Is the evolution of inaccurate mimicry a result of selection by a suite of predators? A case study using myrmecomorphic spiders

Several hypotheses have been put forward to explain the evolution of inaccurate mimicry. Here we investigated the novel hypothesis that inaccurate mimicry (in color and shape) is maintained by opposing selective pressures from a suite of different predators: model-aversive visually oriented predators and model- and mimic-specialized predators indifferent to mimetic cues. We hypothesize that spiders resembling ants in color and shape escape predators that typically avoid ants but fall prey to ant-eating predators. We tested whether inaccurate myrmecomorphic spiders are perceived as their models by two types of predators and whether they can escape from these predators. We found that model-specialized (ant-eating) predators captured mimics significantly less frequently than their ant models, because mimics changed their behavior by fleeing predatory attacks. The fastest escape was found in less accurate mimics, indicating a negative association between visual resemblance and effectiveness of defenses. In trials with spider-eating predators, mimics were not captured more frequently than their models. The quality of defensive mechanisms appears to result from opposing selection forces exerted by the predator complex: mimics are more accurate (in color and shape) in microhabitats dominated by model-aversive predators and less accurate in microhabitats with model- and mimic-specialized predators.     

Is there intraguild predation between winter-active spiders (Araneae) on apple tree bark?

We studied whether there si intraguild predation among overwintering invertebrates in bark traps installed on apple trees. We found that 86% of the overwintering invertebrates in traps were predators, which were dominated by spiders (72%) of different guilds and different body sizes. Spiders had spatially segregated in the traps so that smaller specimens hid in an interstitial space that was inaccessible to larger specimens. Spiders of the bark-dwelling guild, Anyphaena and Philodromus, are winter-active and can prey on other smaller spiders. Analysis of their abundance in traps indicated a negative relationship between Anyphaena and Philodromus or other spiders. Inspection of traps during winter revealed an influx of spider specimens confirming their winter-activity. In a semi-field experiment, where overwintering in cardboard bands was studied under controlled conditions, we observed mortality of both winter-active Philodromus and Anyphaena spiders due to their interspecific predation. The mortality was affected by their size ratio – larger specimens consumed smaller ones. Presence of alternative prey, theridiid spiders, did not affect their mortalities, but the presence of shelters (interstitial spaces) did. In boards with interstitial spaces smaller spiders suffered lower mortality than in boards without the interstitial spaces. Obtained results suggest that intraguild predation between overwintering spiders can decrease their population density during winter.     

Is sexual organ reciprocity related to legitimate pollen deposition in distylous Pulmonaria (Boraginaceae)?

Heterostyly, i.e. the reciprocal positioning of anthers and stigmas, is a floral polymorphism that is thought to promote disassortative (i.e. between‐morph) pollination and to maintain genetic diversity within populations. Recent research, however, has shown several cases of heterostylous plant species in which the reciprocal positioning of the sexual organs varies, which may affect the likelihood of ‘legitimate’ pollination between compatible morphs, and hence morph fitness and ultimately the stability of this floral polymorphism. In this study, we investigated floral morphology and stigmatic pollen deposition patterns in nine Pulmonaria species (Boraginaceae) across Europe to test the hypothesis that sexual organ reciprocity is related to legitimate pollen deposition. We used a recently developed adaptive accuracy concept to assess the level of reciprocity and to relate inaccuracies in positioning of sexual organs to legitimate pollen deposition measured on stigmas in the field. The nine investigated Pulmonaria species showed substantial deviations from perfect reciprocity, with total inaccuracies varying between 2.9 and 20.3% relative to the squared mean of all anther and stigma heights in the population. In almost all cases, most of the inaccuracy was generated by the high‐level organs. Total pollen deposition was always higher on stigmas of long‐styled individuals, but stigmas of short‐styled individuals received significantly more legitimate pollen than stigmas of long‐styled individuals (71.23% and 38.75% respectively). We also found a weak but significant relationship between measures of inaccuracy and the level of disassortative pollination. Under these conditions of pollen flow, the distylous mating system is predicted to persist in only eleven (27%) of all sampled populations. Overall, these results indicate that deviations from perfect reciprocal herkogamy are common in Pulmonaria and have an impact on legitimate pollen deposition.     

The female genitalic morphology of “micronetine” spiders (Araneae,Linyphiidae)

Current knowledge of “micronetine” female genitalia is almost exclusively based on transmitted light microscopy data. As such, our understanding of the epigynal anatomy is incomplete and somewhat misleading, to the extent that it hinders comparative studies of linyphiid diversity. We used scanning electronic microscopy (SEM) to study the complex epigynal morphology of “micronetine” spiders. Enzymatic digestion of soft tissues allowed us to examine the internal chitinized structures in detail using SEM. A taxonomic sample of nine species was selected to represent the morphological genitalic diversity of female “micronetines” (including one member of the Erigoninae clade). Results reveal that the epigynum consists of a pair of grooves formed by integument folds (copulatory and fertilization grooves). The protruding epigynal region is divided into a ventral and a dorsal plate by the grooves; both plates can be modified to form an epigynal cavity and/or a scape. Our observations confirm the widespread occurrence of epigynal grooves, rather than ducts, in “micronetines”. Epigynal grooves seem to be common in linyphioids and other spider groups.     

Is Xysticus kochi (Araneae: Thomisidae) an efficient indigenous biocontrol agent of Frankliniella occidentalis (Thysanoptera: Thripidae)?

According to the present practice of Hungarian greenhouse sweet pepper production, only exotic agents are used for biological control purposes against thrips pests. The suitability for biological control of the second instars of an indigenous species, the common crab spider, Xysticus kochi Thorell (Araneae: Thomisidae) was tested on thrips species, Frankliniella occidentalis (Pergande) and Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) using a cage set-up on greenhouse sweet pepper plants. Effects of introducing second instars of X. kochi on thrips infested plants were judged by assessing the degree of aesthetical damage, the commercial value of the fruits (degree of economic loss) and the quality composition of the harvested peppers. The estimated damaged surface unit was significantly lower in control plants than in plants infested by F. occidentalis. A significant effect of the spider introduction was observed in all of the pepper quality indicators applied. We suspect that direct Xysticus predation or any other predator-induced effect resulted in reduced levels of damage on harvested peppers. However, further investigation is needed to detect the origin (e.g., predation and non-predation effects) of the suppression of thrips damage. Our results suggest that X. kochi could be an effective component of greenhouse antagonistic fauna and the application of mulch may encourage the effectiveness of spiderlings. An erratum to this article can be found at     

Is there a plastid in Perkinsus atlanticus (Phylum Perkinsozoa)?

Perkinsus atlanticus is a pathogenic protist that infects the clam Ruditapes decussatus. The recent proposal for the inclusion of the genus Perkinsus in a new phylum, Perkinsozoa, in the infra-kingdom Alveolata, gave rise to controversies whether this genus should form a phylum on its own. Molecular analysis of some conserved nuclear genes shows a closer proximity of the genus Perkinsus to the dinoflagellates than to the apicomplexans. Studies on extranuclear genomes, however, could also be very helpful for a more precise definition of those phyla. In Perkinsozoa, there have been until now no reports about the isolation of mitochondria as well as no conclusive results about the presence of any plastids, therefore a comparison with the data already obtained in Apicomplexa and Dinoflagellata has not yet been possible. In this work, we identify a plastid in Perkinsus atlanticus, using ultrastructural techniques and inhibition growth tests. It will be important to analyze the plastid genome at a molecular level, in order to confirm if the plastid in Perkinsus is more similar to those of Dinoflagellata or Apicomplexa. Such information will doubtless contribute to a more precise determination of the phylogenetic position of the genus Perkinsus.     

Is variation in susceptibility to Phytophthora ramorum correlated with population genetic structure in coast live oak (Quercus agrifolia)?

California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within- and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high.     

Is dietary niche breadth linked to morphology and performance in Sandveld lizards Nucras (Sauria: Lacertidae)?

The functional characteristics of prey items (such as hardness and evasiveness) have been linked with cranial morphology and performance in vertebrates. In lizards particularly, species with more robust crania generally feed on harder prey items and possess a greater bite force, whereas those that prey on evasive prey typically have longer snouts. However, the link between dietary niche breadth, morphology, and performance has not been explicitly investigated in lizards. The southern African genus Nucras was used to investigate this link because the species exhibit differing niche breadth values and dietary compositions. A phylogeny for the genus was established using mitochondrial and nuclear markers, and morphological clusters were identified. Dietary data of five Nucras species, as reported previously, were used in correlation analyses between cranial shape (quantified using geometric morphometrics) and dietary niche breadth, and the proportion of hard prey taken and bite force capacity. Dietary niche breadth and the proportion of hard prey eaten were significantly related to cranial shape, although not once phylogeny was accounted for using a phylogenetic generalized least squares regression. The proportion of evasive prey eaten was a significant predictor of forelimb length when phylogeny was taken into account. We conclude that, in Nucras, the percentage of evasive prey taken co‐evolves with forelimb morphology, and dietary niche breadth co‐evolves with cranial shape. However, although head width is correlated with the proportion of hard prey eaten, this appears to be the result of shared ancestry rather than adaptive evolution. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 674–688.     

An extraordinary new family of spiders from caves in the Pacific Northwest (Araneae, Trogloraptoridae, new family)

The new spider genus and species Trogloraptor marchingtoni Griswold, Audisio & Ledford is described as the type of the new family Trogloraptoridae. The oblique membranous division of the basal segment of the anterior lateral spinnerets of Trogloraptor suggests that this haplogyne family is the sister group of the other Dysderoidea (Dysderidae, Oonopidae, Orsolobidae and Segestriidae). Trogloraptor is known only from caves and old growth forest understory in the Klamath-Siskiyou region of Oregon and California.     

Does individual internal state affect the presence of a barrier web in Argiope bruennichii (Araneae: Araneidae)?

A barrier web created by some orb-web spiders has a three-dimensional web structure made of nonsticky threads, which is believed to provide a defensive function against predators. To test for a possible antipredatory function, we investigated relationships between the presence of a barrier web and an individuals internal state in the orb-web spider Argiope bruennichii, which builds orb-webs with and without a barrier web. Hunger level and molting as measures of internal state were represented by relative abdominal width and relative web size, respectively. Field survey showed that individuals with a wider abdomen and a smaller web tended to construct a barrier web. The positive relationship between body width and the presence of a barrier web supports the hypothesis of an antipredatory function as well-fed individuals are likely to expend more effort for defense. The small web size, however, may not be representative of molting because a correlation existed between web size and potential web substrates; therefore, the effect of molting on the presence of barrier web remains unclear.     

Is there functional cholinergic innervation in the frog duodenum (Rana catesbiana)?

1. To determine if functional cholinergic innervation occurs in the frog duodenum or not, the effects of exogenous acetylcholine and electrical transmural stimulation, the contractile activity of an acid extract from the frog duodenum, and the distribution of acetylcholinesterase (AChE) activity in the wall of the frog duodenum were investigated.2. Acetylcholine caused non-sustained contraction in a dose-dependent manner (100nM−1 mM). The ed₅₀) value was 17 ± 2.4 μM. Atropine (500 nM) shifted the dose-response curve for acetylcholine parallel to the right.3. Transmural stimulation of the frog duodenum caused frequency-dependent (0.5–50 Hz) contraction which was not decreased by atropine (500 nM) at all.4. The acid extract from the frog duodenum caused contraction of a longitudinal muscle strip of guinea-pig ileum but atropine (500 nM) had no significant effect on the contraction.5. Only a little AChE activity was found in Auerbach's plexus of the frog duodenum compared with that of the rat ileum.6. These results suggest that a cholinergic nerve is present in the frog duodenum but its physiological significance is very small.     

Why is Madagascar special? The extraordinarily slow evolution of pelican spiders (Araneae,Archaeidae)

Although Madagascar is an ancient fragment of Gondwana, the majority of taxa studied thus far appear to have reached the island through dispersal from Cenozoic times. Ancient lineages may have experienced a different history compared to more recent Cenozoic arrivals, as such lineages would have encountered geoclimatic shifts over an extended time period. The motivation for this study was to unravel the signature of diversification in an ancient lineage by comparing an area known for major geoclimatic upheavals (Madagascar) versus other areas where the environment has been relatively stable. Archaeid spiders are an ancient paleoendemic group with unusual predatory behaviors and spectacular trophic morphology that likely have been on Madagascar since its isolation. We examined disparities between Madagascan archaeids and their non‐Madagascan relatives regarding timing of divergence, rates of trait evolution, and distribution patterns. Results reveal an increased rate of adaptive trait diversification in Madagascan archaeids. Furthermore, geoclimatic events in Madagascar over long periods of time may have facilitated high species richness due to montane refugia and stability, rainforest refugia, and also ecogeographic shifts, allowing for the accumulation of adaptive traits. This research suggests that time alone, coupled with more ancient geoclimatic events allowed for the different patterns in Madagascar.     

Is male-infant caretaking related to paternity and/or mating activities in wild Barbary macaques (Macaca sylvanus)?

In species with a promiscuous mating system, the functions of male-infant caretaking remain unclear in the absence of genetic paternity tests. We tested paternal investment and hypotheses concerning reproductive tactics in wild groups of Barbary macaques, including results of genetic paternity tests. Our study revealed that male-infant caretaking was not related to the probability of paternity. In principle, males could use access to females to estimate paternity. However, we found that mating success was not related to paternity, so males could invest in infants that they had not sired, and caretaking of non-offspring was actually observed. Accordingly, males might be 'deceived' with respect to their paternal investment. In that case, one would expect a positive relation between mating success and the subsequent rate of male caretaking of infants. Such a relation is also lacking, leading to comprehensive rejection of the paternal investment hypothesis in Barbary macaques. By contrast, there was evidence that males showing infant care achieved higher mating frequencies than other males with the mothers of the relevant infants. Thus, male Barbary macaques do not show a 'mate-then-care' pattern, but they do exhibit a 'care-then-mate' pattern.     

Is the alkaline tide a signal to activate metabolic or ionoregulatory enzymes in the dogfish shark (Squalus acanthias)?

Experimental metabolic alkalosis is known to stimulate whole-animal urea production and active ion secretion by the rectal gland in the dogfish shark. Furthermore, recent evidence indicates that a marked alkaline tide (systemic metabolic alkalosis) follows feeding in this species and that the activities of the enzymes of the ornithine-urea cycle (OUC) for urea synthesis in skeletal muscle and liver and of energy metabolism and ion transport in the rectal gland are increased at this time. We therefore evaluated whether alkalosis and/or NaCl/volume loading (which also occurs with feeding) could serve as a signal for activation of these enzymes independent of nutrient loading. Fasted dogfish were infused for 20 h with either 500 mmol L(-1) NaHCO3 (alkalosis + volume expansion) or 500 mmol L(-1) NaCl (volume expansion alone), both isosmotic to dogfish plasma, at a rate of 3 mL kg(-1) h(-1). NaHCO3 infusion progressively raised arterial pH to 8.28 (control = 7.85) and plasma [HCO3-] to 20.8 mmol L(-1) (control = 4.5 mmol L(-1)) at 20 h, with unchanged arterial P(CO2), whereas NaCl/volume loading had no effect on blood acid-base status. Rectal gland Na+,K+-ATPase activity was increased 50% by NaCl loading and more than 100% by NaHCO3 loading, indicating stimulatory effects of both volume expansion and alkalosis. Rectal gland lactate dehydrogenase activity was elevated 25% by both treatments, indicating volume expansion effects only, whereas neither treatment increased the activities of the aerobic enzymes citrate synthase, NADP-isocitrate dehydrogenase, or the ketone body-utilizing enzyme beta-hydroxybutyrate dehydrogenase in the rectal gland or liver. The activity of ornithine-citrulline transcarbamoylase in skeletal muscle was doubled by NaHCO3 infusion, but neither treatment altered the activities of other OUC-related enzymes (glutamine synthetase, carbamoylphosphate synthetase III). We conclude that both the alkaline tide and salt loading/volume expansion act as signals to activate some but not all of the elevated metabolic pathways and ionoregulatory mechanisms needed during processing of a meal.     

Is the sperm type of the Nemertodermatida close to that of the ancestral Platyhelminthes?

Results from a transmission electron microscope study of the spermiogenesis and spermatozoon of Meara stichopi (Nemertodermatida, Platyhelminthes) indicate that the sperm type of the Nemertodermatida has evolved from the primitive metazoan sperm type rather than from an aberrant biflagellar sperm type as found in many other flatworms. The spirally coiled mitochondrial derivative in the mature spermatozoon develops from two large oval mitochondria in the early spermatid stages. A single flagellum grows out from a peripheral basal body adjacent to a perpendicularly placed accessory centriole. The basal body moves to a distal depression of the nucleus, and becomes equipped with an anchoring fibre apparatus. Most of the flagellum becomes axially incorporated into the developing spermatid. No trace of a second flagellum was found in any stage of the spermiogenesis. Rounded vesicles appear around the proximal, tapering end of the elongating nucleus. Most probably these vesicles form a thin acrosomal structure in the mature spermatozoon. No dense bodies, characteristic of many other ‘turbellarian’ flatworm sperm types, were found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Is promiscuity associated with enhanced selection on MHC-DQα in mice (genus Peromyscus)?

Reproductive behavior may play an important role in shaping selection on Major Histocompatibility Complex (MHC) genes. For example, the number of sexual partners that an individual has may affect exposure to sexually transmitted pathogens, with more partners leading to greater exposure and, hence, potentially greater selection for variation at MHC loci. To explore this hypothesis, we examined the strength of selection on exon 2 of the MHC-DQα locus in two species of Peromyscus. While the California mouse (P. californicus) is characterized by lifetime social and genetic monogamy, the deer mouse (P. maniculatus) is socially and genetically promiscuous; consistent with these differences in mating behavior, the diversity of bacteria present within the reproductive tracts of females is significantly greater for P. maniculatus. To test the prediction that more reproductive partners and exposure to a greater range of sexually transmitted pathogens are associated with enhanced diversifying selection on genes responsible for immune function, we compared patterns and levels of diversity at the Class II MHC-DQα locus in sympatric populations of P. maniculatus and P. californicus. Using likelihood based analyses, we show that selection is enhanced in the promiscuous P. maniculatus. This study is the first to compare the strength of selection in wild sympatric rodents with known differences in pathogen milieu.