Brachydistomum spp

Heneberg, Petr, Sitko, Jiljí, Casero, María & Rząd, Izabella, 2023, New molecular data help clarify the taxonomy of Central European avian Dicrocoeliidae Looss, 1899 (Trematoda: Plagiorchiida), International Journal for Parasitology: Parasites and Wildlife 22, pp. 276-299 : 286

3.1.5. Brachydistomum spp

Three Brachydistomum spp . were sequenced, Brachyd. ventricosum (Rudolphi, 1802) (ex T. merula , Erithacus rubecula , Phylloscopus collybita , and Fringilla coelebs ), Brachydistomum olssoni (Railliet, 1900) (ex Apus apus ), and Brachydistomum salebrosum (Braun, 1901) (ex A. apus ). Both morphological and molecular evidence support the validity of these three species, but additional evidence for Brachyd. salebrosum is needed. Several issues are associated with Brachydistomum spp ., as follows.

1) Molecular evidence suggests that the questionable reports of morphologically identified Brachylecithum fringillae (Layman, 1923) were incorrect (see Sitko and Okulewicz (2002) for more detailed report on Brachyl. fringillae ). These individuals represented subadult Brachyd. ventricosum , which typically have a long oval or filamentous body shape, whereas only the adult individuals are oval. Also, the position of testes varies; Brachyd. ventricosum individuals have the testes in tandem, diagonals or opposite at high intensities of infection, whereas they have testes always in tandem when the infection intensity is low. Similarly, the previously described Lyperosomum emberizae Yamaguti (1941) ; Yamaguti (1941) likely represented Brachyd. ventricosum from a heavily infected bird host; under these conditions, some Brachyd. ventricosum individuals develop unusual body shapes ( Sitko and Okulewicz 2002). Note that all the numerous findings reported previously as Brachydistomum mosquensis (Skryabin et Isaitchikov, 1927) are also considered to represent Brachyd. ventricosum ( Sitko and Okulewicz 2002) .

2) There is limited molecular support for Brachyd. salebrosum as a valid species. It is difficult to distinguish from Brachyd. olssoni using the CO1 locus (0.003 base substitutions per site; Fig. 1 ), and the two share an identical ITS2 locus ( Fig. 4 ). However, morphological support for the existence of these two species is strong ( Fig. 5 ). Adult Brachyd. salebrosum have a lanceolate body shape, and the ventral sucker and genital organs are large relative to the body size. In contrast, adult Brachyd. olssoni have a long-oval body shape, broadest in the ventral sucker region, and the ventral sucker and genital organs are small relative to the body size. Subadult individuals of Brachyd. salebrosum do not have a lanceolate body shape, a large ventral sucker or large genital organs. The body sizes of Brachyd. salebrosum and Brachyd. olssoni form a continuous gradient. Additional molecular markers are needed to differentiate these two species. Based on the above arguments, the previously suggested synonymy of these two species based on their minimal morphological differences ( Sitko, 1994) was rejected.

Figures

Fig. 1. Maximum likelihood analysis of sequences of the CO1 DNA locus of Dicrocoeliidae. Bootstrap values (n = 1000) are indicated for nodal support. Black circles indicate new sequences. The scale-bar indicates the number of substitutions per nucleotide site.

Fig. 4. Maximum likelihood analysis of sequences of the ITS2 DNA locus of Dicrocoeliidae. Bootstrap values (n = 1000) are indicated for nodal support. Black circles indicate new sequences. The scale-bar indicates the number of substitutions per nucleotide site.

Fig. 5. Representative photographs of slides with Brachydistomum olssoni, Brachydistomum salebrosum, and Brachydistomum ventricosum. Host species, sampling dates and host identification numbers are indicated. All specimens originated from the Czech Republic.