Acute warming in winter eliminates chemical alarm responses in threatened Qinling lenok Brachymystax lenok tsinlingensis

Urgent Conservation Actions Are Needed for Qinling Lenok Brachymystax lenok tsinlingensis Li, 1966: Enlightenment From Model Simulations

The Qinling lenok Brachymystax lenok tsinlingensis Li, 1966, an endemic to China and South Korea, is a rare protected species. Its unique requirements to habitat have made this fish extraordinarily fragile when faced with human pressures and global warming. Hence, predicting and understanding the potential influence of human pressures and global warming on this fish's spatial distribution is quite critical for the conservation and management of the species. To do so, based on its occurrence records and current as well as future environmental dataset, this study constructed a Maximum Entropy (MaxEnt) model for the species to analyze how its potential suitable areas (PSAs) would respond to global warming and human pressures (3 Global Climate Models ×2 Shared Socioeconomic Pathways ×3 future time nodes). The results showed that: (1) the MaxEnt model had strong generalization or transferability ability (AUC > 0.90), was highly reliable to predicting the current and future PSAs of the species; (2) Mean Temperature of Driest Quarter (BIO9), Human Population Density (Pop), Elevation (Elev), and Mean Temperature of Wettest Quarter (BIO8) were the salient environmental factors (given in descending order by significance); (3) the present PSAs for this fish were mainly distributed in Europe, Asia, and North America, and with the intensification of global changes, these areas in all continents would shrink on a large scale, and their distribution centroids would move towards northwest. Based on the above, a series of proposals for conservation and management of the fish were put forward so as to alleviate the loss of this relict species' habitats in the future.

Surviving the heat: The homeostatic regulation mechanism of endangered Brachymystax tsinlingensis

Conservation and utilization of Brachymystax tsinlingensis Li, 1966 (B. tsinlingensis), an endangered cold-water fish, is severely hampered by heat stress. In this study, heat stress and recovery experiments were firstly performed and implied that the intestine of B. tsinlingensis remained capable of self-regulation under heat stress. Therefore, transcriptome analysis was used to investigate the homeostatic mechanisms of B. tsinlingensis during temperature fluctuations. The results showed that a total of 5775 differentially expressed genes (DEGs) (1725 up- and 4050 down-regulated) were identified in the heat stress group, and 4312 DEGs (2024 up- and 2228 down-regulated) were identified in the recovery group when compared to their expression levels in the control group. Through Gene Set Enrichment Analysis (GSEA), citrate cycle (TCA cycle), oxidative phosphorylation, apoptosis, ferroptosis, focal adhesion, and tight junction pathways were found to be significantly up-regulated during heat stress, and declined during the recovery process. The results illustrated that heat stress caused ferroptosis and apoptosis in B. tsinlingensis. However, the organism was able to maintain homeostasis during temperature fluctuations modulating its energy metabolism, as well as the barrier and immune functions of the intestine. These findings help to enhance our understanding of the acclimation mechanisms of cold-water fish in present-day climate change.

Differential effects of parental and developmental temperatures on larval thermal adaptation in oviparous and viviparous model fish species

Phenotypic plasticity has been identified as a major mechanism of response to changing temperatures. Parental effects are potentially important drivers of ecological and evolutionary dynamics, while developmental plasticity also plays a key role in generating phenotypic variation. However, little is known of the interaction between parental effects and developmental plasticity on the thermal phenotypes of fishes with different reproductive modes (i.e. oviparous vs. viviparous). To understand the contributions of inter- and intra-generational plasticity of thermal phenotypes (preferred temperature, avoidance temperatures, critical thermal thresholds) in fishes with different reproductive modes, we carried out a factorial experiment in which both breeding parents and offspring were exposed to lower (22 °C) or higher (28 °C) temperatures, using zebrafish (Danio rerio) and guppies (Poecilia reticulata) as representative oviparous and viviparous species. We found that offspring thermal preference and avoidance of both species were significantly influenced by parental effects and developmental plasticity, with higher thermal preference and avoidance consistent with higher background (parental) temperature treatments. However, parental effects were only found to impose significant effect on the thermal tolerances of guppies. The findings suggest that phenotypic plasticity, both within and across generations, may be an important mechanism to adapt to rapid climate changes, and that future temperature fluctuations may impose more profound effects on viviparous fish species in general.

Ocean warming impairs the predator avoidance behaviour of elasmobranch embryos

Embryogenesis is a vulnerable stage in elasmobranch development due in part to high predation mortality. Embryonic elasmobranchs respond to potential predators by displaying a freezing behaviour, characterized by the cessation of pharyngeal respiration followed immediately by coiling of the tail around the body. We hypothesized that the duration of this freeze response is limited by the embryo's requirement for oxygen. Here, Scyliorhinus canicula embryos were incubated at either 15°C or 20°C during embryogenesis and tested for the duration of, and metabolic consequence of, the freeze response at their respective incubation temperature. Freeze response duration was negatively impacted by routine metabolic rate; embryos at 20°C had 7-fold shorter freeze duration than those at 15°C, potentially increasing their susceptibility to predation. These data demonstrate the capacity for climate change stressors to affect animal behaviour and suggest that this may occur by eliciting changes in the organism's metabolism. We suggest altered predator avoidance behaviour is a new factor to consider when assessing the impact of climate change on the conservation and management of oviparous elasmobranch species.