Effects of genomic homozygosity on total fitness in an invertebrate: lethal equivalent estimates for Drosophila melanogaster

Abstract

Estimates of susceptibility to inbreeding depression for total tness are needed for predicting the cost of inbreeding and for use in population viability analyses, but no such valid estimates are available for any wild invertebrate population. I estimated the number of lethals equivalents for total tness in recently wild-caught populations of Drosophila melanogaster using published data on the total tness of homozygosity versus heterozygosity for each of the major chromosomes (the X, second, and third) under competitive conditions. As there are no data for the tness effects of homozygosity for the small fourth chromosome which represents 1.0% of the euchromatic genome, this was accounted for by attributing the homozygosity for the three large chromosome to an inbreeding coe cient of 0.99 when computing lethal equivalents for total tness. Total genomic homozygosity is predicted to be essentially lethal in D. melanogaster. The corresponding haploid lethal equivalents estimate for total tness was 5.4. The lethal equivalent value lies within the range for vertebrates but tends to be higher than for most outbreeding plants which are often purged as they exhibit up to 20% sel ng (by de nition). As D. melanogaster has its genome sequenced and annotated and has lethal equivalent estimates for total tness for individual chromosomes as well as its total genome, it provides an excellent opportunity for evaluating genomic estimates of mutation load.

Characterizing and Eliminating the Inbreeding Load

“…The Soay sheep ( Ovis aries ), Drosophila ( Drosophila melanogaster ) and killer whale ( Orcinus orca ) studies also followed this trend, where the inbreeding load was much higher for a late life history trait [ 76 , 77 , 78 ]. These studies are also unique from the point of view of the applied methodology, namely that the inbreeding load was determined using genomic methods (F ROH ) [ 76 , 77 , 78 ]. It has to be noted that the lethal equivalents estimated by the various authors presented in Table 1 .…”