Abstract
A remarkable feature of many parasites is a high degree of host specificity but the mechanisms behind are poorly understood. A major challenge for parasites is to identify and infect a suitable host. Many species show a high degree of host specificity, being able to survive only on one or a few related host species. To facilitate transmission, parasite’s behavior and reproduction has been fine tuned to maximize the likelihood of infection of a suitable host. For some species chemical cues that trigger or attract the parasite in question have been identified but how metazoan parasites themselves receive these signals remains unknown. In the present study we show that ionotropic receptors (IRs) in the salmon louse are likely responsible for identification of a specific host. By using RNAi to knock down the expression level of different co-receptors, a significant change of infectivity and settlement of lice larvae was achieved on Atlantic salmon. More remarkably, knock down of the IRs changed the host specificity of the salmon louse and lice larvae settled at a significant rate on host that the wild type lice rejected within minutes. To our knowledge, this has never before been demonstrated for any metazoan parasite. Our results show that the parasites are able to identify the host quickly upon settlement, settle and initiate the parasitic life style if they are on the right host. This novel discovery opens up for utilizing the host recognition system for future parasite control.
Highlights
Chemical sensing plays a crucial role for organisms in order to transmit signals from the environment to an individual resulting in changed behavior or physiological responses
Quantitative Real Time PCR analysis of all the co-receptors and the antennal Ionotropic Receptors (IRs) confirmed that these genes are primarily expressed in the first antenna in the copepodids (Fig 1c)
The transcript levels for the IRs are far higher in copepodids than in the males
Summary
Chemical sensing plays a crucial role for organisms in order to transmit signals from the environment to an individual resulting in changed behavior or physiological responses. Peripheral detection and recognition of chemical cues depends on membrane receptor proteins that bind specific ligands in the environment and convert this interaction into cellular processes. The vast majority of environmental stimuli is recognized by members of two evolutionarily related chemosensory receptor families, the odorant receptors (ORs) and the gustatory receptors (GRs) [1,2,3,4]. Benton et al (2009) [5] identified a novel type of chemosensory receptors in Drosophila that where given the name Ionotropic Receptors (IRs). IRs are a group of evolutionary conserved Ionotropic Glutamate Receptors (iGluRs) and increase.
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