Antagonistic interactions between the african weaver ant Oecophylla longinoda and the parasitoid Anagyrus pseudococci potentially limits suppression of the invasive mealybug Rastrococcus iceryoides

The ant Oecophylla longinoda Latreille forms a trophobiotic relationship with the invasive mealybug Rastrococus iceryoides Green and promotes the latter's infestations to unacceptable levels in the presence of their natural enemies. In this regard, the antagonistic interactions between the ant and the parasitoid Anagyrus pseudococci Girault were assessed under laboratory conditions. The percentage of parasitism of R. iceryoides by A. pseudococci was significantly higher on "ant-excluded" treatments (86.6% ± 1.27%) compared to "ant-tended" treatments (51.4% ± 4.13%). The low female-biased sex-ratio observed in the "ant-tended" treatment can be attributed to ants' interference during the oviposition phase, which disrupted parasitoids' ability to fertilize eggs. The mean foraging time, host handling time and number of successful oviposition in "ant-excluded" treatment were significantly higher compared to "ant-tended" treatments. When ant workers were allowed access to sterilized sand grains, mummified and unmummified R. iceryoides, they selectively removed the mummified mealybugs, indicating that they recognized the mummies as potential foods (1.2 ± 0.46 to 7.8 ± 1.17 mummies at 10 min intervals for 2 h). Percentage emergence from mummified R. iceryoides removed by the ants was significantly lower compared to emergence from mummies not exposed to ants. Although, host seeking parasitoids frequently evaded attacks, some were killed by the foraging ant workers (2.0 ± 0.38 to 6.0 ± 0.88 at 10 min intervals for 2 h). These results suggest for the first time that the presence of O. longinoda has a detrimental effect on the abundance, reproductive success and possibly oviposition strategy of female parasitoids, which might be a delimiting factor in field conditions if both natural enemies are to be recommended for use within the same agro-ecosystem.

Epigeal spider occurrence, abundance and diversity in moist acidic and dry heath tundra at Toolik Lake, Alaska

For the 2004-2006 growing seasons, we trapped a total of 6980 spiders (5066 adults, 1914 immatures) using pitfall traps at the Arctic Long Term Experimental Research (LTER) site in Toolik Lake, Alaska. We found 10 families and 51 putative species, with 45 completely identified, in two distinct habitats: Moist Acidic Tundra (MAT) and Dry Heath (DH) Tundra. We captured spiders belonging to the following families (number of species captured): Araneidae (1), Clubionidae (1), Dictynidae (1), Gnaphosidae (4), Linyphiidae (26), Lycosidae (11), Philodromidae (2), Salticidae (1), Theridiidae (1), and Thomisidae (3). Statistical comparisons of families captured at MAT and DH Tundra indicate that the habitats have significantly different spider communities (Chi Square Test: p < 0.0001, and Fisher's Exact Test: p = 0.0018). This finding is further supported by differences in similarity, diversity, evenness, and species richness between the two habitats. In this report, we present eight new state records and five extensions of previously described ranges for spider species. The following species are new state records for Alaska: Emblyna borealis (O.P.-Cambridge 1877), Horcotes strandi (Sytschevskaja 1935), Mecynargus monticola (Holm 1943), Mecynargus tungusicus (Eskov 1981), Metopobactrus prominulus (O.P. -Cambridge 1872), Poeciloneta theridiformis Emerton 1911, and Poeciloneta vakkhanka (Tanasevitch 1989). The following five species have been reported previously in Alaska, but not near Toolik Lake: Hypsosinga groenlandica Simon 1889, Gnaphosa borea Kulczyn'ski 1908, Gnaphosa microps Holm 1939, Haplodrassus hiemalis (Emerton 1909), and Islandiana cristata Eskov 1987. Pairwise similarity indices were calculated across 13 other arctic and subarctic spider communities and statistical tests show that all sites are dissimilar (p = 0.25). These results fit the general pattern of both the patchiness and habitat specificity of arctic spider fauna.

Temperature tolerance of different larval stages of the spider crab Hyas araneus exposed to elevated seawater PCO2

Exposure to elevated seawater PCO2 limits the thermal tolerance of crustaceans but the underlying mechanisms have not been comprehensively explored. Larval stages of crustaceans are even more sensitive to environmental hypercapnia and possess narrower thermal windows than adults. In a mechanistic approach, we analysed the impact of high seawater CO2 on parameters at different levels of biological organization, from the molecular to the whole animal level. At the whole animal level we measured oxygen consumption, heart rate and activity during acute warming in zoea and megalopa larvae of the spider crab Hyas araneus exposed to different levels of seawater PCO2. Furthermore, the expression of genes responsible for acid-base regulation and mitochondrial energy metabolism, and cellular responses to thermal stress (e.g. the heat shock response) was analysed before and after larvae were heat shocked byrapidly raising the seawater temperature from 10°C rearing temperature to 20°C. Zoea larvae showed a high heat tolerance, which decreased at elevated seawater PCO2, while the already low heat tolerance of megalopa larvae was not limited further by hypercapnic exposure. There was a combined effect of elevated seawater CO2 and heat shock in zoea larvae causing elevated transcript levels of heat shock proteins. In all three larval stages, hypercapnic exposure elicited an up-regulation of genes involved in oxidative phosphorylation, which was, however, not accompanied by increased energetic demands. The combined effect of seawater CO2 and heat shock on the gene expression of heat shock proteins reflects the downward shift in thermal limits seen on the whole animal level and indicates an associated capacity to elicit passive thermal tolerance. The up-regulation of genes involved in oxidative phosphorylation might compensate for enzyme activities being lowered through bicarbonate inhibition and maintain larval standard metabolic rates at high seawater CO2 levels. The present study underlines the necessity to align transcriptomic data with physiological responses when addressing mechanisms affected by an interaction of elevated seawater PCO2 and temperature extremes.

Gene expression profiling in gills of the great spider crab Hyas araneus in respond to ocean acidification and warming, supplementary data

Hypercapnia and elevated temperatures resulting from climate change may have adverse consequences for many marine organisms. While diverse physiological and ecological effects have been identified, changes in those molecular mechanisms, which shape the physiological phenotype of a species and limit its capacity to compensate, remain poorly understood. Here, we use global gene expression profiling through RNA-Sequencing to study the transcriptional responses to ocean acidification and warming in gills of the boreal spider crab Hyas araneus exposed medium-term (10 weeks) to intermediate (1,120 µatm) and high (1,960 µatm) PCO2 at different temperatures (5°C and 10°C). The analyses reveal shifts in steady state gene expression from control to intermediate and from intermediate to high CO2 exposures. At 5°C acid-base, energy metabolism and stress response related genes were upregulated at intermediate PCO2, whereas high PCO2 induced a relative reduction in expression to levels closer to controls. A similar pattern was found at elevated temperature (10°C). There was a strong coordination between acid-base, metabolic and stress-related processes. Hemolymph parameters at intermediate PCO2 indicate enhanced capacity in acid-base compensation potentially supported by upregulation of a V-ATPase. The likely enhanced energy demand might be met by the upregulation of the electron transport system (ETS), but may lead to increased oxidative stress reflected in upregulated antioxidant defense transcripts. These mechanisms were attenuated by high PCO2, possibly as a result of limited acid-base compensation and metabolic down-regulation. Our findings indicate a PCO2 dependent threshold beyond which compensation by acclimation fails progressively. They also indicate a limited ability of this stenoecious crustacean to compensate for the effects of ocean acidification with and without concomitant warming.

Seawater carbonate chemistry and biological processes during experiments with spider crab Hyas araneus, 2011

The combined effects of ocean warming and acidification were compared in larvae from two populations of the cold-eurythermal spider crab Hyas araneus, from one of its southernmost populations (around Helgoland, southern North Sea, 54°N, habitat temperature 3-18°C; collection: January 2008, hatch: January-February 2008) and from one of its northernmost populations (Svalbard, North Atlantic, 79°N, habitat temperature 0-6°C; collection: July 2008, hatch: February-April 2009). Larvae were exposed to temperatures of 3, 9 and 15°C combined with present-day normocapnic (380 ppm CO2) and projected future CO2 concentrations (710 and 3,000 ppm CO2). Calcium content of whole larvae was measured in freshly hatched Zoea I and after 3, 7 and 14 days during the Megalopa stage. Significant differences between Helgoland and Svalbard Megalopae were observed at all investigated temperatures and CO2 conditions. Under 380 ppm CO2, the calcium content increased with rising temperature and age of the larvae. At 3 and 9°C, Helgoland Megalopae accumulated more calcium than Svalbard Megalopae. Elevated CO2 levels, especially 3,000 ppm, caused a reduction in larval calcium contents at 3 and 9°C in both populations. This effect set in early, at 710 ppm CO2 only in Svalbard Megalopae at 9°C. Furthermore, at 3 and 9°C Megalopae from Helgoland replenished their calcium content to normocapnic levels and more rapidly than Svalbard Megalopae. However, Svalbard Megalopae displayed higher calcium contents under 3,000 ppm CO2 at 15°C. The findings of a lower capacity for calcium incorporation in crab larvae living at the cold end of their distribution range suggests that they might be more sensitive to ocean acidification than those in temperate regions.

Chemistry and biological processes during experiments with spider crab Hyas araneus

The combined effects of ocean warming and acidification were compared in larvae from two popula- tions of the cold-eurythermal spider crab Hyas araneus, from one of its southernmost populations (around Helgo- land, southern North Sea, 54°N, habitat temperature 3-18°C; collection: January 2008, hatch: January-February 2008) and from one of its northernmost populations (Svalbard, North Atlantic, 79°N, habitat temperature 0-6°C; collection: July 2008, hatch: February-April 2009). Larvae were exposed to temperatures of 3, 9 and 15°C combined with present-day normocapnic (380 ppm CO2) and projected future CO2 concentrations (710 and 3,000 ppm CO2). Calcium content of whole larvae was measured in freshly hatched Zoea I and after 3, 7 and 14 days during the Megalopa stage. Significant differences between Helgoland and Svalbard Megalopae were observed at all investigated temperatures and CO2 condi- tions. Under 380 ppm CO2, the calcium content increased with rising temperature and age of the larvae. At 3 and 9°C, Helgoland Megalopae accumulated more calcium than Svalbard Megalopae. Elevated CO2 levels, especially 3,000 ppm, caused a reduction in larval calcium contents at 3 and 9°C in both populations. This effect set in early, at 710 ppm CO2 only in Svalbard Megalopae at 9°C. Fur- thermore, at 3 and 9°C Megalopae from Helgoland replenished their calcium content to normocapnic levels and more rapidly than Svalbard Megalopae. However, Svalbard Megalopae displayed higher calcium contents under 3,000 ppm CO2 at 15°C. The findings of a lower capacity for calcium incorporation in crab larvae living at the cold end of their distribution range suggests that they might be more sensitive to ocean acidification than those in temperate regions.

Seawater carbonate chemistry and biological processes during experiments with the spider crab Hyas araneus in Kongsfjorden, Svalbard, 2009

With global climate change, ocean warming and acidification occur concomitantly. In this study, we tested the hypothesis that increasing CO2 levels affect the acid-base balance and reduce the activity capacity of the Arctic spider crab Hyas araneus, especially at the limits of thermal tolerance. Crabs were acclimated to projected oceanic CO2 levels for 12 days (today: 380, towards the year 2100: 750 and 1,120 and beyond: 3,000 ?atm) and at two temperatures (1 and 4 °C). Effects of these treatments on the righting response (RR) were determined (1) at acclimation temperatures followed by (2) righting when exposed to an additional acute (15 min) heat stress at 12 °C. Prior to (resting) and after the consecutive stresses of combined righting activity and heat exposure, acid-base status and lactate contents were measured in the haemolymph. Under resting conditions, CO2 caused a decrease in haemolymph pH and an increase in oxygen partial pressure. Despite some buffering via an accumulation of bicarbonate, the extracellular acidosis remained uncompensated at 1 °C, a trend exacerbated when animals were acclimated to 4 °C. The additional combined exposure to activity and heat had only a slight effect on blood gas and acid-base status. Righting activity in all crabs incubated at 1 and 4 °C was unaffected by elevated CO2 levels or acute heat stress but was significantly reduced when both stressors acted synergistically. This impact was much stronger in the group acclimated at 1 °C where some individuals acclimated to high CO2 levels stopped responding. Lactate only accumulated in the haemolymph after combined righting and heat stress. In the group acclimated to 1 °C, lactate content was highest under normocapnia and lowest at the highest CO2 level in line with the finding that RR was largely reduced. In crabs acclimated to 4 °C, the RR was less affected by CO2 such that activity caused lactate to increase with rising CO2 levels. In line with the concept of oxygen and capacity limited thermal tolerance, all animals exposed to temperature extremes displayed a reduction in scope for performance, a trend exacerbated by increasing CO2 levels. Additionally, the differences seen between cold- and warm-acclimated H. araneus after heat stress indicate that a small shift to higher acclimation temperatures also alleviates the response to temperature extremes, indicating a shift in the thermal tolerance window which reduces susceptibility to additional CO2 exposure.

Spider crab Hyas araneus larval dry weight, C/N ratio and developmental time during experiments from different latitudes (54° vs 79°N), 2010

The combined impacts of future scenarios of ocean acidification and global warming on the larvae of a cold-eurythermal spider crab, Hyas araneus L., were investigated in one of its southernmost populations (living around Helgoland, southern North Sea, 54°N) and one of the northernmost populations (Svalbard, North Atlantic, 79°N). Larvae were exposed at temperatures of 3, 9 and 15°C to present day normocapnia (380 ppm CO2) and to CO2 conditions expected for the near or medium-term future (710 ppm by 2100 and 3000 ppm CO2 by 2300 and beyond). Larval development time and biochemical composition were studied in the larval stages Zoea I, II, and Megalopa. Permanent differences in instar duration between both populations were detected in all stages, likely as a result of evolutionary temperature adaptation. With the exception of Zoea II at 3°C and under all CO2 conditions, development in all instars from Svalbard was delayed compared to those from Helgoland, under all conditions. Most prominently, development was much longer and fewer specimens morphosed to the first crab instar in the Megalopa from Svalbard than from Helgoland. Enhanced CO2 levels (710 and particularly 3000 ppm), caused extended duration of larval development and reduced larval growth (measured as dry mass) and fitness (decreasing C/N ratio, a proxy of the lipid content). Such effects were strongest in the zoeal stages in Svalbard larvae, and during the Megalopa instar in Helgoland larvae.