Comparative study about airborne spores in Cagliari and Perugia

Summary A comparative study was carried in two Italian cities: Cagliari and Perugia. Ninetten fungal genera were assessed in both stations. Some were the same airborne spores, while others were characteristic of the areas. From an analysis of the linear regression coefficients between the concentration of four fungal genera and some meteorological parameters both in Cagliari and Perugia, a highly significative positive correlation could be seen between the presence of airborneCladosporium spores and both mean and maximum temperature. The same significative correlations were obtained both in Cagliari and Perugia forDrechslera/Helminthosporium.     

Environmental stability and the evolution of cooperative breeding in hornbills

Reproductive cooperation in social animals has been the focus of intensive research, yet the role of environmental factors in promoting such cooperation remains uncertain. A recent global analysis suggested that cooperative breeding in birds is a ‘bet-hedging’ strategy associated with climatic uncertainty, but it is unclear whether this mechanism applies generally or is restricted to the insectivorous passerines that predominate as cooperative breeders at the global scale. Here, we use a phylogenetic framework to assess the effect of climate on the evolution of cooperation in hornbills (Bucerotidae), an avian family characterized by frugivory and carnivory. We show that, in contrast to the global pattern, cooperative reproduction is positively associated with both inter- and intra-annual climatic stability. This reversed relationship implies that hornbills are relatively insensitive to climatic fluctuations, perhaps because of their dietary niche or increased body mass, both of which may remove the need for bet-hedging. We conclude that the relationship between climatic variability and cooperative breeding is inconsistent across taxa, and potentially mediated by life-history variation. These findings help to explain the mixed results of previous studies and highlight the likely shortcomings of global datasets inherently biased towards particular categories.     

Functionally homologous representation of vocalizations in the auditory cortex of humans and macaques

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Elevated [CO2] alleviates the impacts of water deficit on xylem anatomy and hydraulic properties of maize stems

Plants can modify xylem anatomy and hydraulic properties to adjust to water status. Elevated [CO₂] can increase plant water potential via reduced stomatal conductance and water loss. This raises the question of whether elevated [CO₂], which thus improves plant water status, will reduce the impacts of soil water deficit on xylem anatomy and hydraulic properties of plants. To analyse the impacts of water and [CO₂] on maize stem xylem anatomy and hydraulic properties, we exposed potted maize plants to varying [CO₂] levels (400, 700, 900, and 1,200 ppm) and water levels (full irrigation and deficit irrigation). Results showed that at current [CO₂], vessel diameter, vessel roundness, stem cross-section area, specific hydraulic conductivity, and vulnerability to embolism decreased under deficit irrigation; yet, these impacts of deficit irrigation were reduced at elevated [CO₂]. Across all treatments, midday stem water potential was tightly correlated with xylem traits and displayed similar responses. A distinct trade-off between efficiency and safety in stem xylem water transportation in response to water deficit was observed at current [CO₂] but not observed at elevated [CO₂]. The results of this study enhance our knowledge of plant hydraulic acclimation under future climate environments and provide insights into trade-offs in xylem structure and function.     

Origin and evolution of C4 photosynthesis in the tribe Salsoleae (Chenopodiaceae) based on anatomical and biochemical types in leaves and cotyledons

 The Chenopodiaceae genus Salsola contains a large number of species with C₄ photosynthesis. Along with derivative genera they have a prominent position among the desert vegetation of Asia and Africa. About 130 species from Asia and Africa were investigated to determine the occurrence of C₃ versus C₄ syndrome in leaves and cotyledons, and to study specific anatomical and biochemical features of photosynthesis in both photosynthetic organs. The species studied belong to all six previously identified sections of the tribe Salsoleae based on morphological characters. Types of photosynthesis were identified using carbon ¹³C/¹²C isotope fractionation. The representatives of all systematic groups were investigated for mesophyll anatomy and biochemical subtypes by determination of enzyme activity (RUBPC, PEPC, NAD- and NADP-ME and AAT) and primary photosynthetic products. Two photosynthetic types (C₃ and C₄) and two biochemical subtypes (NAD- and NADP-ME) were identified in both leaves and cotyledons. Both Kranz and non-Kranz type anatomy were found in leaves and cotyledons, but cotyledons had more diversity in anatomical structure. Strong relationships between anatomical types and biochemical subtypes in leaves and cotyledons were shown. We found convincing evidence for a similar pattern of structural and biochemical features of photosynthesis in leaves and cotyledons within systematic groups, and evaluated their relevance at the evolutionary level. We identified six groups in tribe Salsoleae with respect to photosynthetic types and mesophyll structure in leaves and cotyledons. Two separate lineages of biochemical and anatomical evolution within Salsoleae were demonstrated based on studies of leaves and cotyledons. The sections Caroxylon, Malpighipila, Cardiandra and Belanthera have no C₃ species and only the NAD-ME C₄ subtype has been found in leaves. We suggest the C₄ species in the NADP-ME lineage evolved in Coccosalsola and Salsola sections, and originated in the subsection Arbuscula. Coccosalsola contains many species with C₃ and/or C₃-C₄ intermediate photosynthesis. Within these main evolutionary lineages, species of different taxonomic groups (sections and subsections) had differences in anatomical or/and biochemical features in leaves and cotyledons. We conclude that structural and biochemical changes in the photosynthetic apparatus in species of the tribe Salsoleae were a key factor in their evolution and broad distribution in extreme desert environments. Received January 25, 2001 Accepted July 17, 2001     

Allometric neoteny and the evolution of succulence in cacti

With the objective of analysing the role of heterochrony in the evolution of succulence in the cactus family, a comparative study of xylem development in six species with contrasting morphologies was carried out. Two woody leaf-bearing cacti and four succulent cactus species belong to different subdivisions within the family were analysed. In each species and for different ages, vessel-element length was measured, vessel-element lateral wall-pitting described and the percentage of xylem and parenchyma in the stem quantified. In the succulent species it was found that vessel element length did not change between juvenile and adult wood, that wall-pitting in adult plants was similar to that of seedlings, and that the woody tissue in adult plants was organized in vascular bundles as in the primary tissue of seedlingS. Leaf-bearing cacti, in contrast, changed in both vessel element length and wall-pitting when secondary wood was produced, and the secondary woody tissue of adult plants was organized in a continuous cambial cylinder as in most dicotyledonS. An allometric analysis suggests that a retardation in the developmental rate of woody tissues (allometric neoteny) is the main mechanism in the development of succulence in cacti.     

No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae)

Many defended species use conspicuous visual warning signals to deter potential predators from attacking. Traditional theory holds that these signals should converge on similar forms, yet variation in visual traits and the levels of defensive chemicals is common, both within and between species. It is currently unclear how the strength of signals and potency of defences might be related: conflicting theories suggest that aposematic signals should be quantitatively honest, or, in contrast, that investment in one component should be prioritized over the other, while empirical tests have yielded contrasting results. Here, we advance this debate by examining the relationship between defensive chemicals and signal properties in a family of aposematic Lepidoptera, accounting for phylogenetic relationships and quantifying coloration from the perspective of relevant predators. We test for correlations between toxin levels and measures of wing colour across 14 species of day‐flying burnet and forester moths (Lepidoptera: Zygaenidae), protected by highly aversive cyanogenic glucosides, and find no clear evidence of quantitative signal honesty. Significant relationships between toxin levels and coloration vary between sexes and sampling years, and several trends run contrary to expectations for signal honesty. Although toxin concentration is positively correlated with increasing luminance contrast in forewing pattern in 1 year, higher toxin levels are also associated with paler and less chromatically salient markings, at least in females, in another year. Our study also serves to highlight important factors, including sex‐specific trends and seasonal variation, that should be accounted for in future work on signal honesty in aposematic species.