Pityohyphantes Phrygianus Research Articles

Evaluating the Structure of Enemy Biodiversity Effects on Prey Informs Pest Management

Evaluating the structure of enemy biodiversity effects on prey in agroecosystems can provide insights into biological pest control functioning. With this aim, theoretical models that describe biological mechanisms underlying prey suppression can be developed and confronted with experimental data by means of model selection. Here, we confront multiplicative risk models to evaluate the structure of multiple predator effects on the whitefly Trialeurodes vaporariorum provided in tomatoes by two spiders (Oxyopes lineatus and Pityohyphantes phrygianus) and two mirids (Nesidiocoris tenuis and Macrolophus melanotoma). Biologically meaningful parameters retained in the best models showed that several predator traits differently affected pest control: species-specific per capita predation rates, prey use extent, different type of interactions between predators, and the response of predator species to prey density and environmental temperature. Even from a limited perspective of single-pest control and short term experiment, this study suggests that assembly of the four predator species results in predator complementarity across prey life stages and density, interactions of prey and predators with environmental conditions, and interactions between predators that do not result in whitefly control disruption. Such information about enemy biodiversity and whitefly control functioning can drive hypotheses about sustainable pest management options in local agroecosystems.

Sex ratio, mating behaviour and Wolbachia infections in a sheetweb spider

The solitary sheetweb spider Pityohyphantes phrygianus has a female-biased primary sex ratio. Earlier studies have indicated that female post-copulatory position may influence the degree of bias, but the adaptive significance of the departure from a Fisherian 1 : 1 sex ratio is not known. In this study we show that there is a significant relationship between abdominal position and offspring sex ratio in undisturbed females. Moreover, female mating behaviour (and thus sex ratio) is correlated with female size, but this relationship may shift from negative to positive depending on the presence of the maternally acquired endosymbiotic bacterium Wolbachia in both sexes. A survey of wild-caught individuals shows that the incidence of Wolbachia infection in natural populations is high. This indicates that Wolbachia may be a significant factor influencing female post-copulatory behaviour and sex ratio in natural populations. We discuss various adaptive reasons for sex-ratio bias and behavioural plasticity in females. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 181–186.

Chromosome variation in embryos of a solitary spider, Pityohyphantes phrygianus, with skewed sex ratio

Chromosome numbers were investigated in developing embryos of the solitary sheetweb spider Pityohyphantes phrygianus (Araneae: Linyphiidae). It was concluded that 2n = 25 in males, and 2n = 28 in females, i.e., males are X1X2X30. Aberrant chromosome numbers were found in 3.2 % of the embryos. In 1.8 % of the embryos, the haploid chromosome number, n = 14, was observed, suggesting that unfertilized eggs could start developing. A few polyploid embryos were also observed. The proportion of embryos with aberrant chromosome numbers was significantly higher in the second brood of the females than in the first one. The observed chromosome variation suggests that the meiosis in Pityohyphantes phrygianus is unstable. An unstable genetic mechanism may have implications at the population level in this case as the primary sex ratio is female biased in P. phrygianus. Conceivable mechanisms of the skewed sex ratio are segregation distorsion and sperm selection. The evolutionary implications of the results are discussed.

Variable Female Mating Positions and Offspring Sex Ratio in the Spider Pityohyphantes phrygianus (Araneae: Linyphiidae)

Chromosomal sex determination and male heterogamety have been thought to seriously impede direct sex ratio control. However, in Pityohyphantes phrygianus, a solitary sheetweb spider with a skewed sex ratio, earlier experimental studies suggested that there are options for female control of offspring sex ratio, if females change their position during the normal mating sequence. Here we show that under natural conditions there is considerable between-female variation in positions, especially after termination of mating. Computer simulations of the orientation of female inner genitalia suggest that sperm are placed in different storage sites depending on the positions adopted. This means that a specific position after mating might potentially influence offspring sex ratio. The variance in offspring sex ratio among females in earlier experiments was binomially distributed, which leads us to conclude that females control the mean sex ratio but do not exercise direct control of the sex of individual offspring.

Female genitalia in Pityohyphantes phrygianus, a spider with a skewed sex ratio

AbstractThe functioning of female genitalia in many arthropods, especially the site and mode of sperm storage, may have a strong impact on the pattern of sperm usage, leading to differential male fertilization success and even varying offspring sex ratios. The female genital morphology of the linyphiid spider Pityohyphantes phrygianus was investigated, as this species was shown to possess an intriguing mechanism of sex ratio determination, possibly related to genital morphology. By means of SEM and serial semi‐thin sectioning, two distinctly different spermathecae plus an additional sperm sac, equipped with several valves, were found on each side of the genital apparatus. Sperm is stored under different conditions, as one of the spermathecae exhibits large gland cells of different types that discharge their products into the spermatheca through long secretory ducts, whereas the other spermatheca is surrounded by a simpler type of gland cell. Furthermore, there are folds instead of closed ducts leading to the spermathecae, and from the spermathecae to the oviduct. The latter fertilization‐fold runs inside the copulatory chamber and enters the oviduct from the outside. The mechanisms for sex ratio bias in spiders are discussed. The occurrence of two types of spermatheca of which one is twisted, provides good evidence for the involvement of female genital morphology in sex ratio control of P. phrygianus offspring. Data are compiled on species for which information is available on sex ratio and female genital morphology. We put forward a hypothesis that in species with a skewed sex ratio, there is interaction between female genital morphology and behaviour, i.e. change of body position before, during or immediately after sperm transfer.

Bird predation as a sex‐ and size‐selective agent of the arboreal spider Pityohyphantes phrygianus

1. The solitary sheetweb spider Pityohyphantes phrygianus (Araneae: Linyphiidae) lives in canopies of coniferous trees. Earlier studies in Scandinavia have shown that bird predation affects the spider abundance negatively. 2. In a large‐scale, 2‐year field experiment, passerine birds were excluded from foraging on spruce branches. The experimental branches were net‐enclosed, which prevented bird predation but left spiders free to leave and enter. Samples were taken in the autumn and spring for 2 years. 3. Removal of bird predation increased the mean number of subadult P. phrygianus per branch between 2·1 and 10·6 times the control number for each sex. Bird predation had approximately similar effects on the sexes, except in the second experimental spring when males were affected twice as much as females, and there was a significantly lower proportion of males on control branches exposed to bird predation than on net‐enclosed branches. 4. The mean size of females was larger on net‐enclosed branches than on controls in both spring samples. In males, this was the case in the first spring sample only. 5. This study shows that there are also mortality costs for both sexes associated with large size in the non‐mating season. In certain winters, however, there is an additional mortality risk to males, presumably caused by a higher activity level than in females.

Sex ratio variation in sheet-web spiders: options for female control?

Female biased primary sex ratios are known in many social spiders with highly structured populations and strong inbreeding. However, the primary sex ratio of the solitary spider Pityohyphantes phrygianus is also skewed, producing one-third males and two-thirds females, whereas the sex ratio is even in the related Linyphia triangularis. The female mating behaviours and genitalia were compared, revealing differences in, e.g. apparatus for sperm storing and in mating position; P. phrygianus takes a near perpendicular position before copulation starts. After completion of mating in P. phrygianus, experimental manipulations of the female's position for 24 h significantly changed the proportion of males in the first brood. This suggests that a biasing mechanism acting in the female's spermathecae-ducts is at least partly responsible for the sex ratio bias. However, the sex ratio in first and second broods averaged an overall mean of one-third males. The results suggested that females in the wild have options, which are not used, to direct the primary sex ratio away from one-third males. This deviation from Fisherian sex ratio may be caused by selfish genetic elements and/or meiotic drive.

Skewed Primary Sex Ratio in the Solitary Spider Pityohyphantes phrygianus

Skewed Primary Sex Ratio in the Solitary Spider Pityohyphantes phrygianus

Protandry and Moulting to Maturity in the Spider Pityohyphantes phrygianus

In natural populations in SW Sweden, the overwintering subadult specimens of the sheetweb spider Pityohyphantes phrygianus (C. L. Koch) moult to maturity in late spring, the males on average maturing before the females. In laboratory experiments, three environmental cues were manipulated―photoperiod, temperature and food level―to assess their importance to the decision to moult and protandry in overwintering subadults

Local adjustment of sex ratio in the spider Pityohyphantes phrygianus

The sex ratio in five populations of the sheetweb spider Pityohyphantes phrygianus in southwest Sweden was investigated in July and September, the spiders being juveniles and subadults, respectively. In July, no heterogeneity between the five populations was found and the pooled samples revealed a sex ratio of 36% males and 64% females. A significant heterogeneity in sex ratio was observed in the September samples; the proportion of males varied between 23% and 40%. In several cases, male mean weight differed significantly between the five populations, comparing the July and September samples separately. This suggests that the prey availability varied considerably between the sites. In September, dead spiders were collected in two sites. This mortality was probably caused by starvation and the mortality rates differed significantly between the two sites. Indirect evidence suggested that the local sex ratio was affected by the prey availability, males being at a relative disadvantage in poor sites. Local environmental conditions may govern the adult sex ratio in this spider by causing differential mortality and/or migration.

Effects of simulated acid rain on growth rate in a spruce-living spider

Growing juveniles of the spruce-living spider Pityohyphantes phrygianus were sprayed with water of different acidity—pH ∼7 (control), 4·0 (acid rain) and 2·2-in a 2·5-month laboratory experiment. The growth rates did not differ between control and pH 4·0, while there was a significant growth reduction at pH 2·2. A low mortality occurred only in the pH 2·2 group. P. phrygianus seems to be resistant against acid rain although negative long-term effects cannot be ruled out.

Body Size and Survival: Implications for an Overwintering Spider

The relationship between body size and survival was investigated in overwintering specimens of the winter-active spider Pityohyphantes phrygianus in a natural population in SW Sweden. Size was measured by (1) the carapace width (independent of temporary changes in mass), and (2) the abdominal height (strongly correlated with mass and indicating nutritional condition). Measurements were taken before and after three winters. The mean carapace width increased in overwintering females in one of the three years, suggesting directional selection since moulting does not occur during winter. In the other two years the means were retained but the variance decreased during winter, suggesting stabilizing selection. The females increased their mean abdominal height throughout all three winters investigated; mean weight increases ranged from 5% to 98% of the average fresh mass in autumn. Regression analysis showed that the mass was correlated with the carapace width in autumn and spring. Females with large carapace width increased their weight more than did small females during one of the winters, but the survival of large females did not improve. During the only winter males were possible to analyse, their carapace width increased (directional selection), as did the abdominal height. In a field experiment during one of the winters no significant difference in winter survival was found comparing heavy (autumn weight >9.5 mg) and light (<9.5 mg) females. It was concluded that large size in itself did not increase the survival rate of overwintering spiders. However, the results suggested that both sexes may grow during winter and this may be important for their reproductive success in the following spring.

Sex ratio in the spider Pityohyphantes phrygianus affected by winter severity

The sex ratio of subadult Pityohyphantes phrygianus was recorded before and after five winters in a natural population in coniferous forest in south‐west Sweden. In autumn, the proportion of males was on average 33–8% (range 28–7–40–1) and the proportion of females was 66–2% (59–9–71–3). In each of the winters 1981 82, 1982–83, 1984–5, the proportion of males decreased significantly. The proportion of males decreased more the lower the February mean temperature. Field experiments showed that low ambient temperature in winter caused high mortality among spiders. Experimental data also suggest that males are more vulnerable to low winter temperatures than are females. Indirect evidence indicates that neither predation pressure nor starvation alone are likely to cause the observed changes in sex ratio in the three winters. However, the combined effect of sex differences in predation by birds and cold‐induced mortality may explain why males disappear faster than females in certain winters.

Melanism in the spider Pityohyphantes phrygianus (C. L Koch): the genetics and the occurrence of different colour phenotypes in a natural population

In the sheetweb spider Pityohyphantes phrygianus (C. L. Koch) there is a continuous variation in dark colouration. The specimens may be divided into three main phenotype classes of colouration; pale, intermediate and melanic. Analyses of the genetic basis of colour variation in P. phrygianus showed that a polygenic system is probably involved. The narrow heritability of dark colouration was estimated as 0·43 (±0·25), based on parent-offspring regression using mid-parent and mean offspring scores. A small-scale laboratory experiment indicated that the melanics may have an activity—and hence a foraging—advantage over non-melanics at low temperatures. A temporal variation in the frequencies of the three main phenotype classes was observed in a natural population in SW Sweden. This variation was due to differences between the proportion of pale and intermediate specimens in three cohorts; the proportion of melanics was low in all samples, averaging 3·7 per cent.

Mating Reduces Predation on Male Milkweed Beetles

Previous articleNext article No AccessNotes and CommentsMating Reduces Predation on Male Milkweed BeetlesDavid E. McCauley, and Ellen C. LawsonDavid E. McCauley Search for more articles by this author , and Ellen C. Lawson Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 127, Number 1Jan., 1986 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284472 Views: 4Total views on this site Citations: 21Citations are reported from Crossref Copyright 1986 The University of ChicagoPDF download Crossref reports the following articles citing this article:Madison Hernandez, Paul Masonick, Christiane Weirauch Crowdsourced online images provide insights into predator-prey interactions of putative natural enemies, Food Webs 21 (Dec 2019): e00126.https://doi.org/10.1016/j.fooweb.2019.e00126P. A. Lagos A review of escape behaviour in orthopterans, Journal of Zoology 303, no.33 (Sep 2017): 165–177.https://doi.org/10.1111/jzo.12496Danilo G. Muniz, Glauco Machado Experimental limitation of oviposition sites affects the mating system of an arachnid with resource defence polygyny, Animal Behaviour 109 (Nov 2015): 23–31.https://doi.org/10.1016/j.anbehav.2015.08.007Taís M. Nazareth, Glauco Machado, Claude Wicker-Thomas Egg Production Constrains Chemical Defenses in a Neotropical Arachnid, PLOS ONE 10, no.99 (Sep 2015): e0134908.https://doi.org/10.1371/journal.pone.0134908Gustavo S. Requena, Glauco Machado Lack of costs associated with nest-related behaviors in an arachnid with exclusive paternal care, Oikos 124, no.33 (Sep 2014): 372–380.https://doi.org/10.1111/oik.01641Amanda M. Franklin, Zoe E. Squires, Devi Stuart-Fox, Therésa M. Jones Does Predation Risk Affect Mating Behavior? An Experimental Test in Dumpling Squid (Euprymna tasmanica), PLoS ONE 9, no.1212 (Dec 2014): e115027.https://doi.org/10.1371/journal.pone.0115027Giovanni Benelli, Gabriele Gennari, Alessandra Francini, Angelo Canale Longevity costs of same-sex interactions: first evidence from a parasitic wasp, Invertebrate Biology 132, no.22 (May 2013): 156–162.https://doi.org/10.1111/ivb.12017Stephen F. Matter Abundance of an Herbivorous Beetle: Factors Affecting Dispersal and Local Reproduction, The American Midland Naturalist 162, no.11 (Jul 2009): 19–28.https://doi.org/10.1674/0003-0031-162.1.19Maria Almbro, Cecilia Kullberg The downfall of mating: the effect of mate-carrying and flight muscle ratio on the escape ability of a pierid butterfly, Behavioral Ecology and Sociobiology 63, no.33 (Oct 2008): 413–420.https://doi.org/10.1007/s00265-008-0675-4Stephen F. Matter Changes in landscape structure decrease mortality during migration, Oecologia 150, no.11 (Jul 2006): 8–16.https://doi.org/10.1007/s00442-006-0491-3Rickey D. Cothran Precopulatory mate guarding affects predation risk in two freshwater amphipod species, Animal Behaviour 68, no.55 (Nov 2004): 1133–1138.https://doi.org/10.1016/j.anbehav.2003.09.021O. Y. Martin, D. J. Hosken Copulation reduces male but not female longevity in Saltella sphondylli (Diptera: Sepsidae), Journal of Evolutionary Biology 17, no.22 (Dec 2003): 357–362.https://doi.org/10.1046/j.1420-9101.2003.00668.xQiao Wang, Wenyu Zeng , Environmental Entomology 33, no.33 ( 2004): 657.https://doi.org/10.1603/0046-225X-33.3.657L. M. Hanks INFLUENCE OF THE LARVAL HOST PLANT ON REPRODUCTIVE STRATEGIES OF CERAMBYCID BEETLES, Annual Review of Entomology 44, no.11 (Jan 1999): 483–505.https://doi.org/10.1146/annurev.ento.44.1.483Gary A. Polis, Joseph D. Barnes, Mary K. Seely, Joh R. Henschel, Margit M. 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Interspecific predation as a mortality factor among overwintering spiders.

Results from field experiments indicate that predation occurs among spruce-living spiders during winter in SW Sweden. Field observations of natural activity showed that Philodromus spp and Pityohyphantes phrygianus together make up 80% of the spiders active on spruce in winter. They are therefore potential predators on other overwintering spiders. Laboratory experiments were performed at +4° C to assess the importance of such predation between spiders. Small spiders (length <2.5 mm) had a mean winter mortality of 58% when kept together with large spiders (≧2.5 mm) which had a mean mortality of 3% only. Among the small spiders the Erigninae spp seemed to be more vulnerable to predation than other taxonomic groups. Predation also occurred when large P. phrygianus were kept together, but such predation caused mortality of less importance to the spider populations than the mortality among small spiders. Differences in spider density and food availability did not change this pattern. Considerable weight increase occurred in subadult P. phrygianus when fed during winter. This suggests that winter foraging specimens increase their fitness. Interspecific predation among spiders is suggested to be an important mortality factor in natural populations at high spider densities in November and December, when the ambient temperature often is above 0° C and when the density of large spiders is not yet substantially reduced by bird predation.