"Low relatedness can drive the evolution of reproductive division of labour"Takeuchi, NobutoReproductive division of labour (RDL), where sterile 'helpers' assist specialised 'reproducers' in transmitting genetic information, has evolved repeatedly at vastly different biological scales. Examples include eusocial insects with queens and workers, multicellular organisms with germline and soma cells, ciliates with micronuclei and macronuclei, and cells with genomes and enzymes (enzymes provide catalysis, 'helping' genomes transmit genetic information). What drives this repeated evolution of RDL? The standard theory posits that a critical driver is high relatedness, which is required to select sterile helpers performing altruism. Here, we demonstrate the opposite possibility that the evolution of RDL is driven by low relatedness. Using multilevel modelling, we show that RDL itself can increase relatedness and thus protect collectives against the evolution of cheaters—i.e., selfish individuals that avoid cooperation and replicate uncontrollably, reducing collective fitness. Specifically, RDL restricts the transmission of genetic information to a small number of reproducers per collective (e.g., queens, germline cells, and genomes), thereby reducing the effective population size from which cheaters may arise. Consequently, RDL evolves when relatedness is sufficiently low because the protective benefit of RDL increases with the increasing risk of cheater evolution. Therefore, the evolution of RDL is a cause, rather than a consequence, of high relatedness in our model. Our work provides a novel perspective in evolutionary biology by revealing that the evolution of RDL can be driven by protection against cheaters, the benefit that occurs only if relatedness is sufficiently low. |
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