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ESSENTIAL SYMBIONTS. "To ensure that offspring acquire these microbial partners, insects have evolved diverse mechanisms for vertical transmission of the symbionts, including ovarial transmission in aphids, egg smearing in anobiid beetles, coprophagy in termites, milk gland transmission in tsetse flies, and capsular transmission in plataspid stinkbugs." https://lnkd.in/dvW6NMZ View in LinkedIn

METABOLIC SYMBIOSIS. "Insects that feed exclusively on nutritionally limited or persistent food sources, such as plant phloem sap, vertebrate blood, or woody materials, commonly possess symbiotic microorganisms in their guts. Symbiotic microbes are essential for host survival and reproduction and play pivotal roles in host metabolism, such as providing essential nutrients and digesting food materials." https://lnkd.in/dvW6NMZ View in LinkedIn

SEXUAL SELECTION. "Male and female reproductive traits display some of the most rapid evolution observed in nature, suggesting that sexual selection as well as sexual conflict are major forms of selection. However, natural selection plays an important part as well, as environmental variation might also drive divergence in reproductive traits." https://lnkd.in/dChz5SR View in LinkedIn

VIRAL ECOSYSTEM. "Similar to gut bacteria, interpersonal variation in the virome is high. Changing the focus from individual agents that are implicated in disease toward a community view has already precipitated paradigm shifts in the view of the virome and disease, and the same will likely be true for eukaryotic microbes." https://lnkd.in/dRUEtkS View in LinkedIn

DODGING THE RABBIT HOLE. "Highly reduced genomes of insect symbionts contain mostly genes involved with cell replication, transcription, and translation: Mutations in these genes will impact fitness of individual symbiont cells, where selfishness can originate. Thus, eukaryotic organelles may have escaped the symbiosis rabbit hole primarily because genes controlling symbiont replication are transferred to the host genome." https://lnkd.in/dcBwzRs View in LinkedIn

SO ENDS this contemplation of hereditable endosymbionts, a half-way stop in the spectrum to engulfment of algae to make a permanent organelle such as a chloroplast and mitochondrion. Clearly, there are many examples in nature where critically important symbiotic organisms are inherited, mostly maternally, by a variety of mechanisms, ensuring that the offspring have immediate inoculations of these outsourced metabolic factories. View in LinkedIn

GENETIC STREAMLINING. "Another difference between insect symbionts and organelles is that genomes of the latter encode little of their own machinery for self-replication and depend on import of needed gene products from the host. One consequence is that they typically have fewer genes and thus present a smaller mutational target. More importantly, organelle genes that are retained are subject to strong host-level selection, limiting their deterioration or selfish tendencies." https://lnkd.in/dcBwzRs View in LinkedIn

PURGING COMPETITORS. "Due to imperfect vertical transmission and potential physiological costs imposed on hosts, facultative endosymbionts are relying on various manipulative strategies to persist in a host population. For example, some are male-killers or exert cytoplasmatic incompatibility (CI) when their host engages in reproduction with a partner that harbors an unrelated endosymbiont." https://lnkd.in/dChz5SR View in LinkedIn

LOW MUTATION ACCUMULATION. "The most evolutionarily successful of heritable symbioses are those that gave rise to mitochondria and plastids, raising the question of why organelles have not been limiting baggage for eukaryotic hosts. Although numerous studies have documented excesses of deleterious mutations circulating within organelle genomes, these mutations are generally recent, remain at low frequencies, and do not become fixed within populations." https://lnkd.in/dcBwzRs View in LinkedIn

SYMBIONT FERTILIZATION CONTROL. "Many other heritable endosymbionts are facultative and not absolutely required by their host for survival and reproduction. Although endosymbionts are not directly associated with genitalia, they still form an important part of insect reproduction as manipulators of fertilization." https://lnkd.in/dChz5SR View in LinkedIn