Factors affecting the vulnerability of cane toads (Bufo marinus) to predation by ants

Experimental evidence on the determinants of prey vulnerability is scarce, especially for vertebrates in the field. Invasive species offer robust opportunities to explore prey vulnerability, because the intensity of predation on or by such animals has not been eroded by coevolution. Around waterbodies in tropical Australia, native meat ants (Iridomyrmex reburrus) consume many metamorph cane toads (Bufo marinus, an invasive anuran). We document the determinants of toad vulnerability, especially the roles of toad body size and ant density. Larger metamorphs were attacked sooner (because they attracted more ants), but escaped more often. Overall, smaller toads were more likely to be killed. Ant densities influenced toad responses, as well as attack rate and success. Data on the immediate outcomes of attacks underestimate mortality: more than 73% of apparent ‘escapees’ died within 24 h. Because mortality during this period was independent of toad size, predation was less size selective than suggested by immediate outcomes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 738–751.     

Climate change induced hybridization in flying squirrels

There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels ( Glaucomys volans ) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel ( Glaucomys sabrinus ). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans . There was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.     

Relationships between rust resistance genes at the M locus in flax

Genes at the M locus in flax ( Linum usitatissimum ) that confer resistance to flax rust ( Melampsora lini ) occur in complex haplotypes containing up to 15 related genes or gene fragments. We have cloned two additional functional resistance genes at this locus, M1 and M3 , by transposon tagging and candidate gene approaches, and investigated the genetic relationships between four genes ( M , M1 , M3 and M4 ) by recombination analysis. M1 and M3 , like M , are members of the nucleotide binding site, leucine-rich repeat (NBS-LRR) family. Comparisons of the predicted M1 and M3 amino acid sequences with M and L6 reveal that: (i) M1 contains four additional LRRs, probably as a result of an unequal crossover event between duplicated regions; (ii) M1 shares large segments of exact identity with M and M3, indicative of intragenic recombination events; and (iii) a large number of amino acid differences are scattered throughout the M, M1 and M3 proteins. Recombination analysis (here and in previous studies) has revealed that M readily recombines with M1 , M3 and M4 , whereas these three genes fail to recombine despite large family sizes (>5800) in two test-cross families, suggesting that they may occupy allelic positions in the gene cluster. Several restriction fragment length polymorphism markers within or near the M locus were mapped with respect to seven crossover events between M and M1 . The results of this and previous studies provide evidence of structural differences between: (i) homoeologous loci in the different genomes of flax; (ii) different haplotypes at the M locus; (iii) different resistance genes in the M group; and (iv) the flanking regions downstream of M locus resistance genes.     

Isolation and characterization of microsatellite loci for parentage assessment in captive populations of roseate spoonbill (Ajaia ajaja)

Six microsatellite loci were isolated and characterized to assess genetic diversity and determine parentage in three captive roseate spoonbill (Ajaia ajaja) populations. Analysis of 61 individuals from three zoological parks and one wild population at five polymorphic loci revealed an average of six alleles per locus and expected heterozygosities from 59% to 81% (average 70%). Since spoonbills do not exhibit obvious sexual dimorphism, Aaju4, which exhibited ZW‐specific alleles, was exceptionally useful for sex identification. These loci will be valuable tools for investigating genetic diversity and documenting patterns of parentage in captive roseate spoonbill populations.     

Tempo and mode of early gene loss in endosymbiotic bacteria from insects

Background  

Understanding evolutionary processes that drive genome reduction requires determining the tempo (rate) and the mode (size and types of deletions) of gene losses. In this study, we analysed five endosymbiotic genome sequences of the gamma-proteobacteria (three different Buchnera aphidicola strains, Wigglesworthia glossinidia, Blochmannia floridanus) to test if gene loss could be driven by the selective importance of genes. We used a parsimony method to reconstruct a minimal ancestral genome of insect endosymbionts and quantified gene loss along the branches of the phylogenetic tree. To evaluate the selective or functional importance of genes, we used a parameter that measures the level of adaptive codon bias in E. coli (i.e. codon adaptive index, or CAI), and also estimates of evolutionary rates (Ka) between pairs of orthologs either in free-living bacteria or in pairs of symbionts.     

Red Blood Cells: Centerpiece in the Evolution of the Vertebrate Circulatory System

All vertebrates except cold-water ice fish transport oxygenvia hemoglobin packaged in red blood cells (RBCs). VertebrateRBCs vary in size by thirtyfold. Differences in RBC size havebeen known for over a century, but the functional significanceof RBC size remains unknown. One hypothesis is that large RBCsare a primitive character. Agnathans have larger RBCs than domammals. However, the largest RBCs are found in urodele amphibianswhich is inconsistent with the hypothesis that large RBCs areprimitive. Another possibility is that small RBCs increase bloodoxygen transport capacity. Blood hemoglobin concentration ([Hb])and mean RBC hemoglobin concentration (MCHC) increase from Agnathato birds and mammals. However, the changes in [Hb] and MCHCdo not parallel changes in RBC size. In addition, RBC size doesnot affect blood viscosity. Thus, there is no clear link betweenRBC size and oxygen transport capacity. We hypothesize thatRBC size attends changes in capillary diameter. This hypothesisis based on the following observations. First, RBC width averages25% larger than capillary diameter which insures cell deformationduring capillary flow. Functionally, RBC deformation minimizesdiffusion limitations to gas exchange. Second, smaller capillariesare associated with increased potential for diffusive gas exchange.However, smaller capillaries result in higher resistances toblood flow which requires higher blood pressures. We proposethat the large capillary diameters and large RBCs in urodelesreflect the evolutionary development of a pulmonary vascularsupply. The large capillaries reduced systemic vascular resistancesenabling a single ventricular heart to supply blood to two vascularcircuits, systemic and pulmonary, without developing high pressureson the pulmonary side. The large RBCs preserved diffusive gasexchange efficiency in the large capillaries.     

Linking climate change and species invasion: an illustration using insect herbivores

Climate change and invasive species are two of the most important ecological issues facing the world today. Yet, to date these two factors have largely been viewed independently. In order to prevent large-scale economic and environmental damage and as a first step towards predicting and preventing invasions, it is important to understand the factors affecting invasions. Here, we focus on insect herbivores and link the climate change and invasive research fields. We illustrate using existing published research that life history traits can be useful indicators of future invasive potential. However, climate change will also affect propagule pressure and the communities into which invaders will arrive. With the aid of a meta-analysis we show that climate-induced community changes are likely to increase niche-availability in the future, further exacerbating the problem of invasive species. It is timely and important that further research linking these two important ecological threats is undertaken.     

Clonal variation in the survival and reproduction of Daphniapulicaria under low-food stress

1. Survivorship and reproductive parameters of eight Daphnia pulicaria clones were evaluated in a life-table experiment under four dietary regimes ranging from food limitation to complete food deprivation.
2. D . pulicaria exhibited both diet-independent interclonal differences and genotype–environment interactions in life-span.
3. Reproduction ceased entirely or nearly so under the three treatments with lowest food availability. Under life-long food limitation, differences between clones were evident in clutch sizes and age at first reproduction. Some clones produced ephippia at a markedly higher frequency than others under food-limiting conditions.
4. For most of the life-history traits evaluated, within-lake variation among clones exceeded differences between the two lake populations they represented.
5. Intraspecific variations in response to periods of food deprivation and to extended quantitative or qualitative food-limitation could affect the clonal composition of Daphnia populations. They are therefore of potential importance in determining the effect of altered phytoplankton assemblages on zooplankton communities.     

Life history, ecology and parasite community structure in Soviet birds

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life-history variables, 13 ecological variables and one non-biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.
A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life-history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co-variation between life-history traits and body weight among the host species under investigation.