Rapid body colouration changes in some animals, such as chameleons and octopuses, serve dual functions: camouflage and intraspecific communication. It has been hypothesized that these colouration changes originally evolved to provide camouflage and subsequently were co-opted as social signals; however, experimental model systems that are suitable for studying such evolutionary processes are limited. Here, we investigated the relationship between rapid colouration changes of the blackened markings and aggressive behaviours in male Oryzias celebensis, an Indonesian medaka fish, under triadic relationships (two males and one female) or three males conditions with two different environmental backgrounds. In an algae-covered tank, mimicking the common laboratory rearing conditions, males with blackened markings exhibited more frequent attacks towards different conspecific individuals compared with non-blackened males and females. The blackened males were seldom attacked by non-blackened males and females. By contrast, neither aggressive behaviours nor black colouration changes were observed in the transparent background condition with a brighter environment. These indicated that the blackened markings in O. celebensis serve as a social signal depending on the environmental backgrounds. Considering that such colouration changes for camouflage are widely conserved among teleost fishes, the traits are likely to be co-opted for displaying social signals in O. celebensis.

[This corrects the article DOI: 10.3389/fpsyg.2023.1176067.].

Sexual selection involving female choice or female preference (\'inter-sexual\' selection) and/or male-male competition (\'intra-sexual\' selection) is one of the key mechanisms for evolutionary diversification and speciation. In particular, sexual selection is recently suggested to be an important mode to drive the evolution of the \"novel\" phenotype (i.e., \"evolutionary novelty\"). Despite extensive studies performed on sexually selected traits or male-specific ornaments (or weapon-like structures) with respect to their evolutionary origin, history and fitness benefits, relatively little is known about the molecular genetic mechanisms underlying their developmental process. However, with advances in genomic technologies (including whole transcriptome analysis using Next Generation Sequencing [NGS] techniques; RNA-Seq), progress has been made to unveil the genetic background underpinning diverse sexually selected traits in different animal taxa. In the present review, empirical data on the genes, genetic mechanisms, or regulatory pathways underlying various sexually selected traits were compiled to explore whether \"common\" genetic architectures shape the development and evolution of these traits across evolutionarily distant animal lineages. It is shown that the recruitment of the pre-existing genetic network for a new purpose (i.e., gene network \"co-option\") is rather widespread in the development and evolution of sexually selected traits, indicating that particular genes or gene sets are repeatedly involved in different sexually selected traits. Information on genes or genetic mechanisms regulating the development of sexually selected traits is an essential piece to complete a whole picture of the origin and evolution of sexually selected traits.

Odorant binding proteins (OBPs) are small water-soluble proteins mainly associated with olfaction, facilitating the transport of odorant molecules to their relevant receptors in the sensillum lymph. While traditionally considered essential for olfaction, recent research has revealed that OBPs are engaged in a diverse range of physiological functions in modulating chemical communication and defense. Over the past 10 years, emerging evidence suggests that OBPs play vital roles in purifying the perireceptor space from unwanted xenobiotics including plant volatiles and pesticides, potentially facilitating xenobiotic adaptation, such as host location, adaptation, and pesticide resistance. This multifunctionality can be attributed, in part, to their structural variability and effectiveness in transporting, sequestering, and concealing numerous hydrophobic molecules. Here, we firstly overviewed the classification and structural properties of OBPs in diverse insect orders. Subsequently, we discussed the myriad of functional roles of insect OBPs in communication and their adaptation to xenobiotics. By synthesizing the current knowledge in this field, our review paper contributes to a comprehensive understanding of the significance of insect OBPs in chemical ecology, xenobiotic adaptation, paving the way for future research in this fascinating area of study.

The development of complex phenotypes requires the coordinated action of many genes across space and time, yet many species have evolved the ability to develop multiple discrete, alternate phenotypes1-3. Such polymorphisms are often controlled by supergenes, sets of tightly-linked mutations in one or more loci that function together to produce a complex phenotype4. Although theories of supergene evolution are well-established, the mutations that cause functional differences between supergene alleles remain essentially unknown. doublesex is the master regulator of insect sexual differentiation but functions as a supergene in multiple Papilio swallowtail butterflies, where divergent dsx alleles control development of discrete non-mimetic or mimetic female wing color patterns5-7. Here we demonstrate that the functional elements of the mimetic allele in Papilio alphenor are six new cis-regulatory elements (CREs) spread across 150 kb that are bound by DSX itself. Our findings provide experimental support to classic supergene theory and suggest that the evolution of auto-regulation may provide a simple route to supergene origination and to the co-option of pleiotropic genes into new developmental roles.

Animals consume a wide variety of food sources to adapt to different environments. However, the genetic mechanisms underlying the acquisition of evolutionarily novel feeding morphology remain largely unknown. While the nematode Caenorhabditis elegans feeds on bacteria, the satellite species Pristionchus pacificus exhibits predatory feeding behavior toward other nematodes, which is an evolutionarily novel feeding habit. Here, we found that the astacin metalloprotease Ppa-NAS-6 is required for the predatory killing by P. pacificus. Ppa-nas-6 mutants were defective in predation-associated characteristics, specifically the tooth morphogenesis and tooth movement during predation. Comparison of expression patterns and rescue experiments of nas-6 in P. pacificus and C. elegans suggested that alteration of the spatial expression patterns of NAS-6 may be vital for acquiring predation-related traits. Reporter analysis of the Ppa-nas-6 promoter in C. elegans revealed that the alteration in expression patterns was caused by evolutionary changes in cis- and trans-regulatory elements. This study suggests that the co-option of a metalloprotease is involved in an evolutionarily novel feeding morphology.

For 25 years, the predominant evolutionary theory of romantic love has been Fisher\'s theory of independent emotion systems. That theory suggests that sex drive, romantic attraction (romantic love), and attachment are associated with distinct neurobiological and endocrinological systems which evolved independently of each other. Psychological and neurobiological evidence, however, suggest that a competing theory requires attention. A theory of co-opting mother-infant bonding sometime in the recent evolutionary history of humans may partially account for the evolution of romantic love. I present a case for this theory and a new approach to the science of romantic love drawing on human psychological, neurobiological, and (neuro)endocrinological studies as well as animal studies. The hope is that this theoretical review, along with other publications, will generate debate in the literature about the merits of the theory of co-opting mother-infant bonding and a new evolutionary approach to the science of romantic love.

The emergence of sporophytes, that is, diploid multicellular bodies in plants, facilitated plant diversification and the evolution of complexity. Although sporophytes may have evolved in an ancestral alga exhibiting a haplontic life cycle with a unicellular diploid and multicellular haploid (gametophyte) phase, the mechanism by which this novelty originated remains largely unknown. Ulotrichalean marine green algae (Ulvophyceae) are one of the few extant groups with haplontic-like life cycles. In this study, we show that zygotes of the ulotrichalean alga Monostroma angicava, which usually develop into unicellular cysts, exhibit a developmental variation producing multicellular reproductive sporophytes. Multicellular development likely occurred stochastically in individual zygotes, but its ratio responded plastically to growth conditions. Sporophytes showed identical morphological development to gametophytes, which should reflect the expression of the same genetic programme directing multicellular development. Considering that sporophytes were evolutionarily derived in Ulotrichales, this implies that sporophytes emerged by co-opting the gametophyte developmental programme to the diploid phase. This study suggests a possible mechanism of sporophyte formation in haplontic life cycles, contributing to the understanding of the evolutionary transition from unicellular to multicellular diploid body plans in green plants.

Zhao et al. recently reported results which, they claim, suggest that sexual selection produces the multimodal displays seen in little torrent frogs (Amolops torrentis) by co-opting limb movements that originally evolved to support parasite defense (Zhao et al., 2022). Here, we explain why we believe this conclusion to be premature.

Orchids parasitically depend on external nutrients from mycorrhizal fungi for seed germination. Previous findings suggest that orchids utilize a genetic system of mutualistic arbuscular mycorrhizal (AM) symbiosis, in which the plant hormone gibberellin (GA) negatively affects fungal colonization and development, to establish parasitic symbiosis. Although GA generally promotes seed germination in photosynthetic plants, previous studies have reported low sensitivity of GA in seed germination of mycoheterotrophic orchids where mycorrhizal symbiosis occurs concurrently. To elucidate the connecting mechanisms of orchid seed germination and mycorrhizal symbiosis at the molecular level, we investigated the effect of GA on a hyacinth orchid (Bletilla striata) seed germination and mycorrhizal symbiosis using asymbiotic and symbiotic germination methods. Additionally, we compared the transcriptome profiles between asymbiotically and symbiotically germinated seeds. Exogenous GA negatively affected seed germination and fungal colonization, and endogenous bioactive GA was actively converted to the inactive form during seed germination. Transcriptome analysis showed that B. striata shared many of the induced genes between asymbiotically and symbiotically germinated seeds, including GA metabolism- and signaling-related genes and AM-specific marker homologs. Our study suggests that orchids have evolved in a manner that they do not use bioactive GA as a positive regulator of seed germination and instead autoactivate the mycorrhizal symbiosis pathway through GA inactivation to accept the fungal partner immediately during seed germination.