Germline evolution depends on mitochondrial mutation rate.

(a) Heat map showing fixation probability of an allele encoding early germline sequestration (at generation N_G = 3) in a simple organism that lacks tissue differentiation and produces gametes by somatic gametogenesis (at generation N_G = 10), in relation to the rate of copying errors (μ_S) and background damage (μ_B). The early germline mutation is introduced at a frequency of 0.05 (see Methods). Early germline sequestration is favoured by higher μ_S and lower μ_B (blue, top left). The early germline allele is selected against in organisms with low μ_S and high μ_B (red, bottom right), conditions that instead favour somatic gametogenesis. The solid line represents neutrality. (b) Increasing the number of tissues to eight makes it harder to fix an early germline (N_G = 3)—the region shaded in red expands (solid line versus dotted line) so germline fixation now requires higher μ_S and lower μ_B compared with (a). (c) Increasing the number of mitochondria to 200 in an organism with eight tissues has little effect on early germline sequestration. Thus, increasing the level of complexity (more tissues and mitochondria) does not favour early germline sequestration. Underlying data can be found at: https://github.com/ArunasRadzvilavicius/GermlineEvolution/tree/master/FigureData.