrate whether the benefit given by the use of skates was different in the areas where ice skating appears to have evolved originally. The gain reachable by using bone skates could lead to an extremely high energy saving (equal to 10% of the energy needed to survive during the cold season) and differs significantly between the regions considered in the present study. An analysis of the geometrical shape of lakes associated with fractal analysis of their distribution suggests that, in order to better adapt to the severe conditions imposed by the long lasting winters, Finnish populations could benefit more than others from developing this ingenious locomotion tool. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 1–7.     

Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterols

We investigated the interactions of abscisic acid (ABA) in the responses of grape leaf tissues to contrasting ultraviolet (UV)-B treatments. One-year-old field-grown plants of Vitis vinifera L. were exposed to photosynthetically active radiation (PAR) where solar UV-B was eliminated by using polyester filters, or where PAR was supplemented with UV-B irradiation. Treatments combinations included weekly foliar sprays of ABA or a water control. The levels of UV-B absorbing flavonols, quercetin and kaempferol were significantly decreased by filtering out UV-B, while applied ABA increased their content. Concentration of two hydroxycinnamic acids, caffeic and ferulic acids, were also increased by ABA, but not affected by plus UV-B (+UV-B) treatments. Levels of carotenoids and activities of the antioxidant enzymes, catalase, ascorbate peroxidase and peroxidase were elevated by +ABA treatments, but only if +UV-B was given. Cell membrane β -sitosterol was enhanced by ABA independently of +UV-B. Changes in photoprotective compounds, antioxidant enzymatic activities and sterols were correlated with lessened membrane harm by UV-B, as assessed by ion leakage. Oxidative damage expressed as malondialdehyde content was increased under +UV-B treatments. Our results suggest that the defence system of grape leaf tissues against UV-B is activated by UV-B irradiation with ABA acting downstream in the signalling pathway.