Expression of Genes Involved in Offensive and Defensive Phenotype Induction in the Pituitary Gland of the Hokkaido Salamander (Hynobius retardatus)

Phenotypic and Transcriptomic Analysis Revealed a Lack of Risk Perception by Native Tadpoles Toward Novel Non-Native Fish

The introduction of alien species poses a serious threat to native biodiversity, and mountain lake systems in the southwest of China are particularly vulnerable to the introduction of non-native fish. The prey naivety hypothesis states that native species may not be able to recognize novel introduced species due to a lack of common evolutionary background and therefore become easy targets, so the impacts of non-native fish on mountain endemic amphibians need to be urgently assessed. In an ex-situ experiment, we exposed the tadpoles of the Chaochiao Brown Frog (Rana chaochiaoensis), endemic to western China, to kairomones of both native and translocated fish species, and their phenotypic and genetic response patterns were compared. The results revealed significant phenotypic plasticity responses in total length (TOL), tail length (TL), and tail muscle width (TW) of tadpoles induced by native fish kairomone, while tadpoles exposed to translocated fish kairomone exhibited weaker phenotypic changes. At the transcriptional level, the number of differently expressed genes (DEGs) in the native fish treatment was 3.1-fold (liver) and 52.6-fold (tail muscle) higher than in the translocated fish treatment, respectively. There were more unique DEGs in the native fish treatment, primarily enriched in terms and pathways related to stress response, energy metabolism, and muscle development. The study revealed a lack of risk perception by native tadpoles toward novel non-native fish, providing new evidence for the prey naivety hypothesis from both phenotypic and molecular perspectives. Future conservation efforts should prioritize assessing the impacts of non-native fish on alpine and subalpine threatened and narrowly distributed amphibians. Additionally, prevention, early warning, monitoring, and removal of non-native fish should be carried out as soon as possible.

Evolution of the enhancer-rich regulatory region of the gene for the cell-type specific transcription factor POU1F1

Precise spatio-temporal expression of genes in organogenesis is regulated by the coordinated interplay of DNA elements such as promoter and enhancers present in the regulatory region of a given locus. POU1F1 transcription factor plays a crucial role in the development of somatotrophs, lactotrophs and thyrotrophs in the anterior pituitary gland, and in maintaining high expression of growth hormone, prolactin and TSH. In mouse, expression of POU1F1 is controlled by a region fenced by two CTCF sites, containing 5 upstream enhancer elements, designated E-A (5' to 3'). Elements C, B and A correspond to elements shown previously to play a role in pituitary development and hormonal expression; functional roles for elements E and D have not been reported. We performed comparative sequence analysis of this regulatory region and discovered that three elements, B, C and E, are present in all vertebrate groups except Agnatha. One very long (>2 kb) element (A) is unique to mammals suggesting a specific change in regulation of the gene in this group. Using DNA accessibility assay (ATAC-seq) we showed that conserved elements in anterior pituitary of four non-mammals are open, suggesting functionality as regulatory elements. We showed that, in many non-mammalian vertebrates, an additional upstream exon closely follows element E, leading to alternatively spliced transcripts. Here, element E functions as an alternative promoter, but in mammals this feature is lost, suggesting conversion of alternative promoter to enhancer. Our work shows that regulation of POU1F1 changed markedly during the course of vertebrate evolution, use of a low number of enhancer elements combined with alternative promoters in non-mammalian vertebrates being replaced by use of a unique combination of regulatory units in mammals. Most importantly, our work suggests that evolutionary conversion of alternate promoter to enhancer could be one of the evolutionary mechanisms of enhancer birth.

Phenotypic Plasticity of Salamander Hatchlings in the Pre-Feeding Stage in Response to Future Prey

Vulnerability of animals immediately after hatching may induce plasticity in early ontology that becomes important for subsequent survival and growth. Ezo salamanders (Hynobius retardatus) are amphibians inhabiting ponds in Hokkaido, Japan where ezo brown frogs (Rana pirica) spawn on occasion. The salamander larvae must achieve sufficient size in order to successfully capture frog tadpoles, and we examined whether the presence of tadpoles causes development of greater body and/or gape size in newly hatched salamander larvae, which will in turn result in advantageous future prey-predator interactions. To examine this hypothesis, we conducted three laboratory experiments to demonstrate the phenotypic plasticity of salamander hatchlings in response to the presence or absence of frog tadpoles and to screen the type of signals involved in the expression of the phenotypic plasticity. First, salamander hatchlings were reared alone or with tadpoles, and the growth and morphological traits of the hatchlings were compared. The results showed that hatchling larvae grew faster with a more developed gape in the presence of tadpoles. Next, to identify the type of signals inducing this plasticity, two separate experiments with manipulated chemical and visual signals from tadpoles were conducted. The findings showed that faster growth and a more developed gape were induced by chemical but not visual signals. This plasticity may be an adaptive strategy because it increases the likelihood of preying on tadpoles in future prey-predator interactions.