Amino acid transporters implicated in endocytosis of Buchnera during symbiont transmission in the pea aphid

Abstract Background Many insects host their obligate, maternally transmitted symbiotic bacteria in specialized cells called bacteriocytes. One of the best-studied insect nutritional endosymbioses is that of the aphid and its endosymbiont, Buchnera aphidicola. Aphids and Buchnera are metabolically and developmentally integrated, but the molecular mechanisms underlying Buchnera transmission and coordination with aphid development remain largely unknown. Previous work using electron microscopy to study aphid asexual embryogenesis has revealed that Buchnera transmission involves exocytosis from a maternal bacteriocyte followed by endocytotic uptake by a blastula. While the importance of exo- and endocytic cellular processes for symbiont transmission is clear, the molecular mechanisms that regulate these processes are not known. Here, we shed light on the molecular mechanisms that regulate Buchnera transmission and developmental integration. Results We present the developmental atlas of ACYPI000536 and ACYPI008904 mRNAs during asexual embryogenesis in the pea aphid, Acyrthosiphon pisum. Immediately before Buchnera invasion, transcripts of both genes were detected by whole-mount in situ hybridization in the posterior syncytial nuclei of late blastula embryos. Following Buchnera invasion, expression of both genes was identified in the region occupied by Buchnera throughout embryogenesis. Notably during Buchnera migration, expression of both genes was not concomitant with the entirety of the bacterial mass but rather expression colocalized with Buchnera in the anterior region of the bacterial mass. In addition, we found that ACYPI000536 was expressed in nuclei at the leading edge of the bacterial mass, joining the bacterial mass in subsequent developmental stages. Finally, quantitative reverse transcription real-time PCR suggested that early in development both transcripts were maternally provisioned to embryos. Conclusions We venture that ACYPI000536 and ACYPI008904 function as nutrient sensors at the site of symbiont invasion to facilitate TOR-pathway-mediated endocytosis of Buchnera by the aphid blastula. Our data support earlier reports of bacteriocyte determination involving a two-step recruitment process but suggest that the second wave of recruitment occurs earlier than previously described. Finally, our work highlights that bacteriocyte-enriched amino acid transporter paralogs have additionally been retained to play novel developmental roles in both symbiont recruitment and bacteriome development

Communities of ground-living spiders in deciduous forests: Does tree species diversity matter?

Schuldt A, Fahrenholz N, Brauns M, Migge-Kleian S, Platner C, Schaefer M. Communities of ground-living spiders in deciduous forests: Does tree species diversity matter? BIODIVERSITY AND CONSERVATION. 2008;17(5):1267-1284.The relationships between species diversity and ecosystem functions are in the focus of recent ecological research. However, until now the influence of species diversity on ecosystem processes such as decomposition or mineral cycling is not well understood. In deciduous forests, spiders are an integral part of the forest floor food web. In the present study, patterns of spider diversity and community structure are related to diversity of deciduous forest stands in the Hainich National Park (Thuringia). In 2005, pitfall trapping and quantitative forest floor sampling were conducted in nine plots of forest stands with one (Diversity Level 1), three (DL 2) and five (DL 3) major deciduous tree species. Species richness, measured with both methods, as well as spider abundance in forest floor samples were highest in stands with medium diversity (DL 2) and lowest in pure beech stands (DL 1). The Shannon-Wiener index and spider numbers in pitfall traps decreased from DL 1 to DL 3, while the Shannon-Wiener index in forest floor samples increased in the opposite direction. Spider community composition differed more strongly between single plots than between diversity levels. Altogether, no general relationship between increasing tree species diversity and patterns of diversity and abundance in spider communities was found. It appears that there is a strong influence of single tree species dominating a forest stand and modifying structural habitat characteristics such as litter depth and herb cover which are important for ground-living spiders