Decision making in the face of a deadly predator: high-amplitude behavioural thresholds can be adaptive for rainforest crickets under high background noise levels

Many insect families have evolved ears that are adapted to detect ultrasonic calls of bats. The acoustic sensory cues indicating the presence of a bat are then used to initiate bat avoidance behaviours. Background noise, in particular at ultrasonic frequencies, complicates these decisions, since a response to the background may result in costly false alarms. Here, we quantify bat avoidance responses of small rainforest crickets (Gryllidae, Trigoniinae), which live under conditions of high levels of ultrasonic background noise. Their bat avoidance behaviour exhibits markedly higher thresholds than most other studied eared insects. Their responses do not qualitatively differ at suprathreshold amplitudes up to sound pressure levels of 105 dB. Moreover, they also exhibit evasive responses to single, high-frequency events and do not require the repetitive sequence of ultrasonic calls typical for the search phase of bat echolocation calls. Analysis of bat and katydid sound amplitudes and peak frequencies in the crickets' rainforest habitat revealed that the cricket's behavioural threshold would successfully reject the katydid background noise. Using measurements of the crickets' echo target strength for bat predators, we calculated the detection distances for both predators and prey. Despite their high behavioural threshold, the cricket prey still has a significant detection advantage at frequencies between 20 and 40 kHz. The low-amplitude bat calls they ignore are no predation threat because even much louder calls would be detected before the bat would hear the cricket echo. This leaves ample time for evasive actions. Thus, a simple decision criterion based on a high-amplitude behavioural threshold can be adaptive under the high background noise levels in nocturnal rainforests, in avoiding false alarms and only missing detection for bat calls too far away to pose a risk. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

Causal Inference for Heterogeneous Data and Information Theory

The present Special Issue of Entropy, entitled "Causal Inference for Heterogeneous Data and Information Theory", covers various aspects of causal inference [...].

Expression of transport proteins in the rete mirabile of european silver and yellow eel

BACKGROUND

In physoclist fishes filling of the swimbladder requires acid secretion of gas gland cells to switch on the Root effect and subsequent countercurrent concentration of the initial gas partial pressure increase by back-diffusion of gas molecules in the rete mirabile. It is generally assumed that the rete mirabile functions as a passive exchanger, but a detailed analysis of lactate and water movements in the rete mirabile of the eel revealed that lactate is diffusing back in the rete. In the present study we therefore test the hypothesis that expression of transport proteins in rete capillaries allows for back-diffusion of ions and metabolites, which would support the countercurrent concentrating capacity of the rete mirabile. It is also assumed that in silver eels, the migratory stage of the eel, the expression of transport proteins would be enhanced.

RESULTS

Analysis of the transcriptome and of the proteome of rete mirabile tissue of the European eel revealed the expression of a large number of membrane ion and metabolite transport proteins, including monocarboxylate and glucose transport proteins. In addition, ion channel proteins, Ca2+-ATPase, Na+/K+-ATPase and also F1F0-ATP synthase were detected. In contrast to our expectation in silver eels the expression of these transport proteins was not elevated as compared to yellow eels. A remarkable number of enzymes degrading reactive oxygen species (ROS) was detected in rete capillaries.

CONCLUSIONS

Our results reveal the expression of a large number of transport proteins in rete capillaries, so that the back diffusion of ions and metabolites, in particular lactate, may significantly enhance the countercurrent concentrating ability of the rete. Metabolic pathways allowing for aerobic generation of ATP supporting secondary active transport mechanisms are established. Rete tissue appears to be equipped with a high ROS defense capacity, preventing damage of the tissue due to the high oxygen partial pressures generated in the countercurrent system.

Metabolic complementation between cells drives the evolution of tissues and organs

Although evolutionary transitions of individuality have been extensively theorized, little attention has been paid to the origin of levels of organization within organisms. How and why do specialized cells become organized into specialized tissues or organs? What spurs a transition in organizational level in cases where the function is already present in constituent cell types? We propose a hypothesis for this kind of evolutionary transition based on two features of cellular metabolism: metabolic constraints on functional performance and the capacity for metabolic complementation between parenchymal and supporting cells. These features suggest a scenario whereby pre-existing specialized cell types are integrated into tissues when changes to the internal or external environment favour offloading metabolic burdens from a primary specialized cell type onto supporting cells. We illustrate this process of 'supra-functionalization' using the nervous system and pancreas.

Alien and cryptogenic fungi and oomycetes in Austria: an annotated checklist (2nd edition)

Fungal invasions can have far-reaching consequences, and despite increasing relevance, fungi are notoriously underrepresented in invasion science. Here, we present the second annotated checklist for alien and cryptogenic fungi and oomycetes in Austria. This list contains 375 taxa of which 278 are classified as established; compared to the first checklist from 2002, this amounts to an almost five-fold increase and the number of decade-wise first records is steadily rising since the mid-twentieth century. The introduction pathway is unclear for the vast majority of taxa, while the main means of spread within the country is unassisted secondary spread. Fungi were predominantly introduced from the Northern Hemisphere, especially North America and Temperate Asia. Rates of newly recorded alien fungi differ among phyla; the majority belongs to the Ascomycota, which experienced an 9.6-fold increase in numbers. Orders found most frequently are powdery mildews (Erysiphales, Ascomycota), downy mildews (Peronosporales, Oomycota), agarics (Agaricales, Basidiomycota), Mycosphaerellales (Ascomycota), rusts (Pucciniales, Basidiomycota) and Pleosporales (Ascomycota). The majority (about 80%) of the taxa are plant pathogens, while animal pathogens are few but severely affecting their native hosts. The dominance of pathogens in our checklist underlines the need of better tackling fungal invasions-especially in the light of emerging infectious diseases-and highlights potential knowledge gaps for ectomycorrhizal and saprobic alien fungi, whose invasion processes are often much more inconspicuous. Our results show that fungal invasions are a phenomenon of increasing importance, and collaborative efforts are needed for advancing the knowledge and management of this important group.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10530-022-02896-2.

Regional invasion history and land use shape the prevalence of non-native species in local assemblages

The ecological impact of non-native species arises from their establishment in local assemblages. However, the rates of non-native spread in new regions and their determinants have not been comprehensively studied. Here, we combined global databases documenting the occurrence of non-native species and residence of non-native birds, mammals, and vascular plants at regional and local scales to describe how the likelihood of non-native occurrence and their proportion in local assemblages relate with their residence time and levels of human usage in different ecosystems. Our findings reveal that local non-native occurrence generally increases with residence time. Colonization is most rapid in croplands and urban areas, while it is slower and variable in natural or semi-natural ecosystems. Notably, non-native occurrence continues to rise even 200 years after introduction, especially for birds and vascular plants, and in other land-use types rather than croplands and urban areas. The impact of residence time on non-native proportions is significant only for mammals. We conclude that the continental exchange of biotas requires considerable time for effects to manifest at the local scale across taxa and land-use types. The unpredictability of future impacts, implied by the slow spread of non-native species, strengthens the call for stronger regulations on the exchange of non-native species to reduce the long-lasting invasion debt looming on ecosystems' future.