Proteins and peptides as pheromone signals and chemical signatures

Carbonic anhydrase IV in lizard chemical signals

The evolution of chemical signals is subject to environmental constraints. A multicomponent signal may combine semiochemical molecules with supporting compounds able to enhance communication efficacy. Carbonic anhydrases (CAs) are ubiquitous enzymes catalysing the reversible hydration of carbon dioxide, a reaction involved in a variety of physiological processes as it controls the chemical environment of the different tissues or cellular compartments, thus contributing to the overall system homeostasis. CA-IV isoform has been recently identified by mass spectrometry in the femoral gland secretions (FG) of the marine iguana, where it has been hypothesized to contribute to the chemical stability of the signal, by regulating blend pH. Lizards, indeed, use FG to communicate by delivering the waxy secretion on bare substrate, where it is exposed to environmental stressors. Therefore, we expect that some molecules in the mixture may play supporting functions, enhancing the stability of the chemical environment, or even conferring homeostatic properties to the blend. CA-IV may well represent an important candidate to this hypothesized supporting/homeostatic function, and, therefore, we can expect it to be common in FG secretions of other lizard species. To evaluate this prediction and definitely validate CA identity, we analysed FG secretions of eight species of wall lizards (genus Podarcis), combining mass spectrometry, immunoblotting, immunocytochemistry, and transmission electron microscopy. We demonstrate CA-IV to actually occur in the FG of seven out of the eight considered species, providing an immunochemistry validation of mass-spectrometry identifications, and localizing the enzyme within the secretion mass. The predicted structure of the identified CA is compatible with the known enzymatic activity of CA-IV, supporting the hypothesis that CA play a signal homeostasis function and opening to new perspective about the role of proteins in vertebrate chemical communication.

Protein-lipid Association in Lizard Chemical Signals

Chemical communication in terrestrial vertebrates is often built on complex blends, where semiochemical and structural compounds may form an integrated functional unit. In lizards, many species have specialized epidermal glands whose secretions are waxy, homogeneous blends of lipids and proteins, both active in communication. The intimate co-occurrence of such compounds allows us to hypothesize that they should undergo a certain degree of covariation, considering both their semiochemical role and the support-to-lipid function hypothesized for the protein fraction. In order to assess the occurrence and level of protein-lipid covariation, we compared the composition and complexity of the two fractions in the femoral gland secretions of 36 lizard species, combining phylogenetically-informed analysis with tandem mass spectrometry. We found the composition and complexity of the two fractions to be strongly correlated. The composition of the protein fraction was mostly influenced by the relative proportion of cholestanol, provitamin D₃, stigmasterol, and tocopherol, while the complexity of the protein pattern increased with that of lipids. Additionally, two identified proteins (carbonic anhydrase and protein disulfide isomerase) increased their concentration as provitamin D₃ became more abundant. Although our approach does not allow us to decrypt the functional relations between the proteinaceous and lipid components, nor under the semiochemical or structural hypothesis, the finding that the proteins involved in this association were enzymes opens up to new perspectives about protein role: They may confer dynamic properties to the blend, making it able to compensate predictable variation of the environmental conditions. This may expand the view about proteins in the support-to-lipid hypothesis, from being a passive and inert component of the secretions to become an active and dynamic one, thus providing cues for future research.

Reproductives signature revealed by protein profiling and behavioral bioassays in termite

Proteins are known to be social interaction signals in many species in the animal kingdom. Common mediators in mammals and aquatic species, they have seldom been identified as such in insects' behaviors. Yet, they could represent an important component to support social signals in social insects, as the numerous physical contacts between individuals would tend to favor the use of contact compounds in their interactions. However, their role in social interactions is largely unexplored: are they rare or simply underestimated? In this preliminary study, we show that, in the termite Reticulitermes flavipes, polar extracts from reproductives trigger body-shaking of workers (a vibratory behavior involved in reproductives recognition) while extracts from workers do not. Molecular profiling of these cuticular extracts using MALDI-TOF mass spectrometry reveals higher protein diversity in reproductives than in workers and a sex-specific composition exclusive to reproductives. While the effects observed with extracts are not as strong as with live termites, these results open up the intriguing possibility that social signaling may not be limited to cuticular hydrocarbons or other non-polar, volatile chemicals as classically accepted. Our results suggest that polar compounds, in particular some of the Cuticular Protein Compounds (CPCs) shown here by MALDI to be specific to reproductives, could play a significant role in insect societies. While this study is preliminary and further comprehensive molecular characterization is needed to correlate the body-shaking triggering effects with a given set of polar compounds, this exploratory study opens new perspectives for understanding the role of polar compounds such as proteins in caste discrimination, fertility signaling, or interspecific insect communication.

Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

Heat alters biology from molecular to ecological levels, but may also have unknown indirect effects. This includes the concept that animals exposed to abiotic stress can induce stress in naive receivers. Here, we provide a comprehensive picture of the molecular signatures of this process, by integrating multiomic and phenotypic data. In individual zebrafish embryos, repeated heat peaks elicited both a molecular response and a burst of accelerated growth followed by a growth slowdown in concert with reduced responses to novel stimuli. Metabolomes of the media of heat treated vs. untreated embryos revealed candidate stress metabolites including sulfur-containing compounds and lipids. These stress metabolites elicited transcriptomic changes in naive receivers related to immune response, extracellular signaling, glycosaminoglycan/keratan sulfate, and lipid metabolism. Consequently, non-heat-exposed receivers (exposed to stress metabolites only) experienced accelerated catch-up growth in concert with reduced swimming performance. The combination of heat and stress metabolites accelerated development the most, mediated by apelin signaling. Our results prove the concept of indirect heat-induced stress propagation toward naive receivers, inducing phenotypes comparable with those resulting from direct heat exposure, but utilizing distinct molecular pathways. Group-exposing a nonlaboratory zebrafish line, we independently confirm that the glycosaminoglycan biosynthesis-related gene chs1 and the mucus glycoprotein gene prg4a, functionally connected to the candidate stress metabolite classes sugars and phosphocholine, are differentially expressed in receivers. This hints at the production of Schreckstoff-like cues in receivers, leading to further stress propagation within groups, which may have ecological and animal welfare implications for aquatic populations in a changing climate.

Infection of Trichinella spiralis Affects the Reproductive Capacity of ICR/CD-1 Male Mice by Reducing the Urine Pheromone Contents and Sperm Quality

Female mice can discriminate the urinary odors of male mice due to their olfactory acuity. Parasitic infection or subclinical infection can decrease the odor attractiveness of male mice and finally lead to aversion or avoidance responses in odor selection for female mice. Trichinella spiralis is a kind of tissue-parasitizing nematode that causes trichinellosis, a zoonotic parasitic disease that spreads throughout the world. However, the reproductive injury caused by Trichinella spiralis infection was not fully revealed. In this study, we explored the effect of Trichinella spiralis infection on the reproductive capacity in ICR/CD-1 male mice. We identified eight volatile compounds in urine by GC-MS analysis, and the results indicated that the contents of dimethyl sulfone, Z-7-tetradecen-1-ol, 6-Hydroxy-6-methyl-3-heptanone and (S)-2-sec-butyl-4,5-dihydrothiazole were significantly downregulated after parasitic infection, which might lead to the reduction of attractiveness of male mice urine to females. On the other hand, parasitic infection decreased sperm quality and downregulated the expression levels of Herc4, Ipo11, and Mrto4, and these genes were strongly related to spermatogenesis. In summary, this study revealed that the reproductive injury caused by Trichinella spiralis infection in ICR/CD-1 male mice could be associated with a decrease in urine pheromone content and sperm quality.

Infection with Cryptosporidium parvum Affects Secondary Sexual Characteristics of Male Mice by Altering the Pheromone Content in Preputial Gland

The olfactory acuity of female mice allows them to discriminate the urinary odors of males. Parasitic infection can reduce the odor attractiveness of male mice to females and result in female aversion or avoidance responses in odor selection. However, the chemical signaling changes in the pheromone contents produced by the foreskin gland were not fully revealed after parasitic infection. Cryptosporidium parvum (C. parvum) is a common zoonotic intestinal parasite and has a wide range of hosts, including human, domestic animals, and wild animals. In this study, we immunosuppressed ICR/CD-1 male mice by dexamethasone sodium phosphate treatment. After C. parvum infection, physiological indexes such as body weight and organ weight were significantly decreased. Furthermore, the gene expression level of MUP (major urinary protein) in liver and urine were significantly down-regulated, which could be the reason for the decrease in urine attractiveness to females. GC-MS was performed to analyze the changes in the pheromone produced by the preputial gland before and after parasitic infection, and the results indicated that the levels of different pheromones were significantly reduced after parasitic infection. In summary, this study reveals that C. parvum infection damages the secondary sexual characteristics of male ICR/CD-1 male mice and decreases the pheromone content produced by the foreskin gland.

Non-lethal fungal infection could reduce aggression towards strangers in ants

Many parasites interfere with the behaviour of their hosts. In social animals, such as ants, parasitic interference can cause changes on the level of the individual and also on the level of the society. The ant-parasitic fungus Rickia wasmannii influences the behaviour of Myrmica ants by expanding the host's nestmate recognition template, thereby increasing the chance of the colony accepting infected non-nestmates. Infected ants consistently show an increase of the alkane tricosane (n-C23) in their cuticular hydrocarbon profiles. Although experimental application of single compounds often elicits aggression towards manipulated ants, we hypothesized that the increase of n-C23 might underlie the facilitated acceptance of infected non-nestmates. To test this, we mimicked fungal infection in M. scabrinodis by applying synthetic n-C23 to fresh ant corpses and observed the reaction of infected and uninfected workers to control and manipulated corpses. Infected ants appeared to be more peaceful towards infected but not uninfected non-nestmates. Adding n-C23 to uninfected corpses resulted in reduced aggression in uninfected ants. This supports the hypothesis that n-C23 acts as a 'pacifying' signal. Our study indicates that parasitic interference with the nestmate discrimination of host ants might eventually change colony structure by increasing genetic heterogeneity in infected colonies.

The Chromosome-Level Genome of Hestina assimilis (Lepidoptera: Nymphalidae) Reveals the Evolution of Saprophagy-Related Genes in Brush-Footed Butterflies

Most butterflies feed on nectar, while some saprophagous butterflies forage on various non-nectar foods. To date, little is known about the genomic and molecular shifts associated with the evolution of the saprophagous feeding strategy. Here, we assembled the high-quality chromosome-level genome of Hestina assimilis to explore its saprophagous molecular and genetic mechanisms. This chromosome-level genome of H. assimilis is 412.82 Mb, with a scaffold N50 of 15.70 Mb. In total, 98.11% of contigs were anchored to 30 chromosomes. Compared with H. assimilis and other Nymphalidae butterflies, the genes of metabolism and detoxification experienced expansions. We annotated 80 cytochrome P450 (CYP) genes in the H. assimilis genome, among which genes belonging to the CYP4 subfamily were significantly expanded (p < 0.01). These P450 genes were unevenly distributed and mainly concentrated on chromosomes 6-9. We identified 33 olfactory receptor (OR), 20 odorant-binding protein (OBP), and six gustatory receptor (GR) genes in the H. assimilis genome, which were fewer than in the nectarivorous Danaus plexippus. A decreased number of OBP, OR, and GR genes implied that H. assimilis should resort less to olfaction and gustation than their nectarivorous counterparts, which need highly specialized olfactory and gustatory functions. Moreover, we found one site under positive selection occurred in residue 996 (phenylalanine) of GR genes exclusive to H. assimilis, which is conservative in most lineages. Our study provides support for the adaptive evolution of feeding habits in butterflies.

Protein profiles from used nesting material, saliva, and urine correspond with social behavior in group housed male mice, Mus musculus

Current understanding of how odors impact intra-sex social behavior is based on those that increase intermale aggression. Yet, odors are often promoted to reduce fighting among male laboratory mice. It has been shown that a cage of male mice contains many proteins used for identification purposes. However, it is unknown if these proteins relate to social behavior or if they are uniformly produced across strains. This study aimed to compare proteomes from used nesting material and three sources (sweat, saliva, and urine) from three strains and compare levels of known protein odors with rates of social behavior. Used nesting material samples from each cage were analyzed using LC-MS/MS. Sweat, saliva, and urine samples from each cage's dominant and subordinate mouse were also analyzed. Proteomes were assessed using principal component analyses and compared to behavior by calculating correlation coefficients between PC scores and behavior proportions. Twenty-one proteins from nesting material either correlated with affiliative behavior or negatively correlated with aggression. Notably, proteins from the major urinary protein family, odorant binding protein family, and secretoglobin family displayed at least one of these patterns, making them candidates for future work. These findings provide preliminary information about how proteins can influence male mouse behavior. SIGNIFICANCE: Research on how olfactory signals influence same sex social behavior is primarily limited to those that promote intermale aggression. However, exploring how olfaction modulates a more diverse behavioral repertoire will improve our foundational understanding of this sensory modality. In this proteome analysis we identified a short list of protein signals that correspond to lower rates of aggression and higher rates of socio-positive behavior. While this study is only correlational, it sets a foundation for future work that can identify protein signals that directly influence social behavior and potentially identify new murine pheromones.

Functional Protein Composition in Femoral Glands of Sand Lizards (Lacerta agilis)

Proteins are ubiquitous macromolecules that display a vast repertoire of chemical and enzymatic functions, making them suitable candidates for chemosignals, used in intraspecific communication. Proteins are present in the skin gland secretions of vertebrates but their identity, and especially, their functions, remain largely unknown. Many lizard species possess femoral glands, i.e., epidermal organs primarily involved in the production and secretion of chemosignals, playing a pivotal role in mate choice and intrasexual communication. The lipophilic fraction of femoral glands has been well studied in lizards. In contrast, proteins have been the focus of only a handful of investigations. Here, we identify and describe inter-individual expression patterns and the functionality of proteins present in femoral glands of male sand lizards (Lacerta agilis) by applying mass spectrometry-based proteomics. Our results show that the total number of proteins varied substantially among individuals. None of the identified femoral gland proteins could be directly linked to chemical communication in lizards, although this result hinges on protein annotation in databases in which squamate semiochemicals are poorly represented. In contrast to our expectations, the proteins consistently expressed across individuals were related to the immune system, antioxidant activity and lipid metabolism as their main functions, showing that proteins in reptilian epidermal glands may have other functions besides chemical communication. Interestingly, we found expression of the Major Histocompatibility Complex (MHC) among the multiple and diverse biological processes enriched in FGs, tentatively supporting a previous hypothesis that MHC was coopted for semiochemical function in sand lizards, specifically in mate recognition. Our study shows that mass spectrometry-based proteomics are a powerful tool for characterizing and deciphering the role of proteins secreted by skin glands in non-model vertebrates.

Chemosensory Exploitation and Predator-Prey Arms Races

Thousands of armed predatory species, distributed widely across the metazoan tree-of-life, consume only hard-shell or exoskeleton-bearing organisms (called “durophagy”). Prey armor clearly has evolved in response to selection by predators, but there is little evidence of the contrary, counter-adaptation by predators. Evolved consumer responses to prey, in general, might be more readily expressed in ways other than morphological traits, including via sensory cues. Here, we explored the chemosensory basis for durophagy in a model predator-prey system, and identified intimate associations between durophagous predators and their shelled prey. Barnacles (Balanus glandula and Semibalanus cariosus) bear hard shells and secrete, respectively, a 199 or 201 kDa glycoprotein ortholog (named “MULTIFUNCin”), with expression limited to the body armor (epidermis, cuticle, and live shell). To test for effects of MULTIFUNCin on predators, we constructed faux prey to mimic meaningful physical and chemical characteristics of live barnacles. In separate experiments, each consumer species was presented MULTIFUNCin, purified from either B. glandula or S. cariosus, at a typical armor concentration. All six predatory species (sea star, Pisaster ochraceus; whelks, Acanthinucella spirata, Nucella emarginata, N. ostrina, N. canaliculata, and N. lamellosa) attacked and ate MULTIFUNCin-infused faux prey significantly more than controls. Akin to barnacles, secretion of glycoprotein-rich extracellular matrices is common among armored prey species—from marine sponges to terrestrial vertebrates. Our results, therefore, suggest that chemosensory exploitation of glycoproteins could be widespread, with notable consequences for life on land and in the sea.

Sex Differences in Mouse Exploratory Behaviour to Fel d 1, a Cat ABP-Like Protein

Simple Summary

Fel d 1 is a cat secreted protein, known as the main cat allergen, that is abundantly released and found in their habitat. Cats are one of the main predators of rodents and have been historically used to control rodent populations in human habitats. We assumed that laboratory mice, as a model of wild mice, would be able to detect and avoid this abundant cat molecule as a mechanism to increase chances of survival. In our study, we compared mice exploratory behaviours facing Fel d 1, a fox faeces molecule (TMT) as a positive control, and a negative control (purified water). We found that mice did not avoid Fel d 1 as we expected; however, male mice remained in the area with Fel d 1 longer than females. These results give interesting insights about how sexes can react differently to a predator stimulus and give support to the use of both sexes in behavioural studies, and more precisely in predator-prey interactions research

Abstract

Fel d 1 is a cat protein abundantly released and found in their habitat and is closely related to mouse androgen-binding proteins (ABPs). We hypothesized that mice have developed chemical communication mechanisms to detect and avoid this protein. We tested purified natural Fel d 1, a fox faeces molecule (TMT) as a positive control, and a negative control (purified water) in three different mouse groups (n = 14 each) to evaluate exploratory behaviour and stress responses. The mice did not show clear avoidance or stress responses to Fel d 1. Our results demonstrated a sex-treatment interaction for Fel d 1, with males spending more time in the areas treated with Fel d 1 than in the untreated areas (p = 0.018). This sex-treated area interaction was also not observed for either the blank or TMT. These results suggest that Fel d 1 from domestic cats could be recognized differently by male and female mice. These sex differences could be linked to the sexual role of ABP proteins and the ABP-like characteristics of Fel d 1.

Evolutionary and biogeographical support for species-specific proteins in lizard chemical signals

The species-specific components of animal signals can facilitate species recognition and reduce the risks of mismatching and interbreeding. Nonetheless, empirical evidence for species-specific components in chemical signals is scarce and mostly limited to insect pheromones. Based on the proteinaceous femoral gland secretions of 36 lizard species (Lacertidae), we examine the species-specific component potential of proteins in lizard chemical signals. By quantitative comparison of the one-dimensional electrophoretic patterns of the protein fraction from femoral gland secretions, we first reveal that the protein composition is species specific, accounting for a large part of the observed raw variation and allowing us to discriminate species on this basis. Secondly, we find increased protein pattern divergence in sympatric, closely related species. Thirdly, lizard protein profiles show a low phylogenetic signal, a recent and steep increase in relative disparity and a high rate of evolutionary change compared with non-specifically signal traits (i.e. body size and shape). Together, these findings provide support for the species specificity of proteins in the chemical signals of a vertebrate lineage.

Gross and histological morphology of the cervical gill slit gland of the pygmy sperm whale (Kogia breviceps)

Odontocete cetaceans have undergone profound modifications to their integument and sensory systems and are generally thought to lack specialized exocrine glands that in terrestrial mammals function to produce chemical signals (Thewissen & Nummela, 2008). Keenan-Bateman et al. (2016, 2018), though, introduced an enigmatic exocrine gland, associated with the false gill slit pigmentation pattern in Kogia breviceps. These authors provided a preliminary description of this cervical gill slit gland in their helminthological studies of the parasitic nematode, Crassicauda magna. This study offers the first detailed gross and histological description of this gland and reports upon key differences between immature and mature individuals. Investigation reveals it is a complex, compound tubuloalveolar gland with a well-defined duct that leads to a large, and expandable central chamber, which in turn leads to two caudally projecting diverticula. All regions of the gland contain branched tubular and alveolar secretory regions, although most are found in the caudal diverticula, where the secretory process is holocrine. The gland lies between slips of cutaneous muscle, and is innervated by lamellar corpuscles, resembling Pacinian's corpuscles, suggesting that its secretory product may be actively expressed into the environment. Mature K. breviceps display larger gland size, and increased functional activity in glandular tissues, as compared to immature individuals. These results demonstrate that the cervical gill slit gland of K. breviceps shares morphological features of the specialized, chemical signaling, exocrine glands of terrestrial members of the Cetartiodactyla.

Sexual Dimorphism in Crowned Lemur Scent-Marking

Simple Summary

Primates are typically thought to use hearing and vision more than the sense of smell. However, lemurs show a complex olfactory repertoire which includes conspicuous scent-marking behaviours (i.e., a form of olfactory communication displayed by animals that deposit their odour in specific places to transmit a message to other animals). We studied two pairs of crowned lemurs at Colchester and Twycross zoos (UK) by combining behavioural observations and chemical analyses of odour secretions released via scent-marking. Male lemurs scent-marked most frequently, showing three types of behaviours: ano-genital marking for applying their scent onto females; head marking for placing their secretions on or near the mark left by another individual; and wrist marking to deposit their mark in specific meaningful areas of the enclosure. Female lemurs displayed only ano-genital marking, primarily on feeding devices. We detected a total of 38 volatile compounds in male ano-genital scent-marks and 26 in female ano-genital odour secretions, including many compounds that have been identified in odour profiles of other primates. In conclusion, we found sexual dimorphism in crowned lemur scent-marking. In males, head and wrist marking behaviours would play defensive territorial functions, while ano-genital marking may be related to socio-sexual communication; female ano-genital marking could be involved in resource defense. This study contributes to improving our understanding of lemur communication.

Abstract

Primates are traditionally considered to have a poor sense of smell. However, olfaction is important for non-human primates as demonstrated by conspicuous scent-marking behaviours in lemurs. We studied two pairs (n = 4) of crowned lemurs (Eulemur coronatus) housed at Colchester and Twycross zoos (UK) by combining behavioural observations and chemical analyses of scent-marks and glandular swabs. We recorded observations of olfactory behaviours for 201 h using instantaneous scan sampling. We investigated the volatile compounds of ano-genital odour secretions (n = 16) using solid-phase microextraction and gas chromatography-mass spectrometry. Males scent-marked most frequently, displaying ano-genital marking for allomarking, head marking for countermarking and wrist marking in specific areas of the enclosure. Females displayed ano-genital marking, predominantly on feeding devices. We detected a total of 38 volatile components in all male ano-genital scent-marks and 26 in all female samples of ano-genital odour secretions, including a series of esters, aldehydes, ketones, alcohols, terpenes, volatile fatty acids and hydrocarbons that have been identified in odour profiles of other primates. In conclusion, we found sexual dimorphism in crowned lemur scent-marking. Male head and wrist marking behaviours might play defensive territorial functions, while ano-genital marking would be related to socio-sexual communication as chemical mate-guarding. Female ano-genital marking might be involved in resource defense.

Origin and Evolution of the Gene Family of Proteinaceous Pheromones, the Exocrine Gland-Secreting Peptides, in Rodents

The exocrine-gland secreting peptide (ESP)gene family encodes proteinaceous pheromones that are recognized by the vomeronasal organ in mice. For example, ESP1 is a male pheromone secreted in tear fluid that regulates socio-sexual behavior, and ESP22 is a juvenile pheromone that suppresses adult sexual behavior. The family consists of multiple genes and has been identified only in mouse and rat genomes. The coding region of a mouse ESP gene is separated into two exons, each encoding signal and mature sequences. Here, we report the origin and evolution of the ESP gene family. ESP genes were found only in the Muridea and Cricetidae families of rodents, suggesting a recent origin of ESP genes in the common ancestor of murids and cricetids. ESP genes show a great diversity in number, length, and sequence among different species as well as mouse strains. Some ESPs in rats and golden hamsters are expressed in the lacrimal gland and the salivary gland. We also found that a mature sequence of an ESP gene showed overall sequence similarity to the α-globin gene. The ancestral ESP gene seems to be generated by recombination of a retrotransposed α-globin gene with the signal-encoding exon of the CRISP2 gene located adjacent to the ESP gene cluster. This study provides an intriguing example of molecular tinkering in rapidly evolving species-specific proteinaceous pheromone genes.

Females of the four-eyed frog, Pleurodema thaul (Anura, Leptodactylidae), respond behaviourally to conspecific male scent

Among amphibians, conspecific chemical communication has been widely studied in Caudata. Adult anurans, by contrast, have received less attention. Recently, it was shown that chemical scents are also relevant for adult anuran intraspecific communication. In this context, we evaluate whether females of the four-eyed frog (Pleurodema thaul) respond to conspecific male scents. We carried out a double choice experiment in a Y-maze. Females were repeatedly presented with the scents of several males versus distilled water. To extract the scent from males, we acoustically stimulated males and then used the water from their aquaria for the experiments. Our data suggest that females are capable of responding behaviourally to male scents, since they spent longer periods in the zones with male scent, rather than in zones with water. We propose that under natural breeding conditions, females of P. thaul may use either their chemical sense or chemical cues to facilitate their encounters with males.

Evolutionary history of mental glands in turtles reveals a single origin in an aquatic ancestor and recurrent losses independent of macrohabitat

Despite the relevance of chemical communication in vertebrates, comparative examinations of macroevolutionary trends in chemical signaling systems are scarce. Many turtle and tortoise species are reliant on chemical signals to communicate in aquatic and terrestrial macrohabitats, and many of these species possess specialized integumentary organs, termed mental glands (MGs), involved in the production of chemosignals. We inferred the evolutionary history of MGs and tested the impact of macrohabitat on their evolution. Inference of ancestral states along a time-calibrated phylogeny revealed a single origin in the ancestor of the subclade Testudinoidea. Thus, MGs represent homologous structures in all descending lineages. We also inferred multiple independent losses of MGs in both terrestrial and aquatic clades. Although MGs first appeared in an aquatic turtle (the testudinoid ancestor), macrohabitat seems to have had little effect on MG presence or absence in descendants. Instead, we find clade-specific evolutionary trends, with some clades showing increased gland size and morphological complexity, whereas others exhibiting reduction or MG loss. In sister clades inhabiting similar ecological niches, contrasting patterns (loss vs. maintenance) may occur. We conclude that the multiple losses of MGs in turtle clades have not been influenced by macrohabitat and that other factors have affected MG evolution.

The Role of Urine in Semiochemical Communication between Females and Males of Domestic Dog (Canis familiaris) during Estrus

Simple Summary

Canine reproductive behavior can be easily observed; however, the mechanism of semiochemical signaling in this species is still not well understood. Despite numerous studies, no efficient, artificial canine sex pheromones are available. In most studies of canine semiochemical communication, female urine was believed to be a source of volatile compounds that attract males. We hypothesized that urine is also a source of compounds that are very important in the process of the mating decision but are not so volatile. These compounds are collected by licking urine or the vulva and are transferred into the vomeronasal organ. Such behavior always precedes the male’s mating decision. In two experiments, we assessed the reactions of male dogs in response to air containing odor molecules from estrous females’ urine, from a live female in estrus, and from food, as well as during direct sniffing of urine samples from females in estrus, in anestrus, from male dogs and from humans. It was concluded that urine odor is not used for long-distance semiochemical communication in dogs but rather for close distance signaling.

Abstract

This study aimed to assess the mechanisms of semiochemical signal detection in dogs. In the first experiment, five males were exposed to volatile semiochemicals emitted by a live female in estrus and the female’s urine sample collected during estrus. The odor of canine food and clean air were used as controls. In the second experiment, 25 males could directly sniff and lick the urine samples from females in estrus, from females in anestrus, from males and from humans, placed in a lineup. Sniffing, licking and salivation, as well as keeping dogs at different distances from the source of odor, were recorded in both experiments. Experiment 1 showed that food odor was sniffed by males longer than estrous urine. Volatile semiochemicals from females in estrus evoked interest in males but without visual cues did not cause overt symptoms of sexual arousal. In Experiment 2, the estrous urine evoked interest in males and provoked significantly longer sniffing. Licking accompanied by salivation was observed in all instances only during direct contact with estrous urine. The results suggest a complex character of detection of female reproductive status, in which both volatile and nonvolatile compounds emitted by females and present in female urine are involved.

The chemistry and histology of sexually dimorphic mental glands in the freshwater turtle, Mauremys leprosa

Despite evidence from anatomy, behavior and genomics indicating that the sense of smell in turtles is important, our understanding of chemical communication in this group is still rudimentary. Our aim was to describe the microanatomy of mental glands (MGs) in a freshwater turtle, Mauremys leprosa (Geoemydidae), and to assess the chemical composition of their secretions with respect to variation among individuals and between sexes. MGs are paired sac-like organs on the gular region of the neck and are dimorphic in this species with males having fully functional holocrine glands while those of females appear non-secretory and vestigial. In adult males, the glandular epithelium of the inner portion of the gland provides exocytotic products as well as cellular debris into the lumen of the gland. The contents of the lumen can be secreted through the narrow duct portion of the gland ending in an orifice on the surface of the skin. Females have invaginated structures similar in general outline to male glands, but lack a glandular epithelium. Using gas chromatography coupled to mass spectrometry, we identified a total of 61 compounds in mental gland secretions, the most numerous being carboxylic acids, carbohydrates, alkanes, steroids and alcohols. The number of compounds per individual varied widely (mean (median) ± SD = 14.54 (13) ± 8.44; min = 3; max = 40), but only cholesterol was found in all samples. We found that the relative abundances of only six chemicals were different between the sexes, although males tended to have larger amounts of particular compounds. Although the lipid fraction of mental gland secretions is rich in chemical compounds, most occur in both sexes suggesting that they are metabolic byproducts with no role in chemical signaling. However, the relative amounts of some compounds tended to be higher in males, with significantly larger amounts of two carboxylic acids and one steroid, suggesting their putative involvement in chemical communication.

Molecular evolution of gland cell types and chemical interactions in animals

Across the Metazoa, the emergence of new ecological interactions has been enabled by the repeated evolution of exocrine glands. Specialized glands have arisen recurrently and with great frequency, even in single genera or species, transforming how animals interact with their environment through trophic resource exploitation, pheromonal communication, chemical defense and parental care. The widespread convergent evolution of animal glands implies that exocrine secretory cells are a hotspot of metazoan cell type innovation. Each evolutionary origin of a novel gland involves a process of 'gland cell type assembly': the stitching together of unique biosynthesis pathways; coordinated changes in secretory systems to enable efficient chemical release; and transcriptional deployment of these machineries into cells constituting the gland. This molecular evolutionary process influences what types of compound a given species is capable of secreting, and, consequently, the kinds of ecological interactions that species can display. Here, we discuss what is known about the evolutionary assembly of gland cell types and propose a framework for how it may happen. We posit the existence of 'terminal selector' transcription factors that program gland function via regulatory recruitment of biosynthetic enzymes and secretory proteins. We suggest ancestral enzymes are initially co-opted into the novel gland, fostering pleiotropic conflict that drives enzyme duplication. This process has yielded the observed pattern of modular, gland-specific biosynthesis pathways optimized for manufacturing specific secretions. We anticipate that single-cell technologies and gene editing methods applicable in diverse species will transform the study of animal chemical interactions, revealing how gland cell types are assembled and functionally configured at a molecular level.

Proteome characterization of used nesting material and potential protein sources from group housed male mice, Mus musculus

Laboratory mice (Mus musculus) communicate a variety of social messages through olfactory cues and it is often speculated that these cues are preserved in nesting material. Based on these speculations, a growing number of husbandry recommendations support preserving used nests at cage cleaning to maintain familiar odors in the new cage. However, the content of used nesting material has never been chemically analyzed. Here we present the first comprehensive proteome profile of used nesting material. Nests from cages of group housed male mice contain a variety of proteins that primarily originate from saliva, plantar sweat, and urine sources. Most notably, a large proportion of proteins found in used nesting material belong to major urinary protein (“MUP”) and odorant binding protein (“OBP”) families. Both protein families send messages about individual identity and bind volatile compounds that further contribute to identity cues. Overall, this data supports current recommendations to preserve used nesting material at cage cleaning to maintain odor familiarity.

Neuroanatomy of a hydrothermal vent shrimp provides insights into the evolution of crustacean integrative brain centers

Alvinocaridid shrimps are emblematic representatives of the deep hydrothermal vent fauna at the Mid-Atlantic Ridge. They are adapted to a mostly aphotic habitat with extreme physicochemical conditions in the vicinity of the hydrothermal fluid emissions. Here, we investigated the brain architecture of the vent shrimp Rimicaris exoculata to understand possible adaptations of its nervous system to the hydrothermal sensory landscape. Its brain is modified from the crustacean brain ground pattern by featuring relatively small visual and olfactory neuropils that contrast with well-developed higher integrative centers, the hemiellipsoid bodies. We propose that these structures in vent shrimps may fulfill functions in addition to higher order sensory processing and suggest a role in place memory. Our study promotes vent shrimps as fascinating models to gain insights into sensory adaptations to peculiar environmental conditions, and the evolutionary transformation of specific brain areas in Crustacea.

Morph-specific protein patterns in the femoral gland secretions of a colour polymorphic lizard

Colour polymorphism occurs when two or more genetically-based colour morphs permanently coexist within an interbreeding population. Colouration is usually associated to other life-history traits (ecological, physiological, behavioural, reproductive …) of the bearer, thus being the phenotypic marker of such set of genetic features. This visual badge may be used to inform conspecifics and to drive those decision making processes which may contribute maintaining colour polymorphism under sexual selection context. The importance of such information suggests that other communication modalities should be recruited to ensure its transfer in case visual cues were insufficient. Here, for the first time, we investigated the potential role of proteins from femoral gland secretions in signalling colour morph in a polymorphic lizard. As proteins are thought to convey identity-related information, they represent the ideal cues to build up the chemical modality used to badge colour morphs. We found strong evidence for the occurrence of morph-specific protein profiles in the three main colour-morphs of the common wall lizard, which showed both qualitative and quantitative differences in protein expression. As lizards are able to detect proteins by tongue-flicking and vomeronasal organ, this result support the hypothesis that colour polymorphic lizards may use a multimodal signal to inform about colour-morph.

Sex differences in scent-marking in captive red-ruffed lemurs

Primate chemical communication remains underappreciated, as primates are considered to rely on other sensory modalities. However, various lines of evidence suggest that olfaction plays an important role in primate societies, including the conspicuous scent-marking behavior of many strepsirrhines and callitrichines. Although lemurs typically show scent-marking, little is known about this behavior in red-ruffed lemurs (Varecia variegata rubra). We combined behavioral observations and semiochemistry analyses to improve our understanding of scent-marking in two captive troops housed at Dudley and Twycross zoos (UK). We collected olfactory behavioral observations by focusing on two family troops (N = 7) for 132 hr. We investigated the volatile compounds of ano-genital scent-marks using solid-phase microextraction and gas chromatography-mass spectrometry and compared volatile chemical profiles with features of the signaller. Males scent-marked most frequently and predominantly in specific meaningful areas of the enclosure, while within females the occurrence of scent-marking was related to their age. We found behavioral sexual dimorphism, with male predominantly depositing secretions via neck and mandible glands and females via ano-genital glands. We identified a total of 32 volatile components of ano-genital gland secretion, including compounds that have already been found in other mammals as sex pheromones and cues to fitness, in ano-genital scent-marks spontaneously left on filter paper by adult females. Our findings suggest that red-ruffed lemurs might use scent-marking to convey information about sex and female age, with male neck-marking behavior playing defensive territorial functions and ano-genital marking related to socio-sexual communication.

Smell of Infection: A Novel, Noninvasive Method for Detection of Fish Excretory-Secretory Proteins

Chemical signals are produced by aquatic organisms following predatory attacks or perturbations such as parasitic infection. Ectoparasites feeding on fish hosts are likely to cause release of similar alarm cues into the environment due to the stress, wounding, and immune response stimulated upon infection. Alarm cues are often released in the form of proteins, antimicrobial peptides, and immunoglobulins that provide important insights into bodily function and infection status. Here we outline a noninvasive method to identify potential chemical cues associated with infection in fish by extracting, purifying, and characterizing proteins from water samples from cultured fish. Gel free proteomic methods were deemed the most suitable for protein detection in saline water samples. It was confirmed that teleost proteins can be characterized from water and that variation in protein profiles could be detected between infected and uninfected individuals and fish and parasite only water samples. Our novel assay provides a noninvasive method for assessing the health condition of both wild and farmed aquatic organisms. Similar to environmental DNA monitoring methods, these proteomic techniques could provide an important tool in applied ecology and aquatic biology.

Identification and Field Testing of Volatile Components in the Sex Attractant Pheromone Blend of Female House Mice

Recently, it was reported (i) that the sex pheromone blend of male house mice, Mus musculus, comprises not only volatile components (3,4-dehydro-exo-brevicomin; 2-sec-butyl-4,5-dihydrothiazole) but also a component of low volatility (the sex steroid testosterone), and (ii) that the sex steroids progesterone and estradiol are sex pheromone components of female house mice. Here we tested the hypothesis that the sex attractant pheromone blend of female mice, analogous to that of male mice, also comprises volatile pheromone components. Analyzing by GC-MS the head space volatiles of bedding soiled with urine and feces of laboratory-kept females and males revealed three candidate pheromone components (CPCs) that were adult female-specific: butyric acid, 2-methyl butyric acid and 4-heptanone. In a two-choice laboratory experiment, adult males spent significantly more time in the treatment chamber baited with both the synthetic steroids (progesterone, estradiol) and the synthetic CPCs than in the paired control chamber baited only with the synthetic steroids. In field experiments, trap boxes baited with both the CPCs and the steroids captured 6.7-times more adult males and 4.7-times more juvenile males than trap boxes baited with the steroids alone. Conversely, trap boxes baited with both the CPCs and the steroids captured 4.3-times more adult males and 2.7-fold fewer adult females than trap boxes baited with the CPCs alone. In combination, these data support the conclusion that butyric acid, 2-methyl butyric acid and 4-heptanone are part of the sex attractant pheromone of female house mice. With progesterone and estradiol being pheromone components of both female brown rats, Rattus norvegicus, and female house mice, these three volatile components could impart specificity to the sexual communication system of house mice, brown rats and possibly other rodent species.

Sexually dimorphic venom proteins in long-jawed orb-weaving spiders (Tetragnatha) comprise novel gene families

Venom has been associated with the ecological success of many groups of organisms, most notably reptiles, gastropods, and arachnids. In some cases, diversification has been directly linked to tailoring of venoms for dietary specialization. Spiders in particular are known for their diverse venoms and wide range of predatory behaviors, although there is much to learn about scales of variation in venom composition and function. The current study focuses on venom characteristics in different sexes within a species of spider. We chose the genus Tetragnatha (Tetragnathidae) because of its unusual courtship behavior involving interlocking of the venom delivering chelicerae (i.e., the jaws), and several species in the genus are already known to have sexually dimorphic venoms. Here, we use transcriptome and proteome analyses to identify venom components that are dimorphic in Tetragnatha versicolor. We present cDNA sequences including unique, male-specific high molecular weight proteins that have remote, if any, detectable similarity to known venom components in spiders or other venomous lineages and have no detectable homologs in existing databases. While the function of these proteins is not known, their presence in association with the cheliceral locking mechanism during mating together with the presence of prolonged male-male mating attempts in a related, cheliceral-locking species (Doryonychus raptor) lacking the dimorphism suggests potential for a role in sexual communication.

Divergence of species-specific protein sex pheromone blends in two related, nonhybridizing newts (Salamandridae)

In animals that use chemical communication during courtship and reproduction, speciation is often associated with divergence of their sex pheromones. In multicomponent pheromone systems, divergence can be obtained either by adding or deleting components, or by altering the relative contribution of individual components to the mixture. Protein pheromone systems can additionally evolve by amino acid sequence divergence to produce pheromones with a species-specific effect. The sodefrin precursor-like factor (SPF) pheromone system, a blend of proteins that essentially enhances receptivity in salamanders, has had a long and dynamic evolution of gene duplications, but the mechanisms that govern interspecific divergence and the role they play in reproductive isolation remain elusive. Here, we use transcriptomics and proteomics to characterize the SPF protein repertoire of the alpine newt (Ichthyosaura alpestris), and compare it to the previously identified repertoire of SPF proteins of the palmate newt (Lissotriton helveticus), a related but nonhybridizing species. Subsequent phylogenetic analyses indicate that, despite the availability of multiple SPF gene copies, both species predominantly express the same subset of orthologs. Our study demonstrates that species specificity in the SPF protein pheromone system can be established by gradual sequence divergence of the same set of proteins alone.

Ants regulate colony spatial organization using multiple chemical road-signs

Communication provides the basis for social life. In ant colonies, the prevalence of local, often chemically mediated, interactions introduces strong links between communication networks and the spatial distribution of ants. It is, however, unknown how ants identify and maintain nest chambers with distinct functions. Here, we combine individual tracking, chemical analysis and machine learning to decipher the chemical signatures present on multiple nest surfaces. We present evidence for several distinct chemical 'road-signs' that guide the ants' movements within the dark nest. These chemical signatures can be used to classify nest chambers with different functional roles. Using behavioural manipulations, we demonstrate that at least three of these chemical signatures are functionally meaningful and allow ants from different task groups to identify their specific nest destinations, thus facilitating colony coordination and stabilization. The use of multiple chemicals that assist spatiotemporal guidance, segregation and pattern formation is abundant in multi-cellular organisms. Here, we provide a rare example for the use of these principles in the ant colony.

Quantitative inheritance of volatile pheromones and darcin and their interaction in olfactory preferences of female mice

In this study, we examined how urine-borne volatile compounds (UVCs) and darcin of male mice are inherited from parents and interact to modulate the olfactory preferences of females using two inbred strains of mice, C57Bl/6 (C57) and BALB/c (BALB), and their reciprocal hybrids (BC = BALB♀× C57♂; CB = C57♀ × BALB♂). Chemical analysis revealed that the UVCs of C57BL/6 males were quantitatively distinguishable from those of BALB/c males. Darcin was detected in C57 urine, but not in BALB urine. The levels of UVCs and darcin in both BC and CB were intermediate between those of C57 and BALB. Behaviourally, C57 females consistently preferred BALB male urine over C57 or CB males despite that there are trace amounts of darcin in BALB urine. However, the preference for BALB urine disappeared in contact two-choice tests of BALB vs. BC pairs, and restored when recombinant darcin was added to BALB male urine. Our results suggested that both UVCs and darcin in male mice are quantitatively inherited and interact to affect the olfactory preferences of females.

Inter- and intra-population variability of the protein content of femoral gland secretions from a lacertid lizard

Femoral glands of male lizards produce waxy secretions that are involved in inter- and intraspecific chemical communication. The main components of these secretions are proteins and lipids, the latter having been extensively studied and already associated to male quality. On the opposite, the composition and role of proteins are nearly unknown, the only available information coming from few studies on iguanids. These studies got the conclusion that proteins might have a communicative function, notably they could signal individual identity. A generalization of these findings requires the extension of protein analysis to other lizard families, and the primary detection of some patterns of individual variability. Using the common wall lizard Podarcis muralis as a model species, the protein fraction of the femoral pore secretions was investigated to provide the first characterization of this component in a lacertid lizard and to explore its source of variability, as a first step to support the hypothesized communicative role. Samples of proteins from femoral secretions were collected from 6 Italian populations and subjected to 1-dimensional electrophoresis. The binary vector of the band presence/absence was used to define the individual profiles. Protein fraction is found to have a structured pattern, with both an individual and a population component. Although the former supports the potential communicative role of proteins, the latter offers a double interpretation, phylogenetic or environmental, even though the phylogenetic effect seems more likely given the climatic resemblance of the considered sites. Further studies are necessary to shed light on both these issues.

Ocean acidification affects marine chemical communication by changing structure and function of peptide signalling molecules

Ocean acidification is a global challenge that faces marine organisms in the near future with a predicted rapid drop in pH of up to 0.4 units by the end of this century. Effects of the change in ocean carbon chemistry and pH on the development, growth and fitness of marine animals are well documented. Recent evidence also suggests that a range of chemically mediated behaviours and interactions in marine fish and invertebrates will be affected. Marine animals use chemical cues, for example, to detect predators, for settlement, homing and reproduction. But, while effects of high CO₂ conditions on these behaviours are described across many species, little is known about the underlying mechanisms, particularly in invertebrates. Here, we investigate the direct influence of future oceanic pH conditions on the structure and function of three peptide signalling molecules with an interdisciplinary combination of methods. NMR spectroscopy and quantum chemical calculations were used to assess the direct molecular influence of pH on the peptide cues, and we tested the functionality of the cues in different pH conditions using behavioural bioassays with shore crabs (Carcinus maenas) as a model system. We found that peptide signalling cues are susceptible to protonation in future pH conditions, which will alter their overall charge. We also show that structure and electrostatic properties important for receptor binding differ significantly between the peptide forms present today and the protonated signalling peptides likely to be dominating in future oceans. The bioassays suggest an impaired functionality of the signalling peptides at low pH. Physiological changes due to high CO₂ conditions were found to play a less significant role in influencing the investigated behaviour. From our results, we conclude that the change of charge, structure and consequently function of signalling molecules presents one possible mechanism to explain altered behaviour under future oceanic pH conditions.

MULTIFUNCin: A Multifunctional Protein Cue Induces Habitat Selection by, and Predation on, Barnacles

Foundation species provide critical resources to ecological community members and are major determinants of biodiversity. The barnacle Balanus glandula is one such species and dominates space among the higher reaches on wave-swept shores. Here, we show that B. glandula produces a 199.6-kDa glycoprotein (named "MULTIFUNCin"), and following secretion, a 390-kDa homodimer in its native state. MULTIFUNCin expression is localized in the epidermis, cuticle, and new shell material. Consequently, this molecule can specify upon contact the immediate presence of a live barnacle. Shared, conserved domains place MULTIFUNCin in the α₂-macroglobulin (A2M) subgroup of the thioester-containing protein family. Although previously undescribed, MULTIFUNCin shares 78% nucleotide sequence homology with a settlement-inducing pheromone (SIP) of the barnacle, Amphibalanus amphitrite Based on this and further evidence, we propose that the two proteins are orthologues and evolved ancestrally in structural and immunological roles. More recently, they became exploited as chemical cues for con- and heterospecific organisms, alike. MULTIFUNCin and SIP both induce habitat selection (settlement) by conspecific barnacle larvae. In addition, MULTIFUNCin acts as a potent feeding stimulant to major barnacle predators (sea stars and several whelk species). Promoting immigration via settlement on the one hand, and death via predation on the other, MULTIFUNCin simultaneously mediates opposing demographic processes toward structuring both predator and prey populations. As a multifunctional protein cue, MULTIFUNCin provides valuable sensory information, conveys different messages to different species, and drives complex biotic interactions.

Beyond sodefrin: evidence for a multi-component pheromone system in the model newt Cynops pyrrhogaster (Salamandridae)

Sodefrin, a decapeptide isolated from the male dorsal gland of the Japanese fire belly newt Cynops pyrrhogaster, was the first peptide pheromone identified from a vertebrate. The fire belly salamander and sodefrin have become a model for sex pheromone investigation in aquatically courting salamanders ever since. Subsequent studies in other salamanders identified SPF protein courtship pheromones of around 20 kDa belonging to the same gene-family. Although transcripts of these proteins could be PCR-amplified in Cynops, it is currently unknown whether they effectively use full-length SPF pheromones next to sodefrin. Here we combined transcriptomics, proteomics and phylogenetics to investigate SPF pheromone use in Cynops pyrrhogaster. Our data show that not sodefrin transcripts, but multiple SPF transcripts make up the majority of the expression profile in the dorsal gland of this newt. Proteome analyses of water in which a male has been courting confirm that this protein blend is effectively secreted and tail-fanned to the female. By combining phylogenetics and expression data, we show that independent evolutionary lineages of these SPF’s were already expressed in ancestral Cynops species before the origin of sodefrin. Extant Cynops species continue to use this multi-component pheromone system, consisting of various proteins in addition to a lineage-specific peptide.

Side-by-side secretion of Late Palaeozoic diverged courtship pheromones in an aquatic salamander

Males of the advanced salamanders (Salamandroidea) attain internal fertilization without a copulatory organ by depositing a spermatophore on the substrate in the environment, which females subsequently take up with their cloaca. The aquatically reproducing modern Eurasian newts (Salamandridae) have taken this to extremes, because most species do not display close physical contact during courtship, but instead largely rely on females following the male track at spermatophore deposition. Although pheromones have been widely assumed to represent an important aspect of male courtship, molecules able to induce the female following behaviour that is the prelude for successful insemination have not yet been identified. Here, we show that uncleaved sodefrin precursor-like factor (SPF) protein pheromones are sufficient to elicit such behaviour in female palmate newts (Lissotriton helveticus). Combined transcriptomic and proteomic evidence shows that males simultaneously tail-fan multiple ca 20 kDa glycosylated SPF proteins during courtship. Notably, molecular dating estimates show that the diversification of these proteins already started in the late Palaeozoic, about 300 million years ago. Our study thus not only extends the use of uncleaved SPF proteins outside terrestrially reproducing plethodontid salamanders, but also reveals one of the oldest vertebrate pheromone systems.

Proteomics in evolutionary ecology

Evolutionary ecologists are traditionally gene-focused, as genes propagate phenotypic traits across generations and mutations and recombination in the DNA generate genetic diversity required for evolutionary processes. As a consequence, the inheritance of changed DNA provides a molecular explanation for the functional changes associated with natural selection. A direct focus on proteins on the other hand, the actual molecular agents responsible for the expression of a phenotypic trait, receives far less interest from ecologists and evolutionary biologists. This is partially due to the central dogma of molecular biology that appears to define proteins as the 'dead-end of molecular information flow' as well as technical limitations in identifying and studying proteins and their diversity in the field and in many of the more exotic genera often favored in ecological studies. Here we provide an overview of a newly forming field of research that we refer to as 'Evolutionary Proteomics'. We point out that the origins of cellular function are related to the properties of polypeptide and RNA and their interactions with the environment, rather than DNA descent, and that the critical role of horizontal gene transfer in evolution is more about coopting new proteins to impact cellular processes than it is about modifying gene function. Furthermore, post-transcriptional and post-translational processes generate a remarkable diversity of mature proteins from a single gene, and the properties of these mature proteins can also influence inheritance through genetic and perhaps epigenetic mechanisms. The influence of post-transcriptional diversification on evolutionary processes could provide a novel mechanistic underpinning for elements of rapid, directed evolutionary changes and adaptations as observed for a variety of evolutionary processes. Modern state-of the art technologies based on mass spectrometry are now available to identify and quantify peptides, proteins, protein modifications and protein interactions of interest with high accuracy and assess protein diversity and function. Therefore, proteomic technologies can be viewed as providing evolutionary biologist with exciting novel opportunities to understand very early events in functional variation of cellular molecular machinery that are acting as part of evolutionary processes.

Chemical fingerprints encode mother-offspring similarity, colony membership, relatedness, and genetic quality in fur seals

Chemical communication underpins virtually all aspects of vertebrate social life, yet remains poorly understood because of its highly complex mechanistic basis. We therefore used chemical fingerprinting of skin swabs and genetic analysis to explore the chemical cues that may underlie mother-offspring recognition in colonially breeding Antarctic fur seals. By sampling mother-offspring pairs from two different colonies, using a variety of statistical approaches and genotyping a large panel of microsatellite loci, we show that colony membership, mother-offspring similarity, heterozygosity, and genetic relatedness are all chemically encoded. Moreover, chemical similarity between mothers and offspring reflects a combination of genetic and environmental influences, the former partly encoded by substances resembling known pheromones. Our findings reveal the diversity of information contained within chemical fingerprints and have implications for understanding mother-offspring communication, kin recognition, and mate choice.

Estrogen involvement in social behavior in rodents: Rapid and long-term actions

This article is part of a Special Issue ("Estradiol and cognition"). Estrogens have repeatedly been shown to influence a wide array of social behaviors, which in rodents are predominantly olfactory-mediated. Estrogens are involved in social behavior at multiple levels of processing, from the detection and integration of socially relevant olfactory information to more complex social behaviors, including social preferences, aggression and dominance, and learning and memory for social stimuli (e.g. social recognition and social learning). Three estrogen receptors (ERs), ERα, ERβ, and the G protein-coupled ER 1 (GPER1), differently affect these behaviors. Social recognition, territorial aggression, and sexual preferences and mate choice, all requiring the integration of socially related olfactory information, seem to primarily involve ERα, with ERβ playing a lesser, modulatory role. In contrast, social learning consistently responds differently to estrogen manipulations than other social behaviors. This suggests differential ER involvement in brain regions important for specific social behaviors, such as the ventromedial and medial preoptic nuclei of the hypothalamus in social preferences and aggression, the medial amygdala and hippocampus in social recognition, and the prefrontal cortex and hippocampus in social learning. While the long-term effects of ERα and ERβ on social behavior have been extensively investigated, our knowledge of the rapid, non-genomic, effects of estrogens is more limited and suggests that they may mediate some social behaviors (e.g. social learning) differently from long-term effects. Further research is required to compare ER involvement in regulating social behavior in male and female animals, and to further elucidate the roles of the more recently described G protein-coupled ERs, both the GPER1 and the Gq-mER.

Evolution and role of the follicular epidermal gland system in non-ophidian squamates

Many lizard and amphisbaenian lineages possess follicular glands in the dermis of the inner thighs and/or the area anterior to the cloaca. These tubular glands produce a holocrine secretion that finds its way to the external world through pore-bearing scales (femoral and/or preanal pores). Secretions are composed of proteins and many lipophilic compounds that may function as chemosignals in lizard and amphisbaenian communication. In recent years, we have begun to develop an understanding of the adaptive significance of these secretions, and they are currently thought to play an important role in a variety of processes in these animals. While it appears that epidermal gland secretions function in intra- and interspecific recognition and territoriality, research has focused largely on their role in mate assessment. Despite these recent studies, our knowledge on the true role of the chemicals found in epidermal secretions remains poorly studied, and there are many possible avenues for future research on this topic. Here, we review the literature on the follicular epidermal glands of non-ophidian squamates and provide a first taxon-wide overview of their distribution.