Parent-Offspring Pathogen Transmission: A Selective Agent Promoting Sexual Reproduction

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Abstract
As a parent ages it can be expected to accumulate individual-specific strains of sublethal pathogens for 2 reasons: Over time the parent will experience an increasing diversity of pathogen phenotypes (genotypes) and thus the cumulative probability of being discovered by pathogens capable of infection with monotonically increase. If the generation time of the pathogen is short relative to that of the host, then infective pathogens that are poorly adapted to a particular host individual can evolutionarily respond and increase their host specificity during the lifetime of a single host individual. The sublethal pathogens accumulated by a parent with thus be a nonrandom sample from the pathogen genotype pool and will be preadapted to circumvent many of the genetically coded defenses of the parent phenotype. If reproduction is clonal, there will be a high similarity between parent and progeny and pathogen transmission within a lineage can be enhanced. If reproduction is sexual, there will be reduced concordance between the genetically coded defenses of parent and progeny and the progeny may be protected from the debilitating effects of pathogens preadapted to exploit the parental phenotype (genotype). The sexual reproduction may produce a temporary escape in uniqueness that is an important protection for developing progeny that are exposed to parental pathogens. Extant asexual species can coexist with their pathogens through a variety of coevolutionary interactions with stabilize the microevolutionary changes of the pathogen populations. The probability that pathogen virulence (aggressiveness) will stabilize at a tolerable level is increased when the asexual species is of hybrid (interspecific or intraspecific) origin.