Does interspecific competition with a stronger competitor explain the rarity of an endangered snake on a Mediterranean island?

Interspecific competition has been demonstrated to be an important shaping force for snake communities worldwide, but relatively few studies have investigated its occurrence and extent with island assemblages of snakes. In Sardinia (Mediterranean Sea), two species of whip snakes (Colubridae) co-occur, one of them being abundant and widespread (Hierophis viridiflavus) and the other being localized and critically endangered (Hemorrhois hippocrepis). A previous hypothesis suggested that the latter species would be confined to suboptimal habitats by the former species, which is a stronger competitor for food. As a consequence, He. hippocrepis would not only be rare but would also be smaller in body size in Sardinia than in other regions of its range where Hi. viridiflavus does not occur. In 1999?C2010, we studied habitat selection, food habits, and body sizes of these two snakes in sympatric populations, applying a suite of statistical tools including null models and Monte Carlo simulations. We observed that dietary habits were different between species (compared to Hi. viridiflavus, He. hippocrepis more frequently preyed upon rodents and less frequently on lizards, and within rodent prey, more frequently upon Rattus and less frequently upon Mus), but not in a way compatible with competitively induced trophic niche partitioning. The two species were similar in terms of prey size and predator-size?Cprey-size relationships. They also differed in habitat selection (maquis was the preferred habitat for both, but Hi. viridiflavus was found significantly more often than He. hippocrepis in grasslands, cultivations, and artificial pinewoods) but again in a non-competitively directed way. In addition, there was no evidence for the hypothesis that He. hippocrepis was confined to suboptimal habitats. Body sizes were similar between species (with males being significantly larger than females), and Sardinian He. hippocrepis were not smaller than conspecifics inhabiting regions without Hi. viridiflavus. Overall, our study showed that the two species differed in some aspects of their ecology, but these differences could not be due to competitive interactions. The conservation implications of these results are also discussed.     

Behavioral and physiological adjustments to new predators in an endemic island species, the Galápagos marine iguana

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.     

Population genetics of a polyploid: is there hybridization between lineages of Hyla versicolor?

Several studies have demonstrated that polyploid species can form recurrently from their progenitors, but few studies have evaluated gene flow between the resultant polyploid lineages. Here we examine the possibility of hybridization between lineages of the tetraploid common gray treefrog (Hyla versicolor). We utilize a polymerase chain reaction (PCR) cloning approach to estimate the genotypes of tetraploid individuals and measure genetic differentiation between (1) sympatric populations of two lineages and (2) allopatric populations of a single lineage. We find that allele frequencies in sympatric populations of two lineages do not differ, suggesting that frogs of these two lineages hybridize in areas where they co-occur.     

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.     

Does a top predator reduce the predatory impact of an invasive mesopredator on an endangered rodent?

The mesopredator release hypothesis (MRH) predicts that reduced abundance of top‐order predators results in an increase in the abundance of smaller predators (mesopredators) due to a reduction in intra‐guild predation and competition. The irruption of mesopredators that follows the removal of top‐order predators can have detrimental impacts on the prey of the mesopredators. Here we investigated the mechanisms via which the presence of a top‐order predator can benefit prey species. We tested predictions made according to the MRH and foraging theory by contrasting the abundances of an invasive mesopredator (red fox Vulpes vulpes) and an endangered prey species (dusky hopping mouse Notomys fuscus), predator diets, and N. fuscus foraging behaviour in the presence and absence of a top‐predator (dingo Canis lupus dingo). As predicted by the MRH, foxes were more abundant where dingoes were absent. Dietary overlap between sympatric dingoes and foxes was extensive, and fox was recorded in 1 dingo scat possibly indicating intra‐guild predation. Notomys fuscus were more likely to occur in fox scats than dingo scats and as predicted by the MRH N. fuscus were less abundant in the absence of dingoes. The population increase of N. fuscus following rainfall was dampened in the absence of dingoes suggesting that mesopredator release can attenuate bottom‐up effects, although it remains conceivable that differences in grazing regimes associated with dingo exclusion could have also influenced N. fuscus abundance. Notomys fuscus exhibited lower giving‐up densities in the presence of dingoes, consistent with the prediction that their perceived risk of predation would be lower and foraging efficiency greater in the presence of a top‐predator. Our results suggest that mesopredator suppression by a top predator can create a safer environment for prey species where the frequency of fatal encounters between predators and prey is reduced and the non‐consumptive effects of predators are lower.     

Mesobuthus gibbosus (Scorpiones: Buthidae) on the island of Rhodes — hybridization between Ulysses’ stowaways and native scorpions?

Allozyme data suggest that the Rhodes population of Mesobuthus gibbosus is a hybrid population of recent origin. Namely, it is a mixture between an autochthonous population and an artificially introduced population probably from the Greek mainland. All samples were mainly composed of F1 hybrid genotypes and genotypes either fixed for autochthonous or introduced alleles. Back-cross hybrid genotypes were very rare. Mitochondrial DNA analysis, in contrast, revealed only one group of closely related haplotypes that are unique for the Rhodes populations, thus suggesting asymmetric introgression of the two marker classes.     

Paternal effects on seed germination: a barrier to the genetic assimilation of an endemic plant taxon?

We used a crossing experiment to investigate post-zygotic barriers that might limit introgression between a pair of closely-related, gynodioecious plant species--the widespread weed Silene vulgaris and the local Swedish endemic S. uniflora ssp. petraea. The study not only considered the effects of hybridization on conventionally-used (primary) fitness components such as seed set and progeny survival, but also provided a test for the effects of interspecific hybridization on characters with more subtle or habitat-specific effects on fitness. We detected highly significant paternal effects on seed germination properties, with the germination characteristics of hybrid seed resembling those of the species that served as the pollen donor. These paternal effects on germination represent a potentially strong barrier to interspecific introgression in the two species' natural habitats, where an inappropriate germination response in the habitat of the maternal parent may lead to the failure of seedling establishment. Interspecific crosses had weak or variable effects on progeny survival, flowering and sex ratio, but these effects could not be interpreted in terms of barriers to introgression. Our results indicate that nuclear restorers in S. vulgaris have the capacity to suppress cytoplasmic male-sterility genes in its endemic congener.     

What is a patch in a dynamic metapopulation? Mobility of an endangered woodland butterfly,Euphydryas maturna

In metapopulations of butterflies inhabiting transient forest openings, the dynamic character of biotopes prevents unequivocal delimitation of habitat patches, complicating analyses of inter-patch dispersal. We analyse mobility of one such metapopulation, using mark-recapture data on an endangered butterfly, the scarce fritillary Euphydryas maturna , at its last site in the Czech Republic. The butterfly inhabits woodland clearings, its population numbered 190 individuals in 2002. We modelled movements in eight habitat patchworks delimited according to different criteria and superimposed over the forest, using the Virtual Migration model. Resulting mobility parameters were generally robust against patchwork definitions, the main distinction was between patchworks based on presence of adults and consisting of small patches and patchworks based on distributions of larval nests and consisting of large patches. Emigration constant decreased towards the latter, whereas males suffered higher migration mortality than females in the former. Patchworks delimited according to presence of adults performed better than patchworks based on distribution of larval nests. A comparison of our parameters with those found for the species in Finland showed that the Czech butterflies were more prone to leave individual patches and suffered higher migration mortality, which combined into considerably shorter survival. We conclude that transferring dispersal parameters among different regions and populations is more risky than using less suitable definitions of habitat patches within single region.     

LEA Gene Introns: is the Intron of Dehydrin Genes a Characteristic of the Serine-Segment?

Dehydrins, which belong to group 2 LEA proteins, are a family of intrinsically unstructured plant proteins that accumulate during the late stages of embryogenesis and in response to abiotic stresses. We have previously reported that the OpsDHN1 gene, encoding an SK₃-type acidic dehydrin protein from Opuntia streptacantha, contains an intron inserted within the sequence encoding the S-motif. Herein, we present an in silico analysis of intron sequences in dehydrin genes from mono- and dicotyledonous plants that reveals a preference for insertion within the nucleotide sequence encoding the S-motif. Sequence comparison of ten Dhn genes from Arabidopsis thaliana and the orthologous genes in Arabidopsis lyrata revealed that introns maintain considerable sequence identity and conserve the insertion pattern. Furthermore, syntenic regions were identified among eight orthologous genes of A. thaliana and A. lyrata, showing that correlated gene arrangements are conserved between these Arabidopsis species. Our study shows that most SKn-type dehydrins contain one intron that is conserved in phase and location; this intron is linked to the nucleotide sequence that encodes the S-motif.     

The relative advantages of plasticity and fixity in different environments: when is it good for a plant to adjust?

Plant populations and species differ greatly in phenotypic plasticity. This could be because plasticity is advantageous under some conditions and disadvantageous or not advantageous under others. We distinguish adaptive from injurious and neutral plasticity and discuss when selection should favor adaptive plasticity over genetic differentiation or lack of phenotypic variation. It seems reasonable to hypothesize that selection is likely to favor plasticity when an environmental factor varies on the same spatial scale as the plant response unit, when the plant can respond to an environmental factor faster than the level of the factor changes, and when environmental variation is highly but not completely predictable. Phenotypic plasticity might also tend to be more advantageous when mean resource availability is high rather than low, when a response can occur late in development rather than early, and when a response is reversible rather than irreversible. There is substantial evidence for the hypothesis that predictability favors plasticity. However, available evidence does not support the hypothesis that high mean resource availability necessarily favors plasticity. Testing hypotheses about when it is good for a plant to adjust is central to understanding the diversity of plasticity in plants.     

Distance,dams and drift: what structures populations of an endangered,benthic stream fish?

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Chemical interaction between the larva of a dipteran parasitoid and its coleopteran host: a case of exploitation of the communication system during the searching behaviour?

The robber fly Mallophora ruficauda is one of the principal apicultural pests in the Pampas region of Argentina. As adults, the flies prey on honey bees and other insects; while, as larvae, they parasitize scarab beetle larvae. Females of M. ruficauda lay eggs away from the host in tall grasses. After being dispersed by the wind, larvae drop to the ground, where they dig in search of their hosts. It is known that second instar larvae of M. ruficauda exhibit active host searching behaviour towards its preferred host, third instar larva of Cyclocephala signaticollis, using host-related chemical cues. Furthermore, previous works show that these chemical cues are produced in the posterior body half of hosts. However, the precise anatomical origin of these cues and whether they mediate any behaviour of C. signaticollis larvae remains yet unknown. In order to determine the precise origin of the chemical cue, we carried out olfactometer assays with different stimuli of extracts of the posterior C. signaticollis body half. Additionally, we tested whether C. signaticollis is attracted to any of the same extracts as in the previous experiments. We found that both second instar of M. ruficauda and third instar of C. signaticollis are attracted to extracts of the fermentation chamber (proctodeum). This is the first report of attraction of conspecific larvae in scarab beetles. We discuss a possible case of system communication exploitation in an immature parasitoid-host system.     

Characterization of an interplay between a Mycobacterium?tuberculosis MazF homolog,Rv1495 and its sole DNA topoisomerase I

The MazEF systems are thought to contribute to the capacity for long-term dormancy observed in the human pathogen, Mycobacterium tuberculosis. However, except for their functions as mRNA interferases, little is known regarding any additional cellular functions of these systems in the pathogen. In the present study, we observed a negative interplay between MazF protein Rv1495 and the sole M. tuberculosis DNA topoisomerase I (MtbTopA) with respect to protein functions. Through its C-terminal domain, MtbTopA physically interacted with and inhibited the mRNA cleavage activity of Rv1495. Rv1495, in turn, inhibited the DNA cleavage activity of MtbTopA as well as its function of relaxation of supercoiled DNA. An N-terminus fragment of Rv1495, designated Rv1495-N(29-56), lost mRNA cleavage activity, but retained a significant physical interaction and inhibitory effect on TopA proteins from both M. tuberculosis and M. smegmatis. This fragment, although less effective than the full-length protein, was able to inhibit mycobacterial growth when expressed through a recombinant plasmid in M. smegmatis. The Rv1495 physically interacted with the M. smegmatis TopA both in vitro and in vivo. Our findings imply that MazEF systems can affect bacterial survival by a novel mechanism that allows direct modulation of M. tuberculosis topoisomerase I.     

Do assortative mating and immigrant inviability help maintain population genetic structuring of an herbivore on a crop and a wild relative?

Population genetic structuring is common among herbivorous insects and frequently is associated with divergent host plants, such as crops and their wild relatives. Previous studies showed population genetic structuring in corn leafhopper Dulbulus maidis in Mexico, such that the species consists of two sympatric, host plant-associated populations: an abundant and widespread "pestiferous” population on maize (Zea mays mays), and a small and localized "wild" population on perennial teosinte (Zea diploperennis). a maize wild relative with a limited distribution. This study addressed whether assortative mating and immigrant inviability mediate genetic structuring of corn leafliopper by comparing the mating and reproductive successes of pestiferous and wild females that colonize their nonassociated host plants against the successes of females colonizing their associated host plants. Assortative mating was assessed by comparing mating frequencies and premating and mating times among females of each population on each host plant: immigrant inviability was assessed by comparing, across two generations, the fecundity, survival, development time, sex ratio, and population growth rate among leafhopper populations and host plants. Our results showed that on maize, and compared to resident, pestiferous females, wild females were more likely to mate, and greater proportions of their offspring survived to adult stage and were daughters;consequently, the per-generation population growth rate on maize was greater for immigrant, wild leafhoppers compared to resident, pestiferous leafhoppers. Our results suggested that wild leafhoppers emigrating to maize have a fitness advantage over resident, pestiferous leafhoppers, while immigrant pestiferous and resident wild leafhoppers on teosinte have similar fitnesses.     

Formation of a heterooctameric complex between aspartate α-decarboxylase and its cognate activating factor, PanZ, is CoA-dependent

The existence of a fifth essential protein for pantothenate biosynthesis in some enteric bacteria has recently been reported by Stuecker et al. [10] and Nozaki et al. (in press) [9]. This protein, PanZ, catalyses the activation of the PanD zymogen to form ADC and is essential for prototrophic growth. In this paper, we characterise the interaction of PanZ with coenzyme A and a constitutively inactive mutant of PanD using a combination of isothermal titration calorimetry and mass spectrometry. These approaches reveal that the two proteins interact with nanomolar affinity in a CoA-dependent fashion to form a heterooctameric complex.