Chemosignals, hormones, and amphibian reproduction

Sexy fingers: Pheromones in the glands of male dendrobatid frogs

Many animals exchange chemicals during courtship and mating. In some amphibians, sexual chemical communication is mediated by pheromones produced in male breeding glands that are transferred to the female's nostrils during mating. This has been mostly studied in salamanders, despite frogs having similar glands and courtship behaviours suggestive of chemical communication. In Neotropical poison frogs (Dendrobatidae and Aromobatidae), males of many species develop breeding glands in their fingers, causing certain fingers to visibly swell. Many also engage in cephalic amplexus, whereby the male's swollen fingers are placed in close contact with the female's nares during courtship. Here, we investigate the possible roles of swollen fingers in pheromone production using whole-transcriptome sequencing (RNAseq). We examined differential gene expression in the swollen versus non-swollen fingers and toes of two dendrobatid species, Leucostethus brachistriatus and Epipedobates anthonyi, both of which have specialised mucous glands in finger IV, the latter of which has cephalic amplexus. The overwhelming pattern of gene expression in both species was strong upregulation of sodefrin precursor-like factors (SPFs) in swollen fingers, a well-known pheromone system in salamanders. The differentially expressed SPF transcripts in each species were very high (>40), suggesting a high abundance of putative protein pheromones in both species. Overall, the high expression of SPFs in the swollen fingers in both species, combined with cephalic amplexus, supports the hypothesis that these traits, widespread across members of the subfamilies Colostethinae and Hyloxalinae (ca. 141 species), are involved in chemical signalling during courtship.

Species- and sex-specific chemical composition from an internal gland-like tissue of an African frog family

Intraspecific chemical communication in frogs is understudied and the few published cases are limited to externally visible and male-specific breeding glands. Frogs of the family Odontobatrachidae, a West African endemic complex of five morphologically cryptic species, have large, fatty gland-like strands along their lower mandible. We investigated the general anatomy of this gland-like strand and analysed its chemical composition. We found the strand to be present in males and females of all species. The strand varies in markedness, with well-developed strands usually found in reproductively active individuals. The strands are situated under particularly thin skin sections, the vocal sac in male frogs and a respective area in females. Gas-chromatography/mass spectrometry and multivariate analysis revealed that the strands contain sex- and species-specific chemical profiles, which are consistent across geographically distant populations. The profiles varied between reproductive and non-reproductive individuals. These results indicate that the mandibular strands in the Odontobatrachidae comprise a so far overlooked structure (potentially a gland) that most likely plays a role in the mating and/or breeding behaviour of the five Odontobatrachus species. Our results highlight the relevance of multimodal signalling in anurans, and indicate that chemical communication in frogs may not be restricted to sexually dimorphic, apparent skin glands.

Invading nonnative frogs use different microhabitats and change physiology along an elevation gradient

The coqui frog (Eleutherodactylus coqui) was introduced to the island of Hawai'i in the 1980s, and has spread across much of the island. There is concern they will invade higher elevation areas where negative impacts on native species are expected. It is not known if coqui change behavior and baseline physiology in ways that allow them to invade higher elevations. We investigated where coqui are found across the island and whether that includes recent invasion into higher elevations. We also investigated whether elevation is related to coqui's microhabitat use, including substrate use and height off the forest floor, and physiological metrics, including plasma osmolality, oxidative status, glucose, free glycerol, and triglycerides, that might be associated with invading higher elevations. We found coqui have increased the area they occupy along roads from 31% to 50% and have moved into more high-elevation locations (16% vs. 1%) compared to where they were found 14 years ago. We also found frogs at high elevation on different substrates and closer to the forest floor than frogs at lower elevations-perhaps in response to air temperatures which tended to be warmer close to the forest floor. We observed that blood glucose and triglycerides increase in frogs with elevation. An increase in glucose is likely an acclimation response to cold temperatures while triglycerides may also help frogs cope with the energetic demands of suboptimal temperatures. Finally, we found that female coqui have higher plasma osmolality, reactive oxygen metabolites (dROMs), free glycerol, and triglycerides than males. Our study suggests coqui behavior and physiology in Hawai'i may be influenced by elevation in ways that allow them to cope with lower temperatures and invade higher elevations.

Gene expression of secretory proteins in the nuptial pads of three Lithobates species (Anura: Ranidae)

Many amphibian species possess male-specific secretory breeding glands. In anurans, such specialized glands are often present as nuptial pads at the first digit of the hand, which are pressed against the female during amplexus. However, the role of nuptial pad secretions remains largely unknown. Here, we investigate the inner morphology as well as the RNA expression patterns of the nuptial pads of several Central American Lithobates species (Ranidae). As shown for the breeding glands of other amphibian species, the Lithobates nuptial pads are composed of large specialized mucus glands, excreting proteinaceous content to the surface. Whole-transcriptome sequencing revealed that for one of the species the most highly expressed transcripts encoding secretory proteins in the nuptial pads are sodefrin precursor-like factor (SPF) proteins, known to have a pheromone function in multiple amphibian species. The other two species, however, lack high expression of SPF transcripts but express other secretory proteins, whose roles in amphibian breeding glands remain unknown. Several of these proteins are highly expressed in all samples, suggesting a direct role during courtship or for the maintenance/development of the glands.

Electrophysiological responses to conspecific odorants in Xenopus laevis show potential for chemical signaling

The fully aquatic African clawed frog, Xenopus laevis, has an unusual and highly adapted nose that allows it to separately sample both airborne and waterborne stimuli. The function of the adult water nose has received little study, despite the fact that it is quite likely to receive information about conspecifics through secretions released into the water and could aid the frog in making decisions about social and reproductive behaviors. To assess the potential for chemical communication in this species, we developed an in situ electroolfactogram preparation and tested the olfactory responses of adult males to cloacal fluids and skin secretions from male and female conspecifics. We found robust olfactory responses to all conspecific stimuli, with greatest sensitivity to female cloacal fluids. These results open the door to further testing to identify compounds within cloacal fluids and skin secretions that are driving these responses and examine behavioral responses to those compounds. Understanding the role of chemical communication in social and reproductive behaviors may add to our rich understanding of vocal communication to create a more complete picture of social behavior in this species.

Cinnamomeoventrolide - Double Bond Regioisomerism in Frog Semiochemicals

Frogs of the families Mantellinae and Hyperoliidae possess male specific femoral or gular glands that are used during courtship. These glands release volatile compounds, e. g. the macrocyclic lactone gephyromantolide A (2,6,10-trimethyl-6-undecen-11-olide) in the case of Gephyromantis boulengeri (Mantellinae). During the analysis of the volatiles of Hyperolius cinnamomeoventris (Hyperoliidae) we detected an unknown compound A, which we called cinnamomeoventrolide, whose mass spectrum showed high similarity with the spectrum of gephyromantolide A. Nevertheless, slight spectral differences led to the proposal of a regioisomer of gephyromantolide A as a structure for A, 2,6,10-trimethyl-5-undecen-11-olide. A versatile synthesis of this compound was developed to allow access to all four stereoisomers from a single chiral starting material, the so-called (S)-Roche ester, using ring-closing metathesis as a key step. With these stereoisomers, the absolute configuration of the natural product was established to have the (2R,10S)-configuration by GC on a chiral phase. The configuration of natural gephyromantolide A is the opposite. Both frogs seem to use a similar biosynthetic pathway to access the target compounds, differing in the stereochemistry of the reduction steps, and requiring an additional isomerization in case of G. boulengeri. This unique regioisomeric differentiation of double bonds in semiochemicals has so far only been observed in insects. The compounds are likely to play a role in species-recognition of the frogs.

External nasal gland morphology of Eurycea bislineata (Amphibia, Urodela, Plethodontidae)

Plethodontid salamanders possess numerous courtship glands. Previous studies have shown that the glands are more prominent in male individuals than females, and often experience periods of atrophy and hypertrophy throughout the year that correlate to the nonmating and mating seasons, respectively. We sampled male and female Eurycea bislineata throughout the year to test the hypothesis that external nasal glands are courtship glands. External nasal glands are paired, branched tubular glands that extend from excretory ducts dorsal to the nares to terminal secretory units posterior to the eyes. We found that the glands hypertrophy and stain/react more intensely with histochemical procedures during the mating season. Hypertrophy of the glands is more pronounced in males, and seasonal variation in epithelial height of external nasal glands of males is significantly correlated to that of seasonal variation in mental gland epithelial height, a known courtship gland found in males, when compared throughout the year. This correlation was not as strong in females, confirming sexual dimorphism of external nasal glands in terms of seasonal variation. We found no ultrastructural differences between male and female external nasal glands. In all specimens, the glandular tubules were lined by a simple, columnar epithelium that was packed with secretory granules that often obscured other cytoplasmic contents.

Love bites: male frogs (Plectrohyla, Hylidae) use teeth scratching to deliver sodefrin precursor-like factors to females during amplexus

BACKGROUND

Efficient transfer of chemical signals is important for successful mating in many animal species. Multiple evolutionary lineages of animals evolved direct sex pheromone transmission during traumatic mating-the wounding of the partner with specialized devices-which helps to avoid signal loss to the environment. Although such direct transmission modes of so-called allohormone pheromones are well-documented in invertebrates, they are considered rare in vertebrates. Males of several species of the frog genus Plectrohyla (Hylidae, Anura) have elongated teeth and develop swollen lips during the breeding season. Here we investigated the possibility that these structures are used to scratch the females' skin and apply allohormone pheromones during traumatic mating in several Plectrohyla species.

RESULTS

Our behavioural observations revealed that males press their upper jaw onto the females' dorsum during amplexus, leaving small skin scratches with their teeth. Histological examinations of the males' lips identified specialized mucus glands, resembling known amphibian pheromone glands. Whole-transcriptome sequencing of these breeding glands showed high expression of sodefrin precursor-like factor (SPF) proteins, which are known to have a pheromone function in multiple amphibian species.

CONCLUSIONS

Our study suggests SPF delivery via traumatic mating in several anuran species: the males have specialized breeding glands in the lips for production and secretion and use their elongated teeth as wounding devices for application. We hypothesize that these SPF proteins end up in the females' circulatory system, where understanding their exact function will require further molecular, physiological and behavioural testing.

Conspecific odor cues induce different vocal responses in serrate-legged small treefrogs, but only in the absence of acoustic signals

Background

Signal detection is crucial to survival and successful reproduction, and animals often modify behavioral decisions based on information they obtained from the social context. Undeniably, the decision-making in male-male competition and female choice of anurans (frogs and toads) depends heavily on acoustic signals. However, increasing empirical evidence suggests that additional or alternative types of cue (e.g., visual, chemical, and vibratory) can be used to detect, discriminate and locate conspecifics in many anuran species. Nevertheless, few studies have investigated whether conspecific odor cues affect male’s calling behavior. In this study, we conducted an experiment to investigate whether and how different chemical cues (male odors, female odors, and stress odors) from conspecifics affect male’s calling strategies in serrate-legged small treefrogs (Kurixalus odontotarsus), and whether the combined chemical and acoustic stimuli have additive effects on calling behavior or not.

Results

We found that compared with female odors, male K. odontotarsus reduced calling investment in response to male odors or stress odors, in the absence of rival’s advertisement calls. When odor stimuli and advertisement calls were presented simultaneously, however, there were no differences in the vocal response of focal males among odor groups.

Conclusions

These results provide evidence that male treefrogs switch calling investment according to different odor cues from conspecifics, and further demonstrate that calling behavior can be affected by chemical cues in anuran species. Our study highlights the potential role of airborne chemical cues in sex identification and contributes to increase our understanding of anuran communication.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-021-00415-y.

Immunoreactivities of AR, ERα, ERβ and aromatase in the nuptial pad of Chinese brown frog (<em>Rana dybowskii</em>) during pre-hibernation and the breeding period

There is a prominent local raised pad called nuptial pad on the forelimb of Chinese brown frog (Rana dybowskii), which is hypothetically concluded as an enhancement of the grip and a spreader of pheromone during the amplexus. In this study, we investigated the immunolocalization and protein expression levels of androgen receptors (AR), estrogen receptor α (ERα), ERβ and aromatase in the nuptial pad of R. dybowskii during pre-hibernation and the breeding period. Histologically, the annual development of the nuptial pad in R. dybowskii is manifested as the larger area of specialized mucous gland and the longer length of papillary epidermal projection during the breeding period. AR, ERα, ERβ and aromatase are present in the stratum granulosum, stratum spinosum, stratum basale and the secretory portion of specialized mucous glands during both periods. Western blotting results confirmed that AR, ERα and ERβ protein levels are higher during pre-hibernation than those during the breeding season. These results suggest that nuptial pad is the direct target organ of androgen and estrogen. Androgen may participate in the regulation of annual development and glandular function of nuptial pad, and estrogen may play an endocrine, autocrine or paracrine role during pre-hibernation and the breeding period.

Pheromonal communication in urodelan amphibians

Pheromonal communication is an ancient and pervasive sensory modality in urodelan amphibians. One family of salamander pheromones (the sodefrin precursor-like factor (SPF) family) originated 300 million years ago, at the origin of amphibians. Although salamanders are often thought of as relatively simple animals especially when compared to mammals, the pheromonal systems are varied and complex with nuanced effects on behavior. Here, we review the function and evolution of pheromonal signals involved in male-female reproductive interactions. After describing common themes of salamander pheromonal communication, we describe what is known about the rich diversity of pheromonal communication in each salamander family. Several pheromones have been described, ranging from simple, invariant molecules to complex, variable blends of pheromones. While some pheromones elicit overt behavioral responses, others have more nuanced effects. Pheromonal signals have diversified within salamander lineages and have experienced rapid evolution. Once receptors have been matched to pheromonal ligands, rapid advance can be made to better understand the olfactory detection and processing of salamander pheromones. In particular, a large number of salamander species deliver pheromones across the skin of females, perhaps reflecting a novel mode of pheromonal communication. At the end of our review, we list some of the many intriguing unanswered questions. We hope that this review will inspire a new generation of scientists to pursue work in this rewarding field.

Olfaction across the water-air interface in anuran amphibians

Extant anuran amphibians originate from an evolutionary intersection eventually leading to fully terrestrial tetrapods. In many ways, they have to deal with exposure to both terrestrial and aquatic environments: (i) phylogenetically, as derivatives of the first tetrapod group that conquered the terrestrial environment in evolution; (ii) ontogenetically, with a development that includes aquatic and terrestrial stages connected via metamorphic remodeling; and (iii) individually, with common changes in habitat during the life cycle. Our knowledge about the structural organization and function of the amphibian olfactory system and its relevance still lags behind findings on mammals. It is a formidable challenge to reveal underlying general principles of circuity-related, cellular, and molecular properties that are beneficial for an optimized sense of smell in water and air. Recent findings in structural organization coupled with behavioral observations could help to understand the importance of the sense of smell in this evolutionarily important animal group. We describe the structure of the peripheral olfactory organ, the olfactory bulb, and higher olfactory centers on a tissue, cellular, and molecular levels. Differences and similarities between the olfactory systems of anurans and other vertebrates are reviewed. Special emphasis lies on adaptations that are connected to the distinct demands of olfaction in water and air environment. These particular adaptations are discussed in light of evolutionary trends, ontogenetic development, and ecological demands.

Male serrate-legged treefrogs adjust competition strategies according to visual or chemical cues from females

There is increasing evidence that many anurans use multimodal cues to detect, discriminate and/or locate conspecifics and thus modify their behaviors. To date, however, most studies have focused on the roles of multimodal cues in female choice or male-male interactions. In the present study, we conducted an experiment to investigate whether male serrate-legged small treefrogs (Kurixalus odontotarsus) used visual or chemical cues to detect females and thus altered their competition strategies in different calling contexts. Three acoustic stimuli (advertisement calls, aggressive calls and compound calls) were broadcast in a randomized order after a spontaneous period to focal males in one of four treatment groups: combined visual and chemical cues of a female, only chemical cues, only visual cues and a control (with no females). We recorded the vocal responses of the focal males during each 3 min period. Our results demonstrate that males reduce the total number of calls in response to the presence of females, regardless of how they perceived the females. In response to advertisement calls and compound calls, males that perceived females through chemical cues produced relatively fewer advertisement calls but more aggressive calls. In addition, they produced relatively more aggressive calls during the playback of aggressive calls. Taken together, our study suggests that male Kodontotarsus adjust their competition strategies according to the visual or chemical cues of potential mates and highlights the important role of multisensory cues in male frogs' perception of females.

Female-Based Patterns and Social Function in Avian Chemical Communication

Much of the growing interest in avian chemical signals has focused on the role of kin recognition or mate attraction, often with an emphasis on males, with uropygial gland secretions perhaps providing information about an individual's identity and quality. Yet, data collected to date suggest sexual dimorphism in uropygial glands and secretions are often emphasized in female, rather than in male birds. That is, when a sexual difference occurs (often during the breeding season only), it is the female that typically exhibits one of three patterns: (1) a larger uropygial gland, (2) a greater abundance of volatile or semi-volatile preen oil compounds and/or (3) greater diversity of preen oil compounds or associated microbes. These patterns fit a majority of birds studied to date (23 of 30 chemically dimorphic species exhibit a female emphasis). Multiple species that do not fit are confounded by a lack of data for seasonal effects or proper quantitative measures of chemical compounds. We propose several social functions for these secretions in female-based patterns, similar to those reported in mammals, but which are largely unstudied in birds. These include: (1) intersexual advertisement of female receptivity or quality, including priming effects on male physiology, (2) intrasexual competition, including scent marking and reproductive suppression or (3) parental behaviors, such as parent-offspring recognition and chemical protection of eggs and nestlings. Revisiting the gaps of chemical studies to quantify the existence of female social chemosignals and any fitness benefit(s) during breeding are potentially fruitful but overlooked areas of future research.

Some aspects of the hypothalamic and pituitary development, metamorphosis, and reproductive behavior as studied in amphibians

In this review article, information about the development of the hypothalamo-hypophyseal axis, endocrine control of metamorphosis, and hormonal and pheromonal involvements in reproductive behavior in some amphibian species is assembled from the works conducted mainly by our research group. The hypothalamic and pituitary development was studied using Bufo embryos and larvae. The primordium of the epithelial hypophysis originates at the anterior neural ridge and migrates underneath the brain to form a Rathke's pouch-like structure. The hypothalamo-hypophyseal axis develops under the influence of thyroid hormone (TH). For the morphological and functional development of the median eminence, which is a key structure in the transport of regulatory hormones to the pituitary, contact of the adenohypophysis with the undeveloped median eminence is necessary. For the development of proopiomelanocortin-producing cells, contact of the pituitary primordium with the infundibulum is required. The significance of avascularization in terms of the function of the intermediate lobe of the pituitary was evidenced with transgenic Xenopus frogs expressing a vascular endothelial growth factor in melanotropes. Metamorphosis progresses via the interaction of TH, adrenal corticosteroids, and prolactin (PRL). We emphasize that PRL has a dual role: modulation of the speed of metamorphic changes and functional development of organs for adult life. A brief description about a novel type of PRL (1B) that was detected was made. A possible reason why the main hypothalamic factor that stimulates the release of thyrotropin is not thyrotropin-releasing hormone, but corticotropin-releasing factor is considered in light of the fact that amphibians are poikilotherms. As regards the reproductive behavior in amphibians, studies were focused on the courtship behavior of the newt, Cynops pyrrhogaster. Male newts exhibit a unique courtship behavior toward sexually developed conspecific females. Hormonal interactions eliciting this behavior and hormonal control of the courtship pheromone secretion are discussed on the basis of our experimental results.

Multimodal stimuli regulate reproductive behavior and physiology in male túngara frogs

Unlike in terrestrial animals, the boundary between internal (e.g., hormones) and external (e.g., social) stimulation can be blurred for aquatic and amphibious species. When chemicals such as hormones and glandular secretions leach into the water, they can further interact with other signaling systems, creating multimodal stimuli. It is unclear, however, whether water-borne chemical secretions from courting male frogs affect the physiology and behavior of their rivals. In order to address this question we first established non-invasive, continuous sampling methods for simultaneously measuring both hormones and behavior in amphibious species. Then, we examined whether interactions between water-borne chemical secretions and conspecific calls affect reproductive behavior and physiology (testosterone and corticosterone) of courting male túngara frogs. Our results demonstrate that conspecific acoustic stimulation alone increases locomotor activity, decreases latency to call, and increases calling behavior but does not alter the amount of hormones excreted. In response to water containing chemical secretions from rivals, but in the absence of calls from other males, males excrete more testosterone. Interestingly, the combined acoustic and chemical stimulus causes a multiplicative increase in both calling behavior and hormonal excretion. Taken together, our results suggest that a multimodal chemical-acoustic stimulus physiologically primes males for aggressive behavior.

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.

Skin glands of an aquatic salamander vary in size and distribution and release antimicrobial secretions effective against chytrid fungal pathogens

Amphibian skin is unique among vertebrate classes, containing a large number of multicellular exocrine glands that vary among species and have diverse functions. The secretions of skin glands contain a rich array of bioactive compounds including antimicrobial peptides (AMPs). Such compounds are important for amphibian innate immune responses and may protect some species from chytridiomycosis, a lethal skin disease caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). While the bioactivity of skin secretions against Bd has been assessed for many amphibian taxa, similar studies are lacking for Bsal, a chytrid fungus that is especially pathogenic for salamanders. We studied the skin glands and their potential functions in an aquatic salamander, the three-toed amphiuma (Amphiuma tridactylum). Skin secretions of captive adult salamanders were analyzed by RP-HPLC and tested against the growth of Bd and Bsal using in vitro assays. We found that compounds within collected skin secretions were similar between male and female salamanders and inhibited the growth of Bd and Bsal. Thus, skin secretions that protect against Bd may also provide protection against Bsal. Histological examination of the skin glands of preserved salamanders revealed the presence of enlarged granular glands concentrated within caudal body regions. A site of potential gland specialization was identified at the tail base and may indicate specialized granular glands related to courtship and communication.

Olfactory effects of a hypervariable multicomponent pheromone in the red-legged salamander, Plethodon shermani

Chemical communication via chemosensory signaling is an essential process for promoting and modifying reproductive behavior in many species. During courtship in plethodontid salamanders, males deliver a mixture of non-volatile proteinaceous pheromones that activate chemosensory neurons in the vomeronasal epithelium (VNE) and increase female receptivity. One component of this mixture, Plethodontid Modulating Factor (PMF), is a hypervariable pheromone expressed as more than 30 unique isoforms that differ between individual males-likely driven by co-evolution with female receptors to promote gene duplication and positive selection of the PMF gene complex. Courtship trials with females receiving different PMF isoform mixtures had variable effects on female mating receptivity, with only the most complex mixtures increasing receptivity, such that we believe that sufficient isoform diversity allows males to improve their reproductive success with any female in the mating population. The aim of this study was to test the effects of isoform variability on VNE neuron activation using the agmatine uptake assay. All isoform mixtures activated a similar number of neurons (>200% over background) except for a single purified PMF isoform (+17%). These data further support the hypothesis that PMF isoforms act synergistically in order to regulate female receptivity, and different putative mechanisms are discussed.

Arginine Vasotocin, the Social Neuropeptide of Amphibians and Reptiles

Arginine vasotocin (AVT) is the non-mammalian homolog of arginine vasopressin (AVP) and, like vasopressin, serves as an important modulator of social behavior in addition to its peripheral functions related to osmoregulation, reproductive physiology, and stress hormone release. In amphibians and reptiles, the neuroanatomical organization of brain AVT cells and fibers broadly resembles that seen in mammals and other taxa. Both parvocellular and magnocellular AVT-containing neurons are present in multiple populations located mainly in the basal forebrain from the accumbens-amygdala area to the preoptic area and hypothalamus, from which originate widespread fiber connections spanning the brain with a particularly heavy innervation of areas associated with social behavior and decision-making. As for mammalian AVP, AVT is present in greater amounts in males in many brain areas, and its presence varies seasonally, with hormonal state, and in males with differing social status. AVT's social influence is also conserved across herpetological taxa, with significant effects on social signaling and aggression, and, based on the very small number of studies investigating more complex social behaviors in amphibians and reptiles, AVT may also modulate parental care and social bonding when it is present in these vertebrates. Within this conserved pattern, however, both AVT anatomy and social behavior effects vary significantly across species. Accounting for this diversity represents a challenge to understanding the mechanisms by which AVT exerts its behavioral effects, as well are a potential tool for discerning the structure-function relationships underlying AVT's many effects on behavior.

Structural elucidation of estrus urinary lipocalin protein (EULP) and evaluating binding affinity with pheromones using molecular docking and fluorescence study

Transportation of pheromones bound with carrier proteins belonging to lipocalin superfamily is known to prolong chemo-signal communication between individuals belonging to the same species. Members of lipocalin family (MLF) proteins have three structurally conserved motifs for delivery of hydrophobic molecules to the specific recognizer. However, computational analyses are critically required to validate and emphasize the sequence and structural annotation of MLF. This study focused to elucidate the evolution, structural documentation, stability and binding efficiency of estrus urinary lipocalin protein (EULP) with endogenous pheromones adopting in-silico and fluorescence study. The results revealed that: (i) EULP perhaps originated from fatty acid binding protein (FABP) revealed in evolutionary analysis; (ii) Dynamic simulation study shows that EULP is highly stable at below 0.45 Å of root mean square deviation (RMSD); (iii) Docking evaluation shows that EULP has higher binding energy with farnesol and 2-iso-butyl-3-methoxypyrazine (IBMP) than 2-naphthol; and (iv) Competitive binding and quenching assay revealed that purified EULP has good binding interaction with farnesol. Both, In-silico and experimental studies showed that EULP is an efficient binding partner to pheromones. The present study provides impetus to create a point mutation for increasing longevity of EULP to develop pheromone trap for rodent pest management.

Neuroendocrine control of spawning in amphibians and its practical applications

Across vertebrates, ovulation and sperm release are primarily triggered by the timed surge of luteinizing hormone (LH). These key reproductive events are governed by the action of several brain neuropeptides, pituitary hormones and gonadal steroids which operate to synchronize physiology with behaviour. In amphibians, it has long been recognized that the neuropeptide gonadotropin-releasing hormone (GnRH) has stimulatory effects to induce spawning. Extensive work in teleosts reveals an inhibitory role of dopamine in the GnRH-regulated release of LH. Preliminary evidence suggests that this may be a conserved function in amphibians. Emerging studies are proposing a growing list of modulators beyond GnRH that are involved in the control of spawning including prolactin, kisspeptins, pituitary adenylate cyclase-activating polypeptide, gonadotropin-inhibitory hormone and endocannabinoids. Based on these physiological data, spawning induction methods have been developed to test on selective amphibian species. However, several limitations remain to be investigated to strengthen the evidence for future applications. The current state of knowledge regarding the neuroendocrine control of spawning in amphibians will be reviewed in detail, the elements of which will have wide implications towards the captive breeding of endangered amphibian species for conservation.

From molecules to mating: Rapid evolution and biochemical studies of reproductive proteins

Sexual reproduction and the exchange of genetic information are essential biological processes for species across all branches of the tree of life. Over the last four decades, biochemists have continued to identify many of the factors that facilitate reproduction, but the molecular mechanisms that mediate this process continue to elude us. However, a recurring observation in this research has been the rapid evolution of reproductive proteins. In animals, the competing interests of males and females often result in arms race dynamics between pairs of interacting proteins. This phenomenon has been observed in all stages of reproduction, including pheromones, seminal fluid components, and gamete recognition proteins. In this article, we review how the integration of evolutionary theory with biochemical experiments can be used to study interacting reproductive proteins. Examples are included from both model and non-model organisms, and recent studies are highlighted for their use of state-of-the-art genomic and proteomic techniques.

SIGNIFICANCE

Despite decades of research, our understanding of the molecular mechanisms that mediate fertilization remain poorly characterized. To date, molecular evolutionary studies on both model and non-model organisms have provided some of the best inferences to elucidating the molecular underpinnings of animal reproduction. This review article details how biochemical and evolutionary experiments have jointly enhanced the field for 40 years, and how recent work using high-throughput genomic and proteomic techniques have shed additional insights into this crucial biological process.