Abstract
As populations differentiate across geographic or host‐association barriers, interpopulation fertility is often a measure of the extent of incipient speciation. The bed bug, Cimex lectularius 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 F1 “hybrid” generation was found to be reproductively viable. In addition, we evaluated interpopulation genetic variation in Wolbachia among host‐associated lineages. We did not find any clear patterns related to host association, nor did we observe a homogenization of Wolbachia lineages across populations that might explain a breakdown of reproductive incompatibility. These results indicate that while the HA and BA populations of C. lectularius 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.
Highlights
Understanding the mechanisms responsible for incipient speciation is critical to our understanding of evolution
The bed bug, Cimex lectularius L., was recently found to form two host-associated lineages within Europe: one found with humans and the other found with bats
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 and geographic origin (North America vs. Europe)
Summary
Understanding the mechanisms responsible for incipient speciation is critical to our understanding of evolution. Broad geographic overlap of C. lectularius populations and the lack of interlineage gene flow suggest that these host-associated lineages have differentiated into two host races that may be undergoing incipient, and arguably sympatric, speciation. Wawrocka, Balvín, and Bartonička (2015) further showed that HA and BA bed bugs were reproductively incompatible, with no eggs produced from interlineage crosses despite mating and sperm transfer. To better understand reproductive compatibility between different host-associated lineages of C. lectularius, we (a) investigated the relationship between assayed populations using mitochondrial markers previously found to reveal host-lineage differentiation; (b) conducted reproductive crosses that spanned geographic locations, and both within and between the two host-associated lineages; and (c) investigated the patterns of genetic variation of Wolbachia among populations for evidence of interpopulation homogenization
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