The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells

Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existance of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use

Spillover but no spillback of two invasive parasitic copepods from invasive Pacific oysters (Crassostrea gigas) to native bivalve hosts

Invasive species can cause indirect effects on native biota by modifying parasite-host interactions and disease occurrence in native species. This study investigated the role of the invasive Pacific oyster (Crassostrea gigas) in potential spillover (co-introduced parasites infect native hosts) and spillback (native or established parasites infect invasive hosts and re-infect native hosts) scenarios of recently introduced (Mytilicola orientalis) and previously established (Mytilicola intestinalis) marine parasitic copepods in two regions in northern Europe, the Dutch Delta and the Wadden Sea. By examining 3416 individuals of 11 potential host species from sympatric host populations, we found that the recently introduced parasite M. orientalis does not only infect its principal host, the invasive Pacific oyster (prevalence at infected sites 2–43 %, mean intensity 4.1 ± 0.6 SE), but also native blue mussels (Mytilus edulis; 3–63 %, 2.1 ± 0.2), common cockles (Cerastoderma edule; 2–13 %, 1.2 ± 0.3) and Baltic tellins (Macoma balthica; 6–7 %, 1.0 ± 0), confirming a spillover effect. Spillback effects were not observed as the previously established M. intestinalis was exclusively found in blue mussels (prevalence at infected locations 3–72 %, mean intensity 2.4 ± 0.3 SE). The high frequency of M. orientalis spillover, in particular to native mussels, suggests that Pacific oysters may cause strong parasite-mediated indirect impacts on native bivalve populations