Generalism: Not all it's cracked up to be

So we have seen how mutualistic interactions can benefit ecosystems and even forge the evolution of a new branch of life such as the eusocial termites but what happens when an organism loses it’s host? For some such as the Bobtail squid and many coral species it can mean certain death, while generalists have the chance to have a new lease of life on a similar host…but not without consequences.

Studies by Appelgren et al. (2016) & Appelgren et al. (2018) found that while the hen flea Ceratophyllus gallinae can swap mingling great tit Parus major and collared flycatcher Ficedula albicollis birds during the breeding season, the fitness and reproductive success of the flea reduces depending on how specialized they were to their original host. They also found that the fleas were affected differently in different geographical locations. Appelgren at al. (2018) suggested that because hen fleas cannot disperse independently, they become genetically isolated while living with their host. As a result they become more specialized to their particular host as time goes by.

Therefore, the generalist capability of the flea species really depends on the environmental constraints it has been subjected to and the behaviour of it’s host. As the isolated fleas lose genetic variability they are less able to keep up with the evolutionary arms race between bird and parasite (Appelgren at al. 2018).

A eusocial 'Queen bee' snapping shrimp Synalpheus regalis with eggs. (Duffy year unknown)

 Becoming a generalist is not all bad news though, studies examining the evolution of generalist mutualists have suggested that abundant species may become generalists because they need more resources and are looking for a new symbiotic partner that they could eventually specialize with (Fort et al. 2015). For some Sponge host generalists like the Snapping shrimp genus Synalpheus, generalizing has allowed some Synalpheus species to evolve into the only known eusocial animals living in the ocean today (Brooks et al. 2017). This study has given evidence to the latter of two conflicting theories regarding the evolution of sociality: The Social conquest theory and the Social transition hypothesis (Brookes et al. 2017). These are two of many hypothesis as to why animals become eusocial (Chi et al. 2017).

More information on the snapping shrimp here: https://www.nationalgeographic.com/news/2018/03/animals-shrimp-oceans-queens-evolution/

Thanks for reading! 😊