Mitochondrial effects on male and female fitness in the copepod Tigriopus californicus

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This project tests the hypothesis that mutations that harm males, can accumulate in parts of the genome, the mitochondria, that are inherited only through the female line. These male-harming mutations are not removed because the effects of natural selection acting on males are not passed to the next generation. Most familiar organisms have a large genome that resides in the nucleus of their cells, which is inherited from both parents, plus a small genome in the mitochondria. The mitochondria are the batteries of each cell, which are inherited only from the mother. Mitochondrial gene products interact with nuclear gene products to perform critical life functions. Male-harming mutations are predicted to accumulate in the mitochondrial genome and result in their reduced fitness. The project will examine interactions between the nuclear and mitochondrial genomes and the effects on male and female fitness in a small marine shellfish, the copepod Tigriopus californicus. The results will test whether the hypothesized negative effects on male fitness are widespread and examine whether and how the nuclear-mitochondrial interactions impact these effects. This hypothesis has profound implications for sex-specific medical interventions, because harmful mitochondrial mutations are implicated in male infertility, and diseases such as diabetes, cardiomyopathy, and male deafness, as well as in the overall aging process. Beyond the research itself, the project will train a postdoctoral researcher, Ph.D. students and undergraduate researchers. Further, the project will support outreach to diverse Los Angeles communities, including collaborations with the Aquarium of the Pacific (aimed at promoting public awareness of evolution) and with university programs for middle- and high-school students (aimed at enhancing the evolution curriculum in classes serving under-represented minorities). Male-specific mutational load will be assessed by creating 12 cytoplasmic hybrids in which mitochondria from 12 divergent populations will each be transferred onto the same isogenic nuclear background by approximately 15 generations of backcrossing. These 12 lines will include 11 interpopulation hybrids and one control. Each of the 12 lines will be used for assays of sex-specific fertility and survivorship over the full lifespan (180+ days). These data will be used to test the magnitude of the gender gap in mitochondrial effects, to test if the gender gap is larger for fertility than longevity, and to test whether this gender gap is aggravated in later life stages and under higher metabolic demand (e.g. higher temperature). The 12 mitochondrial genomes will be fully sequenced, allowing tests of the genomic extent of mitochondrial mutations with sex-specific effects. Further, gene expression will be assessed in one interpopulation hybrid and the control to identify nuclear genes associated with sex-specific mito-nuclear conflict.