Grow, stay and change together - The effects of co-evolution

Co-evolution between symbionts can not only lead to the development of new organs but also potentially the evolution of a whole new phylum. This can be seen in the evolution from sub social Cockroaches to Eusocial Termites. Termites were once thought to have evolved as a sister group to cockroaches but thanks to recent research into their obligate gut symbionts, there is mounting evidence that termites have evolved from cockroaches (Nalepa 2017).

Although the main ancestor is not known, (Nalepa 2017) believes that termites may have evolved from sub-social termites such as the family Cryptocercus. Termites & Cryptocercus both tend to live in logs and have wood as their main food source which they cannot digest without their symbionts. Both share an obligate symbiotic relationship with a diverse array of gut microbiota that digest plant fibres and convert them into a bioaccessable form for their hosts to eat (Ohkuma & Brune 2010: Nalepa 2017). As a result, both the host and the microbiota have a reliable food source.

A 'wood roach' family: Cryptocercus (Potterfield 2017)

Since young are born without gut microsymbionts, they rely on regurgitated food and microsymbionts from their parents for an extended period of time to colonise their gut with the wood digesting microbes. It is believed that this high dependence on their parents has led to the development of co-parenting and then finally eusociality where there are specific castes that specialize in raising the young (Nalepa 2017).  

A recent genetic analysis has found that between various termite colonies there were four main genes that may have come from co-evolved gut protists which respond to various factors such as immune response, hormones, diet and the environment (Scharf et al. 2017). Inagaki & Matsuura (2018) found that the termite Zootermopsis nevadensis dispersed their symbiotic bacteria Serratia marcescens around their nest, it is believed that this protects the nest from pathogenic bacteria and fungi.

The soldier caste of the eusocial termite Zootermopsis nevadensis (Minkley 2014)

The evolution of sociality can be seen in countless organisms and is believed to be forged by obligate symbiotic relationships and the need for transmission young (Munger et al. 2018). This is just one example of many.

Thankyou for reading. 😊

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