Spatial aggregation in small spring-fed tributaries leads to a potential metapopulation structure in a parasitic fish leech

Abstract

Large-bodied ectoparasites are often observed only in low numbers in the field. How such rarely found parasites persist and maintain viable populations has been an intriguing question inadequately addressed. The simplest hypothesis is the existence of distribution hot spots, and another, but not mutually exclusive, possibility is a form of metapopulation structure where local populations are effectively connected via dispersal. In this study, we conducted an intensive epidemiological survey of a piscicolid leech Taimenobdella amurensis to elucidate spatial population structure and potential dispersal of this rarely found parasite. Four years of potential-host screening (n = 20 664) from 28 tributaries and 10 main stem reaches in a mountain river system of Hokkaido, northern Japan, revealed that occurrences of T. amurensis (n = 1348) were confined to spring-fed tributaries. Since most spring-fed tributaries were small (<1 km in length), it would seem to be unlikely for the ectoparasite to form a persistent local population in each tributary. The main host fish was Dolly Varden charr, which is known to disperse among neighbouring tributaries. These findings suggest that, along with the host, the ectoparasite displays a potential metapopulation structure, in which host-dependent dispersion may overcome local extinction by keeping the local populations connected.

<i>Salmincola edwardsii</i> (Copepoda: Lernaeopodidae) Parasitic on Southern Asian Dolly Varden, <i>Salvelinus malma</i> <i>krascheninnikova</i>, from Hokkaido Island, Japan, with the Southernmost Distribution Record of the Copepod in Asia

“…), Salmonema ephemeridarum (von Linstow, 1872) (as Cystidicoloides ephemeridarum), Rhabdochona oncorhynchi (Fujita, 1921), and Rhabdochona sp. (Seki 1975;Ito et al 1987)-and a leech Taimenobdella amurensis (Epshtein, 1964) (Katahira et al 2017). Another subspecies of Dolly Varden, Miyabe charr, Salvelinus malma miyabei Oshima, 1938, also occurs on Hokkaido Island and is endemic to Lake Shikaribetsu (Maekawa 1984;Dunham et al 2008: 539).…”

“…In the past parasitological papers, several scientific names were used for southern Asian Dolly Varden from Japan [Salvelinus malma (Walbaum, 1792) (Seki 1975;Ito et al 1987;Shedko and Shedko 2002); S. m. krascheninnikovi (Katahira et al 2017)] and the Russian Far East [S. malma (Shedko and Shedko 2002); S. curilus (Pallas, 1814) (Shedko et al 2005)], but S. m. krascheninnikova is herein used based on WoRMS Editorial Board (2020). Following Dunham et al (2008: 539), "southern Asian Dolly Varden" is used as the common name of S. malma krascheninnikova.…”

A strategic sampling design revealed the local genetic structure of cold-water fluvial sculpin: a focus on groundwater-dependent water temperature heterogeneity

“…The flow rate, which is another major factor in the stream environment, is also strongly influenced by groundwater. In addition, because groundwater flow is affected by not only geological conditions but also geomorphological conditions, it is possible to separate streams with high and low groundwater discharge even in the same geological watershed (e.g., Katahira et al 2017), indicating that the elimination of correlations between distance and environment is also possible in smaller-scale studies.…”