Effects of forest edges, fruit display size, and fruit colour on bird seed dispersal in a New Zealand mistletoe,

This study examined how forest edges, fruit display size, and fruit colour influenced rates of seed dispersal in an endemic, bird-dispersed, New Zealand mistletoe species, Alepis flavida. To examine rates of seed dispersal, fruit removal rates were compared between plants growing on forest edges and in forest interior, and also between two morphs of plants with different coloured fruits. Two aspects of fruit display size were examined: plant size and the neighbourhood of conspecific plants. There was no overall difference in fruit removal rates on forest edges and in forest interior, but birds removed fruits from red-fruited plants at a faster rate than from orange-fruited plants. Proximity of plant neighbours interacted with edges to influence fruit removal rates. The smaller the distance to nearest neighbours, the greater the fruit removal rates for orange-fruited plants in both habitats, but this relationship was significant for red-fruited plants only in the interior. Plant size affected fruit removal rates for orange-fruited plants, but not for red-fruited plants, and these differences were consistent in both habitats. Thus, fruit colour had the strongest effects on rates of fruit removal in this system, but forest edges also affected fruit removal rates, via altering the effects of neighbouring plants. Although birds prefer red fruits, there appears to be little selection pressure against orange-fruited plants because fruit removal rates are very high for both morphs.     

Micro‐geographical scale variation in Drosophila melanogaster larval olfactory behaviour is associated with host fruit heterogeneity

Organisms utilize environmental cues to deal with heterogeneous environments. In this sense, behaviours that mediate interactions between organisms and their environment are complex traits, especially sensitive to environmental conditions. In animals, olfaction is a critical sensory system that allows them to acquire chemical information from the environment. The genetic basis and physiological mechanisms of the olfactory system of Drosophila melanogaster Meigen (Diptera: Drosophilidae) are well known, but the effects of ecological factors on the olfactory system have received less attention. In this study, we analysed the effect of environmental heterogeneity (different host fruits) on variation in larval olfactory behaviour in a natural population of D. melanogaster. We generated half‐sib lines of D. melanogaster derived from two nearby fruit plantations, Vitis vinifera L. (Vitaceae) (‘grape’) and Prunus persica L. (Rosaceae) (‘peach’), and measured, using a simple behavioural assay, larval olfactory response to natural olfactory stimuli. Results indicate that patterns of variation for this trait depend on host fruit plantation where lines were collected. In fact, only lines derived from ‘grape’ showed phenotypic plasticity for larval olfaction, whereas a genotype*environment interaction was detected solely in lines derived from ‘peach’. Therefore, our results demonstrate the existence of genetic differences in D. melanogaster larval olfactory behaviour at a micro‐geographical scale and also reveal that the trait studied presents a dynamic genetic architecture which is strongly influenced by the environment.     

Ecological correlates of seed mass variation in Phoradendron juniperinum,a xylem-tapping mistletoe

Summary We investigated several ecological correlates of seed mass variation in the hemiparasitic, xylemtapping mistletoe, Phoradendron juniperinum. Mean seed mass varied two-fold among plants between the ages of 4 and 14 years old and was positively correlated with parental plant age. Both the standard deviation and the coefficient of variation in mean seed mass decreased with increasing plant age demonstrating that, on average, younger plants produced seed with more variable mass. Nitrogen concentrations (mg nitrogen per gram of seed) of both the seed and fruit (pericarp) were not correlated with mass or the age of the parent plant from which the seed was taken. However, the nitrogen content per seed (mg nitrogen per seed) was positively correlated with the mean seed dry mass and the age of the seed parent, suggesting that the carbon to nitrogen ratio of individual seeds remained relatively constant as seed mass increased and plants grew older. Seed germination ranged between 20% and 86% and was positively correlated with mass and parental plant age. Heavier seeds (seeds from older plants) also had the highest root radicle growth rates. Furthermore, the final root radicle length after 76 d of growth was positively correlated with seed dry mass. When grown on a medium containing an extract prepared from the host plant foliage, all seeds showed lower germination, grew more slowly and had shorter overall root radicles, but had significantly greater development of the haustorial disks (the holdfast which forms the host-parasite junction in Phoradendron) than seeds grown on a control medium. Our results suggest that, on average, seeds of greater mass produced by older plants have a greater total resource pool per propagule (fruit + seed). This resource pool may be important in conferring a greater potential for dispersal (fruit), survival, colonization, and establishment.     

Geographic variation in seed removal of a myrmecochorous herb: influence of variation in functional guild and species composition of the disperser assemblage through spatial and temporal scales

The ecological influence of changes in the functional guild and species composition of ant assemblages on ant‐dispersal mutualisms is still poorly known. Using a multi‐scale approach over an 800 km range within the Iberian Peninsula, we tested the hypothesis that variation in seed removal rate was related to functional guild rather than to species composition variations of disperser assemblages in the myrmecochore herb Helleborus foetidus. At least two premises must be confirmed to validate this hypothesis: 1) ant assemblages that are dissimilar in species composition but with similar functional guild composition will not differ significantly in seed removal, and 2) assemblages with different functional guild composition will render different seed removal services. We conducted 3328 ant‐visitor censuses on 462 individual plants to identify both the species composition and functional guild variation of the ant‐disperser assemblage, and the plant seed removal rate. Functional guild composition of the ant assemblage was determined by the proportion of visits of ants acting as legitimate dispersers, facultative dispersers or elaiosome predators. Results showed that ant‐seed dispersal success seemed to be more sensitive to species composition changes of the ant assemblage than to functional guild shifts. However, this sensitivity was scale‐dependent. Thus, at the fine, inter‐individual scale, seed removal covaried with the species and functional guild composition of the ant assemblages; at the inter‐populational scale, differences in seed removal tended to be related to the dissimilarity of the assemblage species composition rather than the assemblage functional guild; finally, inter‐regional differences in seed removal were unrelated to dissimilarities of the ant assemblage composition or functional guild. Though differences in seed removal and the relative frequency of the legitimate dispersers tended to be positively correlated, none of the above premises were fully confirmed in this study. Therefore, our results did not support in full the hypothesis that the variation in seed removal was explained by shifts in functional guild composition, rather than shifts in species composition.     

Altered leaf colour is associated with increased superoxide‐scavenging activity in aureusidin‐producing transgenic plants

The health‐promoting property of diets rich in fruits and vegetables is based, in part, on the additive and synergistic effects of multiple antioxidants. In an attempt to further enhance food quality, we introduced into crops the capability to synthesize a yellow antioxidant, aureusidin, that is normally produced only by some ornamental plants. For this purpose, the snapdragon (Antirrhinum majus) chalcone 4′‐O‐glucosyltransferase (Am4’CGT) and aureusidin synthase (AmAs1) genes, which catalyse the synthesis of aureusidin from chalcone, were expressed in tobacco (Nicotiana tabacum) and lettuce (Lactuca sativa) plants that displayed a functionally active chalcone/flavanone biosynthetic pathway. Leaves of the resulting transgenic plants developed a yellow hue and displayed higher superoxide dismutase (SOD) inhibiting and oxygen radical absorbance capacity (ORAC) activities than control leaves. Our results suggest that the nutritional qualities of leafy vegetables can be enhanced through the introduction of aurone biosynthetic pathways.     

Detecting trophic‐level variation in consumer assemblages

1. Stable isotopes of nitrogen are useful for quantifying the trophic structure of food webs, but only if the variation in trophic enrichment (Δ_N), which is the difference in δ¹⁵N between a consumer and its food, is small relative to the value of Δ_N itself. 2. We examined the sources of variation in zooplankton Δ_N by measuring the trophic enrichment (Δ_N) of seven species of freshwater cladocerans, and by testing for an effect of age and temperature on the Δ_N of Daphnia pulicaria. 3. We found that Δ_N was similar among Cladocera and was not correlated with body size. Overall, the Δ_N for D. pulicaria was 1.4‰ (SE = 0.69, n = 57), as was expected for the detritus diet that we used in our experiments. We found no effect of temperature (15–25 °C) on Δ_N, but found that Δ_N of D. pulicaria increased with increasing age (10–30 days). 4. We developed a new method to test for trophic‐level variation in a group of consumers that explicitly accounts for the uncertainty in Δ_N. Using this approach, we confirmed that natural assemblages of zooplankton feed at several trophic levels in lake food webs.     

Relationships between intra‐specific variation in seed size and recruitment in four species in two contrasting habitats

Large seeds contain more stored resources, and seedlings germinating from large seeds generally cope better with environmental stresses such as shading, competition and thick litter layers, than seedlings germinating from small seeds. A pattern with small‐seeded species being associated with open habitats and large‐seeded species being associated with closed (shaded) habitats has been suggested and supported by comparative studies. However, few studies have assessed the intra‐specific relationship between seed size and recruitment, comparing plant communities differing in canopy cover. Here, seeds from four plant species commonly occurring in ecotones between open and closed habitats (Convallaria majalis, Frangula alnus, Prunus padus and Prunus spinosa) were weighed and sown individually (3200 seeds per species) in open and closed‐canopy sites, and seedling emergence and survival recorded over 3 years. Our results show a generally positive, albeit weak, relationship between seed size and recruitment. In only one of the species, C. majalis, was there an association between closed canopy habitat and a positive seed size effect on recruitment. We conclude that there is a weak selection gradient favouring larger seeds, but that this selection gradient is not clearly related to habitat.     

Predation is associated with variation in colour pattern, but not body shape or colour reflectance, in a rainbowfish (Melanotaenia australis)

1. In freshwater fishes, inter-population variation in male phenotype is often associated with differences in predation intensity, but these effects can be difficult to disentangle from environmental influences. 2. The western rainbowfish Melanotaenia australis exhibits marked sexual dimorphism - females are plain with a slender body, while males have striking coloration and are deeper in the body. Male traits differ in expression among populations, but this has not been described or explored in the literature. 3. This paper describes a study designed to test for geographic structuring of male phenotype in M. australis and to determine whether between-population variation in male phenotype is attributable to variation in predation regime, after accounting for environment. 4. We collected data describing habitat, and the size, activity and abundance of predators at sites containing M. australis populations. We then used photography, spectrometry and geometric morphometrics to describe colour pattern, spectral reflectance and body shape in males from these populations. Finally, we used permutation-based multivariate statistics to partition variance in these traits according to environment and predation regime. 5. Downstream environments posed higher predation risk to M. australis. Furthermore, males from these sites consistently exhibited larger cheek spots and fewer coloured lateral stripes than those from upstream sites. Variation in predation regime accounted for a significant proportion of the total variance in these traits (30·9%), after controlling for the effects of environment. 6. Variation in predation regime did not explain variation in reflectance or shape. Environmental variation, however, explained a significant portion of the total variance in reflectance (74·9%), and there was a strong trend towards it explaining a portion of the total variance in body shape (34·9%). 7. We conclude that natural selection by predators may be an important determinant of the evolution of colour pattern variation in M. australis, but not of that of body shape or colour reflectance. 8. Further study of M. australis will complement existing models, which show complex relationships between predation regime, environment and phenotype. Understanding these relationships is prerequisite to predicting the evolution of phenotypic variation in natural systems.     

Microsites of seed arrival: spatio–temporal variations in complex seed‐disperser networks

Microsites where seeds arrive during the dispersal process determine plant reproductive success, affecting the quality of dispersal. Despite their crucial role for plant recruitment, very few studies have addressed spatio–temporal variations in microsites of seed arrival in complex seed‐disperser networks. Using an endozoochorous dispersal system, we characterized the microsites of seed arrival of eight fleshy‐fruited plant species dispersed by five mammal species during two consecutive seasons across three sites in a Mediterranean environment (n = 383 feces with seeds; 261 453 seeds). We evaluated spatial and temporal variations in the probability of a seed to arrive at open microsites or at microsites with varying plant cover, considering selection by frugivores and assessing the extent to which seeds of particular species arrived under conspecifics or heterospecifics. We found strong spatio–temporal variations in the amounts of seeds of the eight target species arriving at different microsites. These variations were strongly driven by frugivores’ selection of different landscape elements (i.e. open areas and microsites dominated by different plant species), which differed from expectations based on their local availability. In general, more seeds than expected arrived at vacant (open) microsites. Using bipartite network graphs to connect seeds with their arrival microsites, we found that the proportion of seeds of fleshy‐fruited species arriving near conspecifics or heterospecifics, or at vacant microsites, varied depending on the target plant species, but also on the frugivore species dispersing it, on the study site and on the dispersal season. Our study revealed marked spatio–temporal variations in the microsites of seed arrival, which will potentially have implications for the quality of dispersal effectiveness, ultimately affecting plant population dynamics and community structure. Such a strong context‐dependence in the microsites of seed arrival is likely to confer resilience against unpredictable environmental conditions, like those typical of Mediterranean ecosystems.     

Aquatic macroinvertebrate assemblages associated with two floating macrophyte species of contrasting root systems in a tropical wetland

Limnology - Aquatic macrophytes play an important role in structuring biotic communities. A comparative study of macroinvertebrate community structures associated with Salvinia auriculata Aublet...     

Landscape-scale variation in the seed banks of floodplain wetlands with contrasting hydrology in China

1. At a local scale, the species composition, diversity and spatial variation of wetland plant communities are determined primarily by spatial and temporal heterogeneity in their environments. Less is known about variation at a landscape‐level. The floodplain of the Changjiang (Yangtze) River in China includes hydrologically connected, subtropical wetlands with different hydrological characteristics. 2. We examined seed‐bank species composition and richness in marshes of two contrasting hydrological types: permanent marshes, fed by local runoff, and lakeshore marshes more closely connected to the regulated river. Lakeshore marshes are flooded annually to depth of approximately 1 m and during flooding they support an alternate, aquatic vegetation type. The soil seed bank in March was a comparative estimator of species diversity. At the beginning of the growing season it included seeds from both phases of alternating vegetation types associated with the annual hydrological cycle. 3. A regional pool of 101 species was detected in the seed banks of six wetlands associated with the river and its tributaries: 56 occurred in permanent marshes and 59 in lakeshore marshes, with only 15 common to both. Species rarefaction curves indicated that more species occurred in permanent than lakeshore marshes at equal numbers of individuals sampled. However, the more heterogeneous lakeshore seed banks were estimated (Chao 2) to have greater total species richness (81) than permanent marsh (60). 4. Analysis using Sørensen's coefficient of similarity and DCA ordination revealed complex variation, with much greater differences between hydrological types than within them, irrespective of geographical distance. The types also differed significantly in the composition of four functional groups of species. 5. Despite the potential for dispersal of propagules via the annually pulsing river system (hydrochory), at a regional and landscape scale, diversity is maintained largely by large‐scale temporal hydrological heterogeneity and smaller scale spatial and topographic heterogeneity.     

Density‐dependent pre‐dispersal seed predation and fruit set in a tropical tree

Negative density‐dependent demographic processes operating at post‐dispersal seed, seedling, and juvenile stages are the dominant explanation for the coexistence of high numbers of tree species in tropical forests. At adult stages, the effect of pollinators and pre‐dispersal fruit predators are often dependent on the density or abundance of flowers and fruit in the canopy, but each have opposite effects on individual realized reproduction. We studied the effect of density on total and mature fruit set and pre‐dispersal predation rates within individual tree canopies in a common canopy tree species, Jacaranda copaia in a 50‐ha forest census plot in central Panama. We sampled all reproductive sized trees in the plot (n = 188) across three years and estimated fruit set and predation rates. Population‐wide pre‐dispersal seed predation averaged between 6–37% across years. Using linear mixed effects models, we found that increased density and fecundity of conspecific neighbours increased focal tree fruit set, but also the rate of pre‐dispersal predation. An interaction between individual and neighbourhood fruit production predicted lower predation rates at high individual and neighbourhood fecundities, which suggests predator satiation at high fruit abundance levels. However, the rate at which fruit set increased with conspecific neighbour fruit production was greater than the rate at which fruit were lost to predation, resulting in an overall positive effect of neighbour density on mature fruit production in focal trees. Our results run counter to the expectation of a uniformly negative effect of density across all life stages in tropical trees and suggest further exploration of the role of spatial clumping, pollen dispersal limitation, and predation at pre‐dispersal adult stages in maintenance of species diversity in plant communities.     

Tithonia oxfordiana,a new irregular echinoid associated with Jurassic seep deposits in south‐east France

Abstract: The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep‐marine middle Oxfordian deposits are exposed in south‐east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chemosynthetic organic matter produced by such bacteria. In view of the fact that T. oxfordiana is the sole species of the Jurassic genus Tithonia known from Oxfordian strata, it is postulated that chemoherms possibly acted as refugia for these peculiar echinoids, which have an episodic record between the Callovian and Valanginian.     

Predicting impacts of south‐to‐north water transfer project on fish assemblages in Hongze Lake,China

The Chinese government implemented the ambitious south‐north water transfer project (SNWTP), which aims to transport water from the Yangtze to the north of China where water shortages are severe. Although the ecological impacts of this project have been addressed publically, there remains a poor understanding of the effects of such large‐scale water transfers on the populations of aquatic species. The potential ecological impacts of such water transfers on the Hongze Lake fish assemblages are assessed here using Self‐Organizing Map (SOM) and Random Forest (RF) modeling. Using SOM, twenty‐three fish species in 15 sampling sites were classified into two assemblages and four sub‐assemblages corresponding to four distinct habitats (deep water macrophytes, deep water bare silt, shallow water bare silt, and shallow water macrophytes). The RF model further showed that water depth and transparency were the abiotic drivers underpinning fish assemblages in Hongze Lake. As the SNWTP is forecasted to modify the distribution of water depth and water clarity, major knock‐on effects are expected on downstream lake fish assemblages.     

Structure and composition of snake assemblages across three types of plantation in south‐eastern Nigeria

Assemblage structure, diversity measures and diversity/dominance patterns of snakes were studied between 1996 and 2013 in three types of plantation in the Niger River delta of southern Nigeria. The investigated plantation types were pineapple, banana/plantain, and cassava/yam. Over 74% of the census species (n = 27) were found in all three plantation types, with, overall, just two singletons (Bitis nasicornis, Lamprophis olivaceus) being observed. Despite an overall similarity in the taxonomic species composition, a principal component analysis placed the three plantation types in distinct zones of the multivariate space. Diversity/dominance diagrams for the three plantation types showed that banana/plantain and cassava/yam were nearly identical in terms of evenness profile, whereas the pineapple plantation had a higher evenness.     

Trans‐species variation in Dmrt1 is associated with sex determination in four European tree‐frog species

Empirical studies on the relative roles of occasional XY recombination versus sex‐chromosome turnover in preventing sex‐chromosome differentiation may shed light on the evolutionary forces acting on sex‐determination systems. Signatures of XY recombination are difficult to distinguish from those of homologous transitions (i.e., transitions in sex‐determination systems that keep sex‐chromosome identity): both models predict X and Y alleles at sex‐linked genes to cluster by species. However, the XY‐recombination model specifically predicts the reverse pattern (clustering by gametologs) for those genes that are directly involved in sex determination. Hence, the latter model can only be validated by identification of an ancestral sex‐determining region (SDR) with trans‐species polymorphism associated to sex. Here we combine a candidate‐gene approach with a genome scan to identify a small SDR shared by four species of a monophyletic clade of European tree frogs. This SDR encompasses at least the N‐terminal part of Dmrt1 and immediate upstream sequences. Our findings provide definitive evidence that sex‐chromosome homomorphy in this clade results only from XY recombination, and take an important step toward the identification of the sex‐determining locus. Moreover, the sex‐diagnostic markers we identify will enable research on environmental sex reversal in a wider range of frog species.