Reproductive plasticity in response to food source in the fungal-feeding nematode Bursaphelenchus okinawaensis

<jats:title>Summary</jats:title> <jats:p>Organisms use various strategies to cope with fluctuating environments. Some organisms express different phenotypes in alternative conditions through a process known as ‘phenotypic plasticity’, which is presumably an evolutionary adaptation to environmental variation. Nematodes adapt to various environments; it has been suggested that phenotypic plasticity is a contributing factor in their high level of environmental adaptability. We investigated the reproductive plasticity in response to a food source in the fungal-feeding nematode, <jats:italic>Bursaphelenchus okinawaensis. Bursaphelenchus okinawaensis</jats:italic> is known to reproduce primarily as a self-fertilising hermaphrodite on a filamentous fungus and yeast; here, we showed that newly isolated SH3 strain hermaphrodites produced a small number of progenies (⩽9 progenies per hermaphrodite) on the yeast test plate, while they laid similar numbers of eggs to the SH1 strain on the fungus test plate. Subsequent sperm observation by 4′,6-diamidino-2-phenylindole (DAPI) revealed that SH3 hermaphrodites could produce only a small number of sperm on the yeast test plate. Some hermaphrodites did not produce any eggs, indicating that they had become females rather than hermaphrodites. These results showed that the hermaphrodite or female status of SH3 nematodes was a plastic character, dependent on the food stimulus. An intra-strain crossing test between SH1 and SH3 suggested that the reproductive plasticity was controlled by a single recessive gene. This study provided an insight into a novel type of phenotypic plasticity in nematodes.</jats:p>