Summer Dynamics of Microbial Diversity on a Mountain Glacier

Glaciers are rapidly receding under climate change. A melting cryosphere will dramatically alter global sea levels, carbon cycling, and water resource availability. Glaciers host rich biotic communities that are dominated by microbial diversity, and this biodiversity can impact surface albedo, thereby driving a feedback loop between biodiversity and cryosphere melt. However, the microbial diversity of glacier ecosystems remains largely unknown outside of major ice sheets, particularly from a temporal perspective. Here, we characterized temporal dynamics of bacteria, eukaryotes, and algae on the Paradise Glacier, Mount Rainier, USA, over nine time points spanning the summer melt season. During our study, the glacier surface steadily darkened as seasonal snow melted and darkening agents accumulated until new snow fell in late September. From a community-wide perspective, the bacterial community remained generally constant while eukaryotes and algae exhibited temporal progression and community turnover. Patterns of individual taxonomic groups, however, were highly stochastic. We found little support for our a priori prediction that autotroph abundance would peak before heterotrophs. Notably, two different trends in snow algae emerged-an abundant early- and late-season operational taxonomic unit (OTU) with a different midsummer OTU that peaked in August. Overall, our results highlight the need for temporal sampling to clarify microbial diversity on glaciers and that caution should be exercised when interpreting results from single or few time points. IMPORTANCE Microbial diversity on mountain glaciers is an underexplored component of global biodiversity. Microbial presence and activity can also reduce the surface albedo or reflectiveness of glaciers, causing them to absorb more solar radiation and melt faster, which in turn drives more microbial activity. To date, most explorations of microbial diversity in the mountain cryosphere have only included single time points or focused on one microbial community (e.g., bacteria). Here, we performed temporal sampling over a summer melt season for the full microbial community, including bacteria, eukaryotes, and fungi, on the Paradise Glacier, Washington, USA. Over the summer, the bacterial community remained generally constant, whereas eukaryote and algal communities temporally changed through the melt season. Individual taxonomic groups, however, exhibited considerable stochasticity. Overall, our results highlight the need for temporal sampling on glaciers and that caution should be exercised when interpreting results from single or few time points.

Brown meets green: light and nutrients alter detritivore assimilation of microbial nutrients from leaf litter

In aquatic detrital-based food webs, research suggests that autotroph-heterotroph microbial interactions exert bottom-up controls on energy and nutrient transfer. To address this emerging topic, we investigated microbial responses to nutrient and light treatments during Liriodendron tulipifera litter decomposition and fed litter to the caddisfly larvae Pycnopsyche sp. We measured litter-associated algal, fungal, and bacterial biomass and production. Microbes were also labeled with ¹⁴ C and ³³ P to trace distinct microbial carbon (C) and phosphorus (P) supporting Pycnopsyche assimilation and incorporation (growth). Litter-associated algal and fungal production rates additively increased with higher nutrient and light availability. Incorporation of microbial P did not differ across diets, except for higher incorporation efficiency of slower-turnover P on low-nutrient, shaded litter. On average, Pycnopsyche assimilated fungal C more efficiently than bacterial or algal C, and Pycnopsyche incorporated bacterial C more efficiently than algal or fungal C. Due to high litter fungal biomass, fungi supported 89.6-93.1% of Pycnopsyche C growth, compared to 0.2% to 3.6% supported by bacteria or algae. Overall, Pycnopsyche incorporated the most C in high nutrient and shaded litter. Our findings affirm others' regarding autotroph-heterotroph microbial interactions and extend into the trophic transfer of microbial energy and nutrients through detrital food webs.

Oviposition Responses and Potential Larval Control Methods of Aedes albopictus (Diptera: Culicidae) in Downspout Extensions

Aedes albopictus (Skuse) is an important invasive species and vector of several important arboviruses across the globe. This species uses small water-holding cryptic containers as egg laying sites, which pose serious challenges to effective control of adult mosquito populations. Herein, we examined the response of gravid female Ae. albopictus to various features of common downspout extension tubes associated with human dwellings and the effectiveness of control efforts to eliminate larvae. Controlled field trials quantified oviposition in 1) extensions versus rubber bowls meant to mimic other container types, 2) among different shapes and materials of extensions, and 3) among different colors of extensions. We also investigated how flushing and use of Bti larvicides could control larvae. Females were more likely to lay eggs in flat plastic or metal extensions compared to rubber bowls. Eggs were also more plentiful in flat plastic extensions versus either corrugated or metal, and dark brown corrugated extensions had more eggs compared to tan or white. Flushing reduced nearly all larvae when the extensions were properly angled, and applications of Bti pellets or dunks were effective at killing most larvae. We show that dark extensions were preferred over other colors, and that larvae can be effectively removed with minimal effort. However, effective control will likely only come from better education of the public about proper installation of extensions.

Serotonin plays a permissive role in conditioned olfactory learning induced by norepinephrine in the neonate rat

This study examined the role of serotonin (5-hydroxytryptamine; 5-HT) in conditioned olfactory learning in the rat pup. By injecting various combinations of the 5-HT(2A/2C) receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and the beta adrenoceptor agonist, isoproterenol, we observed that isoproterenol alone acted as an unconditioned stimulus (US) to induce learning, as reported previously, whereas DOI alone did not induce learning. DOI combined with isoproterenol produced a leftward shift in the effective US dose such that suboptimal isoproterenol was effective, and previously optimal levels of isoproterenol were ineffective. Thus, 5-HT plays a facilitative but not an obligatory role in conditioned olfactory learning in the neonate rat.

Serotonin plays a permissive role in conditioned olfactory learning induced by norepinephrine in the neonate rat

This study examined the role of serotonin (5-hydroxytryptamine; 5-HT) in conditioned olfactory learning in the rat pup. By injecting various combinations of the 5-HT(2A/2C) receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and the beta adrenoceptor agonist, isoproterenol, we observed that isoproterenol alone acted as an unconditioned stimulus (US) to induce learning, as reported previously, whereas DOI alone did not induce learning. DOI combined with isoproterenol produced a leftward shift in the effective US dose such that suboptimal isoproterenol was effective, and previously optimal levels of isoproterenol were ineffective. Thus, 5-HT plays a facilitative but not an obligatory role in conditioned olfactory learning in the neonate rat.

Pheromonal composition of two species of African Amblyomma ticks: similarities, differences and possible species specific components

Two species of bont ticks, Amblyomma hebraeum and Amblyomma variegatum, common to Africa were studied to compare types and quantities of compounds known or believed to serve as components of the attraction-aggregation-attachment pheromone (AAAP). A complex of attraction, aggregation and attachment stimulating pheromone components are used by these ticks to detect hosts, mates and, perhaps, minimize interspecific breeding. Solvent extraction of pheromone emitting ticks followed by gas chromatography and mass spectrometry revealed little qualitative difference in the composition of the AAAP in these two species. However, subtle differences in the relative proportions of the pheromonal blend are noted suggesting that such differences in concentration may facilitate species-specific discrimination during aggregation and attachment. Differences in the relative abundance of benzaldehyde and methyl salicylate in the males of the two species were especially noteworthy. Possible means by which such differences in phenolic compound composition may affect the behavior of these ticks are discussed.

5-HT3 receptor agonism may be responsible for the emetic effects of zacopride in the ferret

The racemic 5-HT3 receptor antagonist, zacopride (10-100 micrograms kg-1, i.m.) evoked an emetic response in ferrets. This property appeared to reside totally in the S-enantiomer which also produced emesis over the same dose range. This emesis could be prevented by pretreatment with ondansetron (1 mg kg-1, i.m.) or by R-zacopride (100 micrograms kg-1, i.m.). In urethane-anaesthetized ferrets, S-zacopride (0.3 micrograms kg-1, i.v.) evoked a profound Bezold-Jarisch reflex which was blocked by both ondansetron (30 micrograms kg-1, i.v.) and by R-zacopride (100 micrograms kg-1, i.v.). These results suggest that, in the ferret, S-zacopride possesses 5-HT3 receptor agonist properties which may be responsible for the emetic effect. In contrast R-zacopride does not appear to possess 5-HT3 receptor agonist properties in this species.