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Open Access Publications from the University of California

Recent Work

Multicampus Research Programs and Initiatives (MRPI) fund innovative multicampus or systemwide research collaborations that go beyond individual PI-driven projects to benefit the UC research enterprise, strengthen UC’s position as a leading public research university, launch pioneering research in thematic, multidisciplinary or inter-disciplinary areas, and benefit California and its people. The program is open to all fields of research and scholarship.

Joint Impacts of Drought and Habitat Fragmentation on Native Bee Assemblages in a California Biodiversity Hotspot

(2021)

Global climate change is causing more frequent and severe droughts, which could have serious repercussions for the maintenance of biodiversity. Here, we compare native bee assemblages collected via bowl traps before and after a severe drought event in 2014 in San Diego, California, and examine the relative magnitude of impacts from drought in fragmented habitat patches versus unfragmented natural reserves. Bee richness and diversity were higher in assemblages surveyed before the drought compared to those surveyed after the drought. However, bees belonging to the Lasioglossum subgenus Dialictus increased in abundance after the drought, driving increased representation by small-bodied, primitively eusocial, and generalist bees in post-drought assemblages. Conversely, among non-Dialictus bees, post-drought years were associated with decreased abundance and reduced representation by eusocial species. Drought effects were consistently greater in reserves, which supported more bee species, than in fragments, suggesting that fragmentation either had redundant impacts with drought, or ameliorated effects of drought by enhancing bees’ access to floral resources in irrigated urban environments. Shifts in assemblage composition associated with drought were three times greater compared to those associated with habitat fragmentation, highlighting the importance of understanding the impacts of large-scale climatic events relative to those associated with land use change.

Cover page of Characterizing the cellular architecture of dynamically remodeling vascular tissue using 3-D image analysis and virtual reconstruction

Characterizing the cellular architecture of dynamically remodeling vascular tissue using 3-D image analysis and virtual reconstruction

(2020)

Epithelial tubules form critical structures in lung, kidney and vascular tissues. However, the processes that control their morphogenesis and physiological expansion and contraction are not well understood. Here we examine the dynamic remodeling of epithelial tubes in vivo using a novel model system: the extracorporeal vasculature of Botryllus schlosseri, in which the disruption of the basement membrane triggers rapid, massive vascular retraction without loss of barrier function. We developed and implemented 3-D image analysis and virtual reconstruction tools to characterize the cellular morphology of the vascular wall in unmanipulated vessels and during retraction. In both control and regressed conditions, cells within the vascular wall were planar polarized, with an integrin- and curvature-dependent axial elongation of cells and a robust circumferential alignment of actin bundles. Surprisingly, we found no measurable differences in morphology between normal and retracting vessels under ECM disruption. However, inhibition of integrin signaling through FAK inhibition caused disruption of cellular actin organization. Our results demonstrate that epithelial tubes can maintain tissue organization even during extreme remodeling events, but that the robust response to mechanical signals – such as the response to loss of vascular tension after ECM disruption - requires functional force sensing machinery via integrin signaling.

Cover page of Non-native honey bees disproportionately dominate the most abundant floral resources in a biodiversity hotspot

Non-native honey bees disproportionately dominate the most abundant floral resources in a biodiversity hotspot

(2019)

Most plant-pollinator mutualisms are generalized. As such, they are susceptible to perturbation by abundant, generalist, non-native pollinators such as the western honey bee (Apis mellifera), which can reach high abundances and visit flowers of many plant species in their expansive introduced range. Despite the prevalence of non-native honey bees, their effects on pollination mutualisms in natural ecosystems remain incompletely understood. Here we contrast community-level patterns of floral visitation by honey bees with that of the diverse native pollinator fauna of southern California, USA. We show that the number of honey bees visiting plant species increases much more rapidly with flower abundance than does that of non-honey bee insects, such that the percentage of all visitors represented by honey bees increases with flower abundance. Thus, honey bees could disproportionately impact the most abundantly blooming plant species and the large numbers of both specialised and generalised pollinator species that they sustain. Honey bees may preferentially exploit high-abundance floral resources because of their ability to recruit nestmates; these foraging patterns may cause native insect species to forage on lower-abundance resources to avoid competition. Our results illustrate the importance of understanding foraging patterns of introduced pollinators in order to reveal their ecological impacts.

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Cover page of Myeloid differentiation factor 88 (MyD88) and IL-1R1 signaling contribute to resistance to Coccidioides immitis.

Myeloid differentiation factor 88 (MyD88) and IL-1R1 signaling contribute to resistance to Coccidioides immitis.

(2018)

Rodents are a natural host for the dimorphic pathogenic fungi Coccidioides immitis and posadasii, and mice are a good model for human infection. Humans and rodents both express Dectin-1 and TLR2 on myeloid cells and those receptors collaborate to maximize the cytokine/chemokine responses to spherules (the tissue form of the fungi), and to formalin killed spherules (FKS). We showed that Dectin-1 is necessary for resistance to pulmonary coccidioidomycosis, but the importance of TLR2 in vivo is uncertain. MyD88 is the adapter protein for TLR2 and 4, and IL-1R1 and IL-18R1. MyD88/TRIF -/-and MyD88 -/- mice were equally susceptible to C. immitis infection, compared to C57BL/6 (B6) controls. Of the four surface receptors, only IL-1R1 was required for resistance to C. immitis, partially explaining the susceptibility of MyD88 -/- mice. We also found that FKS stimulated production of IL-1Ra by BMDC, independent of MyD88 and Dectin-1. There also was a very high concentration of IL-1Ra in the lungs of infected B6 mice, supporting the potential importance of this regulatory IL-1 family protein in the largely ineffective response of B6 mice to coccidioidomycosis. These results suggest that IL-1R1 signaling is important for defense against C. immitis infection.