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Transcript
ARUNAS RADZVILAVICIUS SELECTION FOR MITOCHONDRIAL QUALITY DRIVES THE EVOLUTION OF GERMLINE AND TWO SEXES SOMATIC GAMETOGENESIS OR GERMLINE SEQUESTRATION? WHY IS OOGAMY UNIVERSAL IN MULTICELLULAR ORGANISMS? MATING TYPE A MATING TYPE B MODELLING THE INVOLVEMENT OF MITOCHONDRIA Random partitioning of mitochondria generates variation ZYGOTE + x2 Isogamy: mitochondria inherited from only one (UPI) or both (BPI) mating types. Ancestral metazoan state. BPI if mutation rate was low. MALE FEMALE Two types of mitochondrial mutations: ZYGOTE + ROS, UV Oogamy: universal in multicellular plants and animals, seldom seen in unicellulars. mtDNA replication errors Background damage Zygote fitness Totipotent stem cells Stem cell fitness Tissue stem cells Fixation probability of oogamy (evolutionary advantage) OOGAMY EVOLVES TO ENSURE UPI AND MAINTAIN SOMATIC FITNESS Somatic fitness Adult fitness depends on the worst tissue, so high mitochondrial fitness variation between tissues is selected against. ISOGAMY: BPI, low variation between organisms Small zygote, high variation in soma + Egg size (log, units of sperm size) OOGAMY: UPI, high variation between organisms Large zygote, low variation in soma + INCREASING MITOCHONDRIAL MUTATION RATE DRIVES THE EVOLUTION OF GERMLINE Replication mutation rate (x10-3) A trade-off between the generated beneficial variation and the amount of accumulated deleterious mutations 5 More tissues Large egg Metazoan motility, predation Faster accumulation of mtDNA mutations M50 0T BPI Q0 4 Early germline sequestration 3 Unlimited somatic differentiation, greater activity, ageing 2 Cambrian explosion 1 0 2 4 6 8 Increasing somatic complexity makes somatic gametogenesis even more stable. Only high mtDNA replication rates make early germline sequestration evolutionary advantageous. 10 Background mutation rate (x10-3) Somatic gametogenesis advantageous (10 divs) 0 More mitochondria Neoproterozoic oxygenation 0.05 Germline advantageous (3 divs) 0.1 0.2 0.3 Fixation probability of g CoMPLEX AND DEPARTMENT OF GENETICS, EVOLUTION AND ENVIRONMENT UNIVERSITY COLLEGE LONDON [email protected] Twitter @LukeArn THANKS TO: CoMPLEX NICK LANE ANDREW POMIANKOWSKI