Paranybelinia otobothrioides, Dollfus, 1966

Morales-Ávila, José Raúl, Gómez-Gutiérrez, Jaime, Hernandez-Saavedra, Norma Y., Robinson, Carlos J. & Palm, Harry W., 2019, Phylogenetic placement and microthrix pattern of Paranybelinia otobothrioides Dollfus, 1966 (Trypanorhyncha) from krill Nyctiphanes simplex Hansen, 1911, International Journal for Parasitology: Parasites and Wildlife 10, pp. 138-148 : 142-143

3.4. Phylogenetic placement of Paranybelinia otobothrioides

The 1989 bp concatenated fragment of the small subunit rDNA (ssrDNA) of Pa. otobothrioides showed the nucleotide composition proportion of T = 25.4, C = 22, A = 23.9, G = 28.7, and G + C = 50.7%. The analyzed molecular data set consisted of 58 trypanorhynch sequences, including 11 species belonging to the Tentaculariidae and 2 species belonging to the Rhinoptericolidae , both families considered to be related with the Paranybeliniidae . The aligned 18S partition comprised 1913 positions of which 525 (26%) positions were variable and 400 (20%) were parsimony informative.

The Maximum likelihood analysis of the ssrDNA was largely congruent with the known topology of trypanorhynch cestodes (see Palm et al., 2009; Olson et al., 2010) with two major clades, the suborders Trypanoselachoida and Trypanobatoida (bootstrap values range 70–100). Inside the suborder Trypanobatoida , the genera subtropical. krill Nyctiphanes simplex . SD = Standard deviation.

Prochristianella , Parachristianella , Trimacracanthus (Eutetrathynchiidae) together with Trygonicola and Halysiorhynchus ( Mixodigmatidae ) formed a high supported clade (bootstrap 100%). This group placed sister to a weak supported clade (bootstrap <70%), consisting of H. australiensis , Mecistobothrium johnstonei (Southwell, 1929) Beveridge & Campbell, 1998 and Oncomegas celatus (Beveridge and Campbell, 2005) Schaeffner and Beveridge, 2012 [= Oncomegoides celatus ]) and the well supported clade formed by the Tetrarhynchobothrium Diesing, 1854 , Dollfusiella Campbell and Beveridge, 1994 , and Paroncomegas Campbell, Marques and Ivanov, 1999 (bootstrap 100%) ( Fig. 5 ).

The superfamily Tentacularioidea was represented in a distinct major clade (bootstrap 100%) ( Fig. 5 ). The phylogenetic analysis placed Pa. otobothrioides in a clade with high nodal support (bootstrap 100%) as sister taxon to the tentaculariids. The species Rhinoptericola megacantha Carvajal and Campbell, 1975 and Nataliella marcelli Palm, 2010 ( Rhinoptericolidae ), despite considered as members of the Eutetrarhynchoidea , were placed as sister taxon to the superfamily Tentacularioidea (i.e., Tentaculariidae and Paranybeliniidae ) with strong nodal support (bootstrap> 90).

Estimates of evolutionary divergence based on Kimura-2-parameters corrected distances (K2P) and the number of base differences per site between sequences were calculated between the Tentacularioidea ( Table 2), including the Tentaculariidae and the Paranybeliniidae . Paranybelinia otobothrioides showed no intraspecific genetic variation. Estimates of K2P between Pa. otobothrioides and the 11 tentaculariid species ranged from 0.027 to 0.039 (average = 0.033) and the number of base differences per sequence (nd) ranged from 44 to 62. Inside the Tentaculariidae , the genetic distance resulted in a considerably lower K2P range from 0.003 to 0.03 (average = 0.018) with the nd ranging from 5 to 49. Of the analyzed Tentaculariidae , Tentacularia coryphaenae Bosc, 1802 was the closest species to Pa. otobothrioides (K2P = 0.027, nd = 44), whilst Nybelinia africana Dollfus, 1960 showed to be the most divergent sequence (K2P = 0.039, nd = 62) ( Table 2).

Figures

Fig. 5. Maximum Likelihood tree under the General Time Reversible model of selected trypanorhynchs including Paranybelinia otobothrioides. Major families, superfamilies, and orders are indicated. Numbers on the branches show nodal support.