Submitted to: Conservation Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2013
Publication Date: N/A
Interpretive Summary: Worldwide declines in bees may be resulting from inbreeding within populations. Inbred populations reduce harmful recessive alleles by over-producing male bees at the expense of females. The purging of deleterious alleles in this way appears as a steady rise in pollinator sex ratio, which favor male bees, and whose haploid genomes fully express deleterious traits. Thus, more males can be eliminated along with lethal recessives from the population. However, this genetic balancing act can wreak havoc on pollinator populations when overly inflated male sex ratios and a higher mortality in males reduce by attrition the number of nesting females, thus ultimately causing a populations extinction. To curb the erosive effects of genetic depletion on small pollinator populations, we used mitochondrial DNA fingerprinting to identify viable breeding units that can increase heterozygosity and the proportion of female bees for a small quarantined population of wild orchard bees Osmia ribifloris. Supplemental breeding experiments tested the relative fitness of each breeding unit, which was introduced as part of a pollinator management program. DNA analysis of mostly male bees shows clear genetic distinctions between southern O. ribifloris from Texas and California and those from northern Utah. The Texas bees exhibited greater nesting success in Mississippi, a climate similar to that of their home. Our results were the first to reveal that inseminated females were more successful nesters than were unmated bees. Remarkably, unmated females nest late and one-quarter of these females tried to usurp the occupied nests of other bees. Such usurpation proved harmful and led to the death of one-third of O. ribifloris offspring. Thus, genetic costs of the long-term propagation of bees make quarantine impractical for small pollinator populations. The key to conserving wild bees is the relocation of both males and females to locales with ample food and nesting substrate.
Technical Abstract: Viable breeding units, which may increase heterozygosity and the proportion of female bees for a population of orchard bees Osmia ribifloris, were indentifyied with PCR-amplified polymorphic mtDNA. Breeding experiments tested the relative fitness of each breeding unit as part of a pollinator management program. Phylogenetic analysis of mostly male mtDNA shows clear genetic distinctions between southern O. ribifloris from Texas and California and those from northern Utah; a phylogenetic pattern running contrary to the east-west subspecific designations for this pollinator species. While in quarantine, southern bees exhibit greater nesting success in a climate similar to that of their native range. Percentage of successful nest starts by O. ribifloris females and the size of their broods were weakly influenced by a bee's genetic background or that of their mates. Mated females founded more nests with larger broods than than had unmated bees. Interestingly, however, unmated females rarely nested or they nested very late. A portion of unmated bees without nests consistently usurped both occupied and vacated nests, even when fresh empty nests were plentiful. Seizing host brood may come at a high cost for O. ribifloris in captivity, as inadvertent injury to brood or deliberate infanticide may have led to the death of one-third of progeny. Thus, propagating haplodiploid Hymenoptera under a quarantine would seem to be impractical long-term. Even supportive bee releases may ineffectively reduce higher genetic loads of inbred populations. The key to conserving wild bees, whether the species is threatened or not, is quickly to relocate bees to locales with ample food and nesting substrate.