Taxonomic resolution of Stylonychia notophora (Alveolata, Ciliophora, Hypotricha) sensu Sapra and Dass 1970 using an integrative approach

Abstract

The spirotrichean ciliate Stylonychia notophora has previously been recorded in India although the descriptions are lacking in detail. It has been suggested several times that the Indian population, S. notophora sensu Sapra and Dass, 1970 collected along the Delhi stretch of the River Yamuna, is identical to Tetmemena pustulata, but this has never been confirmed due to insufficient data for the former. The present study includes detailed descriptions (classical and molecular) of populations of Tetmemena isolated from six locations along the River Yamuna, India. These include four from the Delhi stretch including that from which Sapra and Dass, 1970 isolated their population of S. notophora. Due to the lack of a sufficiently detailed description, the taxonomic status of S. notophora sensu Sapra and Dass, 1970 was not clear. Comparisons among the populations isolated in the present study with previous descriptions of T. pustulata and S. notophora sensu Sapra and Dass, 1970 show only minor differences in morphometry, morphogenesis and in 18S rDNA sequences. The 18S rDNA sequences of all six populations had 99% similarity to both T. pustulata and S. notophora. These findings support the contention that S. notophora sensu Sapra and Dass, 1970 was misidentified and is a population of T. pustulata. This study supports the need for adopting an integrative approach based on morphological, morphogenetic and molecular data in order to understand species delimitation in ciliated protists.

Polymorphism, gigantism, and cannibalism, one stylonychid ciliate (Ciliophora, Hypotricha) to rule them all

“…(75–76 × 35–39 μm vs. 87–126 × 33–53 μm in vivo ). Kaur et al ( 2020 ) mentioned that the resting cysts have a smooth wall and a size of about 11.9 μm across. However, the scale bar on their figure shows that the cyst is about 26 μm across.…”

“…The second subclade contains another 16 sequences, three Stylonychia notophora , one T. saprai , and 12 T. pustulata . The Stylonychia notophora sequences lack morphological identification, two of them are identical to a sequence of an Indian population (MH000394) of T. pustulata and the third sequence of S. notophora shows a similarity of 99.5% to and clusters with another Indian sequence (MH782169) of T. pustulata (Kaur et al, 2020 ). These data suggest that these sequences very likely belong to the Tetmemena pustulata complex.…”

“…These data suggest that these sequences very likely belong to the Tetmemena pustulata complex. The invalid species Tetmemena saprai , which is a distinct species mainly based on the cyst morphology (Gupta et al, 2020 ), shows a similarity of 99.9% to each of the Indian T. pustulata population (MH000394) (Kaur et al, 2020 ) and the two S. notophora (FM209297 and KY855573) sequences. Within the 12 T. pustulata sequences, only the six Indian populations studied by Kaur et al ( 2020 ) are characterized morphologically.…”

“…The invalid species Tetmemena saprai , which is a distinct species mainly based on the cyst morphology (Gupta et al, 2020 ), shows a similarity of 99.9% to each of the Indian T. pustulata population (MH000394) (Kaur et al, 2020 ) and the two S. notophora (FM209297 and KY855573) sequences. Within the 12 T. pustulata sequences, only the six Indian populations studied by Kaur et al ( 2020 ) are characterized morphologically. Interestingly, the morphometric characters of these populations are identical to each other but their rRNA gene sequences are different (i.e., showing 98.9–99.9% similarity among the six populations) and scattered within the subclade.…”

“…For many years, several stylonychid populations were assigned to T. pustulata mainly because they possess 18 frontal-ventral-transverse cirri and their transverse cirri are arranged in a single group. Furthermore, there was an underestimation of other characteristics, such as the resting cyst morphology and the dorsal ciliature, as only population-dependent variations (Berger, 1999 ; Bharti et al, 2019 ; Kaur et al, 2020 ). The formation of cannibalistic giants is a very rare and unusual character within the hypotrich ciliates.…”