RESUMEN
Polymorphisms in immunity genes can have large effects on susceptibility to infection. To understand the origins of this variation, we have investigated the genetic basis of resistance to the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster. We found that increased expression of the gene lectin-24A after infection by parasitic wasps was associated with a faster cellular immune response and greatly increased rates of killing the parasite. lectin-24A encodes a protein that is strongly up-regulated in the fat body after infection and localizes to the surface of the parasite egg. In certain susceptible lines, a deletion upstream of the lectin-24A has largely abolished expression. Other mutations predicted to abolish the function of this gene have arisen recurrently in this gene, with multiple loss-of-expression alleles and premature stop codons segregating in natural populations. The frequency of these alleles varies greatly geographically, and in some southern African populations, natural selection has driven them near to fixation. We conclude that natural selection has favored the repeated loss of an important component of the immune system, suggesting that in some populations, a pleiotropic cost to lectin-24A expression outweighs the benefits of resistance.
Asunto(s)
Parásitos , Avispas , Animales , Drosophila/genética , Drosophila melanogaster/genética , Interacciones Huésped-Parásitos , Avispas/fisiología , Lectinas/genética , Selección GenéticaRESUMEN
We report a draft genome sequence of a strain of the nonfermentative yeast Nadsonia starkeyi-henricii, isolated from soil in a forest in Ireland. Comparison to Nadsonia fulvescens shows few rearrangements and a level of divergence similar to that of Saccharomyces cerevisiae versus Saccharomyces paradoxus Its mitochondrial genome lacks NAD genes.