Introduction

The American dipper Cinclus mexicanus Swainson (Passeriformes: Cinclidae) is an aquatic passerine that inhabits high-gradient, fast-flowing river systems from Alaska to Central America. Distinctive traits of this species include frequent dipping into turbulent water even at ambient temperatures well below 0°C (Kingery & Wilson, 2019). To date, only the cestode Cinclotaenia filamentosa Macy, 1973 and the trematodes Laterotrema cascadensis Macy & Strong, 1967 and Metoliophilus uvaticus Macy & Bell, 1968 have been described in C. mexicanus (see Macy & Strong, 1967; Macy & Bell, 1968; Macy, 1973)

Coccidians are obligate intracellular parasitic protists. Species infecting birds are homoxenous and are thought to be reasonably host-specific (Tenter et al., 2002). To date only one coccidian species, I. cincli Gottschalk, 1972, has been described from a bird species of the family Cinclidae, the white-throated dipper C. cinclus (L.) based on material from Europe. Here, we describe a new species of Isospora Schneider, 1881 from C. mexicanus in Yosemite National Park, California, USA.

Materials and methods

During a trip to Yosemite National Park (37°44′39″N, 119°34′12″W; 37°44′22″N, 119°33′53″W), California, USA, American dippers (C. mexicanus) were observed and photographed. Birds were observed dipping into shallows along stream of River Merced to feed. During photographic sessions at two different locations, 4 adult dippers left droppings on rocks of the riverbanks. The faecal samples were collected by using a toothpick, avoiding urate deposits and soil and were placed in plastic vials containing 2.5% (w/v) potassium dichromate solution (K2Cr2O7) at a ratio of 1:4 (v/v). Eight days later, samples were placed in a thin layer (c.5 mm) of K2Cr2O7 2.5% solution in Petri dishes, incubated at 20–26°C and monitored daily under a light microscope (Duszynski & Wilber, 1997). Oöcysts (n = 30) were microscopically examined using the technique described by Duszynski & Wilber (1997) and Berto et al. (2014). Morphological observations, photomicrographs and measurements were made using a Nikon Eclipse 80i binocular microscope coupled to a digital camera Nikon DS-Fi2. All measurements are in micrometres and are given as the range followed by the mean in parentheses. Line drawing was made using Adobe Illustrator CC2019 and Adobe Photoshop CC2018 programs.

Results

All four faecal samples examined contained oöcysts. Eight days after the collection of samples, more than 70% of the oöcysts were sporulated (under the conditions used in this study).


Family Eimeriidae Minchin, 1903

Genus Isospora Schneider, 1881

Isospora dipperia n. sp.


Type-host: Cinclus mexicanus Swainson (Aves: Passeriformes: Cinclidae), American dipper.


Type-locality: Yosemite National Park (37°44′39″N, 119°34′12″W; 37°44′22″N, 119°33′53″W), California, USA.


Type-material: Oöcysts in dichromate solution, phototypes and line drawings of sporulated oöcysts are deposited and available in the Repository (www.ibirds.org) of the Institute for Biodiversity Research, Development & Sustainability (iBIRDS). Photographs of the type-host specimens (symbiotypes) are deposited in the same collection. The repository number is ESV-28/2019. Photomicrographs of sporulated oöcysts are deposited and available in the Repository of iBIRDS (www.ibirds.org). The repository number is ESV-28/2019.

Prevalence: Oöcysts of this species were found in 4/4 (100%) of the fresh faecal samples examined.

Site of infection: Unknown. Oöcysts were recovered from faeces.

ZooBank registration: To comply with the regulations set out in article 8.5 of the amended 2012 version of the International Code of Zoological Nomenclature (ICZN, 2012), details of the new species have been submitted to ZooBank. The Life Science Identifier (LSID) for Isospora dipperia n. sp. is urn:lsid:zoobank.org:act:01D92CDC-53D7-46C2-9398-7B8A2E965E0F.


Etymology: The specific epithet is derived from the common name of the type-host.


Description (Figs. 1, 2)

Fig. 1
figure 1

Line drawing of a sporulated oöcyst of Isospora dipperia n. sp. from Cinclus mexicanus. Scale-bar: 10 µm

Full size image
Fig. 2
figure 2

Photomicrographs of sporulated oöcysts and sporocysts of Isospora dipperia n. sp. A, Subspherical oöcysts with clearly visible lemon-shaped sporocyst; B, Two sporocysts with a polar granule between them; C, Two sporocysts released from the oöcyst showing sporocyst residuum, consisting of many spherules. Scale-bars: 10 µm

Full size image

Sporulated oöcyst

Oöcysts (n = 30) subspherical, 20–24 × 17–21 (20.9 × 18.7), with smooth bi-layered wall (c.1.1 thick); length/width (L/W) ratio 1.0–1.1 (1.1). Micropyle and oöcyst residuum absent (Fig. 2A); one polar granule present (1.6 × 2.2) (Fig. 2B).


Sporocyst and sporozoites

Sporocyst (n = 30) lemon-shaped, 14–16 × 8–11 (15.5 × 9.8); length/width (L/W) ratio 1.45–1.75 (1.6). Stieda body present, knob-like shaped (1.1 high × 1.9 wide); sub-Stieda body present, rounded, prominent, 1.7–2.2 high × 3.3–4.0 wide; para-Stieda body absent. Sporocyst residuum present, consisting of many spherules of different sizes (0.5–1.0) (Fig. 2C). Sporozoites 4, vermiform, 2.5–3.0 × 13.0–14.0, with posterior refractile body (3.5 in length) and anterior refractile body (2.2 in diameter).


Remarks


To date, not protist parasites have been described in C. mexicanus. To our knowledge, only a single species of Isospora has been reported for birds of the Cinclidae in Europe: I. cincli Gottschalk, 1972 from the white-throated dipper C. cinclus (L.) (see Gottschalk, 1972; Brown et al., 2010). The description of I. cincli was based on unsporulated oöcysts, and the mean dimensions (15.9 × 13.8 µm) appear to be considerably smaller than those in I. dipperia n. sp. (20.9 × 18.7 µm) (see Gottschalk, 1972; Table 1).

Table 1 Comparative morphological data for Isospora spp. recorded from species of the Cinclidae in Europe and Sturnidae in the Americas
Full size table

This new species was compared with two species of Isospora described in the Americas from birds of the family Sturnidae, related to Cinclidae (Voelker & Spellman, 2004): I. graculai Bhatia, Chauhan, Arora & Agrawal, 1973 from Gracula religiosa L. (see Upton et al., 1984) and I. rothschildi Upton, Wilson, Norton & Greiner, 2001 from Leucopsar rothschildi (Stresemann) (see Upton et al., 2001). The mean dimensions of the sporulated oöcysts in I. dipperia n. sp. (20.9 × 18.7 µm) appear to be considerably smaller than those in I. graculai (24.6 × 22.4 µm) and I. rothschildi (22.3 × 21.6 µm). Furthermore, the Stieda body in I. graculai is rounded whereas in I. rothschildi the sub-Stieda body is compartmentalised (Table 1).

Isospora dipperia n. sp. represents the first species of Isospora infecting a bird host of the family Cinclidae in the Americas.