Sharing a predator: can an invasive alien pest affect the predation on a local pest?

Invasive species can strongly affect biotic interactions in ecosystems, interacting both directly and indirectly with local species. In European tomato greenhouses, the invasive alien pest Tuta absoluta may impact the population dynamics of other pests like whiteflies. Besides inducing damages to the host plant and competing for resources with local pests, this alien species may exert a predator-mediated interaction on local pests sharing common natural enemies. Biocontrol agents usually used against whiteflies may also prey upon T. absoluta and this could alter the dynamics of local pest populations. We evaluated possible resource competition and predator-mediated interactions in a system involving one mirid predator Macrolophus pygmaeus and two pests, T. absoluta and a local whitefly, Bemisia tabaci, on greenhouse tomatoes. Results showed that both resource competition and predator-mediated interactions occurred simultaneously. In the presence of the shared predator, there was a short-term positive effect of T. absoluta on B. tabaci [up to 5.9-fold increase of B. tabaci juveniles (egg + larvae) after four weeks]. However, in the long-term there was a negative predator-mediated interaction of T. absoluta on B. tabaci, i.e., after ten weeks the density of B. tabaci was 7.3-fold lower in the presence of the invasive pest. We emphasize the critical role of generalist predators in managing both local and invasive alien pest populations and that the strength and direction of predator-mediated indirect interactions can depend on the time scale considered.     

Is there an urban effect in alien plant invasions?

Cities are known to be extraordinarily rich in alien plant species compared to rural environments. This is related to specific attributes of urban areas including the availability of natural resources and habitats (namely geological substrates and land cover), the dispersal pathways and associated propagule pressure due to trade and traffic, and the proximity many urban hubs have to rivers. Here we explored how richness and proportions of alien species introduced after the discovery of the Americas (so-called neophytes), can be explained by environmental covariates along the urbanization gradient from very rural to very urbanized grid cells. We tested whether there is a specific urban effect, either as an interaction effect of urbanized areas that changes these general relationships, or if there is an effect due to specific urban conditions. We found that the environmental covariates explaining richness as well as proportions of neophytes remain largely the same across the rural–urban gradient. There is, however, an effect of urbanized area on neophyte species richness and proportions, which also incorporates strictly urban conditions. Rivers, roads and railroads contribute disproportionately less to the increase of neophyte species diversity in more urbanized areas, which might be due to the already higher number of neophytes in cities. We argue that the conditions determining neophyte richness in cities are not fundamentally different from those in rural environments, but extend on the same environmental axis, i.e. having different positions along the gradient towards the upper end.     

Do seed harvesting ants threaten the viability of a critically endangered non-myrmecochorous perennial plant population? A complex interaction

This study analyzes the fate of seeds removed by ants, as well as the seed supply, seedling survival, and the ability to form persistent seed banks in the soil, in a critically endangered population of the non-myrmecochorous perennial halophyte Helianthemum polygonoides, in order to determine the extent to which seed removal by ants represents a real bottleneck for recruitment and thus a threat for long-term population viability. Apparently, the impact of seed-harvester ants was dramatic: the primary seed shadow was reduced by up to 93% by the activity of Messor bouvieri and Aphaenogaster dulcineae. However, M. bouvieri lost 7% of fruits collected by dropping them on trunk trails, mostly under plant cover, the most propitious microenvironment for recruitment. In addition, some seeds were mistakenly rejected in refuse piles, although here recruitment was extremely low. A significant fraction of seeds (≈40%) remained viable in the soil for over 2 years. In addition, H. polygonoides had the ability to form short-term persistent seed banks, in spite of the intense ant seed removal. In general, seedling recruitment was very low, denoting the scarcity of safe sites in the habitat. Overall, the data corroborate that seed removal by ants, although highly intense, does not compromise the viability of perennial-plant populations, because seed supply and seed reserve in the soil are enough to exploit current and future safe sites. A population viability analysis demonstrated that other threats affecting the survival of reproductive H. polygonoides plants actually constitute the real risk for the conservation of this critically endangered species.     

Does invasion by an alien plant species affect the soil seed bank?

Questions: How does invasion affect old‐field seed bank species richness, composition and density? How consistent are these effects across sites? Does the soil seed bank match vegetation structure in old‐fields? Location: Menorca, Balearic Islands, Spain, western Mediterranean basin. Methods: We monitored seed germination in soils from old‐fields that were both uninvaded and invaded (legacy effect) by the annual geophyte Oxalis pes‐caprae. We also added O. pes‐caprae bulbs to uninvaded soils to test O. pes‐caprae interference with seedling emergence (competitive effect). We compared species composition in the seed bank with that of the vegetation. Results: Species richness in the seed bank and in the vegetation was not significantly different between invaded and uninvaded areas. Uninvaded areas did not have larger seed banks than invaded areas. More seedlings, especially of geophytes, emerged when O. pes‐caprae bulbs were added to the soil. Species similarity between invaded and uninvaded areas was higher in the seed bank (74%) than in the vegetation (49%). Differences in species composition were as important as differences among sites. The degree of species similarity between the seed bank and the vegetation was very low (17%). Conclusions: Despite invasion by O. pes‐caprae not affecting species richness, the variation in the seed bank species composition in invaded and uninvaded areas, and the differences between the seed bank and the mature vegetation, highlights that even if the invader could be eradicated the vegetation could not be restored back to the exact composition as found in uninvaded areas.     

Historical Biogeography of endemic seed plant genera in the Caribbean: Did GAARlandia play a role?

The Caribbean archipelago is a region with an extremely complex geological history and an outstanding plant diversity with high levels of endemism. The aim of this study was to better understand the historical assembly and evolution of endemic seed plant genera in the Caribbean, by first determining divergence times of endemic genera to test whether the hypothesized Greater Antilles and Aves Ridge (GAARlandia) land bridge played a role in the archipelago colonization and second by testing South America as the main colonization source as expected by the position of landmasses and recent evidence of an asymmetrical biotic interchange. We reconstructed a dated molecular phylogenetic tree for 625 seed plants including 32 Caribbean endemic genera using Bayesian inference and ten calibrations. To estimate the geographic range of the ancestors of endemic genera, we performed a model selection between a null and two complex biogeographic models that included timeframes based on geological information, dispersal probabilities, and directionality among regions. Crown ages for endemic genera ranged from Early Eocene (53.1 Ma) to Late Pliocene (3.4 Ma). Confidence intervals for divergence times (crown and/or stem ages) of 22 endemic genera occurred within the GAARlandia time frame. Contrary to expectations, the Antilles appears as the main ancestral area for endemic seed plant genera and only five genera had a South American origin. In contrast to patterns shown for vertebrates and other organisms and based on our sampling, we conclude that GAARlandia did not act as a colonization route for plants between South America and the Antilles. Further studies on Caribbean plant dispersal at the species and population levels will be required to reveal finer‐scale biogeographic patterns and mechanisms.     

Can a seed bank maintain the genetic variation in the above ground plant population?

There are indications that a persistent seed bank can protect small and isolated plant populations from local extinction. Genetic mechanisms contributing to this phenomenon are the increase of local effective population size – and hence the decrease of genetic drift – through a reservoir of persistent seeds, and the accumulation of intergenerational genetic diversity in the seed bank. To find evidence for these mechanisms, we conducted two formal meta-analyses. First, we analyzed 42 published habitat fragmentation studies and investigated whether the degree of genetic differentiation between fragmented plant populations was mediated by seed longevity. Second, we reviewed 13 published studies reporting the genetic diversity of both the seed bank and the above ground plants, aiming at comparing genetic diversity contained in the seed bank with the above ground vegetation. We conclude that a persistent seed bank may indeed mitigate the consequences of habitat fragmentation and protect a species from genetic drift and population genetic differentiation. We found no evidence, however, of high levels of genetic diversity accumulating in the soil seed bank. If genetic differences are present between the standing crop and the seed bank, they are very likely the result of local selection acting either directly or indirectly as a filter on the alleles present in the seed bank. We finally suggest that 1) the role of the seed bank should not be neglected in habitat fragmentation studies and 2) it is not very fruitful to continue comparing seed bank genetic diversity with above ground plant genetic diversity, unless this is performed under different selection regimes.     

Adaptation to the new land or effect of global warming? An age-structured model for rapid voltinism change in an alien lepidopteran pest

1. Hyphantria cunea Drury invaded Japan at Tokyo in 1945 and expanded its distribution gradually into northern and south-western Japan. All populations in Japan were bivoltine until the early 1970s, at which time trivoltine populations appeared in several southern regions. Presently, H. cunea exists as separate bivoltine and trivoltine populations divided around latitude 36 degrees . In the course of this voltinism change, the mean surface temperature in Japan rose by 1.0 degrees C. 2. To determine whether and how this temperature increase might be responsible for the voltinism change, we constructed an age-structured model incorporating growth speed driven by actual daily temperature and detailed mechanisms of diapause induction triggered by both daily photoperiod and temperature. 3. The simulation result suggests that both the acceleration of the growth speed and the prolongation of diapause induction are necessary to cause changes in voltinism, regardless of temperature increase. We concluded that the H. cunea population changed its life-history traits as an adaptation parallel with its invasion into the south-western parts of Japan. 4. Though the temperature increase had little effect on the fitness and heat stress in bivoltine and trivoltine populations, the trivoltine life cycle has become advantageous at least in marginal regions such as Tokyo.     

Does governance play a role in the distribution of invasive alien species?

Invasive alien species (IAS) constitute a major threat to global biological diversity. In order to control their spread, a detailed understanding of the factors influencing their distribution is essential. Although international trade is regarded as a major force structuring spatial patterns of IAS, the role of other social factors remains unclear. Despite studies highlighting the importance of strong governance in slowing drivers of biodiversity loss such as logging, deforestation, and agricultural intensification, no study has yet analyzed its contribution to the issue of IAS. Using estimates of governance quality and comprehensive spatiotemporal IAS data, we performed multiple linear regressions to investigate the effect of governance quality upon the distribution of species listed under “100 of the worst” IAS in 38 Eurasian countries as defined by DASIE. Our model suggested that for countries with higher GDP, stronger governance was associated with a greater number of the worst IAS; in contrast, for the lowest GDP countries under analysis, stronger governance was associated with fewer of these IAS. We elucidate how the quality of governance within a country has implications for trade, tourism, transport, legislation, and economic development, all of which influence the spread of IAS. While our findings support the common assumption that strengthening governance benefits conservation interventions in countries of smaller economy, we find that this effect is not universal. Stronger governance alone cannot adequately address the problem of IAS, and targeted action is required in relatively high‐GDP countries in order to stem the influx of IAS associated with high volumes of trade.     

Is the mass emergence of Themisto libellula in the northern Bering Sea an invasion or a bloom?

The mass occurrence of the large hyperiid Themisto libellula was recorded in both the western and the eastern Bering Sea within 2007–2011. Those were the years of a relatively long 6-year period of cold, which was caused mainly by the inflow of cold waters from the north; this is confirmed by the distribution of bottom and surface temperatures and also by the ice-cover values. This hyperiid became dominant in the diet of salmon, walleye pollock, herring, and several other nekton fish species. T. libellula periodically spreads southward with cold northern waters, finding favorable conditions in “new” areas. Being a rapidly growing species with a short life cycle, within 1 or 2 years it reaches a high abundance, which then gradually declines and remains at a mean or low level, as usually occurs with species that were introduced into a new habitat. After the environmental conditions deteriorate, as a “warm” period arrives with changes in the general circulation and a growing inflow of warmed Pacific waters, the southern boundary of the species range moves back far northward and it completely disappears in the areas where it prevailed in the plankton and was a main forage item in the diet of many fish species. Taking into account the durations of warm and cold periods from 1980 until 2010, an event like this in the Bering Sea can be expected within 1 or 2 years. In the eastern Bering Sea, the abundance and dominance of a number of zooplankton species may vary simultaneously. This effect is more pronounced in T. libellula and for this reason the species is considered as a biological indicator of the described climatic changes in the Bering Sea.     

Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?

Populations on continental islands are often distinguishable from mainland conspecifics with respect to body size, appearance, behaviour or life history, and this is often congruent with genetic patterns. It is commonly assumed that such differences developed following the complete isolation of populations by sea-level rise following the Last Glacial Maximum (LGM). However, population divergence may predate the LGM, or marine dispersal and colonization of islands may have occurred more recently; in both cases, populations may have also diverged despite ongoing gene flow. Here, we test these alternative hypotheses for the divergence between wedge-tailed eagles from mainland Australia (Aquila audax audax) and the threatened Tasmanian subspecies (Aquila audax fleayi), based on variation at 20 microsatellite loci and mtDNA. Coalescent analyses indicate that population divergence appreciably postdates the severance of terrestrial habitat continuity and occurred without any subsequent gene flow. We infer a recent colonization of Tasmania by marine dispersal and cannot discount founder effects as the cause of differences in body size and life history. We call into question the general assumption of post-LGM marine transgression as the initiator of divergence of terrestrial lineages on continental islands and adjacent mainland, and highlight the range of alternative scenarios that should be considered.     

On the occurrence of the fireworm Eurythoe?complanata complex (Annelida,Amphinomidae) in the Mediterranean Sea with an updated revision of the alien Mediterranean amphinomids

The presence of two species within the Eurythoe complanata complex in the Mediterranean Sea is reported, as well as their geographical distributions. One species, Eurythoe laevisetis, occurs in the eastern and central Mediterranean, likely constituting the first historical introduction to the Mediterranean Sea and the other, Eurythoe complanata, in both eastern and Levantine basins. Brief notes on their taxonomy are also provided and their potential pathways for introduction to the Mediterranean are discussed. A simplified key to the Mediterranean amphinomid genera and species of Eurythoe and Linopherus is presented plus an updated revision of the alien amphinomid species reported previously from the Mediterranean Sea. A total of five exotic species have been included; information on their location, habitat, date of introduction and other relevant features is also provided.     

Do pygidial secretions of dung beetles have the potential to repel urban pest ants?

Various organisms emit malodorous secretions against competitors, and the potential use of these secretions in pest management should be investigated. For example, some ant species feed on similar resources as dung beetles, which might have led to counter chemical defences in dung beetles. We tested whether pygidial secretions of the dung beetle Canthon smaragdulus (Fabricius) (Coleoptera: Scarabaeidae, Scarabaeinae) alter the locomotor behaviour of the exotic urban pest ant Tapinoma melanocephalum (Fabricius) (Hymenoptera: Formicidae), specifically whether these secretions repel those ants. We also tested whether the disturbance in the locomotor behaviour of T. melanocephalum increases with the amount of pygidial secretion. We found that individual T. melanocephalum displayed changes in their locomotor behaviour when exposed to pygidial secretions of coupled dung beetles, single males, and single females. Additionally, the pygidial secretions from male and female dung beetles could repel ants. The change in the locomotor behaviour of T. melanocephalum increased with the amount of pygidial secretion. Our results suggest that the pygidial secretions of dung beetles have potential as a biological repellent of T. melanocephalum. Hence, pygidial secretions from dung beetles may be used in the future for the development of urban pest management strategies.     

Uncommon specialization in a mutualism between a temperate herbaceous plant guild and an ant: are Aphaenogaster ants keystone mutualists?

Ant‐dispersed herbs (myrmecochores) can account for more than one‐third of the stems in the temperate deciduous forests of eastern North America. Because many ant species have been observed collecting the seeds, this interaction is often described as a generalized mutualism. Here, we combine fieldwork and meta‐analyses to test this assumption. Our meta‐analysis demonstrated that Aphaenogaster ants (predominantly A. rudis) collect approximately 74±26% (mean±SD) of the myrmecochorous seeds in eastern North American forests where any encounters with Aphaenogaster were reported, and approximately 61±37% of the seeds in all the eastern forests where any seed collection has been monitored. This remarkable monopolization of seeds is due to at least two factors: 1) Aphaenogaster are significantly more likely to collect the ant‐adapted seeds they discover than are ten other ant genera found in these forests and 2) the densities of Aphaenogaster and myrmecochorous plants are positively correlated at three nested spatial scales (within 20×20 m patches, among patches within a forest, and among 41 forests in the eastern United States). Although other ants can collect seeds, our analyses demonstrate that A. rudis is the primary seed dispersal vector for most of this rich temperate ant‐dispersed flora. The low levels of plant partner diversity for myrmecochores demonstrated here rivals that of tropical ant‐plants (myrmecophytes) and well exceeds that typically observed in temperate plant–frugivore and plant–pollinator mutualisms and myrmecochory in other biomes.     

Was it an explosion? Using population genetics to explore the dynamics of a recent radiation within Protea (Proteaceae L.)

Adaptive radiations likely underlie much of the world’s diversity, especially that of hyper‐diverse regions. They are usually characterized by a burst of speciation early in their evolutionary history, a pattern which can be detected using population genetic tools. The Cape Floristic Region (CFR) of southwestern South Africa is home to many spectacular plant radiations. Here, we investigate the white proteas (Protea section Exsertae), a typical CFR radiation, to determine if it demonstrates the burst of speciation associated with adaptive radiations in recent models. Inferences from individual assignment, tree‐based population relationships, and pairwise F‐statistics based on 10 microsatellite loci reveal that while the white proteas radiated recently they did not radiate explosively. In addition, we found evidence that there is little gene flow between sampled populations of most species. Taken together, these results demonstrate that within a small clade, the processes underlying the radiation are different from those envisioned by current models of adaptive radiation and suggest that geographical isolation could have played a role in the diversification of the group. Our study implicates both adaptive and non‐adaptive processes in the evolution of botanical diversity of the CFR.     

Did Cyclic Metaphosphates Have a Role in the Origin of Life?

How life began still eludes science life, the initial progenote in the context presented herein, being a chemical aggregate of primordial inorganic and organic molecules capable of self-replication and evolution into ever increasingly complex forms and functions.

Presented is a hypothesis that a mineral scaffold generated by geological processes and containing polymerized phosphate units was present in primordial seas that provided the initiating factor responsible for the sequestration and organization of primordial life’s constituents. Unlike previous hypotheses proposing phosphates as the essential initiating factor, the key phosphate described here is not a polynucleotide or just any condensed phosphate but a large (in the range of at least 1 kilo-phosphate subunits), water soluble, cyclic metaphosphate, which is a closed loop chain of polymerized inorganic phosphate residues containing only phosphate middle groups. The chain forms an intrinsic 4-phosphate helix analogous to its structure in Na Kurrol’s salt, and as with DNA, very large metaphosphates may fold into hairpin structures. Using a Holliday-junction-like scrambling mechanism, also analogous to DNA, rings may be manipulated (increased, decreased, exchanged) easily with little to no need for additional energy, the reaction being essentially an isomerization.

A literature review is presented describing findings that support the above hypothesis. Reviewed is condensed phosphate inorganic chemistry including its geological origins, biological occurrence, enzymes and their genetics through eukaryotes, polyphosphate functions, circular polynucleotides and the role of the Holliday junction, previous biogenesis hypotheses, and an Eoarchean Era timeline.

     

Effects of food rewards offered by ant–plant Macaranga on the colony size of ants

Myrmecophytes (ant–plants) have special hollow structures (domatia) in which obligate ant partners nest. As the ants live only on the plants and feed exclusively on plant food bodies, sap-sucking homopterans in the domatia, and/or the homopterans honeydew, they are suitable for the study of colony size regulation by food. We examined factors regulating ant colony size in four myrmecophytic Macaranga species, which have strictly species-specific association with Crematogaster symbiont ants. Intra- and interspecific comparison of the plants showed that the ant biomass per unit food biomass was constant irrespective of plant developmental stage and plant species, suggesting that the ant colony size is limited by food supply. The primary food offered by the plants to the ants was different among Macaranga species. Ants in Macaranga beccariana and Macaranga bancana relied on homopterans rather than food bodies, and appeared to regulate the homopteran biomass and, as a consequence, regulate the ants own biomass. In contrast, ants in Macaranga winkleri and Macaranga trachyphylla relied primarily on food bodies rather than homopterans, and the plants appeared to manipulate the ant colony size. Per capita plant investment in ants (ant dry weight plant dry weight^–1) was different among the four Macaranga species. The homoptera-dependent M. beccariana and M. bancana harbored lower biomass of ants than the food-body dependent M. winkleri, suggesting that energy loss is involved in the homoptera-interposing symbiotic system which has one additional trophic level. The plants investment ratio to the ants generally decreased as plants grew. The evolution of the plant reward-offering system in ant–plant–homopteran symbioses is discussed with an emphasis on the role of homopterans.