Transposable elements (TEs) are a major determinant of eukaryotic genome size. The collective properties of a genomic TE community reveal the history of TE/host evolutionary dynamics and impact present-day host structure and function, from genome to organism levels. In rare cases, TE community/genome size has greatly expanded in animals, associated with increased cell size and changes to anatomy and physiology. Here, we characterize the TE landscape of the genome and transcriptome in an amphibian with a giant genome — the caecilianIchthyophis bannanicus, which we show has a genome size of 12.2 Gb. Amphibians are an important model system because the clade includes independent cases of genomic gigantism. The I. bannanicus genome differs compositionally from other giant amphibian genomes, but shares a low rate of ectopic recombination-mediated deletion. We examine TE activity using expression and divergence plots; TEs account for 15% of somatic transcription, and most superfamilies appear active. We quantify TE diversity in the caecilian, as well as other vertebrates with a range of genome sizes, using diversity indices commonly applied in community ecology. We synthesize previous models that integrate TE abundance, diversity, and activity, and test whether the caecilian meets model predictions for genomes with high TE abundance. We propose thorough, consistent characterization of TEs to strengthen future comparative analyses. Such analyses will ultimately be required to reveal whether the divergent TE assemblages found across convergent gigantic genomes reflect fundamental shared features of TE/host genome evolutionary dynamics.

Chemical communication is an important mode of communication in the courtship and breeding processes of amphibians. In caudates, multiple components of sexual pheromones have been identified and functionally verified. One of these pheromone systems is plethodontid modulating factor (PMF). In anurans, the pheromone called amplexin was found in nuptial pads of ranids and was considered a member of the PMF system, yet its bio-function has not been tested. In this study, we obtained 18 amplexin transcript sequences from nuptial pads of Nidirana pleuraden (Amphibia, Ranidae) by transcriptome sequencing and found that the proteins translated by these transcripts are diversified, hydrophilic, and relatively stable. We also acquired a N. pleuraden amplexin isoform with the highest expression level in the transcriptome analysis through the prokaryotic expression system. Using two different animal behavioral experimental settings, we have tested the bio-function of the recombinant PMF protein (rPMF) in N. pleuraden’s reproduction and found that the rPMF does not attract females but shortens the duration of amplexus significantly. This is the first study to verify the function of the PMF pheromone in Anura, indicating the pervasiveness of chemical communication during breeding in amphibians.

Pheromones play a pivotal role in chemical communication across various taxa, with protein-based pheromones being particularly significant in amphibian courtship and reproduction. In this study, we investigate the Emei music frog (Nidirana daunchina), which utilizes both acoustic and chemical signals for communication. Base on a de novo assembled genome of a male Emei music frog, we identify substantial expansion in four pheromone-related gene families associated with chemical communication. Notably, six members of the two-domain three-finger protein (2D-TFP) family, belonging to the sodefrin precursor-like factor (SPF) pheromone system, exhibited high and specific expression in the male post-axillary glands during the breeding season. Structural and evolutionary analyses confirm the presence of the SPF system across amphibians, classifiable into four distinct classes (two within urodeles and two within anurans). We propose a complete regulatory network governing SPF secretion via the hypothalamic-pituitary-testicular-breeding gland axis, and suggest testosterone synthesis as the pivotal pathway. Behavioral experiments further reveal a previously unknown female-attractant role of SPF in anurans. Overall, these findings not only highlight the underestimated diversity and function of pheromones in anurans, but also provide important insights into the evolution of protein-based pheromones in vertebrates.

The Taliang crocodile newt, Liangshantriton taliangensis , which is endemic to south-western China, is a rare salamandrid species with a distinct evolutionary history. Using combined field observations and captive experiments, we studied the courtship behaviour and male sexual interference of this species and composed a complete ethogram of its courtship behaviour. Unlike previous reports on sperm transfer, male L. taliangensis did not deposit spermatophores during ventral amplexus and females did not pick up sperm masses in this courtship phase. Sperm transfer was only performed during arm-hooking pin-wheel circling, which distinguishes L. taliangensis from Tylototriton species and supports the validity of genus Liangshantriton . Whether L. taliangensis shows bimodality in sperm transfer needs to be explored in additional populations. In the presence of sexual competitors, male L. taliangensis adjusted the duration of their behaviour. We found that males with longer snout-vent length, heavier mass, and higher tailfins may have an advantage in intrasexual competition.

Maintaining a dynamic balance among various life-history traits is crucial for survival in a warming world, yet the underlying mechanisms remain enigmatic. In this study, we employed the western clawed frog (Xenopus tropicalis) as a model and conducted a long-tern experiment from zygotes to adult stage. We find that even within the previously considered normal temperature range, a 5 °C increase in ambient temperature can establish a new metabolic state, resulting in elevated oxidative stress and a shift in energy allocation towards immune defense at the expense of sexual development. This conceptual framework of temperature-dependent trade-off strategy suggests that, while some studies observed that warm temperature reduces the risk of infection, it is important to note that this change may present challenges in the form of accelerated aging and reduced fertility, especially in ectotherms. These results not only indicate a far more complex adaptive response to future climate change than previously anticipated, but also provide a concise method for constructing animal models to explore diseases related to homeostatic disorders.