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Multivalent ligands of ion channels have proven to be both very rare and highly valuable in yielding unique insights into channel structure and pharmacology. Here, we describe a bivalent peptide from the venom of Xibalbanus tulumensis, a troglobitic arthropod from the enigmatic class Remipedia, that causes persistent calcium release by activation of ion channels involved in muscle contraction. The high-resolution solution structure of φ-Xibalbin3-Xt3a reveals a tandem repeat arrangement of inhibitor-cysteine knot (ICK) domains previously only found in spider venoms. The individual repeats of Xt3a share sequence similarity with a family of scorpion toxins that target ryanodine receptors (RyR). Single-channel electrophysiology and quantification of released Ca2+ stores within skinned muscle fibers confirm Xt3a as a bivalent RyR modulator. Our results reveal convergent evolution of RyR targeting toxins in remipede and scorpion venoms, while the tandem-ICK repeat architecture is an evolutionary innovation that is convergent with toxins from spider venoms. Insect toxins with tandem repeats of neurotoxin domains have been found with enhanced receptor avidity. Here, the authors describe a bivalent toxin from remipede venom that targets ryanodine receptors, a rare target for animal venoms. [ABSTRACT FROM AUTHOR]

Active portfolio managers are judged on their ability to outperform agent's benchmarks, so optimising fund returns is important. Maximising fund outperformance is, however, non-trivial because active portfolios are subject to tracking error (TE) and other constraints. Feasible portfolios constrained by TE are bounded by an elliptical frontier in mean/variance space and may not be efficient. Also, 'optimal' can involve different objectives for different investors. Previous attempts to isolate optimal portfolios on the constant TE frontier have been limited to the maximum return, minimum risk and benchmark risk portfolios. More recently, the maximum risk-adjusted return portfolio on this frontier was identified. Using a highly stylised portfolio comprising only three assets for clarity and ease of explanation, we review for the first time existing optimal portfolio assemblies and introduce other possibilities: TE-constrained portfolios which are maximally diversified, exhibit risk parity, and have minimal intra-correlation between constituents. The methodology to generate optimal risk weights for these portfolios is explained and the way risk/return profiles change as TE changes is characterised. The way portfolios move in risk/return space in a changing TE milieu could initiate novel investment strategies for active fund managers. [ABSTRACT FROM AUTHOR]

Sexual cannibalism, the attack and consumption of the opposite sex by a conspecific during courtship, copulation, or soon after copulation, is widespread among invertebrates, but the causes of this behavior are not fully understood. We examine the mistaken identity hypothesis, which posits that non-copulatory cannibalism occurs because females do not recognize conspecific males as potential mates. This hypothesis predicts indiscriminate predatory behavior by females towards conspecific males and heterospecific prey. This prediction remains largely unexamined. We tested this prediction in the praying mantis Mantis religiosa (Mantodea: Mantidae) through two behavioral experiments. In experiment 1, we presented targets in isolation to females: dead conspecific males or dead common prey items from the field (grasshopper Chrysochraon dispar). In experiment 2, we presented simultaneous live targets to females: conspecific males and grasshoppers. In both experiments, we varied female mating status (virgin vs. mated). Results indicate some degree of attack discrimination by the females. In experiment 1, the females were significantly more likely to strike at the grasshoppers, and showed a shorter latency to strike at grasshoppers. In experiment 2, females tended to preferentially strike at the grasshoppers, although this result fell short of statistical significance. Female discrimination between the males and grasshoppers may be explained, in part, by the size difference between the males and grasshoppers. Female mating status did not affect the occurrence or latency to strike in either experiment. These results fail to strongly support the prediction of indiscriminate predatory behavior by females, while contributing to a broader taxonomic assessment of the mistaken identity hypothesis. [ABSTRACT FROM AUTHOR]

Six microsatellite loci are described for the squid Loligo pealeii. All loci exhibit some degree of allelic diversity. The pattern of inheritance was tested for 3 loci through an analysis of the filial genotypes from a female-male mating. At all 3 loci, the ratios of the filial genotypes conformed to the ratios expected by Mendelian inheritance. The hypervariable loci will be useful in studies on sexual selection in this species, whereas the relatively less variable loci will be useful to address questions of population structure. [ABSTRACT FROM AUTHOR]