<P> As the endosymbiont adapts to the host's lifestyle the endosymbiont changes dramatically . There is a drastic reduction in its genome size, as many genes are lost during the process of metabolism, and DNA repair and recombination, while important genes participating in the DNA to RNA transcription, protein translation and DNA / RNA replication are retained . The decrease in genome size is due to loss of protein coding genes and not due to lessening of inter-genic regions or open reading frame (ORF) size . Species that are naturally evolving and contain reduced sizes of genes can be accounted for an increased number of noticeable differences between them, thereby leading to changes in their evolutionary rates . When endosymbiotic bacteria related with insects are passed on to the offspring strictly via vertical genetic transmission, intracellular bacteria go across many hurdles during the process, resulting in the decrease in effective population sizes, as compared to the free living bacteria . The incapability of the endosymbiotic bacteria to reinstate their wild type phenotype via a recombination process is called Muller's ratchet phenomenon . Muller's ratchet phenomenon together with less effective population sizes leads to an accretion of deleterious mutations in the non-essential genes of the intracellular bacteria . This can be due to lack of selection mechanisms prevailing in the relatively "rich" host environment . </P> <P> Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped . It is derived from the English word commensal, used of human social interaction . It derives from a medieval Latin word meaning sharing food, formed from com - (with) and mensa (table). </P> <P> Commensal relationships may involve one organism using another for transportation (phoresy) or for housing (inquilinism), or it may also involve one organism using something another created, after its death (metabiosis). Examples of metabiosis are hermit crabs using gastropod shells to protect their bodies, and spiders building their webs on plants . </P> <P> In a parasitic relationship, the parasite benefits while the host is harmed . Parasitism takes many forms, from endoparasites that live within the host's body to ectoparasites and parasitic castrators that live on its surface and micropredators like mosquitoes that visit intermittently . Parasitism is an extremely successful mode of life; as many as half of all animals have at least one parasitic phase in their life cycles, and it is also frequent in plants and fungi . Moreover, almost all free - living animal species are hosts to parasites, often of more than one species . </P>

What is the relationship between a clownfish and a sea anemone