Justina Panchuk

The addition of nutrients to soil can induce changes through “bottom-up” effects in soil–plant–animal interactions, impacting higher levels in food chains. Changes in foliar nutrient content may influence diets of herbivorous insects, subsequently altering their feeding rates and abundance. Spiders established in foliage rely on these insects for sustenance; therefore, fluctuations in the abundance of herbivorous insect communities ultimately determine the population dynamics of their spider predators. We established a long-term field experiment to investigate the effects of nutrient addition of N (nitrogen), P (phosphorus), K (potassium) and their combinations on plant–arthropod interactions. We carried out sampling in 32 plots under different nutrient addition treatments, where we captured herbivorous insects and spiders on Nothofagus antarctica plants, the most abundant plant species in the Patagonian scrubland. Our results showed that foliar nutrient concentrations had cascading effects throughout the forest food chain. Herbivorous insects (Diptera, Coleoptera, Hemiptera and Lepidoptera orders) exhibited a positive response to the increased foliar phosphorus content, resulting in higher population densities. In addition, we found a strong positive relationship between herbivorous insect abundance and spider abundance. Our findings indicate that variations in the availability of soil nutrients play a crucial role in defining the structure of predator–prey interactions in forest ecosystems.

Thermal preference and thermal performance are used to describe the thermal biology of an ectothermic organism through parameters, i.e., estimating locomotor performance by maximum running speed. In this study, we assessed the thermal preference and locomotor performance of the spider Mecicobothrium thorelli Holmberg, 1882, a wintry mygalomorph spider endemic to the native mountainous grasslands of central Argentina and Uruguay. The preferred temperatures of the 72.4% of the individuals were in the range of 10–20 °C. The highest frequencies of preferred temperatures were 10–15 °C in males and 15–20 °C in females. The sprint speed showed significant differences between all the temperatures evaluated and showed the highest speeds at 25 °C and the lowest at 3 °C. The optimal temperature was 26.09 °C, which was significantly higher than the preferred temperature in both males and females. We concluded that M. thorelli selects a wide range of temperatures and prefers to stay in medium and low temperatures, which are correlated with winter activity in the wild. However, the species showed maximum speed at higher temperatures, which implies that spiders would perform even better in nature and maximize their locomotion by being active during a warmer period.

Reportamos un nuevo registro en la distribución geográfica de Chaco tucumana en la provincia de Salta, norte de Argentina. Es la localidad más al norte conocida para la especie. Además, presentamos datos sobre la historia natural de la especie y mapas de distribución incluyendo comentarios de las provincias biogeográficas y ecorregiones involucradas.

Paraje Tres Cerros is a low altitude hilly natural area surrounded by cattle fields and characterized by three isolated rocky formations of about 150-180 m a.s.l. located in the Corrientes province of Argentina. Their topographic and environmental conditions are unique across the whole Mesopotamian littoral of Argentina and, therefore, can be considered as a biogeographic island that hosts several endemic species of plants and animals. The lack of knowledge of the mygalomorph spider species of the area led us to conduct a field study at Paraje Tres Cerros with the objective of surveying these spiders. From this survey, we described two new endemic species, Stenoterommata isa sp. nov. (Pycnothelidae) and Catumiri sapucai sp. nov. (Theraphosidae); and we recorded Xenonemesia platensis for the first time in the Corrientes province. In addition, we described the sexual behavior of Stenoterommata isa sp. nov. and Catumiri sapucai sp. nov. for the first time. We presented distribution maps for the Argentinean species of Stenoterommata , for the genus Catumiri as well as for Xenonemesia platensis . Stenoterommata isa sp. nov. constitutes the eighth known species of the genus in Argentina and according to its distribution is the only exclusive species recorded in the Corrientes province. Regarding its sexual behavior, we obtained one mating, which consisted in touches the female legs with legs I and II by the male, who starts the courtship by beating the female's cephalothorax and sternum with legs II and palps respectively. Then the male clasps with the first pair of legs between the palp base and chelicerae of the female and elevate her to reach the genital opening for the palpal insertions. Catumiri sapucai sp. nov. is the third species described from Argentina with a new spermathecae shape with two additional elongated digitiform domes external to the inner receptacles. We obtained five matings for this species, two of which involved males contacting females without an evident courtship. For the remaining three, the males initiated courtship by performing a few quick body vibrations. All males achieved the typical copulation position observed in most mygalomorphs and made about 3 to 5 palpal insertions, with the exception of one case in which spiders lost equilibrium and separated from each other. The presence of Xenonemesia platensis at this area is based on one adult female, thus further campaigns to collect more specimens will lead us to confirm this record or to better elucidate its taxonomic identity.

Mecicobothrium thorelli is a very small mygalomorph spider that exclusively inhabits native mountainous grasslands of southern South America (Argentina and Uruguay). Several aspects of the biology of M. thorelli are still unknown. The goal of this study is to provide knowledge about the ecology of this species in a threatened habitat for the first time, based on extensive field work carried out during one year. A total of 119 individuals were registered. The species was found to select large refuges (rocks) and avoid small refuges, while the temperature of these did not seem to influence refuge selection. Juveniles and adults represented 69.9% and 30.1% of the total, respectively. Juveniles were found throughout the whole sampling period, while females were found mostly in June and males were recorded in May (winter in the southern hemisphere). The spatial distribution was random on most dates, with the exception of June, July and May. Also, a regular spatial pattern was observed in June. Mecicobothrium thorelli has a wintery life cycle, increasing its abundance during the coldest months of the year, and chooses particular characteristics of the microenvironment, such as refuge size. It usually presents a random spatial distribution, except at smaller scales during the reproductive period.