Ontogeny of melanophore photosensitivity in rainbow trout (Oncorhynchus mykiss).
ABSTRACT: Migratory species experience morphological and physiological changes during transitions between different life stages. In particular, modification of sensory systems is critical for animals to adapt to new environments. For example, to prepare for entry into seawater, salmonids undergo smoltification with dramatic changes in ultraviolet photoreceptors and polarized vision, which are important for orientation and foraging behaviours. Extraretinal organs are also involved in photoreception; however, the ontogenetic development of extraretinal photoreceptors is not well known, especially in migratory species. Here, we investigated whether rainbow trout dermal photoreceptors, melanophores, undergo change in spectral sensitivity during smoltification and which candidate molecules may account for this ontogenetic alteration. Our results showed that, contrary to parr melanophores which are insensitive to light, smolt melanophores displayed chromatic photoresponses with the emergence of cryptochrome and melanopsin expression. We suggest that these modifications may benefit the active foraging behaviour of smolts and enable adaptation to variable environments.
Project description:Dermal specialized pigment cells (chromatophores) are thought to be one type of extraretinal photoreceptors responsible for a wide variety of sensory tasks, including adjusting body coloration. Unlike the well-studied image-forming function in retinal photoreceptors, direct evidence characterizing the mechanism of chromatophore photoresponses is less understood, particularly at the molecular and cellular levels. In the present study, cone opsin expression was detected in tilapia caudal fin where photosensitive chromatophores exist. Single-cell RT-PCR revealed co-existence of different cone opsins within melanophores and erythrophores. By stimulating cells with six wavelengths ranging from 380 to 580 nm, we found melanophores and erythrophores showed distinct photoresponses. After exposed to light, regardless of wavelength presentation, melanophores dispersed and maintained cell shape in an expansion stage by shuttling pigment granules. Conversely, erythrophores aggregated or dispersed pigment granules when exposed to short- or middle/long-wavelength light, respectively. These results suggest that diverse molecular mechanisms and light-detecting strategies may be employed by different types of tilapia chromatophores, which are instrumental in pigment pattern formation.
Project description:Multiple sites of extraretinal photoreception are present in vertebrates, but the molecular basis of extraretinal phototransduction is poorly understood. This study reports the cloning of the first opsin specifically expressed in the directly photosensitive pineal and parapineal of cold-blooded vertebrates. This opsin, identified in channel catfish and termed parapinopsin, defines a new gene family of vertebrate photopigments and is expressed in a majority of parapinealocytes and a subset of pineal photoreceptor cells. Parapinopsin shows a caudal-rostral gradient of expression within the pineal organ. This study also reports the cloning of partial cDNAs encoding the channel catfish orthologues of rhodopsin and the red cone pigment-the full complement of retinal opsins in the species. In situ hybridization studies using probes derived from these retinal opsins, together with parapinopsin, reveal no expression of retinal opsins in pineal and parapineal organ and no expression of any opsin tested in the "deep brain," iris, or dermal melanophores. These data imply that phototransduction in these sites of extraretinal photoreception must be mediated by novel opsins.
Project description:Determining location and timing of ontogenetic shifts in the habitat use of highly migratory species, along with possible intrapopulation variation in these shifts, is essential for understanding mechanisms driving alternate life histories and assessing overall population trends. Measuring variations in multi-year habitat-use patterns is especially difficult for remote oceanic species. To investigate the potential for differential habitat use among migratory marine vertebrates, we measured the naturally occurring stable nitrogen isotope (?15 N) patterns that differentiate distinct ocean regions to create a 'regional isotope characterization', analysed the ?15 N values from annual bone growth layer rings from dead-stranded animals, and then combined the bone and regional isotope data to track individual animal movement patterns over multiple years. We used humeri from juvenile North Pacific loggerhead turtles (Caretta caretta), animals that undergo long migrations across the North Pacific Ocean (NPO), using multiple discrete regions as they develop to adulthood. Typical of many migratory marine species, ontogenetic changes in habitat use throughout their decades-long juvenile stage is poorly understood, but each potential habitat has unique foraging opportunities and spatially explicit natural and anthropogenic threats that could affect key life-history parameters. We found a bimodal size/age distribution in the timing that juveniles underwent an ontogenetic habitat shift from the oceanic central North Pacific (CNP) to the neritic east Pacific region near the Baja California Peninsula (BCP) (42·7 ± 7·2 vs. 68·3 ± 3·4 cm carapace length, 7·5 ± 2·7 vs. 15·6 ± 1·7 years). Important to the survival of this population, these disparate habitats differ considerably in their food availability, energy requirements and threats, and these differences can influence life-history parameters such as growth, survival and future fecundity. This is the first evidence of alternative ontogenetic shifts and habitat-use patterns for juveniles foraging in the eastern NPO. We combine two techniques, skeletochronology and stable isotope analysis, to reconstruct multi-year habitat-use patterns of a remote migratory species, linked to estimated ages and body sizes of individuals, to reveal variable ontogeny during the juvenile life stage that could drive alternate life histories and that has the potential to illuminate the migration patterns for other species with accretionary tissues.
Project description:The timing and propensity for migration between fresh- and seawater is a key theme in the diversity of life histories within the salmonid fishes. Across salmonid species, life-history strategies range from wholly freshwater-resident populations, to migratory and nonmigratory variation within populations, to populations and species that are primarily migratory. Despite the central theme of migration to the evolution of these fishes, the genetic architecture of migration-related processes is poorly understood. Using a genetic cross of clonal lines derived from migratory and nonmigratory life-history types of Onchorhynchus mykiss (steelhead and rainbow trout, respectively), we have dissected the genetic architecture of the complex physiological and morphological transformation that occurs immediately prior to seaward migration (termed smoltification). Quantitative trait loci (QTL) analyses were used to identify the number, effects, and genomic location of loci associated with smoltification-related traits, including growth and condition factor, body coloration, morphology, and osmoregulatory enzymes during the smoltification period. Genetic analyses revealed numerous QTL, but one locus in particular is associated with multiple traits in single and joint analyses. Dissecting the genetic architecture of this highly complex trait has profound implications for understanding the genetic and evolutionary basis of life-history diversity within and among migratory fishes.
Project description:The body coloration of animals is due to pigment cells derived from neural crest cells, which are multipotent and differentiate into diverse cell types. Medaka (Oryzias latipes) possesses four distinct types of pigment cells known as melanophores, xanthophores, iridophores, and leucophores. The few melanophore (fm) mutant of medaka is characterized by reduced numbers of melanophores and leucophores. We here identify kit-ligand a (kitlga) as the gene whose mutation gives rise to the fm phenotype. This identification was confirmed by generation of kitlga knockout medaka and the findings that these fish also manifest reduced numbers of melanophores and leucophores and fail to rescue the fm mutant phenotype. We also found that expression of sox5, pax7a, pax3a, and mitfa genes is down-regulated in both fm and kitlga knockout medaka, implicating c-Kit signaling in regulation of the expression of these genes as well as the encoded transcription factors in pigment cell specification. Our results may provide insight into the pathogenesis of c-Kit-related pigmentation disorders such as piebaldism in humans, and our kitlga knockout medaka may prove useful as a tool for drug screening.
Project description:"White pigment cells" are derived from melanophore precursors and contain both melanophore-specific and iridophore-specific pigment organelles. Whereas melanophores differentiate in the wild type regenerating tail, white pigment cells appear in the regenerating tail in the periodic albino mutant (a(p)/a(p)) of Xenopus laevis. The localization and density of white pigment cells in the mutant regenerating tail are similar to those of melanophores in the wild type regenerating tail. Here, white pigment cells in the mutant regenerating tail have been compared with melanophores in the wild type regenerating tail in the presence of phenylthiourea (PTU), which inhibits melanosome maturation in melanophores but does not affect reflecting platelet formation in white pigment cells. Ultrastructural analysis shows that reflecting platelet formation in white pigment cells is different from that in iridophores. Reflecting platelets in iridophores are formed from spherical vesicles with electron-dense material, whereas they are formed from stage II melanosomes characteristic of melanophore precursors in white pigment cells. Ultrastructural features of pigment organelles, except reflecting platelets, are similar between mutant melanophores and white pigment cells. In an attempt to identify specific genes in white pigment cells, a subtracted cDNA library enriched for mutant cDNAs has been prepared. Subtracted cDNA fragments have been cloned and selected by whole mount in situ hybridization. Among cDNA fragments examined so far, the ferritin H subunit gene is specifically expressed in white pigment cells, but not in melanophores. Pigment organellogenesis and specific gene expression in white pigment cells are also discussed.
Project description:The zebrafish adult pigment pattern has emerged as a useful model for understanding the development and evolution of adult form as well as pattern-forming mechanisms more generally. In this species, a series of horizontal melanophore stripes arises during the larval-to-adult transformation, but the genetic and cellular bases for stripe formation remain largely unknown. Here, we show that the seurat mutant phenotype, consisting of an irregular spotted pattern, arises from lesions in the gene encoding Immunoglobulin superfamily member 11 (Igsf11). We find that Igsf11 is expressed by melanophores and their precursors, and we demonstrate by cell transplantation and genetic rescue that igsf11 functions autonomously to this lineage in promoting adult stripe development. Further analyses of cell behaviors in vitro, in vivo, and in explant cultures ex vivo demonstrate that Igsf11 mediates adhesive interactions and that mutants for igsf11 exhibit defects in both the migration and survival of melanophores and their precursors. These findings identify the first in vivo requirements for igsf11 as well as the first instance of an immunoglobulin superfamily member functioning in pigment cell development and patterning. Our results provide new insights into adult pigment pattern morphogenesis and how cellular interactions mediate pattern formation.
Project description:Development in foraging behaviour and dietary intake of many vertebrates are age-structured. Differences in feeding ecology may correlate with ontogenetic shifts in dispersal patterns, and therefore affect foraging habitat and resource utilization. Such life-history traits have important implications in interpreting tropho-dynamic linkages. Stable isotope ratios in the whiskers of sub-yearling southern elephant seals (Mirounga leonina; n?=?12) were used, in conjunction with satellite telemetry and environmental data, to examine their foraging habitat and diet during their first foraging migration. The trophic position of seals from Macquarie Island (54°30'S, 158°57'E) was estimated using stable carbon (?(1) (3)C) and nitrogen (?(15)N) ratios along the length of the whisker, which provided a temporal record of prey intake. Satellite-relayed data loggers provided details on seal movement patterns, which were related to isotopic concentrations along the whisker. Animals fed in waters south of the Polar Front (>60°S) or within Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Statistical Subareas 88.1 and 88.2, as indicated by both their depleted ?(1) (3)C (<-20‰) values, and tracking data. They predominantly exploited varying proportions of mesopelagic fish and squid, and crustaceans, such as euphausiids, which have not been reported as a prey item for this species. Comparison of isotopic data between sub-yearlings, and 1, 2 and 3 yr olds indicated that sub-yearlings, limited by their size, dive capabilities and prey capture skills to feeding higher in the water column, fed at a lower trophic level than older seals. This is consistent with the consumption of euphausiids and most probably, Antarctic krill (Euphausia superba), which constitute an abundant, easily accessible source of prey in water masses used by this age class of seals. Isotopic assessment and concurrent tracking of seals are successfully used here to identify ontogenetic shifts in broad-scale foraging habitat use and diet preferences in a highly migratory predator.
Project description:Light perception in birds is composed of the retina and extraretinal sites, located in the brain. Previous studies indicate that selective photostimulation of the eye decreased reproductive performance, whereas extraretinal photostimulation increases it. Differential photostimulation of the retina and extraretinal sites is based on the retina's sensitivity to green wavelengths and on the red wavelengths' ability to penetrate body tissues. We previously found that short-day exposure to green light within a long-day exposure to red light increases reproductive activity in female turkeys and broiler breeder hens. Furthermore, in a study conducted recently in our laboratory, we found that blue light repressed expression of green light receptor in the retina, which can further enhance reproduction activity in broiler breeders. Here, we examined the "brain activate/eye deactivate" hypothesis on gonadal axis activity and reproductive performance in a broiler breeder flock. Broiler breeder hens and roosters (ROSS 308) were divided into 5 light-treatment groups (controlled rooms with light-emitting diodes [LED] lamps): warm white (control), long-day (14 h) red (630 nm) and short-day (6 h) green (514 nm) (red-green), long-day green and short-day red (green-red), long-day red and short-day blue (456 nm) (red-blue), and long-day blue and short-day red (blue-red). Birds were reared from 20 to 55 wk of age. Eggs were collected daily. Weekly egg production calculated. All eggs were incubated for fertility and hatchability examination. Blood was drawn monthly for plasma analysis. At 35 wk of age (after peak production) and 55 wk of age (end of the experiment), 10 hens from each treatment group were euthanized, and selected tissues and glands were taken for gene expression trials. Providing long-day red light to extraretinal photoreceptors while maintaining retinal photoreceptors on short day with blue or green light significantly improved reproductive activities, manifested by elevated egg production and gonadal axis activity compared with Controls and primary breeder recommendations. Long-day green light reduced reproductive performances. We suggest that targeted photostimulation enhances reproductive and gonadal axis activities in broiler breeders.
Project description:Spiders show a repertoire of strategies to increase their foraging success. In particular, some orb-weaver spiders use attractive body colorations to lure prey. Interestingly, coloration varies with age in many species, which may result in ontogenetic variation of foraging success. By using field observations, laboratory experiments and spectrophotometric analysis, we investigated whether pale juveniles and bright adults of the orb-weaver Alpaida tuonabo use different foraging strategies due to ontogenetic variation in coloration. Field observations revealed that foraging success of juveniles and adults was influenced by web properties. However, foraging success increased with body size only in adults, supporting the idea that larger individuals produce a stronger visual signal for prey. The attractiveness of the adult coloration for prey was confirmed in the laboratory with frame-web-choice experiments, in which webs bearing a spider intercepted more bees than empty webs. Our spectrophotometric analysis suggests that the yellow coloration may produce the deceiving signal for prey. Moreover, we identified potential alternative foraging strategies: cryptic juveniles at higher heights and 'attractive' adults at lower heights. This study reveals how ontogenetic colour variation may favour the use of alternative foraging strategies in orb-weaver spiders and reduces intraspecific competition.