Abstract
Background and objectivesThe diversity of eutherian reproductive strategies has led to variation in many traits, such as number of offspring, age of reproductive maturity and gestation length. While reproductive trait variation has been extensively investigated and is well established in mammals, the genetic loci contributing to this variation remain largely unknown. The domestic dog, Canis lupus familiaris is a powerful model for studies of the genetics of inherited disease due to its unique history of domestication. To gain insight into the genetic basis of reproductive traits across domestic dog breeds, we collected phenotypic data for four traits, cesarean section rate, litter size, stillbirth rate and gestation length, from primary literature and breeders' handbooks.MethodologyBy matching our phenotypic data to genomic data from the Cornell Veterinary Biobank, we performed genome-wide association analyses for these four reproductive traits, using body mass and kinship among breeds as covariates.ResultsWe identified 12 genome-wide significant associations between these traits and genetic loci, including variants near CACNA2D3 with gestation length, MSRB3 and MSANTD1 with litter size, SMOC2 with cesarean section rate and UFM1 with stillbirth rate. A few of these loci, such as CACNA2D3 and MSRB3, have been previously implicated in human reproductive pathologies, whereas others have been associated with domestication-related traits, including brachycephaly (SMOC2) and coat curl (KRT71).Conclusions and implicationsWe hypothesize that the artificial selection that gave rise to dog breeds also influenced the observed variation in their reproductive traits. Overall, our work establishes the domestic dog as a system for studying the genetics of reproductive biology and disease.LAY SUMMARYThe genetic contributors to variation in mammalian reproductive traits remain largely unknown. We took advantage of the domestic dog, a powerful model system, to test for associations between genome-wide variants and four reproductive traits (cesarean section rate, litter size, stillbirth rate and gestation length) that vary extensively across breeds. We identified associations at a dozen loci, including ones previously associated with domestication-related traits, suggesting that selection on dog breeds also influenced their reproductive traits.
Highlights
Mammals exhibit wide variation in traits associated with reproduction (Derrickson 1992, Harrison 2001, Behringer et al 2006)
To identify SNPs that are significantly associated with four reproductive traits in domestic dog breeds, we conducted across-breed genome wide association (GWAS) analyses using a multivariate linear mixed model implemented in the program GEMMA (Zhou and Stephens, 2012)
To validate our GWAS approach and analytical choices, we first used our collected values for body mass, a trait whose genetic associations have been previously extensively studied in dogs (36,37)
Summary
Mammals exhibit wide variation in traits associated with reproduction (Derrickson 1992, Harrison 2001, Behringer et al 2006). (Jones et al 2009, Kiltie 1992, Martin et al 1985); neonate size can range from less than one gram in the shrew family (Soricidae), to more than a metric ton in the baleen whales (Balaenopteridae) ( Jones et al 2009, Martin et al 1985); and neonates can be either precocial (e.g., cricetid rodents, rabbits, and canids) or altricial (e.g., hystricomorph rodents, ungulates, and cetaceans) (Derrickson 1992) This variation in reproductive traits extends to methods of implantation (Cross et al 1994), structure of the placenta (Enders et al 2004, Elliot et al 2009), and lactation strategies (Pond 1977, Lefèvre et al 2011). Body fat percentages, which are associated with the energetics of reproduction, vary greatly between wild and captive baboons, and intraspecific variation among captive lemurs can vary from 8 – 41% (Dufour et al 2002)
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