Density dependent shifts in attachment site by the ectosymbiotic chironomid Nanocladius asiaticus on its megalopteran host Protohermes grandis

Abstract

Intraspecific interactions among ectosymbionts may occur when suitable attachment sites are limited to specific parts of their hosts. In this study, we examined attachment site selection by the ectosymbiotic chironomid Nanocladius (Plecopteracoluthus) asiaticus. Larvae and pupae of this chironomid attach to larvae of the megalopteran Protohermes grandis: they feed on algae and detrital materials caught on the chironomid's silken nets and on the body surface of the host. Sampling at approximately monthly intervals in central Japan revealed that the proportion of hosts with chironomids was relatively high and stable during the 2 year study period. When attached singly, larvae were usually found on the ventral side of the host's mesothorax. However, when two or more larvae were attached to a host, the mesothorax was occupied by only one larva (usually a large individual) and the other(s) were attached to the ventral side of the abdomen. Density dependent shifts in attachment sites were confirmed by a reattachment experiment in which a larva was removed from its host and released onto a new host with or without symbiosis by another individual. All of the larvae released singly on a host devoid of symbionts attached to the thoracic region and survived, whereas those released in pairs and not occupying this site were frequently lost. Thus, the thorax (particularly the mesothorax) is the most suitable attachment site, and there is a possibility that chironomid larvae compete for this site.

The influence of environmental factors on abundance and prevalence of a commensal ostracod hosted by an invasive crayfish: are ‘parasite rules’ relevant to non‐parasitic symbionts?

“…As parasite-induced host mortality is a regulatory mechanism of symbiont abundances exclusively affecting parasitic symbionts, our results suggest that other mechanisms are able to constrain the upper limits of symbiont infrapopulations. There are three possible mechanisms for regulating entocytherid infrapopulations: symbiont intraspecific competition (Mori et al, 2001;Hayashi & Ichiyanagi, 2005), hostinduced symbiont removal through behavioural responses (i.e. grooming activity; Jones & Lester, 1996) and host-induced removal through ecdysis (Walton & Hobbs, 1971;Young, 1971;Castillo-Escriv a et al, 2013).…”

Phoretic associations betweenNanocladius asiaticus(Diptera, Chironomidae) and its hostsGestroiella(Heteroptera, Naucoridae) andEuphaea masoni(Odonata, Euphaeidae) in streams in Western Thailand

“…Hayashi (1998) reported that larvae of this species are also found on the ventral thorax of the megalopterans. The mesothorax is the most suitable attachment site for the ectosymbiotic chironomid, N. asiaticus, on its megalopteran host, P. grandis (Hayashi and Ichiyanagi, 2005). The ventral mesothorax may be a preferred attachment site because hosts groom around the head region (Hayashi, 1998).…”

Living on a catfish: nested occupation of ectosymbiotic chironomids on host body

“…Several previous studies have shown that the number of chironomid larvae per host increases in large hosts, either for freshwater macroinvertebrates (e.g. Svensson 1980;Tokeshi 1986;Pennuto 1997;Hayashi and Ichiyanagi 2005) and armored catfish (Sydow et al 2008). Differing from these studies, however, we assessed whether the site occupation by larvae follows a nested pattern regarding body size, i.e.…”