It is widely accepted that biological interactions are stronger or more important in generating and maintaining biodiversity in the tropics than in temperate regions. However, this hypothesis has not been fully tested in ecology and evolutionary biology.

In a study published in Nature Ecology and Evolution, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences have provided strong support for this central prediction by examining phytochemical diversity and herbivory in 60 tree communities ranging from species-rich tropical rainforests to species-poor subalpine forests.

The researchers investigated tree communities in Yunnan, one of the world’s floristic hotspots, which contains an elevation gradient from tropical rainforest to subtropical forest to subalpine forest within a relatively short distance. In 2011 and 2012, they established 60 long-term forest inventory plots ranging from species-rich tropical rainforest to species-poor subalpine forest along the gradient.

Using community metabolomic approaches, they tested the predictions that phytochemical diversity is higher within and among communities in tropical forests as compared to less species-rich subtropical and subalpine forests. They also measured herbivore damage and leaf specialization.

Combining these data, they tested the prediction that these variables are higher in the tropics. They then quantified the phylogenetic signal in the phytochemical similarity between species to test whether closely related species diverged more in their phytochemicals than expected.

They found that phytochemical diversity was higher within tropical tree communities compared to subtropical and subalpine communities. Along with increased alpha and beta phytochemical diversity in leaves in tropical tree communities, they found an increase in leaf herbivory and the degree of specialized herbivory in the tropics. Furthermore, herbivory pressure and specialization were highest in the tropics.

The researchers then constructed a phylogeny including all species in their system and quantified phylogenetic signal in phytochemical similarity. They found little phylogenetic signal in tree phytochemical similarity, suggesting rapid divergence among closely related species.

The results also highlight multiple dimensions of tropical biodiversity that are often unquantified and of value to human society, but which are threatened by ongoing global change. Tropical forests not only contain more species than temperate forests, but also spectacular levels of phytochemical diversity. There are likely numerous abiotic covariates (e.g., temperature and precipitation) and biotic covariates (e.g., herbivores, pathogens, neighborhood composition and diversity) that may be associated with phytochemical diversity and cannot be clearly separated to elucidate specific mechanisms.

“Our study provides multiple lines of evidence from entire tree communities from the tropics to the subalpine that biotic interactions are likely to play an increasingly important role in generating and maintaining tree diversity at lower and lower latitudes,” said Yang Jie of XTBG.

Nightmare material or truly man’s best friend? A team of researchers equipped a dog-like quadruped robot with a mechanized arm that takes air samples from potentially treacherous situations, such as an abandoned building or fire. The robot dog walks samples to a person who screens them for potentially hazardous compounds, says the team that published its study in Analytical Chemistry. While the system needs further refinement, demonstrations show its potential value in dangerous conditions.

Testing the air for dangerous chemicals in risky workplaces or after an accident, such as a fire, is an important but very dangerous task for scientists and technicians. To keep humans out of harm’s way, Bin Hu and colleagues are developing mobile detection systems for hazardous gases and volatile organic compounds (VOCs) by building remote-controlled sampling devices like aerial drones and tiny remotely operated ships.

The team’s latest entry into this mechanical menagerie is a dog-like robot with an articulated testing arm mounted on its back. The independently controlled arm is loaded with three needle trap devices (NTDs) that can collect air samples at any point during the robot’s terrestrial mission.

The researchers test-drove their four-legged “lab” through a variety of inaccessible environments, including a garbage disposal plant, sewer system, gasoline fireground and chemical warehouse, to sample the air for hazardous VOCs. While the robot had trouble navigating effectively in rainy and snowy weather, it collected air samples and returned them to the portable mass spectrometer (MS) for onsite analysis in less time than it would take to transfer the samples to an off-site laboratory—and without putting a technician in a dangerous environment.

The researchers say the robot-MS system represents a “smart” and safer approach for detecting potentially harmful compounds.

Maternal immunity refers to the immunity transferred across the placenta, colostrum, milk or eggs from mother to offspring. It plays a key role in protecting the vulnerable offspring against pathogenic attacks, and is present in nearly all vertebrates and invertebrates.

As one of the ancient vertebrates, teleost fish continuously secrete a substantial amount of mucus due to their unique living environment, and often exhibit schooling behavior. Previous studies have highlighted the presence of numerous immune components in the mucus of fish, which plays a crucial role in resisting pathogens.

This information prompted a team of researchers in China to investigate whether adult fish mucus can serve as a form of maternal immunity in fish, and function as an immunomodulator during the larvae stage of their offspring when faced with pathogen threats.

“The role of zebrafish adult mucus in dextran sulfate sodium (DSS)-induced inflammatory response and microbial imbalance was studied through the morphology of zebrafish larvae, changes in intestinal pathology, changes in expression of immune genes, fluorescence imaging of immune cells, and changes in microbial composition and structure,” says corresponding author Zhen Xu.

The team found that the mortality rate of larvae and the number of goblet cells in the intestines decreased. Meanwhile, the height of the intestinal villi was enhanced, weakening the expression of immune-related genes.

“Further, the infiltration of neutrophils and macrophages in the intestine of larvae was effectively mitigated,” adds Xu. “Notably, adult zebrafish mucus can significantly upregulate the abundance of beneficial bacteria and regulate the microbiota to reach a new equilibrium.”

The results of this study, published in Water Biology and Security, indicate that adult zebrafish mucus plays an important immunomodulatory role in the immune response induced by DSS in larvae, and that adult mucus may also be used as a form of maternal immunity with an immunomodulatory function that is similar to that of mammalian milk.

“Meanwhile, adult fish mucus can be used as a potential protective and therapeutic measure to enhance the immunity of larvae in aquaculture, improve the survival rate, prevent mass mortality of fish in the early stages of life, and play a function in breeding, immunity and other aspects to promote the sustainable development of aquaculture in China,” says Xu.