Replicability of results in biomedical animal research has been seriously questioned. Besides scientific and economic concerns, poor replicability has important ethical implications, as it hampers scientific and medical progress, puts patients in clinical trials at risk, and harms animals for inconclusive research. Causes of poor replicability are manifold and often multi-factorial. We have previously shown that common flaws in study design are an important source of poor replicability, and have devised practicable solutions. Here, we propose to investigate another related, but different aspect: the prevailing reliance on inbred mice in both basic and preclinical research, and its implications for the replicability of animal research and animal welfare.
Typical mouse models are based on inbred strains, which after more than 20 generations of inbreeding are homozygous on almost all alleles. As inbreeding eliminates genetic variation within strains, inbred strains are thought to produce results that are more precise (i.e. less variable). However, empirical evidence does not support this assertion. Homozygosity might lead to more variable and less replicable results, as allelic variation contributes to the buffering of organisms against developmental perturbations. In addition, homozygosity may increase disease susceptibility and compromise animal welfare, if allelic variation contributes to adaptive plasticity, thereby enhancing the organisms' resilience to stress.
We will, therefore, investigate whether homozygous (inbred) mice are developmentally less robust, showing more signs of developmental instability, than heterozygous (outbred and F1 hybrid) mice, and whether homozygous mice are less resilient to stressors compared to heterozygous mice. For this purpose, we will use three separate but complementary methodological approaches, comprising data analyses based on large publicly available databases of mouse phenotype data, a systematic review and meta-analysis of published literature, and a comprehensive experimental study based on a representative panel of inbred, outbred, and F1 hybrid mice.
We predict that homozygous (inbred) mice are developmentally less stable (as shown by fluctuating asymmetry), and less resilient to environmental stressors (as shown by increased morbidity and mortality, as well as behavioral, physiological, and cellular indicators of acute and chronic stress) than heterozygous (F1 hybrid and outbred) mice. Moreover, we predict that environmental robustness and mutational robustness are correlated, and that homozygous mice show less plasticity in plastic traits, and less stability in canalized traits.
These new results will advance our understanding of the effects of inbreeding on developmental robustness, adaptive phenotypic plasticity, and resilience to stress. They will elucidate the implications of the widespread use of inbred strains of mice for both within-study variation (precision) and between-study variation (replicability) of experimental results, as well as for the health and well-being of the animals. Such knowledge is key in view of promoting scientifically valid and ethically responsible animal research.
