Dear Colleagues,

Semiochemical signaling is one of the oldest means of communication and is used by organisms of all taxa. This kind of communication plays an important role in initiating and modifying many types of behavior, including sexual behavior, territory marking, food location, mate selection, alarm responses, and other social behaviors indicating social status.

Pheromones can be airborne chemical substances (“signals”) released in excretions such as urine and feces or can be secreted from various cutaneous glands. They can also be less volatile compounds, and direct contact with a medium containing, e.g., protein pheromones, is at times required to elicit a specific response in the receivers of the signal. Proteins are important in this semiochemical communication, particularly for pheromone transportation processes and influencing these signals’ availability by moderating the time of release of the active compounds into the environment. They are also involved in the process of bonding and transportation of the collected semiochemicals within specialized organs of the signal receiver. In response, pheromones detected by specialized organs elicit both behavioral and endocrine responses in conspecifics. Mentioned modifications in behavior or physiology can be immediately observed (i.e. changes in heart rate, local blood flow etc.) or take some time before being expressed (e.g., evidenced through an acceleration in reaching puberty).

Pheromones cause specific, repeatable responses in conspecifics upon receiving this signal. Current observations show, however, that some substances acting as a pheromone within individuals from the same species act by influencing the behavior of the individuals of another species. These substances are called interomones. In fact, pheromones are most often associated with reproduction, because their influence on animal behavior and physiology in this context is very easy to observe. Moreover, phenomena related to the influence of sex pheromones in the context of reproduction are used by breeders in daily practice to moderate and to improve breeding procedures. 

However, traditionally, the vomeronasal organ is recognized as the organ responsible for pheromone detection. The roles of other organs (including olfactory epithelium) are being investigated, and the meaning of alternative pathways of pheromone passage to the target structures in the nervous system have been identified and described in various species, e.g., pigs.

Moreover, chemical communication besides pheromones includes other chemical compounds that can bring information to the signal receivers. Volatile compounds can pass on information via the main olfactory system; however, in some species, additional structures such as Grüneberg ganglion or the septal organ (SO) of Masera may be involved. This information about the chemical signal emitter is at times detectable by the olfactory system, and animals can be trained to recognize specific chemical signals that may bring certain benefits. In this context, the detection of various diseases (including cancers) by trained dogs or mice is a good example (e.g., recognizing sick and/or infected individuals).

Despite the many published reports and studies investigating pheromones and other chemical signals, there are still many unanswered questions in this area, and further studies are required to shed light on the issue of chemical communication. The coexistence of chemical visual, tactile and auditory stimuli complicate the study of the response to the signal recipient. Progress in the field of identification, as well as in the creation of artificial analogues, is still inadequate, especially in the context of animal reproduction. The study of other types of semiochemicals involved in other behavioral responses, such as mood modification, could also be advanced.

Studies nowadays focus on the Evaluation of the responses to the natural or artificial pheromones as well as substances called putative pheromones, which are used to observe and measure behavior, or on the biochemical, endocrinological reaction. However, advanced visualization tools, such as PET or fMRI, provide new opportunities to track changes in the nervous system. This kind of approach to monitoring chemical communication mechanisms should not be over-relied upon; however, it is an interesting addition to the researchers' toolbelt in dealing with pheromones.

We are pleased to invite you to submit articles, reviews, case reports, and other types of contributions supported by Animals.

This Special Issue aims to focus on issues connected with chemical signaling in domestic as well as wild animals, with an emphasis on pheromones in the context of reproduction, behavior and communication We welcome papers on new identified active compounds; factors influencing the modification of signal structure; the influence of the chemical compounds involved in inter-individual communication on the recipient’s behavior and physiology (e.g., endocrinology); processes of semiochemical detection and signaling pathways within organisms, including biochemical and genomic reactions; and processing signals in the central nervous system. The spontaneously acquired as well as taught skills of animals in detecting certain chemical signals, for example, those related with the condition of the signal emitter, are also of interest (e.g., for disease detection). Since proper communication is crucial for proper coexistence, manuscripts describing the influence of chemical and semiochemical signals on animal welfare are also welcome.

We look forward to receiving your contributions. 

Dr. Michał Dzięcioł
Prof. Dr. Tadeusz Jezierski
Dr. Sankar Ganesh Devaraj
Guest Editors

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• semiochemicals/ pheromones/interomones/chemical signatures
• sources of pheromones
• chemical signals detection/organs/receptors
• olfactory system/vomeronasal system/septal organ (SO) of Masera/Grüneberg ganglion (GG)
• brain activity visualization/PET/fMRI
• reproductive behavior/endocrinology
• scent marking
• volatile and nonvolatile signals
• GC-MS/LC-MS
• genomic/transcriptomic/proteomic/metabolomic
• microbiota
• welfare
• disease detection