Habitat amount mediates the effect of fragmentation on a pollinator's reproductive performance, but not on its foraging behaviour.

Agricultural intensification, with its associated habitat loss and fragmentation, is among the most important drivers of the ongoing pollination crisis. In this quasi-experimental study, conducted in intensively managed vineyards in southwestern Switzerland, we tested the separate and interdependent effects of habitat amount and fragmentation on the foraging activity and reproductive performance of bumblebee Bombus t. terrestris colonies. Based on a factorial design, we selected a series of spatially replicated study sites across a dual gradient of habitat amount (area of ground-vegetated vineyards) and fragmentation (density of ground-vegetated vineyard fields) in a landscape predominantly consisting of vineyards with bare grounds. The foraging activity of individual bumblebees was measured using the radio frequency identification (RFID) technology, and we assessed final colony size to measure reproductive performance. We found an interactive effect of habitat amount and fragmentation on colony size. More specifically, the degree of fragmentation had a negative effect on bumblebee colony size when the amount of habitat was low, while it had a weak positive effect on colony size in landscapes with high amounts of habitat. At the level of individual vineyard fields, ground vegetation cover exerted a positive effect on bumblebee colony size. Fragmentation, but not habitat amount, significantly influenced foraging activity, with more foraging trips in sites with lower degrees of fragmentation. Our results emphasise the importance of studying the separate and interdependent effects of habitat amount and fragmentation to understand their influence on pollinators, providing guidance for optimising the spatial configuration of agricultural landscapes from a biodiversity viewpoint.

Murine and Human Spermatids Are Characterized by Numerous, Newly Synthesized and Differentially Expressed Transcription Factors and Bromodomain-Containing Proteins.

Much of spermatid differentiation takes place in the absence of active transcription, but in the early phase, large amounts of mRNA are synthesized, translationally repressed, and stored. Most nucleosomal histones are then degraded, and chromatin is repackaged by protamines. For both transcription and the histone-to-protamine transition in differentiating spermatids, chromatin must be opened. This raises the question of whether two different processes exist. It is conceivable that for initiation of the histone-to-protamine transition, the already accessible, actively transcribed chromatin regions are utilized or vice versa. We analyzed the enrichment of different canonical TATA-box-binding, protein-associated factors and their variants in murine spermatids, diverse bromodomain-containing proteins, and components of the Polycomb repressive complexes PRC1 and PRC2 using quantitative PCR. We compared the enrichment of corresponding proteins in human and murine spermatids and analyzed the time frame of postmeiotic transcription and expression of histones, transition proteins, and protamines in human and murine spermatids using immunohistology. We correlated the expression of different transcription factors and bromodomain-containing proteins and the pattern of acetylated histones to active transcription and to the histone-to-protamine transition in both human and murine spermatids. Our findings suggest that differentiating spermatids use both common and specific features to open chromatin first for transcription and subsequently for histone-to-protamine transition.