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Persistent uplift means the Qinghai-Tibet Plateau (QTP) is an ideal natural laboratory to investigate genome evolution and adaptation within highland environments. However, how paleogeographic and paleoclimatic events influence the genome and population of endemic fish species remains unclear. Glyptosternon maculatum is an ancient endemic fish found on the QTP and the only critically endangered species in the Sisoridae family. Here, we found that major transposons in the G. maculatum genome showed episodic bursts, consistent with contemporaneous geological and climatic events during the QTP formation. Notably, histone genes showed significant expansion in the G. maculatum genome, which may be mediated by long interspersed nuclear elements (LINE) repetitive element duplications. Population analysis showed that ancestral G. maculatum populations experienced two significant depressions 2.6 million years ago (Mya) and 10 000 years ago, exhibiting excellent synchronization with Quaternary glaciation and the Younger Dryas, respectively. Thus, we propose that paleogeography and paleoclimate were dominating driving forces for population dynamics in endemic fish on the QTP. Tectonic movements and temperature fluctuation likely destroyed the habitat and disrupted the drainage connectivity among populations. These factors may have caused severe bottlenecks and limited migration among ancestral G. maculatum populations, resulting in the low genetic diversity and endangered status of the species today.

Summary The aim of the study was to determine the distribution and relative frequency of Glyptosternon maculatum taste buds (TB) using paraffin sectioning, the HE staining method and light microscopy. TBs were found on a variety of surface body areas (lips, barbels, lateral, ventral and dorsal areas, and the dorsal, pelvic, pectoral, anal and adipose fins), as well as in the oropharyngeal cavity. In the epithelium of histological figures of sampled body parts, TB was pear-shaped from the bottom to the top. The ratio of height/width value of the taste bud was above 1.0, with a range from 1.2 to 2.0. Highest TB frequencies were in the mandibular outer barbel (18.5 ± 3.7 mm−2), mandibular inner barbel (17.1 ± 5.4 mm−2), nasal barbel (16.8 ± 4.2 mm−2) and maxillar barbel (15.9 ± 2.7 mm−2), lips (14.6 ± 3.6 mm−2) and oropharyngeal cavity (13.2 ± 3.5 mm−2). TBs occurred in moderate quantities on the forehead (6.9 ± 2.1 mm−2), anal fin (5.8 ± 2.3 mm−2), and La2 (3.9 ± 1.6 mm−2, between pelvic and anal fins), then decreased to a few in the La1 area (3.4 ± 1.3 mm−2), operculum (2.5 ± 1.3 mm−2) and other examined areas. Type I (elevated), type II (slightly elevated) and type III (not elevated or sunken) TBs were found in the epithelium of various sampling locations. These are the first descriptions of taste buds in G. maculatum.

Glyptosternon maculatum (Regan 1905) Parexostoma maculatum Regan 1905: 183. Type locality: Lhasa, Tibet [Brahmaputra drainage]. Syntypes: BMNH 1904.12.28.87-88 (2). Distribution: Brahmaputra drainage, India and China (Hora & Silas, 1952b; Chu et al., 1999; Jayaram, 1999)., Published as part of Alfred W. Thomson & Lawrence M. Page, 2006, Genera of the Asian Catfish Families Sisoridae and Erethistidae (Teleostei: Siluriformes)., pp. 1-96 in Zootaxa 1345 on page 70

The purpose of this study was to develop a reliable method of age estimation for Glyptosternon maculatum (Sisoridae, Siluriformes) in the Yarlung Tsangpo River basin of Tibetan Plateau using whole and sectioned vertebrae. Sectioned vertebrae showed that translucent bands were separated by distinct opaque bands through the focus to the margin. Although whole vertebrae showed clear band patterns in the intermediate region, such band patterns are obscure around the region of the focus of the vertebrae in older fish. The whole and sectioned vertebrae methods produced consistent ages until age 6, but there was a trend towards greater differences between the two methods as age increased. These findings indicate that sectioned vertebrae are suitable for age estimation of this species.