Subjective resource value affects aggressive behavior independently of resource-holding-potential and color morphs in male common wall lizard

Impact of Microplastic Exposure on Sand Crab Scopimera globosa Behavior: Implications for Microplastic Transport and Sulfur Cycling through Bioturbation

The accumulation of microplastics (MPs) in estuarine regions and their ecological consequences have become global environmental concerns. Estuarine sediments function as major sinks for MPs and hotspots for critical biogeochemical processes, which are significantly influenced by benthic bioturbation. However, the impacts of MPs on the behavior of highly mobile benthic organisms and the ecological effects of bioturbation activities remain poorly understood. This study utilized laboratory simulation experiments, AI-based behavioral tracking, and metagenomic sequencing to systematically examine the effects of sand crab bioturbation on MPs migration, sediment physicochemical properties and sulfur cycling processes. Results demonstrated that sand crab bioturbation substantially enhanced the vertical migration of MPs, with fluxes to surface layers and the overlying water increasing by 27-fold compared to undisturbed conditions. Exposure to PE-MPs reduced sand crabs' surface foraging intensity and induced behavioral abnormalities. The crabs actively avoided MPs, exhibiting a preference for burrowing and residing in deeper sediment layers. This behavioral shift significantly altered microbial community distributions, with an increase of Pseudomonadota abundance and a decline of sulfate-reducing bacteria Thermodesulfobacteriota abundance. Furthermore, bioturbation accelerated sulfate oxidation in deeper sediments while inhibited dissimilatory sulfate reduction. This study is the first to identify the role of bioturbation in promoting the upward migration of MPs in sediments. Altered sand crab bioturbation will impact sediment biogeochemistry, estuarine function, and coastal resilience.

The size of a smell: assessment of rival’s relative size from femoral secretions in the common wall lizards, Podarcis muralis (Laurenti, 1768)

Animal communication depends on signals conveying information to a receiver who must perceive and decode them. Signals involved in territoriality are usually complex stimuli that should be correctly interpreted to avoid unnecessary conflicts. Lacertids use both visual and chemical stimuli in modulating their aggressive response against conspecifics and the rival’s size is one of the most important information, affecting the success probability in combat. To assess the actual ability of decoding information about a rival’s size based on its chemical stimulus alone, 60 males of Podarcis muralis were tested for three consecutive days in an arena bearing a mirror (to simulate an equal-sized intruder), and the chemical cues (femoral secretions) from an unknown individual of different size. Significant differences were observed in tongue-flicks number, which grew as the size difference between the focal lizard and the secretion donor decreased. This can be interpreted as the need for the lizard to better evaluate the potential competitor’s characteristics. The size difference also affected the number of bites against the mirror. They increased when the size of the focal lizard was larger than the donor triggering the aggressive response with a higher probability of winning the contest. This confirms that the focal lizard had correctly decoded the information about the opponent’s size by chemical stimulus. Although previous studies have shown that some components of the chemical signals are potentially informative about the signaler’s size, this is the first demonstration that male P. muralis is actually able to decode and use such information.

Close encounters of the three morphs: Does color affect aggression in a polymorphic lizard?

Color polymorphism is genetically controlled, and the process generating and maintaining morphs can affect speciation/extinction rates. Color badges are useful signals in intraspecific communication because they convey information about alternative strategies and can potentially decrease unnecessary conflicts among different color morphs. Competition and aggressive interactions among color morphs can contribute to polymorphism maintenance. This could lead to an uneven spatial distribution of morphs in a population because the local frequency of each morph establishes the intensity of the competition and the fitness of each male. We used a polymorphic lizard, Podarcis muralis, to assess if aggression varies among morphs under two contrasting hypotheses: a heteromorphic versus homomorphic aggression. We used laboratory mirror tests after lizard color manipulation, and we verified the consistency of results with an analysis of the spatial distribution of morphs in a wild population. Both the experiments confirmed that aggression is more common during homomorphic than heteromorphic contests. The adoption of alternative behavioral strategies that minimize risks and costs could facilitate the stable coexistence of the phenotypes and reduce competition. A bias in aggression would advantage rarer morph, which would suffer less harassment by common morphs obtaining a fitness advantage. This process would be negatively-frequency-dependent and would stabilize polymorphism, possibly contributing to sympatric speciation.