Strong assortative mating in ninespine stickleback <i>Pungitius tymensis</i> demonstrated in no-choice mating trials between pairs of three congeneric species

<p>No-choice mating trials were conducted in three sympatric ninespine stickleback species (Pungitius tymensis, Pungitius sinensis and Pungitius pungitius) to elucidate the degree of assortative mating among them. Pungitius tymensis males had higher mating rates (95%) with P. tymensis females than with females of the other two species. However, P. tymensis females had the mating rates with heterospecific males was very low (0-4.5%). One instance of mating between a P. tymensis female and P. sinensis male continued for 1293 seconds, the longest mating time observed in the trial. These findings demonstrated that P. tymensis females were strongly incompatible with heterospecific males. Conversely, P. tymensis males exhibited mating behaviour toward females of all three species, heterospecific mating occurring in 7 of 22 trials with P. sinensis females, and 6 of 17 trials with P. pungitius females. The median time of successful mating by P. tymensis males did not differ significantly between conspecific (median: 106 s, range: 25–1165 s) and heterospecific mating (P. sinensis: median: 40 s, range: 8–652 s; P. pungitius: median: 140 s, range: 22–835 s). Accordingly, P. tymensis males may potentially cross with females of the other species, as evidenced by reports of naturally occurring hybrid individuals of P. tymensis with the latter. The mating trials strongly suggested a behavioural context wherein introgression of mtDNA genes occurred from P. sinensis to P. tymensis.</p>