Reproductive compatibility among populations and host-associated lineages of the common bed bug ( L.).

As populations differentiate across geographic or host-association barriers, interpopulation fertility is often a measure of the extent of incipient speciation. The bed bug, L., was recently found to form two host-associated lineages within Europe: one found with humans (human-associated, HA) and the other found with bats (bat-associated, BA). No unequivocal evidence of contemporary gene flow between these lineages has been found; however, it is unclear whether this is due to an inability to produce viable "hybrid" offspring. To address this question and determine the extent of compatibility between host-associated lineages, we set up mating crosses among populations of bed bugs based on both their host association (human-HA vs. bat-BA) and geographic origin (North America vs. Europe). Within-population fecundity was significantly higher for all HA populations (>1.7 eggs/day) than for BA populations (<1 egg/day). However, all within-population crosses, regardless of host association, had >92% egg hatch rates. Contrary to previous reports, in all interlineage crosses, successful matings occurred, fertile eggs were oviposited, and the F "hybrid" generation was found to be reproductively viable. In addition, we evaluated interpopulation genetic variation in among host-associated lineages. We did not find any clear patterns related to host association, nor did we observe a homogenization of lineages across populations that might explain a breakdown of reproductive incompatibility. These results indicate that while the HA and BA populations of represent genetically differentiated host-associated lineages, possibly undergoing sympatric speciation, this is in its incipient stage as they remain reproductively compatible. Other behavioral, physiological, and/or ecological factors likely maintain host-associated differentiation.