Mate-guarding Behaviour Research Articles

Prezygotic reproductive barriers in precopulatory behavior of tidepool copepod species.

Complexity in prezygotic mating behavior can contribute to the emergence of sexual incompatibility and reproductive isolation. In this study, we performed behavioral tests with two tidepool copepod species of the genus Tigriopus to explore the possibility of precopulatory behavioral isolation. We found that interspecific mating attempts failed prior to genital contact, and that this failure occurred at different behavioral steps between reciprocal pairings. Our results suggest that prezygotic barriers may exist at multiple points of the behavioral process on both male and female sides, possibly due to interspecific differences in mate-recognition cues used at those "checkpoints". While many copepod species are known to show unique precopulatory mate-guarding behavior, the potential contribution of prezygotic behavioral factors to their isolation is not widely recognized. The pattern of sequential mate-guarding behaviors may have allowed diversification of precopulatory communication and contributed to the evolutionary diversity of the Tigriopus copepods.

Menses and Positive Partner Interactions Increase Mate Guarding Behaviors in Established Romantic Couples

Mate Guarding (Alberts et al., 1996), behaviors intended to decrease a romantic partner’s sexual access to potential extradyadic partners (e.g., touching partner around others, not attending gatherings), are thought to change throughout the menstrual cycle. Rooted in theories suggesting ovulating women’s sexual interest/behaviors increase during times of fertility, couples increase their mate guarding behaviors to limit reproductive costs (Gangestad et al., 2006). Yet, much of the research fails to examine mate guarding behaviors and fertility in established, committed couples. Using an ecological momentary assessment, romantically committed, heterosexual couples (n = 42 pairs) completed daily surveys tracking relationship dynamics for one menstrual cycle (e.g., 28 days; all naturally cycling). Dependent t-tests showed mate guarding behaviors increased during menses compared to ovulation (women, t = 4.5, p <.001; men, t = 3.5, p<.001), but positive couple interactions were unchanged. We tested actor-partner effects between positive daily partner interactions and mate guarding during menses and ovulation. Positive actor effects were found for both (menses women ß = 3.276, p <.001, men ß = 3.049, p =.002; ovulation women ß = 1.637, p =.041, men ß = 3.089, p =.011); whereas partner effects were only observed for men during ovulation (ß = 2.806, p =.006). Results demonstrate evolutionary psychological theories suggesting mate guarding increases during ovulation may not be predictive in established couples. For committed couples, times when female partners are unlikely to conceive are opportunities when couples demonstrate their fidelity.

The Neurobiology of Love and Pair Bonding from Human and Animal Perspectives.

Love is a powerful emotional experience that is rooted in ancient neurobiological processes shared with other species that pair bond. Considerable insights have been gained into the neural mechanisms driving the evolutionary antecedents of love by studies in animal models of pair bonding, particularly in monogamous species such as prairie voles (Microtus ochrogaster). Here, we provide an overview of the roles of oxytocin, dopamine, and vasopressin in regulating neural circuits responsible for generating bonds in animals and humans alike. We begin with the evolutionary origins of bonding in mother-infant relationships and then examine the neurobiological underpinnings of each stage of bonding. Oxytocin and dopamine interact to link the neural representation of partner stimuli with the social reward of courtship and mating to create a nurturing bond between individuals. Vasopressin facilitates mate-guarding behaviors, potentially related to the human experience of jealousy. We further discuss the psychological and physiological stress following partner separation and their adaptive function, as well as evidence of the positive health outcomes associated with being pair-bonded based on both animal and human studies.

An evaluation of sexual dimorphism in head size and shape of Red Salamanders (Pseudotriton ruber)

For many secretive species of amphibians and reptiles, observations of reproductive behavior are limited to sparse anecdotes from the field or to animals held in captivity. However, a careful examination of morphological differences between the sexes can help shape hypotheses about behaviors with which they may be correlated. For example, sexual dimorphism in head size and shape are correlated with courtship, territoriality, and mate-defense behaviors in some salamanders. One widespread species with a poorly described reproductive natural history is the Red Salamander (Pseudotriton ruber). Here, we measure head size and employ geometric morphometric methods to evaluate head shape in P. ruber, with the goals of: 1) quantifying and visualizing sexual variation; 2) forming hypotheses about reproductive behavior. We found preliminary evidence for differences in head size and shape that are consistent with mate-guarding behavior, and we remark upon directions for future research.

Mate-guarding duration is mainly influenced by the risk of sperm competition and not by female quality in a golden orb-weaver spider.

Males are expected to mate with as many females as possible, but can maximize their reproductive success through strategic mating decisions. For instance, males can increase their own fitness by mating with high quality females that produce more offspring. Additionally, males can adjust mating effort based on the relative distribution of females and male competitors. To test factors that influence male mate choice, we assessed male mating decisions in the golden silk orb-weaver spider, Trichonephila clavipes (Nephilidae), a species in which females are polyandrous, males guard females before and after copulation occurs and large males are the most successful at guarding mates. We tested the hypothesis that males spend more time guarding high quality females that are spatially isolated, and when the risk of sperm competition is higher. We also hypothesized that this effect increases with male body size. We assessed solitary and aggregated female webs in the field and quantified female quality (i.e., female body condition), male size (i.e., male body size), the risk of sperm competition (i.e., number of males in each female web), and mate-guarding duration (i.e., number of days each male spent in each web). We found that mate-guarding behaviour is largely influenced by the presence of male competitors. In addition, male body size seems to moderately influence male guarding decisions, with larger males guarding for a longer time. Finally, female body condition and type of web (i.e., solitary or aggregated) seem to play small roles in mate-guarding behaviour. As mate-guarding duration increased by 0.718 day per each additional male competitor in the web, and guarding behaviour prevents males from seeking additional mates, it seems that guarding females can be considerably costly. We conclude that failing to guard a sexual partner promotes high costs derived from sperm competition, and a male cannot recover his relative loss in fertilization success by seeking and fertilizing more females. In addition, the search for more sexual partners can be constrained by possible high costs imposed by weight loss and fights against other males, which may explain why the type of web only moderately influenced male mate choice. Following the same rationale, if high-quality females are not easy to find and/or mating with a high-quality female demands much effort, males may search females and guard them regardless of female quality. In conclusion, the factor that most influences male mate-guarding behaviour among T. clavipes in the field is the risk of sperm competition.

Does anthropogenic noise affect the acoustic courtship interactions of Gryllus bimaculatus?

Acoustic courtship displays are ubiquitous among animals. Signallers use these acoustics to advertise their willingness to mate, while receivers may be able to infer something of the signaller's quality from them. However, increases in anthropogenic noise may reduce the production, transmission and reception of these signals, leading to consequences for reproductive success. In this study, we conducted behavioural observations of courtship interactions of the Mediterranean field cricket, Gryllus bimaculatus , under anthropogenic noise conditions. We found that the presence of traffic noise had no effect on the outcome courtship interactions in this species, and their behaviour during courtship did not appear to be altered either. However, we found that the presence of white noise led to a reduction in male signal production, resulting in fewer successful matings. Males that did signal under white noise conditions had altered signal characteristics, including increased song frequency and reduced tick rate. Mate-guarding behaviour was also found to differ between individuals that courted and those that did not. The use of typical anthropogenic noise and white noise in this experiment allows us to consider the importance of specific characteristics of the acoustic pollutant in causing this disruption. • Human-generated acoustics can have a significant impact on the behaviour of animals. • We observed the courtship of field crickets under anthropogenic noise conditions. • Traffic noise did not affect the mating behaviour or acoustics of these crickets. • White noise affected male signalling behaviour, but not female response behaviour.

Genotype-by-environment interactions for precopulatory mate guarding in a lek-mating insect.

In sexually reproducing species, males often experience strong pre‐ and postcopulatory sexual selection leading to a wide variety of male adaptations. One example is mate guarding, where males prevent females from mating with other males either before or after they (will) have mated themselves. In case social conditions vary short term and in an unpredictable manner and if there is genetic variation in plasticity of mate guarding (i.e., genotype‐by‐environment interaction, G × E), adaptive behavioral plasticity in mate guarding may evolve.Here, we test for genetic variation in the plasticity of precopulatory mate‐guarding behavior in the lek‐mating lesser wax moth Achroia grisella. When offered two females in rapid succession, virgin males of this species usually copulate around 10–20 min with the first female. With the second female, however, they engage in copulation posture for many hours until they have produced another spermatophore, an unusual behavior among insects possibly functioning as precopulatory mate guarding. Previous studies showed the mating latency with the second female to be shorter under higher perceived sperm competition risk. We accordingly measured the mate‐guarding behavior of males from six inbred lines under either elevated perceived male–male competition risk or under control conditions allowing us to test for G × E interactions.We found significant inbred line‐by‐competitor treatment interactions on mating latency and copulation duration with the second female suggesting genetic variation in the degree of behavioral plasticity. However, we found no significant G × E interaction on the sum of mating latency and copulation duration. Our results suggest a potential for adaptive evolution of mate‐guarding plasticity in natural populations of lek‐mating species. Future studies using selection experiments and experimental evolution approaches in laboratory populations, or comparisons of multiple natural populations will be helpful to study under which conditions plasticity in male mate‐guarding behavior evolves.

Sexually dimorphic role of oxytocin in medaka mate choice

Oxytocin is a central neuromodulator required for facilitating mate preferences for familiar individuals in a monogamous rodent (prairie vole), irrespective of sex. While the role of oxytocin in mate choice is only understood in a few monogamous species, its function in nonmonogamous species, comprising the vast majority of vertebrate species, remains unclear. To address this issue, we evaluated the involvement of an oxytocin homolog (isotocin, referred herein as oxt) in mate choice in medaka fish (Oryzias latipes). Female medaka prefer to choose familiar mates, whereas male medaka court indiscriminately, irrespective of familiarity. We generated mutants of the oxt ligand (oxt) and receptor genes (oxtr1 and oxtr2) and revealed that the oxt-oxtr1 signaling pathway was essential for eliciting female mate preference for familiar males. This pathway was also required for unrestricted and indiscriminate mating strategy in males. That is, either oxt or oxtr1 mutation in males decreased the number of courtship displays toward novel females, but not toward familiar females. Further, males with these mutations exhibited enhanced mate-guarding behaviors toward familiar females, but not toward novel females. In addition, RNA-sequencing (seq) analysis revealed that the transcription of genes involved in gamma-amino butyric acid metabolism as well as those encoding ion-transport ATPase are up-regulated in both oxt and oxtr1 mutants only in female medaka, potentially explaining the sex difference of the mutant phenotype. Our findings provide genetic evidence that oxt-oxtr1 signaling plays a role in the mate choice for familiar individuals in a sex-specific manner in medaka fish.

First come, first served: precopulatory mate-guarding behavior and male-male contests by a hymenopteran saproxylic parasitoid.

Precopulatory mate-guarding behavior is a common strategy that maximizes male reproductive success when female receptivity to copulation is low. This behavior has been demonstrated in vertebrates, aquatic crustaceans, terrestrial isopods, and some species of insects, but there is very little available information about hymenopteran insects. A few studies have clarified the factor that determines the outcome of a contest between a guarding male and an invader male. We investigated the male-male contest and mating behavior of a saproxylic parasitoid wasp, Ibalia japonica (Hymenoptera: Cynipoidea: Ibaliidae) using field observations in Japan. These observations indicated that I. japonica males show precopulatory mate-guarding behavior and that four types of male-male contests occur on the Magnolia liliiflora (Magnoliales: Magnoliaceae) tree that virgin females emerge from. We show that the arrival order of I. japonica males that found the future emergence point of a female was key factor that allowed males to secure virgin females.

Sex or food? Effects of starvation, size and diet on sexual cannibalism in the amphipod crustacean Gammarus zaddachi

Cannibalism of females by males before, during or immediately following sex has been attributed to misidentification of females, rejection of females as mates and prioritisation of feeding over reproduction. In the gammarid amphipod Gammarus zaddachi, males demonstrate that they have identified a female and accepted her as a suitable mate by engaging in precopula pairing behaviour. However, a male may later decide to eat the female after pairing with her. Laboratory experiments were performed in which survival of females in precopula pairs of G. zaddachi was monitored after their male partners had been subjected to starvation, herbivorous diets or diets containing animal matter. These indicate that the female is less likely to survive when she is abnormally small relative to the male, when the male is at risk of death by starvation or when the male’s diet has lacked animal content. Decisions by males to forgo reproductive opportunities in favour of cannibalism, even after engaging in costly mate-guarding behaviour, emphasise the importance of carnivory in the trophic ecology of Gammarus species.

Oxytocin modulates mate-guarding behavior in marmoset monkeys

In socially-monogamous species, intolerance of interactions between a pairmate and a sexual rival (i.e., mate-guarding) promotes the preservation of long-lasting partnerships. One promising neurobiological candidate for the regulation of mate-guarding behavior in monogamous primates is the oxytocin (OT) system, given its established role in both the development of monogamous bonds and the behavioral processes that facilitate the preservation of those bonds. In this study, male and female marmosets were exposed to a same-sex intruder in their home environment during conditions when their pairmate was present and absent, and across three treatment conditions (OT receptor agonist; saline control; OT receptor antagonist). Saline-treated marmosets spent significantly more time in proximity to the intruder, relative to the empty pairmate enclosure, when their pairmate was absent. However, when marmosets received OT they spent less time in proximity to the intruder, indicating that OT may reduce interest in a same-sex stranger in a territorial context. When their pairmate was present, saline-treated marmosets spent equal time in proximity to both intruder and pairmate; yet when they received OT they spent significantly more time in proximity to the intruder, indicating that OT may increase interest in a same-sex stranger in a mate-guarding context. While OT treatment did not directly influence the expression of aggression, OT system manipulations impacted the expression of selective social interest during an intruder challenge, suggesting that OT may enhance adaptive responses to social challenges. Moreover, these findings add to the converging evidence that the OT system regulates behavioral processes that underlie the preservation of established relationships.

Individual Culturing of Tigriopus Copepods and Quantitative Analysis of Their Mate-guarding Behavior.

Copepods of the genus Tigriopus, which are common zooplankton in rocky tide pools, show precopulatory mate-guarding behavior where a male clasps a potential mate to form a pair. While this phenomenon has attracted interest of researchers, methods for its analysis have not been well described. Here we describe procedures for: 1) individual culturing and staging of Tigriopus juveniles and adults, and 2) video-based analysis of their mate-guarding behavior. The culturing method enables experimental control of paring experience of animals as well as the ability to track their development before behavioral tests. The analysis method allows quantitative evaluation of several aspects of the mate-guarding behavior, including capturing attempts by males and swimming trajectory of mate-guarding pairs. Although these methods were originally established for ethological studies on Tigriopus, with proper modifications they can also be applied to studies of other zooplankton in different research fields, such as physiology, toxicology, and ecological genetics.

Individual Culturing of &lt;em&gt;Tigriopus&lt;/em&gt; Copepods and Quantitative Analysis of Their Mate-guarding Behavior

Copepods of the genus Tigriopus, which are common zooplankton in rocky tide pools, show precopulatory mate-guarding behavior where a male clasps a potential mate to form a pair. While this phenomenon has attracted interest of researchers, methods for its analysis have not been well described. Here we describe procedures for: 1) individual culturing and staging of Tigriopus juveniles and adults, and 2) video-based analysis of their mate-guarding behavior. The culturing method enables experimental control of paring experience of animals as well as the ability to track their development before behavioral tests. The analysis method allows quantitative evaluation of several aspects of the mate-guarding behavior, including capturing attempts by males and swimming trajectory of mate-guarding pairs. Although these methods were originally established for ethological studies on Tigriopus, with proper modifications they can also be applied to studies of other zooplankton in different research fields, such as physiology, toxicology, and ecological genetics.

Mate-guarding in free-ranging Carpet Pythons (Morelia spilota)

ABSTRACT Carpet Pythons (Morelia spilota) exhibit substantial geographic variation not only in size and colour, but also in mating systems: reproductive males in some populations battle with their rivals, whereas courting males in other locations tolerate the proximity of others. During the spring mating season (August–September) of 2017, a large male Carpet Python took up residence with a reproductive female on the roof of a house in northeastern New South Wales for at least six weeks, and was observed in intense battles with two rival males that arrived at the site. Bouts progressed from stereotyped wrestling to vigorous biting, causing severe lesions. This (apparently successful) mate defence constitutes the first report of prolonged mate-guarding behaviour in any pythonid species.

Inhibition of lysine-specific demethylase enzyme disrupts sexually conditioned mate guarding in the female rat

Although female rats are typically described as having a promiscuous mating strategy, if sexually naïve females have their formative sexually rewarding experiences paired with the same male, they will recognize that male and display mate-guarding behavior towards him in the presence of a female competitor. Female rats that display mate guarding behavior also show enhanced activation of oxytocin and vasopressin neurons in the supraoptic and paraventricular hypothalamic nucleus. Here, we examined the potential role that histone demethylation might have in establishing this pair-bonded behavior, and whether the corresponding changes in oxytocin and vasopressin neuronal activation depended on demethylation. To accomplish this, we examined the effect of a lysine-specific demethylase-1 inhibitor to block the action of demethylase enzymes and maintain the methylation state of corresponding genes. Female rats treated with the demethylase inhibitor failed to show any measure of mate guarding, whereas females treated with vehicle displayed mate guarding behavior. Demethylase inhibitor treatment also blocked the ability of familiar male cues to activate oxytocin and vasopressin neurons, whereas vehicle-treated females showed this enhanced activation. These data indicate that histone demethylation is a crucial component in the epigenetic modification of neural circuitry that underlies conditioned mate guarding in female rats. These results are the first to demonstrate the role of histone demethylation underlying changes in mating strategy.

Influence of food availability on mate-guarding behaviour of ladybirds.

A recent study on ladybird, Menochilus sexmaculatus (Fabricius) demonstrates that males perform post-copulatory mate guarding in the form of prolonged mating durations. We investigated whether food resource fluctuation affects pre- and post-copulatory behaviour of M. sexmaculatus. It has not been studied before in ladybirds. For this, adults were subjected to prey resource fluctuations sequentially at three levels: post-emergence (Poe; 10 days), pre-mating (Prm; 24 h) and post-mating (Pom; 5 days; only female). The food resource conditions at each level could be any one of scarce, optimal or abundant. Pre-copulatory and post-copulatory behaviour, and reproductive output were assessed. Post-emergence and pre-mating nutrient conditions significantly influenced the pre-copulatory behaviour. Males reared on scarce post-emergence conditions were found to require significantly higher number of mating attempts to establish mating unlike males in the other two food conditions. Under scarce post-emergence and pre-mating conditions, time to commencement of mating and latent period were high but opposite result was obtained for mate-guarding duration. Fecundity and per cent egg viability were more influenced by post-mating conditions, with scarce conditions stopping oviposition regardless of pre-mating and post-emergence conditions. Present results indicate that pre- and post-copulatory behaviour of ladybird is plastic in nature in response to food resource fluctuations.

Revision of the Madagascan genera Oncodopus Brongniart and Colossopus Saussure (Orthoptera: Tettigoniidae: Conocephalinae; Euconchophorini), with description of Malagasopus gen. nov.

The endemic Madagascan genera Oncodopus Brongniart and Colossopus Saussure are revised using museum specimens, including the types, and recently collected material. A new genus, Malagasopus gen. nov., and seven new species, Malagasopus desutterae sp. nov., Malagasopus meridianus sp. nov., Oncodopus janetae sp. nov., Oncodopus brongniarti sp. nov., Oncodopus saussurei sp. nov., Oncodopus soalalaensis sp. nov. and Colossopus parvicavus sp. nov. are described. Lectotypes are designated for Oncodopus zonatus Brongniart, 1897 and Colossopus redtenbacheri (Brongniart, 1897). A new term, mesothoracic auricle, is proposed for a structure on the episternum of the mesothorax. A tabulated key to the genera and keys to the species are presented. All species are described and diagnosed, and their phylogenetic relationships, geographical distributions, habitat preferences and phenologies are documented. The life history of Colossopus grandidieri is described, and the unusual possible mate-guarding behaviour of several species is discussed. Maps showing the distribution of the species are presented, as too are 57 photographs of museum specimens, 51 drawings of morphological characters, 17 photographs of living specimens and one habitat photograph.

Sex-specific rejection in mate-guarding pair formation in the intertidal copepod, Tigriopus californicus.

Securing a potential mate is one of the most important processes in sexual reproduction of animals. Intertidal copepods of the genus Tigriopus show mate-guarding behavior where a male captures a female and continues to clasp her for up to two weeks prior to copulation. Although these copepods form a mate-guarding pair between a male and a female with high accuracy, interactions between the sexes in pair formation have not been well described and the mechanism allowing successful male-female pair formation is not yet understood. In this study, we performed experiments with Tigriopus californicus to analyze the behavior of both a capturer (male) and a captured individual (female or male) in formation of a guarding pair. While capturer males were attracted by both females and males, capture of virgin males was terminated in a significantly shorter time than that of virgin females. However, when presented freshly killed females or males, regardless of the sex of the body, capturer males continued to clasp the body for a comparable time as in an attempt on a living female. Our results suggest that a sex-specific rejection signal actively sent by captured males prevents male-male pair formation. Experiments also suggest that mated females reject an attempt of pair formation. To our knowledge, this is the first study to suggest involvement of active rejection by a captured individual in facilitation of reproductively successful male-female guarding pair formation in the genus Tigriopus.

Molecular basis of social competence in medaka fish.

Oryzias latipes (Medaka) is an established vertebrate model for studying developmental genetics, genomics, and evolutionary biology. The physiology, embryology, and genetics of this species have been extensively investigated for centuries. Medaka fish recently attracted attention in the field of social neuroscience. This review introduces recent advances in medaka behavioral studies, focusing on female mating preferences and male mate-guarding behaviors. The medaka female has the ability to discriminate male individuals and prefers to mate with socially familiar males (female mating preference). In triadic relationships (two males and one female), the dominant male remains closer to the female and repels the other male (mate-guarding). Interestingly, mate-guarding blocks female social familiarization of the rival male, which can increase the mating success of the dominant male. Importantly, behavioral analyses using a series of medaka mutants revealed critical roles of neuropeptide neuromodulatory systems in regulating their social behaviors. The extra-hypothalamic gonadotropin-releasing hormone system has a central role in activating female mating preference. The arginine-vasotocin system is required for the emergence of mate-guarding behavior.

Preface to Vertebrate Brains: evolution, structures and functions.

Living organisms have a strategy to integrate environmental information, and skillfully change physiological functions and actions so as to increase their own survival and reproductive success rates. In the vertebrate animals, the brain is playing crucial roles in the center of this strategy. Thus, vertebrates living in different environments show diversity in the brain morphology and function to achieve different survival and reproductive strategies. Indeed, if we look at the external form of the vertebrate brains, their structures are quite diverse (Fig. 1). With the remarkable development and expansion of the field of molecular neuroscience in recent years, genes important for the brain function and morphology have been elucidated one after another using experimental model organisms. However, most of the evolutionary mechanisms that generate the brain diversity remain unresolved. Although the structure and function of the brains are diverse, it is obvious that they are maintaining a lot of commonality. For example, the brains of vertebrates acquired their basic forms such as the forebrain (telencephalon and diencephalon), midbrain, and hindbrain in the early stage of evolution, and have changed the morphology and function of each region while maintaining the basic structures during evolution. Studies on the brain evolution had already been conducted by comparative anatomical approaches by scientists such as Ramon y Cajal (1995) and Johnston (1906) in the early twentieth century. Knowledge has accumulated since then, and MacLean (1990), Striedter (2005) and others have attempted to find certain patterns for the brain evolution. In spite of those efforts, the current status is still far from elucidating the whole picture of the mechanism of the brain evolution. In this special issue, we collected review and research articles from scientists performing cutting-edge research in evolutionary neuroscience. Sugahara et al. (2017) speculate the ancestral vertebrate brain architecture through comparison of the cyclostome and gnatostome brains. Yamamoto et al. (2017a) review regionalization of the anterior part of the forebrain of Osteichtyes (bony fish). The anterior part of the forebrain is subdivided into the telencephalon dorsally and the hypothalamus ventrally. They propose a new morphogenetic unit, optic recess area, between the telencephalon and the hypothalamus. Yamamoto et al. (2017bb) review descending pathways to the spinal cord in teleosts, which play crucial roles in controlling locomotion, including the rubospinal tract which originates from the nucleus ruber identified recently, and compare them with the descending pathways in mammals. Oltrabella et al. (2017) review roles of the endocannabinoid system (eCBs) in synaptic transmission, behaviors, and development in mammals, amphibians and zebrafish, and discuss evolutionary considerations. Takeuchi et al. (2017) review mating-related behaviors in the medaka fish, namely female mating preference and male mate-guarding behavior, and their control by neuropeptide neuromodulatory systems. Matsui (2017) reviews the structure and function of the dopamine system, cerebellum and nucleus ruber, commonly shared in the teleost and human brains. Hibi et al. (2017) review and discuss evolutionary mechanisms that generate the structure and neural circuit diversity of the vertebrate cerebellum. Kumamoto & Hanashima (2017) review pleiotropic roles of a forkhead box protein family gene, Foxg1, in the vertebrate brain development, and discuss its roles in emergence of the telencephalon and its repetitive use in sequential events of the telencephalic development. Nomura & Izawa (2017) focus on avian brains, and introduce developmental aspects of the brain organization and neuronal networks for specific avian behaviors. Noguchi et al. (2017) studied Sema3A expression in embryos of Chinese soft-shelled turtle, chick, ocelot gecko and mouse, and indicated that Sema3A plays a crucial role for neurolal network formation. Hatakeyama et al. (2017) introduce the guinea pig brain as a model system to study mechanisms and principles of cortical folding. We think that vertebrates acquired a basic program for building the brain on the genome at the early stage of divergence, in which the flexibility to create subsequent diversity and innovation was already pre-installed. Then a variety of brains that we are currently observed have been created upon accomplishment of numerous innovations (i.e., mutations, deletions, duplications etc.) on the genome. Recently we have been encountering dramatic advances in techniques for imaging, gene and genome engineering and large-scale sequencing, and are hoping that we will be able to open up the new field of scientific research to understand the evolutionary principle of the brain by studying model and non-model vertebrate animals.