Convergent Evolutionary Dead-End and Breakdown of Hard Chorion in Parental-Egg-Care Fish Reproductive Strategies.

Fish exhibit a diverse array of reproductive strategies adapted to various ecological niches. Parental egg-care, including live-bearing, mouth-brooding, and male egg protection by brood pouches, represents an effective strategy for ensuring larval survival and has emerged independently in multiple lineages. Despite the recognised evolutionary bias that favours a strategy transition from non-carer to egg-carer, the genetic mechanisms underlying this bias and the commonalities among parental egg-care species remain elusive.

Possible Involvement of Ghost Introgressions in the Striking Diversity of Vomeronasal Type 1 Receptor Genes in East African Cichlids.

Cichlids that have undergone adaptive radiation are genetically close but exhibit extreme ecological and morphological diversity, making them useful for understanding speciation mechanisms. Vomeronasal type 1 receptors (V1R) are highly conserved among teleost fish at the amino acid sequence level and are believed to play a fundamental role in reproduction. We previously reported the surprisingly high sequence diversity of V1Rs among certain cichlid species, suggesting a possible role for V1Rs in their speciation.

Ventral-to-dorsal electrocyte development in electric organs of electric eel (Electrophorus).

Electric eels (Electrophorus) are renowned for their ability to generate electric discharge, which is used for prey capture and defense. Their electric organs (EOs) are located along the lateral-ventral region of the tail and contain electrocytes, which are multinucleated syncytium cells. The developmental origin of the electrocyte is mesodermal lineage cells observed in the ventral part of the myotome.

Pronounced expression of extracellular matrix proteoglycans regulated by Wnt pathway underlies the parallel evolution of lip hypertrophy in East African cichlids.

Cichlid fishes inhabiting the East African Great Lakes, Victoria, Malawi, and Tanganyika, are textbook examples of parallel evolution, as they have acquired similar traits independently in each of the three lakes during the process of adaptive radiation. In particular, 'hypertrophied lip' has been highlighted as a prominent example of parallel evolution. However, the underlying molecular mechanisms remain poorly understood.

Type 2 vomeronasal receptor expression in the olfactory organ of African lungfish, Protopterus annectens.

The olfactory organ of tetrapods, with few exceptions, comprises the main and accessory organs: olfactory epithelium (OE) and vomeronasal organ (VNO). Unlike tetrapods, teleost fish lack a VNO. However, lungfish, a type of sarcopterygian fish closely related to tetrapods, possesses a lamellar OE similar to the OE of teleosts and a recess epithelium (RecE) resembling the amphibian VNO.

Severe Bottleneck Impacted the Genomic Structure of Egg-Eating Cichlids in Lake Victoria.

Within 15,000 years, the explosive adaptive radiation of haplochromine cichlids in Lake Victoria, East Africa, generated 500 endemic species. In the 1980s, the upsurge of Nile perch, a carnivorous fish artificially introduced to the lake, drove the extinction of more than 200 endemic cichlids. The Nile perch predation particularly harmed piscivorous cichlids, including paedophages, cichlids eat eggs and fries, which is an example of the unique trophic adaptation seen in African cichlids.

Localized Expression of Olfactory Receptor Genes in the Olfactory Organ of Common Minke Whales.

Baleen whales (Mysticeti) possess the necessary anatomical structures and genetic elements for olfaction. Nevertheless, the gene () repertoire has undergone substantial degeneration in the cetacean lineage following the divergence of the Artiodactyla and Cetacea. The functionality of highly degenerated mysticete s within their olfactory epithelium remains unknown.

In situ hybridization analysis of odorant receptor expression in the olfactory organ of the pig-nosed turtle Carettochelys insculpta.

The turtle olfactory organ consists of upper (UCE) and lower (LCE) chamber epithelium, which send axons to the ventral and dorsal portions of the olfactory bulbs, respectively. Generally, the UCE is associated with glands and contains ciliated olfactory receptor neurons (ORNs), while the LCE is devoid of glands and contains microvillous ORNs. However, the olfactory organ of the pig-nosed turtle Carettochelys insculpta appears to be a single olfactory system morphologically: there are no associated glands; ciliated ORNs are distributed throughout the olfactory organ; and the olfactory bulb is not divided into ventral and dorsal portions.

Expression of type 1 vomeronasal receptors in the olfactory organ of the African lungfish, Protopterus dolloi.

The vomeronasal organ is an olfactory organ found in amphibians and higher vertebrates. Type 1 vomeronasal receptors, one of the major olfactory receptors in vertebrates, are expressed in the vomeronasal organ in mammals. In amphibians and fish, they are expressed in the olfactory epithelium.

Plastic loss of motile cilia in the gills of in response to high CO or terrestrial environments.

The evolutionary transition of vertebrates from water to land during the Devonian period was accompanied by major changes in animal respiratory systems in terms of physiology and morphology. Indeed, the fossil record of the early tetrapods has revealed the existence of internal gills, which are vestigial fish-like traits used underwater. However, the fossil record provides only limited data on the process of the evolutionary transition of gills from fish to early tetrapods.

Type 1 vomeronasal receptor expression in juvenile and adult lungfish olfactory organ.

Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods.

c-fos expression in the olfactory epithelium of the East African cichlid (Haplochromis chilotes) in response to odorant exposure.

Fishes use olfaction to gain varied information vital for survival and communication. To understand biodiversity in fishes, it is important to identify what receptors individual fish use to detect specific chemical compounds. However, studies of fish olfactory receptors and their ligands are still limited to a few model organisms represented primarily by zebrafish.

Type 1 vomeronasal receptors expressed in the olfactory organs of two African lungfish, Protopterus annectens and Protopterus amphibius.

Lungfish are the fish related most closely to tetrapods. The olfactory organ of lungfish contains two distinct sensory epithelia: the lamellar olfactory epithelium (OE) and the recess epithelium (RecE). Based on their ultrastructural and histological characteristics, the lamellar OE and the RecE are considered to correspond respectively to the teleost OE and a primitive vomeronasal organ (VNO).

SINEs as Credible Signs to Prove Common Ancestry in the Tree of Life: A Brief Review of Pioneering Case Studies in Retroposon Systematics.

Currently, the insertions of SINEs (and other retrotransposed elements) are regarded as one of the most reliable synapomorphies in molecular systematics. The methodological mainstream of molecular systematics is the calculation of nucleotide (or amino acid) sequence divergences under a suitable substitution model. In contrast, SINE insertion analysis does not require any complex model because SINE insertions are unidirectional and irreversible.

Alternative splicing plays key roles in response to stress across different stages of fighting in the fish Betta splendens.

Background: Aggression is an evolutionarily conserved behavior critical for animal survival. In the fish Betta splendens, across different stages of fighting interactions, fighting opponents suffer from various stressors, especially from the great demand for oxygen. Using RNA sequencing, we profiled differential alternative splicing (DAS) events in the brains of fish collected before fighting, during fighting, and after fighting to study the involvement of alternative splicing (AS) in the response to stress during the fight.

New Sex Chromosomes in Lake Victoria Cichlid Fishes (Cichlidae: Haplochromini).

African cichlid fishes harbor an extraordinary diversity of sex-chromosome systems. Within just one lineage, the tribe Haplochromini, at least 6 unique sex-chromosome systems have been identified. Here we focus on characterizing sex chromosomes in cichlids from the Lake Victoria basin.

Remarkable diversity of vomeronasal type 2 receptor (OlfC) genes of basal ray-finned fish and its evolutionary trajectory in jawed vertebrates.

The vomeronasal type 2 receptor (V2R, also called OlfC) multigene family is found in a broad range of jawed vertebrates from cartilaginous fish to tetrapods. V2Rs encode receptors for food-related amino acids in teleost fish, whereas for peptide pheromones in mammals. In addition, V2Rs of teleost fish are phylogenetically distinct from those of tetrapods, implying a drastic change in the V2R repertoire during terrestrial adaptation.

A transcriptomic reevaluation of the accessory olfactory organ in Bichir (Polypterus senegalus).

Fish possess one olfactory organ called the olfactory epithelium (OE), by which various chemical substances are detected. On the other hand, tetrapods possess two independent olfactory organs called the main olfactory epithelium (MOE) and vomeronasal organ (VNO), each of which mainly detects general odorants and pheromones, respectively. Traditionally, the VNO, so-called concentrations of vomeronasal neurons, was believed to have originated in tetrapods.

Genomic Signatures for Species-Specific Adaptation in Lake Victoria Cichlids Derived from Large-Scale Standing Genetic Variation.

The cichlids of Lake Victoria are a textbook example of adaptive radiation, as >500 endemic species arose in just 14,600 years. The degree of genetic differentiation among species is very low due to the short period of time after the radiation, which allows us to ascertain highly differentiated genes that are strong candidates for driving speciation and adaptation. Previous studies have revealed the critical contribution of vision to speciation by showing the existence of highly differentiated alleles in the visual opsin gene among species with different habitat depths.