COMPARATIVE MORPHOLOGY OF RADULAR TEETH IN CONUS: OBSERVATIONS WITH SCANNING ELECTRON MICROSCOPY

Radular teeth of 22 Indo-Pacific species of the genus Conus(Neogastropoda: Toxoglossa) were compared. On morphologicalfeatures all can be related to one of three known feeding modes:piscivorous, vermivorous and molluscivorous. Observations arereported on the radular teeth of six piscivores, thirteen vermivoresand three molluscivores. The radular teeth of piscivores areof two general types. In the first, two barbs and a posteriorly-directedprocess with a recurved tip are found at the anterior end. Inthe second, two barbs are located at the anterior end and theshaft is serrated for most of its length. An enlarged posteriorregion (terminal knob) is present in the first and absent inthe second. Molluscivores possess radular teeth with two anteriorbarbs and in some species a serrated shaft or terminal knob.The radular teeth of vermivores, which show much greater interspecificvariation than those of piscivores or molluscivores, are characterizedby one or two anterior barbs and in most species a serratedregion near the apex. A forwardly-projecting cone (basal spur)is usually located on the terminal knob. Piscivores and molluscivoreslack such basal spurs. The radular teeth of Conus are used toconvey a potent venom and hold prey firmly during feeding. Previouslyundescribed morphological features are noted on the teeth ofC. obscurus and C. lividus. Figured here for the first timeare the radular teeth of C. abbreviatus, C. aureus, C. catus,C. litoglyphus, C. pennaceus, C. rattus and C. sponsalis. ^*Present address: Department of Paleontology, University ofCalifornia, Berkeley, California 94720, U.S.A. (Received 2 April 1979;     

Overcoming the issue of small sample sizes in fragmentation genetics

Nazareno & Jump (2012) highlight potential issues with using small sample sizes in population genetic studies. By reanalysing allelic richness data from our recent publication on habitat fragmentation (Struebig et al. 2011), they assert that the observed relationship has been driven by three sites with the lowest number of individuals sampled. While sample size issues have been raised before in the genetic literature, Nazareno & Jump’s (2012) comment serves as a useful reminder to us all. Nevertheless, we disagree that our findings were significantly biased by sampling limitations. Here, we demonstrate by jackknifing that, contrary to the claims of Nazareno & Jump (2012), our correlations of allelic richness and fragment area are not driven solely by sites with low sample sizes. We maintain that small sample sizes can be accounted for in fragmentation studies and that sampling limitations should not detract from undertaking conservation genetic research.     

The evolution of sex pheromones in an ecologically diverse genus of flies

In theory, pheromones important in specific mate recognition should evolve via large shifts in composition (saltational changes) at speciation events. However, where other mechanisms exist to ensure reproductive isolation, no such selection for rapid divergence is expected. In Bactrocera fruit flies (Diptera: Tephritidae), males produce volatile chemicals to attract females for mating. Bactrocera species exhibit great ecological diversity, with a wide range of geographical locations and host plants used. They also have other mechanisms, including temporal and behavioural differences, which ensure reproductive isolation. Therefore, we predicted that their sex pheromones would not exhibit rapid divergence at speciation events. In the present study, we tested this idea by combining data on male sex pheromone composition for 19 species of Bactrocera with a phylogeny constructed from DNA sequence data. Analyses of the combined data revealed positive correlations between pheromone differences and nucleotide divergence between species, and between the number of pheromone changes along the phylogeny and the branch lengths associated with these changes. These results suggest a gradual rather than saltational mode of evolution. However, remarkable differences in sex pheromones composition exist, even between closely-related species. It appears therefore that the mode of evolution of sex pheromones in Bactrocera is best described by rapid saltational changes associated with speciation, followed by gradual divergence thereafter. Furthermore, species that do not overlap ecologically are just as different pheromonally as species that do. Thus, large changes in pheromone composition appear to be achieved, even in cases where other mechanisms to ensure reproductive isolation exist. We suggest that these differences are closely associated with rapid changes in host plant use, which is a characteristic feature of Bactrocera speciation. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97 , 594–603.     

Using parentage analysis to examine gene flow and spatial genetic structure

Numerous approaches have been developed to examine recent and historical gene flow between populations, but few studies have used empirical data sets to compare different approaches. Some methods are expected to perform better under particular scenarios, such as high or low gene flow, but this, too, has rarely been tested. In this issue of Molecular Ecology , Saenz-Agudelo et   al . (2009 ) apply assignment tests and parentage analysis to microsatellite data from five geographically proximal (2–6 km) and one much more distant (1500 km) panda clownfish populations, showing that parentage analysis performed better in situations of high gene flow, while their assignment tests did better with low gene flow. This unusually complete data set is comprised of multiple exhaustively sampled populations, including nearly all adults and large numbers of juveniles, enabling the authors to ask questions that in many systems would be impossible to answer. Their results emphasize the importance of selecting the right analysis to use, based on the underlying model and how well its assumptions are met by the populations to be analysed.     

Extensive expression regulation and lack of heterologous enzymatic activity of the Class II trehalose metabolism proteins from Arabidopsis thaliana

Trehalose metabolism has profound effects on plant growth and metabolism, but the mechanisms involved are unclear. In Arabidopsis , 21 putative trehalose biosynthesis genes are classified in three subfamilies based on their similarity with yeast TPS1 (encoding a trehalose-6-phosphate synthase, TPS) or TPS2 (encoding a trehalose-6-phosphate phosphatase, TPP). Although TPS1 (Class I) and TPPA and TPPB (Class III) proteins have established TPS and TPP activity, respectively, the function of the Class II proteins (AtTPS5-AtTPS11) remains elusive. A complete set of promoter- β -glucurinidase/green fluorescent protein reporters demonstrates their remarkably differential tissue-specific expression and responsiveness to carbon availability and hormones. Heterologous expression in yeast furthermore suggests that none of the encoded enzymes displays significant TPS or TPP activity, consistent with a regulatory rather than metabolic function for this remarkable class of proteins.     

Do virus‐resistant plants pose a threat to non‐target ecosystems? II. Risk assessment of an Australian pathosystem using multi‐scale field experiments

It has been widely argued that the acquisition of novel disease resistance genes by wild host populations following the release of novel pathogen‐resistant plants into agricultural systems could pose a significant threat to non‐target plant communities. However, predicting the magnitude of ecological release in wild plant populations following the removal of disease remains a major challenge. In this paper we report on the second phase of a tiered risk assessment designed to investigate the role of disease on host growth, survival, fecundity and fitness in a model pathosystem (the pasture species Trifolium repens infected with Clover yellow vein virus, ClYVV) and to assess the level of risk posed to at‐risk native plant communities in southeast Australia by newly developed genetically modified and conventionally bred virus‐resistant T. repens genotypes. Multi‐year field experiments conducted in woodland and grassland environments using host‐pathogen arrays derived from 14 ClYVV isolates and 21 T. repens genotypes indicate that viral infection reduces fecundity, growth and survival of wild T. repens plants but that the severity of these effects depends on host tolerance to infection, isolate aggressiveness and specific spatial and temporal environmental conditions. Demographic modelling showed that by reducing host survival and growth, ClYVV also limits the intrinsic population growth rate and niche size of wild T. repens populations. Given the significant fitness cost associated with viral infection we conclude that virus‐resistant T. repens genotypes may pose a threat to some high conservation‐value non‐target ecosystems in SE Australia. We also argue that long‐term, multi‐tiered experiments conducted in a range of controlled and non‐controlled environments are necessary to detect and accurately quantify risks associated with the release of disease‐resistant plants in general.     

Bispectral Index Analysis of Opioid Immobilization of Rocky Mountain Elk

Abstract: We immobilized elk with either isoflurane to produce general anesthesia (control), 0.01 mg/kg carfentanil plus 0.1 mg/kg xylazine, or 0.25 mg/kg butorphanol plus 0.4 mg/kg azaperone plus 0.15 mg/kg medetomidine (BAM) and measured the bispectral index (BIS). The carfentanil-xylazine BIS (70.4 + 1.4) and the BAM BIS (60.2 + 1.5) were higher than the control BIS (47.2 + 4.1; P ≤ 0.001). These data indicate that opioids produce neuroleptanalgesia and not general anesthesia or sedation, which explains observed elk responses to these drugs.     

An invasive species imposes selection on life‐history traits of a native frog

As well as their direct ecological impacts on native taxa, invasive species can impose selection on phenotypic attributes (morphology, physiology, behaviour, etc.) of the native fauna. In anurans, body size at metamorphosis is a critical life‐history trait: for most challenges faced by post‐metamorphic anurans, larger size at metamorphosis probably enhances survival. However, our studies on Australian frogs (Limnodynastes convexiusculus) show that this pattern can be reversed by the arrival of an invasive species. When metamorph frogs first encounter invasive cane toads (Bufo marinus), they try to eat the toxic invader and, if they are able to do so, are likely to die from poisoning. Because frogs are gape‐limited predators, small metamorphs cannot ingest a toad and thus survive long enough to disperse away from the natal pond (and thus from potentially deadly toads). These data show that larger size at metamorphosis can reduce rather than increase anuran survival rates, because larger metamorphs are more easily able to ingest (and thus be poisoned by) metamorph cane toads. Our results suggest that patterns of selection on life‐history traits of native taxa (such as size and age at metamorphosis, seasonal timing of breeding and duration of pondside aggregation prior to dispersal) can be modified by the arrival of an invasive species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 329–336.     

Genomic islands of speciation or genomic islands and speciation?

Populations of the malaria mosquito, Anopheles gambiae, are comprised of at least two reproductively isolated, sympatric populations. In this issue, White et al. (2010) use extensive sampling, high‐density tiling microarrays, and an updated reference genome to clarify and expand our knowledge of genomic differentiation between these populations. It is now clear that DNA near the centromeres of all three chromosomes are in near‐perfect disequilibrium with each other. This is in stark contrast to the remaining 97% of the assembled genome, where fixed differences between populations have not been found, and many polymorphisms are shared. This pattern, coupled with direct evidence of hybridization in nature, supports models of “mosaic” speciation, where ongoing hybridization homogenizes variation in most of the genome while loci under strong selection remain in disequilibrium with each other. However, unambiguously demonstrating that selection maintains the association of these pericentric “speciation islands” in the face of gene flow is difficult. Low recombination at all three loci complicates the issue, and increases the probability that selection unrelated to the speciation process alters patterns of variation in these loci. Here, we discuss these different scenarios in light of this new data.