Iridescent ultraviolet signal in the orange sulphur butterfly (Colias eurytheme): spatial, temporal and spectral properties

Many of nature's most striking animal colours are iridescent, exhibiting a high degree of spectral purity and strong angular dependence of intensity and hue. Although a growing number of studies have detailed the intricate mechanisms responsible for producing iridescent colours, few attempts have been made to describe their dynamic appearance in ecologically and behaviourally realistic contexts. We suggest that the optical properties unique to iridescent structural colours are important for understanding how they function as signals during behavioural interactions. Using males of the orange sulphur butterfly, Colias eurytheme , which exhibit an iridescent ultraviolet (UV) reflectance on their dorsal wing surfaces, we develop a holistic framework for inferring the appearance of this signal to conspecifics under field conditions that incorporate data on their spectral sensitivity. We show that, during flight, the UV signal is brightest within a wing beat cycle when viewed from directly above the male. Spectral properties of the signal under natural lighting indicate that male wing colour should be readily perceived and distinguished from that of females and from the dark green visual background of UV-absorbing vegetation. Finally, our analyses permit predictions regarding how signal senders and receivers should orientate themselves for maximal transmission and reception of this ultraviolet iridescent signal.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 349–364.     

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.     

Population differentiation in the marginal populations of the great tit (Paridae: Parus major)

The major subspecies group of the great tit, Parus major , has experienced demographic and spatial expansions during the last century in several sites at the edges of its distribution range. These expansions, although temporarily very even, have resulted in dissimilar patterns of molecular diversity. Populations locating at regions of contact to other subspecies groups (in Amur, Kirghizia–Kazakhstan, and Iran) show divergence from central population by nuclear and mitochondrial markers. In Amur, gene flow from minor group could be detected based on the existence of private minor alleles in the major population. In Kirghizia and Kazakhstan, the bokharensis and major groups share almost all the microsatellite alleles detected though frequencies differ. In Iran, three geographically close populations are distinct according to the mitochondrial sequences but also indications of present or recent admixture is detected. Populations, which have expanded to regions previously unoccupied by the species (northern UK and Finland), show divergence only by one of the markers. The variability in molecular differentiation may be due to dissimilar expansions, depending on whether the colonized regions have previously been occupied by another subspecies or not, on the amount of colonizing birds, and on the amount of past and present gene flow.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 201–210.     

Characterization of microsatellite loci for the redbanded seabream,Pagrus auriga (Teleostei,Sparidae)

The redbanded seabream Pagrus auriga (Teleostei, Sparidae) is a species of a high commercial value in Spain. There is currently little information available about the genetic characteristics of both wild and cultured populations. In this survey, we have developed eight polymorphic microsatellites for the redbanded seabream using an enriched genome library protocol. All of them were polymorphic in the 64 individuals tested, 22 of which were wild specimens, and 42 were individuals from a captive reproductive broodstock. These markers can potentially be useful tools for use in population genetic studies.     

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.     

Phylloclade anatomy in Phyllanthus section Choretropsis (Phyllanthaceae)

The phylloclade anatomy of nine Brazilian species of the genus Phyllanthus section Choretropsis was studied, and its systematic significance was analysed. The arrangement of epidermal cells varied according to the species, with the guard cells of the stomatal apparatus distributed randomly or with the longitudinal axis parallel to the branch. In both branch types, the stomata were distributed on the phylloclade surface, except in P. gladiatus which showed hypostomatic branches. In most of the species, phylloclades developed a vascular system surrounded by clusters of fibres and cortical parenchyma, which could differentiate into palisade‐like tissue and ground tissue like a true leaf blade. The distribution of the vascular system followed the cylindrical or flattened diameter shape of the branch. In subsection Choretropsis, the cylindrical branches of P. choretroides, contrary to other species, developed a second ring formed by clusters of fibres surrounded by large parenchymal cells. In subsection Applanata, the palisade‐like cells of P. flagelliformis phylloclades acquired an isodiametric shape. The highest level of specialization was observed in P. gladiatus, which developed phylloclades with a dorsiventral structure, a main vein, and small sets of lateral vascular bundles like a typical leaf blade. The tissue arrangement of different species showed a gradual pattern, which was correlated with the different branch morphology and plant architecture. Despite the transitional pattern, it was suggested that some of the phylloclades had an independent origin and convergent evolution in the Choretropsis section. The anatomy of different branch types was shown to be useful, either in isolation or in association with other morphological characters, to delimit the species and to further understand their relationships and phylogeny. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 91–102.