Female's war: a story of the invasion and competitive displacement between two xylophilus group nematode species

Interspecific competition occurs fiercely between invasive and native species which occupy similar niche. Here, we report the competitive mechanism underlying the displacement of Bursaphelenchus mucronatus by Bursaphelenchus xylophilus . In the early stage of the competition, population of both species increase significantly, but their abundance rates were differentiated, B. xylophilus increased, whereas B. mucronatus decreased. Unexpectedly, sex ratio of female to male of both species increased sharply and peaked at 4.87 and 3.88, respectively, which were outclassed that of noncompetitive conditions (2.77 and 2.21). Thereafter, the sex ratio of B. xylophilus declined and stabilized at 2.81, but the sex ratio of B. mucronatus declined till no B. mucronatus was left, indicating the interspecific competition could be dominated by female. The mating behaviors showed that for both species, the mating success rate of one couple dropped slightly when one male or female of other species was added, but dropped significantly when two males or females were added. Surprisingly, almost no successful mating was observed when three males or females of other species were added. We therefore hypothesize that the mating opportunity of one couple could be deprived by the other species once three or more male or female were added. Further, threshold value of competitive displacement experiments and model analysis were completely consistent with the above experiments. Our results elucidate the crucial role of sex ratio in interspecific competition for the first time, as well as their mating disruption, directing a wonderful story of female-dominated war between two xylophilus group nematode species.