Biology subjects

Mao, T.-R.

Publications and source records attributed to Mao, T.-R..

3 recordsLinked to original sources

bioRxiv2023

Wall-following: phylogenetic context of an enhanced behaviour in stygomorphic Sinocyclocheilus (Cypriniformes: Cyprinidae) cavefishes

With 75 known species, the freshwater-fish genus Sinocyclocheilus is the largest cavefish radiation in the world, emerging as a model system for evolutionary studies. They show multiple adaptations for cave dwelling (stygomorphic adaptations), which include a range of traits such as eye degeneration (Normal-eyed, Micro-eyed and Eyeless), depigmentation of skin, and in some species, the presence of "horns". Their behavioural adaptations to subterranean environments, however, are poorly understood. Wall-following (WF) behaviour, where an organism remains in close contact with the boundary demarcating its habitat when in the dark, is a peculiar behaviour observed in a wide range of animals and is enhanced in some cave dwellers. Hence, we hypothesize wall-following to be present also in Sinocyclocheilus, possibly enhanced in Eyeless species compared to species with visual cues (Normal / Micro-eyed species). Using 13 species representative of Sinocyclocheilus radiation and eye-morphs, we designed a series of assays, based on pre-existing methods for Astyanax mexicanus behavioural experiments, to examine wall-following behaviour under three stimulation conditions. Our results indicate that eyeless species exhibit significantly enhanced levels of WF compared to Normal-eyed species, with Micro-eyed forms demonstrating intermediate levels. Using a mtDNA based dated phylogeny (chronogram with four clades A - D), we traced the degree of WF of these forms to outline common patterns. We show that intensity of WF behaviour is high in the subterranean clades (B & C) compared to clades with free-living species (A & D). Experiments on WF behaviour revealed that eyeless species are highly sensitive to vibrations, whereas normal-eyed species are the least sensitive. Since WF behaviour is present to some degree in all Sinocyclocheilus species, and given that these fishes evolved in the late Miocene, we identify this behaviour as being ancestral with WF enhancement related to cave occupation. Our results from this diversification-scale study of cavefish behaviour suggest that enhanced wall-following behaviour may be a convergent trait across all stygomorphic cavefish lineages. Significance statementSinocyclocheilus, a genus of 75 species of freshwater cavefish, is an emerging model system in evolutionary studies. Their adaptations for subterranean life, including eye degeneration, skin depigmentation, and horn-like structures, are well-known, but their behavioural adaptations remain understudied. Here we focus on a phenomenon, called "wall-following," where fish stay close to the cave walls in absence of light. We hypothesized that this behaviour would be more pronounced in eyeless species. We selected 13 species, representative of the diversity of the genus and eye types, and observed their wall-following behaviour under different conditions. Results were intriguing; eyeless species exhibited heightened wall-following behaviour compared to their sighted counterparts, with small-eyed species falling in between. Researchers also mapped this behaviour on a phylogenetic tree, discovering a pattern: cave-dwelling clades showed stronger wall-following than free-living ones. Wall-following is prevalent in all Sinocyclocheilus species and, given the evolutionary history of the genus, is considered an ancestral behaviour that intensified with cave adaptation. These findings contribute to our understanding of convergent evolution, suggesting that enhanced wall-following may be a shared trait among diverse cavefish lineages.

animal behavior and cognition↗

bioRxiv2021

Evolving in the darkness: phylogenomics of Sinocyclocheilus cavefishes highlights recent diversification and cryptic diversity

Troglomorphism-- any morphological adaptation enabling life to the constant darkness of caves, such as loss of pigment, reduced eyesight or blindness, over-developed tactile and olfactory organs--has long intrigued biologists. However, inferring the proximate and ultimate mechanisms driving the evolution of troglomorphism in freshwater fish requires a sound understanding of the evolutionary relationships between surface and troglomorphic lineages. We use Restriction Site Associated DNA Sequencing (RADseq) to better understand the evolution of the Sinocyclocheilus fishes of China. With a remarkable array of derived troglomorphic traits, they comprise the largest cavefish diversification in the world, emerging as a multi-species model system to study evolutionary novelty. We sequenced a total of 120 individuals throughout the Sinocyclocheilus distribution. The data comprised a total of 646,497bp per individual, including 4378 loci and 67,983 SNPs shared across a minimum of 114 individuals at a given locus. Phylogenetic analyses using either the concatenated RAD loci (RAxML) or the SNPs under a coalescent model (SVDquartets, SNAPP) showed a high degree of congruence with similar topologies and high node support (> 95 for most nodes in the phylogeny). The major clades recovered conform to a pattern previously established using Sanger-based mt-DNA sequences, with a few notable exceptions. We now recognize six major clades in this group, elevating the blind cavefish S. tianlinensis and the micro-eyed S. microphthalmus as two new distinct clades due to their deep divergence from other clades. PCA plots of the SNP data also supports the recognition of six major clusters of species congruent with the identified clades based on the spatial arrangement and overlap of the species in the PC space. A Bayes factor delimitation (BFD) analysis showed support for 21 species, recognizing 19 previously described species and two putative new cryptic ones. Two species whose identities were previously disputed, S. furcodorsalis and S. tianeensis, are supported here as distinct species. In addition, our multi-species calibrated tree in SNAPP suggests that the genus Sinocyclocheilus originated around 10.5 Mya, with most speciation events occurring in the last 2 Mya, likely favored by the uplift of the Qinghai-Tibetan Plateau and cave occupation induced by climate-driven aridification during this period. These results provide a firm basis for future comparative studies on the evolution of Sinocyclocheilus and its adaptations to cave life.

evolutionary biology↗

bioRxiv2020

Evolution in Sinocyclocheilus cavefish is marked by rate shifts, reversals and origin of novel traits

Epitomized by the well-studied Astyanax mexicanus, cavefishes provide important model organisms to understand adaptations in response to divergent natural selection. However, the spectacular Sinocyclocheilus diversification of China, the most diverse cavefish clade in the world harboring nearly 75 species, demonstrate evolutionary convergence for many traits, yet remain poorly understood in terms of their morphological evolution. Here, using a broad sample of 49 species representative of this diversification, we analyze patterns of Sinocylocheilus evolution in a phylogenetic context. We categorized species into morphs based on eye-related condition: Blind, Micro-eyed (small-eyed), and Normal-eyed and we also considered three habitat types (Troglodytic - cave-restricted; Troglophilic - cave-associated; Surface - outside of caves). Geometric morphometric analyses show Normal-eyed morphs with fusiform shapes being segregated from Blind/Micro-eyed (Eye-regressed) morphs with deeper bodies along the first principal component ("PC") axis. The second PC axis accounts for shape complexity related to the presence of horns. Ancestral character reconstructions of morphs suggest at least three independent origins of Blind morphs, each with different levels of modification in relation to the typical morphology of ancestral Normal-eyed morphs. Interestingly, only some Blind or Micro-eyed morphs bear horns and they are restricted to a single clade (Clade B) and arising from a Troglodytic ancestral species. Our geophylogeny shows an east-to-west diversification spanning the Pliocene and the Pleistocene, with Troglodytic species dominating karstic subterranean habitats of the plains whereas predominantly Surface species inhabit streams and pools in hills to the west (perhaps due to the scarcity of caves). Integration of morphology, phylogeny and geography suggests Sinocyclocheilus are pre-adapted for cave dwelling. Analyses of evolutionary rates suggest that lineages leading to Blind morphs were characterized by significant rate shifts, such as a slowdown in body size evolution and a 3.3 to 12.5 fold increase in the evolutionary rate of eye regression. Furthermore, body size and eye size have undergone reversals, but horns have not, a trait that seem to require substantial evolutionary time to form. These results, compared to the Astyanax model system, indicate Sinocyclocheilus fishes demonstrate extraordinary morphological diversity and variation, offering an invaluable model system to explore evolutionary novelty.

evolutionary biology↗