Defense Hypothesis Research Articles

Bite force and body mass of the fossil rodent Telicomys giganteus (Caviomorpha, Dinomyidae)

An exceptionally well-preserved skull of the Pliocene rodent Telicomys giganteus allowed the first estimation of body mass and analysis of the bite mechanics of this species of South American giant rodent. In this study, we reconstructed the main anatomical features of the skull of this Pliocene rodent and related them to the bite force at the incisors. The average of an estimation body mass gives 100 kg. We also estimated the bite force using three different techniques. Two methods suggest that bite forces at the incisors have a range of 500–1000 N. However, the incisors seem to be stronger than expected for this bite force, implying that the bite forces may have been greater than 2000 N. We consider the hypothesis of defense against predators or other agonistic behavior to explain our results.

Phytoplankton defenses: Do Emiliania huxleyi coccoliths protect against microzooplankton predators?

AbstractThe calcium carbonate plates (coccoliths) surrounding most coccolithophorid cells are strikingly reminiscent of armor, and defense against predators has been hypothesized as a selective advantage provided by these mineral structures. Although microzooplankton are the main predators of small phytoplankton such as coccolithophores, few putative phytoplankton defenses have been tested against this group. In this study, predation by the heterotrophic dinoflagellate Amphidinium longum on three calcifying strains of Emiliania huxleyi was compared with predation on cells acid‐treated to remove coccoliths. As a control for acidification effects on other cell properties, we also compared predation on acid‐treated and untreated non‐calcifying (haploid) E. huxleyi strains. We found no systematic support for the defense hypothesis in this predator‐prey system. Acid‐treated cells experienced predation rates that were higher, the same as, and lower than rates on untreated cells, depending on E. huxleyi strain. Other cell properties showing no relationship to predation included size, dimethylsulfoniopropionate (DMSP) content, and DMSP release. For untreated cells, however, hydrogen peroxide (H2O2) concentration in the cell suspension was positively related to predation, suggesting that H2O2 acts as a signal promoting prey detection, or that H2O2 co‐varies with other (unmeasured) predation‐enhancing cell properties. A. longum uses two different prey capture and ingestion strategies, depending on prey type. This plasticity suggests co‐evolution of predation and defense strategies, facilitating a generalist feeding strategy compatible with the diversity of potential phytoplankton prey.

Behavioral response to conspecific songs on foraging territories of the heart-nosed bat

Singing to create and defend territory boundaries is common among birds but rare in mammals. The African heart-nosed bat, Cardioderma cor, is hypothesized to use loud, low-frequency songs to reestablish foraging territories nightly. Territoriality can be defined ecologically, whereby an individual exclusively uses an area repeatedly, and behaviorally, through defense of an area. C. cor males sing on tightly abutting, exclusive areas nightly, which they return to throughout the season and sometimes across seasons. C. cor meets the ecological determinants of territoriality, but assessments of the use of song to maintain territories are lacking. We explore the singing behavior in this species by conducting song playback experiments within the borders of singing areas of 10 target individuals, with echolocation playbacks conducted as a control. In addition, we further explore the influence of song metrics on the behavioral response. Song playbacks prompted investigative and aggressive behavior, including passing by, approaching, and in one case, attacking the speaker, whereas echolocation did not. Additional post hoc analyses suggested that major song parameters, including song length, syllable frequency, intersyllable interval, and the number of double syllables comprising song stimuli influenced the level of response. For five bats we assessed whether their songs changed in response to the playback, and found that they sang faster, lower-frequency songs. These results are consistent with observations in other territorial animals including birds and gibbons, and provide a basis for further exploration of the territory defense hypothesis in the heart-nosed bat. We conclude that C. cor song features likely play an important role in mediating behavioral interactions within signaling networks of foraging bats. It has been hypothesized that birdsong first evolved in support of territorial defense because it offered a cost-effective alternative to patrolling large spaces by flight. Singing-like behaviors have also been documented in several species of bats but never as a tool for maintaining foraging territories. However, evidence of foraging territoriality is scarce for bats, likely due to technical challenges associated with documenting such behaviors for a small, flying animal that may travel large distances at night. Here, we show for the first time that a bat responds to conspecific songs in a manner strikingly similar to many songbirds, providing support from outside songbirds for the hypothesis that territorial defense is a key selective pressure for singing in small, flying animals. This work provides the important basis for continuing to explore the role of singing, including song variability, in natural bat behavior outside of the roost.

Pyrrolizidine alkaloid variation in Senecio vulgaris populations from native and invasive ranges.

Biological invasion is regarded as one of the greatest environmental problems facilitated by globalization. Some hypotheses about the invasive mechanisms of alien invasive plants consider the plant–herbivore interaction and the role of plant defense in this interaction. For example, the “Shift Defense Hypothesis” (SDH) argues that introduced plants evolve higher levels of qualitative defense chemicals and decreased levels of quantitative defense, as they are released of the selective pressures from specialist herbivores but still face attack from generalists. Common groundsel (Senecio vulgaris), originating from Europe, is a cosmopolitan invasive plant in temperate regions. As in other Senecio species, S. vulgaris contains pyrrolizidine alkaloids (PAs) as characteristic qualitative defense compounds. In this study, S. vulgaris plants originating from native and invasive ranges (Europe and China, respectively) were grown under identical conditions and harvested upon flowering. PA composition and concentration in shoot and root samples were determined using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). We investigated the differences between native and invasive S. vulgaris populations with regard to quantitative and qualitative variation of PAs. We identified 20 PAs, among which senecionine, senecionine N-oxide, integerrimine N-oxide and seneciphylline N-oxide were dominant in the roots. In the shoots, in addition to the 4 PAs dominant in roots, retrorsine N-oxide, spartioidine N-oxide and 2 non-identified PAs were also prevalent. The roots possessed a lower PA diversity but a higher total PA concentration than the shoots. Most individual PAs as well as the total PA concentration were strongly positively correlated between the roots and shoots. Both native and invasive S. vulgaris populations shared the pattern described above. However, there was a slight trend indicating lower PA diversity and lower total PA concentration in invasive S. vulgaris populations than native populations, which is not consistent with the prediction of SDH.

Testing the optimal defense hypothesis in nature: Variation for glucosinolate profiles within plants.

Plants employ highly variable chemical defenses against a broad community of herbivores, which vary in their susceptibilities to specific compounds. Variation in chemical defenses within the plant has been found in many species; the ecological and evolutionary influences on this variation, however, are less well-understood. One central theory describing the allocation of defenses in the plant is the Optimal Defense Hypothesis (ODH), which predicts that defenses will be concentrated in tissues that are of high fitness value to the plant. Although the ODH has been repeatedly supported within vegetative tissues, few studies have compared vegetative and reproductive tissues, and the results have not been conclusive. We quantified variation in glucosinolate profile and tissue value between vegetative and reproductive tissues in Boechera stricta, a close relative of Arabidopsis. B. stricta manufactures glucosinolates, a set of defensive compounds that vary genetically and are straightforward to quantify. Genetic diversity in glucosinolate profile has been previously demonstrated to be important to both herbivory and fitness in B. stricta; however, the importance of glucosinolate variation among tissues has not. Here, we investigate whether allocation of glucosinolates within the plant is consistent with the ODH. We used both clipping experiments on endogenous plants and ambient herbivory in a large-scale transplant experiment at three sites to quantify fitness effects of loss of rosette leaves, cauline leaves, and flowers and fruits. We measured glucosinolate concentration in leaves and fruits in the transplant experiment, and asked whether more valuable tissues were more defended. We also investigated within-plant variation in other aspects of the glucosinolate profile. Our results indicated that damage to fruits had a significantly larger effect on overall fitness than damage to leaves, and that fruits had much higher concentrations of glucosinolates, supporting the ODH. This is, to the best of our knowledge, the first study to explicitly compare both tissue value and chemical defense concentrations between vegetative and reproductive tissues under natural conditions.

Score based procedures for the calculation of forensic likelihood ratios – Scores should take account of both similarity and typicality

Score based procedures for the calculation of forensic likelihood ratios are popular across different branches of forensic science. They have two stages, first a function or model which takes measured features from known-source and questioned-source pairs as input and calculates scores as output, then a subsequent model which converts scores to likelihood ratios. We demonstrate that scores which are purely measures of similarity are not appropriate for calculating forensically interpretable likelihood ratios. In addition to taking account of similarity between the questioned-origin specimen and the known-origin sample, scores must also take account of the typicality of the questioned-origin specimen with respect to a sample of the relevant population specified by the defence hypothesis. We use Monte Carlo simulations to compare the output of three score based procedures with reference likelihood ratio values calculated directly from the fully specified Monte Carlo distributions. The three types of scores compared are: 1. non-anchored similarity-only scores; 2. non-anchored similarity and typicality scores; and 3. known-source anchored same-origin scores and questioned-source anchored different-origin scores. We also make a comparison with the performance of a procedure using a dichotomous “match”/“non-match” similarity score, and compare the performance of 1 and 2 on real data.

Both heavy metal-amendment of soil and aphid-infestation increase Cd and Zn concentrations in phloem exudates of a metal-hyperaccumulating plant

Plants that are able to hyperaccumulate heavy metals show increased concentrations of these metals in their leaf tissue. However, little is known about the concentrations of heavy metals and of organic defence metabolites in the phloem sap of these plants in response to either heavy metal-amendment of the soil or biotic challenges such as aphid-infestation. In this study, we investigated the effects of heavy metal-exposure and of aphid-infestation on phloem exudate composition of the metal hyperaccumulator species Arabidopsis halleri L. O'Kane & Al-Shehbaz (Brassicaceae). The concentrations of elements and of organic defence compounds, namely glucosinolates, were measured in phloem exudates of young and old (mature) leaves of plants challenged either by amendment of the soil with cadmium and zinc and/or by an infestation with the generalist aphid Myzus persicae. Metal-amendment of the soil led to increased concentrations of Cd and Zn, but also of two other elements and one indole glucosinolate, in phloem exudates. This enhanced defence in the phloem sap of heavy metal-hyperaccumulating plants can thus potentially act as effective protection against aphids, as predicted by the elemental defence hypothesis. Aphid-infestation also caused enhanced Cd and Zn concentrations in phloem exudates. This result provides first evidence that metal-hyperaccumulating plants can increase heavy metal concentrations tissue-specifically in response to an attack by phloem-sucking herbivores. Overall, the concentrations of most elements, including the heavy metals, and glucosinolates were higher in phloem exudates of young leaves than in those of old leaves. This defence distribution highlights that the optimal defence theory, which predicts more valuable tissue to be better defended, is applicable for both inorganic and organic defences.

Sponge symbioses between Xestospongia deweerdtae and Plakortis spp. are not motivated by shared chemical defense against predators.

The recently described epizoic sponge-sponge symbioses between Xestospongia deweerdtae and two species of Plakortis present an unusual series of sponge interactions. Sponges from the genus Plakortis are fierce allelopathic competitors, rich in cytotoxic secondary metabolites, and yet X. deweerdtae flourishes as an epizoic encrustation on Plakortis deweerdtaephila and Plakortis symbiotica. Our objective in this study was to evaluate the hypothesis that X. deweerdtae grows epizoic to these two species of Plakortis due to a shared chemical defense against predators. We collected free-living individuals of X. deweerdtae and symbiotic pairs from a wide geographical range to generate crude organic extracts and a series of polarity fractions from sponge extract. We tested the deterrency of these extracts against three common coral reef predators: the bluehead wrasse, Thalassoma bifasciatum, the Caribbean sharpnose puffer, Canthigaster rostrata, and the white spotwrist hermit crab, Pagurus criniticornis. While the chemical defenses of P. deweerdtaephila and P. symbiotica are more potent than those of X. deweerdtae, all of the sponge species we tested significantly deterred feeding in all three generalist predators. The free-living form of X. deweerdtae is mostly defended across the region, with a few exceptions. The associated form of X. deweerdtae is always defended, and both species of Plakortis are very strongly defended, with puffers refusing to consume extract-treated pellets until the extract was diluted to 1/256× concentration. Using diode-array high performance liquid chromatography (HPLC) coupled with high-resolution mass spectrometry (LC-MS/IT-TOF), we found two secondary metabolites from P. deweerdtaephila, probably the cyclic endoperoxides plakinic acid I and plakinic acid K, in low concentrations in the associated—but not the free-living—form of X. deweerdtae, suggesting a possible translocation of defensive chemicals from the basibiont to the epibiont. Comparing the immense deterrency of Plakortis spp. extracts to the extracts of X. deweerdtae gives the impression that there may be some sharing of chemical defenses: one partner in the symbiosis is clearly more defended than the other and a small amount of its defensive chemistry may translocate to the partner. However, X. deweerdtae effectively deters predators with its own defensive chemistry. Multiple lines of evidence provide no support for the shared chemical defense hypothesis. Given the diversity of other potential food resources available to predators on coral reefs, it is improbable that the evolution of these specialized sponge-sponge symbioses has been driven by predation pressure.

Optimal defense theory explains deviations from latitudinal herbivory defense hypothesis.

The latitudinal herbivory defense hypothesis (LHDH) postulates that the prevalence of species interactions, including herbivory, is greater at lower latitudes, leading to selection for increased levels of plant defense. While latitudinal defense clines may be caused by spatial variation in herbivore pressure, optimal defense theory predicts that clines could also be caused by ecogeographic variation in the cost of defense. For instance, allocation of resources to defense may not increase plant fitness when growing seasons are short and plants must reproduce quickly. Here we use a common garden experiment to survey genetic variation for constitutive and induced phenylpropanoid glycoside (PPG) concentrations across 35 Mimulus guttatus populations over a ~13° latitudinal transect. Our sampling regime is unique among studies of the LHDH in that it allows us to disentangle the effects of growing season length from those of latitude, temperature, and elevation. For five of the seven PPGs surveyed, we find associations between latitude and plant defense that are robust to population structure. However, contrary to the LHDH, only two PPGs were found at higher levels in low latitude populations, and total PPG concentrations were higher at higher latitudes. PPG levels are strongly correlated with growing season length, with higher levels of PPGs in plants from areas with longer growing seasons. Further, flowering time is positively correlated with the concentration of nearly all PPGs, suggesting that there may be a strong trade-off between development time and defense production. Our results reveal that ecogeographic patterns in plant defense may reflect variation in the cost of producing defense compounds in addition to variation in herbivore pressure. Thus, the biogeographic pattern predicted by the LHDH may not be accurate because the underlying factors driving variation in defense, in this case, growing season length, are not always associated with latitude in the same manner. Given these results, we conclude that LHDH cannot be interpreted without considering life history, and we recommend that future work on the LHDH move beyond solely testing the core LHDH prediction and place greater emphasis on isolating agents of selection that generate spatial variation in defense and herbivore pressure.

Local loss of the zebra-like coloration supports the aposematic and other visual defense hypotheses in Silybum marianum

ABSTRACTThe question of the spread of an aposematic or of an otherwise visually defended plant type within a non-aposematic or a visually non-defended population is a long-standing enigma that has received considerable theoretical attention. However, the spreading of aposematic or otherwise visually defended plant genotypes within a non-aposematic or a non-visually-defended population has never, as far as is known, been shown or studied in nature in wild plant populations. This study investigates the loss of the various simultaneous types of defensive coloration in the spiny thistle Silybum marianum by a mutation that occurred independently and found in 13 wild populations in Israel. Mutant plants have plain leaves rather than leaves of the zebra-like wild-type, which has a white network of stripes on the upper leaf surface. The mutants never spread beyond several dozen meters and usually only over several meters. The mutation has a simple developmental origin, since the white variegation is the result of...

Testing the optimal defense hypothesis in Stryphnodendron adstringens (Fabaceae, Mimosoideae) leaves: the role of structure, number, position and nectar composition of extrafloral nectaries

Stryphnodendron adstringens is a common Cerrado tree that possesses extrafloral nectaries (EFNs) on its leaves, which are located at the base and apex of the rachis and along the secondary veins. The position of EFNs and their nectar production can be affected by defense strategies because plant organs possess different values and herbivory vulnerability. Here we aimed to elucidate anatomy, histochemistry, nectar composition and EFN number on leaves of S. adstringens in the light of the optimal defense hypothesis. We found a convergence on anatomy and histochemical characterization because the three studied types of EFNs have epidermis, secretory parenchyma and vascular tissue, showing phenolic compounds and polysaccharides in the secretory parenchyma cells. The nectar contained glucose, fructose and sucrose, which attract ants of the Camponotus and Cephalotes genus. We found differences in the number of EFNs along the secondary veins and in the nectar composition between EFNs located at the base and apex of the rachis of the leaf. The number of EFNs on the secondary veins increases from the base to the apex, suggesting a strategy to induce ant patrolling over the entire leaf region. EFNs at the base secreted more nectar, which should be related to the protection of the leaf base, which is the part most vulnerable to herbivore attack and the most valued organ. We concluded that EFNs of S. adstringens are anti‐herbivore defenses whose pattern matches the predictions of the optimal defense hypothesis.

Zinc hyperaccumulation substitutes for defense failures beyond salicylate and jasmonate signaling pathways of Alternaria brassicicola attack in Noccaea caerulescens.

The hypothesis of metal defense as a substitute for a defective biotic stress signaling system in metal hyperaccumulators was tested using the pathosystem Alternaria brassicicola-Noccaea caerulescens under low (2 µM), medium (12 µM) and high (102 µM) Zn supply. Regardless the Zn supply, N. caerulescens responded to fungal attack with the activation of both HMA4 coding for a Zn transporter, and biotic stress signaling pathways. Salicylate, jasmonate, abscisic acid and indoleacetic acid concentrations, as well as biotic stress marker genes (PDF1.2, CHIB, LOX2, PR1 and BGL2) were activated 24 h upon inoculation. Based on the activation of defense genes 24 h after the inoculation an incompatible fungal-plant interaction could be predicted. Nonetheless, in the longer term (7 days) no effective protection against A. brassicicola was achieved in plants exposed to low and medium Zn supply. After 1 week the biotic stress markers were even further increased in these plants, and this compatible interaction was apparently not caused by a failure in the signaling of the fungal attack, but due to the lack of specificity in the type of the activated defense mechanisms. Only plants receiving high Zn exhibited an incompatible fungal interaction. High Zn accumulation in these plants, possibly in cooperation with high glucosinolate concentrations, substituted for the ineffective defense system and the interaction turned into incompatible. In a threshold-type response, these joint effects efficiently hampered fungal spread and, consequently decreased the biotic stress signaling.

Heavy metal (hyper)accumulation in leaves of Arabidopsis halleri is accompanied by a reduced performance of herbivores and shifts in leaf glucosinolate and element concentrations

Abiotic and biotic factors can significantly influence and modify the chemical composition of a plant. In this study the influences of exposure to cadmium and zinc and of herbivory on plant-insect interactions were investigated. We studied the performance of two herbivore species with different feeding modes (chewing versus sucking) on the metal-hyperaccumulator species Arabidopsis halleri (Brassicaceae) as well as individual glucosinolate (GLS) and element concentrations of young and old leaves in response to different soil and herbivore treatments. The performance of both insect species was reduced on plants grown on metal-amended soil compared to plants grown on unamended soil. This result supports the elemental defense hypothesis, which postulates that high internal metal concentrations can protect plants from herbivores and which was mostly tested with chewing herbivores so far. Alongside higher levels of heavy metals in plants grown on metal-amended soil, GLS and element concentrations were differentially affected in young versus old leaves and responded differently to herbivory. Concentrations of most GLS and elements were higher in young compared to old leaves, which is in line with the optimal defense theory, which predicts a better defense in more valuable tissue. Our results highlight that various organic as well as inorganic compounds in plants can be affected in different directions by the complex interplay between plants, herbivores, and heavy metal contamination of soil.

What should a forensic practitioner's likelihood ratio be?

We argue that forensic practitioners should empirically assess and report the precision of their likelihood ratios. Once the practitioner has specified the prosecution and defence hypotheses they have adopted, including the relevant population they have adopted, and has specified the type of measurements they will make, their task is to empirically calculate an estimate of a likelihood ratio which has a true but unknown value. We explicitly reject the competing philosophical position that the forensic practitioner's likelihood ratio should be based on subjective personal probabilities. Estimates of true but unknown values are based on samples and are subject to sampling uncertainty, and it is standard practice to report the degree of precision of such estimates. We discuss the dangers of not reporting precision to the courts, and the problems with an alternative approach which instead reports a verbal expression corresponding to a pre-specified range of likelihood ratio values. Reporting precision as an interval requires an arbitrary choice of coverage, e.g., a 95% or a 99% credible interval. We outline a normative framework which a trier of fact could employ to make non-arbitrary use of the results of forensic practitioners' empirical calculations of likelihood ratios and their precision.

A combined proteomic and transcriptomic analysis of slime secreted by the southern bottletail squid, Sepiadarium austrinum (Cephalopoda)

Sepiadarium austrinum, the southern bottletail squid, is a small squid that inhabits soft sediments along Australia's south-east coast. When provoked, it rapidly secretes large volumes of slime, presumably as a form of chemical defense. We analyzed the proteomic composition of this slime using tandem mass spectrometry and transcriptomics and found that it was remarkably complex with 1735 identified protein groups (FDR:0.01). To investigate the chemical defense hypothesis we performed an Artemia toxicity assay and used sequence analysis to search for toxin-like molecules. Although the slime did not appear to be toxic to Artemia we found 13 proteins in slime with the hallmarks of toxins, namely cysteine richness, short length, a signal peptide and/or homology to known toxins. These included three short (80-130AA) cysteine rich secreted proteins with no homology to proteins on the NCBI or UniProt databases. Other protein families found included, CAP, phospholipase-B, ShKT-like peptides, peptidase S10, Kunitz BPTI and DNase II. Quantitative analysis using intensity based absolute quantification (iBAQ via MaxQuant) revealed 20 highly abundant proteins, accounting for 67% of iBAQ signal, and three of these were toxin-like. No mucin homologues were found suggesting that the structure of the slime gel may be formed by an unknown mechanism. Biological significanceThis study is the first known instance of a slime secretion from a cephalopod to be analyzed by proteomics methods and is the first investigation of a member of the family Sepiadariidae using proteomic methods. 1735 proteins were identified with 13 of these fitting criteria established for the identification of putative toxins. The slime is dominated by 20 highly abundant proteins with secreted, cysteine rich proteins. The study highlights the importance of ‘omics approaches in understanding novel organisms.

Inordinate Spinescence: Taxonomic Revision and Microtomography of the Pheidole cervicornis Species Group (Hymenoptera, Formicidae).

The ant genus Pheidole—for all of its hyperdiversity and global ubiquity—is remarkably conservative with regard to morphological disparity. A striking exception to this constrained morphology is the spinescent morphotype, which has evolved multiple times across distantly related lineages of Indoaustralian Pheidole. The Pheidole cervicornis group contains perhaps the most extraordinary spinescent forms of all Pheidole. Here we present a taxonomic revision of the P. cervicornis group, and use microtomographic scanning technology to investigate the internal anatomy of the thoracic spines. Our findings suggest the pronotal spines of Pheidole majors, are possibly skeletomuscular adaptations for supporting their disproportionately large heads. The ‘head support hypothesis’ is an alternative to the mechanical defense hypothesis most often used to explain spinescence in ants. The P. cervicornis group is known only from New Guinea and is represented by the following four species, including two described here as new: P. barumtaun Donisthorpe, P. drogon sp. nov., P. cervicornis Emery, and P. viserion sp. nov. The group is most readily identified by the minor worker caste, which has extremely long pronotal spines and strongly bifurcating propodeal spines. The major and minor workers of all species are illustrated with specimen photographs, with the exception of the major worker of P. cervicornis, which is not known.

Invasive and non-invasive congeneric Centaurea (Asteraceae) show contrasting patterns of herbivory by snails

Background and aims – Once introduced into new regions, exotic species often experience shifts in resource allocation in response to the different environmental conditions found in the introduction range. Plants naturally respond to specialist herbivores with quantitative defences, by producing large amounts of toxic and non-toxic compounds that typically difficult digestion (e.g. tannins, cellulose), and to generalist herbivores with qualitative defences, like specialized noxious chemicals (e.g. alkaloids). The Shifting Defence Hypothesis (SDH) poses that invasive plants decrease the production of defences against specialist herbivores in their introduction range, where specialist herbivores are usually absent, while boosting the production of defences against generalist herbivores.Methods – We empirically assessed the response of a generalist herbivore, the common garden snail ( Helix aspersa ), to feeding with leaves of the annual herb Centaurea sulphurea, native to Europe and naturalized in North America; and the congeneric species C. solstitialis, which is also native to Europe and invasive in the Americas.Key results – Snails fed with leaves from Spanish native populations the non-invasive C. sulphurea grew significantly less compared to snails fed with leaves from non-native California. For snails fed with the invasive C. solstitialis significant differences were also found among regions, but the response was more complex, depending on population, with snails fed with Turkish and Australian plants presenting higher growth rates than the rest of the regions.Conclusions – Overall, our results stressed the importance of colonization history in shaping adaptive responses, and the stochasticity associated with colonization events of two closely related species, with contrasting invasive success and responses to herbivory.

Screening fatty acid composition of British heterotrophic microalgae thraustochytrids for production of omega-3 oils and biodiesel

Sepiadarium austrinum, the southern bottletail squid, is a small squid that inhabits soft sediments along Australia's south-east coast. When provoked, it rapidly secretes large volumes of slime, presumably as a form of chemical defense. We analyzed the proteomic composition of this slime using tandem mass spectrometry and transcriptomics and found that it was remarkably complex with 1735 identified protein groups (FDR:0.01). To investigate the chemical defense hypothesis we performed an Artemia toxicity assay and used sequence analysis to search for toxin-like molecules. Although the slime did not appear to be toxic to Artemia we found 13 proteins in slime with the hallmarks of toxins, namely cysteine richness, short length, a signal peptide and/or homology to known toxins. These included three short (80-130AA) cysteine rich secreted proteins with no homology to proteins on the NCBI or UniProt databases. Other protein families found included, CAP, phospholipase-B, ShKT-like peptides, peptidase S10, Kunitz BPTI and DNase II. Quantitative analysis using intensity based absolute quantification (iBAQ via MaxQuant) revealed 20 highly abundant proteins, accounting for 67% of iBAQ signal, and three of these were toxin-like. No mucin homologues were found suggesting that the structure of the slime gel may be formed by an unknown mechanism.This study is the first known instance of a slime secretion from a cephalopod to be analyzed by proteomics methods and is the first investigation of a member of the family Sepiadariidae using proteomic methods. 1735 proteins were identified with 13 of these fitting criteria established for the identification of putative toxins. The slime is dominated by 20 highly abundant proteins with secreted, cysteine rich proteins. The study highlights the importance of ‘omics approaches in understanding novel organisms.

Zinc triggers signaling mechanisms and defense responses promoting resistance to Alternaria brassicicola in Arabidopsis thaliana

According to the elemental defense hypothesis the accumulation of trace elements by plants may substitute for organic defenses, while the joint effects hypothesis proposes that trace elements and organic defenses can have additive or synergistic effects against pathogens or herbivores. To evaluate these hypotheses the response of the pathosystem Alternaria brassicicola-Arabidopsis thaliana to control (2μM) and surplus (12μM) Zn was evaluated using the camalexin deficient mutant pad3-1 and mtp1-1, a mutant with impaired Zn vacuolar storage, along with the corresponding wildtypes. In vitro, a 50% inhibition of fungal growth was achieved by 440μM Zn. A. thaliana leaves could accumulate equivalent concentrations without harm. In fact, surplus Zn enhanced the resistance of A. thaliana to fungal attack in Columbia (Col-0), Wassilewskija (WS), and mtp1-1. However, surplus Zn was unable to protect pad3-1 demonstrating that Zn cannot substitute for camalexin, the main organic defense in A. thaliana. High, non phytotoxic leaf Zn concentrations enhanced the resistance to A. brassicicola of A. thaliana genotypes able to produce camalexin. This was mainly due to Zn-induced enhancement of the JA/ETH signaling pathway leading to enhanced PAD3 expression. These results support the joint effects hypothesis and highlight the importance of adequate Zn supply for reinforced pathogen resistance.

CEESIt: A computational tool for the interpretation of STR mixtures

In forensic DNA interpretation, the likelihood ratio (LR) is often used to convey the strength of a match. Expanding on binary and semi-continuous methods that do not use all of the quantitative data contained in an electropherogram, fully continuous methods to calculate the LR have been created. These fully continuous methods utilize all of the information captured in the electropherogram, including the peak heights. Recently, methods that calculate the distribution of the LR using semi-continuous methods have also been developed. The LR distribution has been proposed as a way of studying the robustness of the LR, which varies depending on the probabilistic model used for its calculation. For example, the LR distribution can be used to calculate the p-value, which is the probability that a randomly chosen individual results in a LR greater than the LR obtained from the person-of-interest (POI). Hence, the p-value is a statistic that is different from, but related to, the LR; and it may be interpreted as the false positive rate resulting from a binary hypothesis test between the prosecution and defense hypotheses. Here, we present CEESIt, a method that combines the twin features of a fully continuous model to calculate the LR and its distribution, conditioned on the defense hypothesis, along with an associated p-value. CEESIt incorporates dropout, noise and stutter (reverse and forward) in its calculation. As calibration data, CEESIt uses single source samples with known genotypes and calculates a LR for a specified POI on a question sample, along with the LR distribution and a p-value. The method was tested on 303 files representing 1-, 2- and 3-person samples injected using three injection times containing between 0.016 and 1ng of template DNA. Our data allows us to evaluate changes in the LR and p-value with respect to the complexity of the sample and to facilitate discussions regarding complex DNA mixture interpretation. We observed that the amount of template DNA from the contributor impacted the LR – small LRs resulted from contributors with low template masses. Moreover, as expected, we observed a decrease of p-values as the LR increased. A p-value of 10−9 or lower was achieved in all the cases where the LR was greater than 108. We tested the repeatability of CEESIt by running all samples in duplicate and found the results to be repeatable.