INCIPIENT SPECIATION IN THE FLOUR BEETLE, TRIBOLIUM CONFUSUM - PREMATING ISOLATION BETWEEN NATURAL-POPULATIONS

We report the existence of partial reproductive isolation between two natural populations of the flour beetle, Tribolium confusum, collected in Kaduna, Nigeria and Zagreb, Croatia. When a female from either pop ulation is paired with a single sympatric or allopatric male, she prod uces near normal numbers of semifertile offspring. However, when femal es are multiply mated with allopatric and sympatric males, the sympatr ic males sire the large majority of offspring. When measured in offspr ing numbers, the mean relative fitness of allopatric males is 0.425 wi th Nigerian females and 0.085 with Croatian females. Thus, the reprodu ctive isolation is reciprocal but asymmetric. Behavioural observations indicate that only a fraction of mating attempts by allopatric males are successful because females do not become quiescent as often when m ounted by allopatric males. The premating isolation is also reciprocal but asymmetric: Nigerian females are more accepting of allopatric mal es as mates than are Croatian females. The prezygotic behavioural isol ation between these two populations is different from the postmating, prezygotic isolation observed between two other species in the genus, ir: castaneum and T. freemani. Furthermore, the I: confusum interpopul ation hybrids are fertile although they exhibit a weak female bias.