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Abstract Background Long wave-sensitive (LWS) opsin genes have undergone multiple lineage-specific duplication events throughout the evolution of teleost fishes. LWS repertoire expansions in live-bearing fishes (family Poeciliidae) have equipped multiple species in this family with up to four LWS genes. Given that color vision, especially attraction to orange male coloration, is important to mate choice within poeciliids, LWS opsins have been proposed as candidate genes driving sexual selection in this family. To date the genomic organization of these genes has not been described in the family Poeciliidae, and little is known about the mechanisms regulating the expression of LWS opsins in any teleost. Results Two BAC clones containing the complete genomic repertoire of LWS opsin genes in the green swordtail fish, Xiphophorus helleri, were identified and sequenced. Three of the four LWS loci identified here were linked in a tandem array downstream of two tightly linked short wave-sensitive 2 (SWS2) opsin genes. The fourth LWS opsin gene, containing only a single intron, was not linked to the other three and is the product of a retrotransposition event. Genomic and phylogenetic results demonstrate that the LWS genes described here share a common evolutionary origin with those previously characterized in other poeciliids. Using qualitative RT-PCR and MSP we showed that each of the LWS and SWS2 opsins, as well as three other cone opsin genes and a single rod opsin gene, were expressed in the eyes of adult female and male X. helleri, contributing to six separate classes of adult retinal cone and rod cells with average λmax values of 365 nm, 405 nm, 459 nm, 499 nm, 534 nm and 568 nm. Comparative genomic analysis identified two candidate teleost opsin regulatory regions containing putative CRX binding sites and hormone response elements in upstream sequences of LWS gene regions of seven teleost species, including X. helleri. Conclusions We report the first complete genomic description of LWS and SWS2 genes in poeciliids. These data will serve as a reference for future work seeking to understand the relationship between LWS opsin genomic organization, gene expression, gene family evolution, sexual selection and speciation in this fish family.

Abstract Background Cichlid fishes have radiated into hundreds of species in the Great Lakes of Africa. Brightly colored males display on leks and vie to be chosen by females as mates. Strong discrimination by females causes differential male mating success, rapid evolution of male color patterns and, possibly, speciation. In addition to differences in color pattern, Lake Malawi cichlids also show some of the largest known shifts in visual sensitivity among closely related species. These shifts result from modulated expression of seven cone opsin genes. However, the mechanisms for this modulated expression are unknown. Results In this work, we ask whether these differences might result from changes in developmental patterning of cone opsin genes. To test this, we compared the developmental pattern of cone opsin gene expression of the Nile tilapia, Oreochromis niloticus, with that of several cichlid species from Lake Malawi. In tilapia, quantitative polymerase chain reaction showed that opsin gene expression changes dynamically from a larval gene set through a juvenile set to a final adult set. In contrast, Lake Malawi species showed one of two developmental patterns. In some species, the expressed gene set changes slowly, either retaining the larval pattern or progressing only from larval to juvenile gene sets (neoteny). In the other species, the same genes are expressed in both larvae and adults but correspond to the tilapia adult genes (direct development). Conclusion Differences in visual sensitivities among species of Lake Malawi cichlids arise through heterochronic shifts relative to the ontogenetic pattern of the tilapia outgroup. Heterochrony has previously been shown to be a powerful mechanism for change in morphological evolution. We found that altering developmental expression patterns is also an important mechanism for altering sensory systems. These resulting sensory shifts will have major impacts on visual communication and could help drive cichlid speciation.

Visual systems adapt to different light environments through several avenues including optical changes to the eye and neurological changes in how light signals are processed and interpreted. Spectral sensitivity can evolve via changes to visual pigments housed in the retinal photoreceptors through gene duplication and loss, differential and coexpression, and sequence evolution. Frogs provide an excellent, yet understudied, system for visual evolution research due to their diversity of ecologies (including biphasic aquatic-terrestrial life cycles) that we hypothesize imposed different selective pressures leading to adaptive evolution of the visual system, notably the opsins that encode the protein component of the visual pigments responsible for the first step in visual perception. Here, we analyze the diversity and evolution of visual opsin genes from 93 new eye transcriptomes plus published data for a combined dataset spanning 122 frog species and 34 families. We find that most species express the four visual opsins previously identified in frogs but show evidence for gene loss in two lineages. Further, we present evidence of positive selection in three opsins and shifts in selective pressures associated with differences in habitat and life history, but not activity pattern. We identify substantial novel variation in the visual opsins and, using microspectrophotometry, find highly variable spectral sensitivities, expanding known ranges for all frog visual pigments. Mutations at spectral-tuning sites only partially account for this variation, suggesting that frogs have used tuning pathways that are unique among vertebrates. These results support the hypothesis of adaptive evolution in photoreceptor physiology across the frog tree of life in response to varying environmental and ecological factors and further our growing understanding of vertebrate visual evolution. [ABSTRACT FROM AUTHOR]

Since its introduction to Harp Lake, Ontario, Canada, summer abundance of the cladoceran zooplanktivore Bythotrephes longimanus has fluctuated substantially both among and within years. The principal planktivorous fish in Harp Lake is the cold-water Coregonus artedi (cisco). Previous studies hypothesized that Bythotrephes abundance was affected by the thickness of an ephemeral, dark, daytime refuge from cisco that potentially established at the bottom of the metalimnion. During summer of 2003, we estimated peak daytime refuge thickness by simulating light energy visible to cisco and found it was always negative and did not correlate with Bythotrephes death rates. Direct observations using gill- netting and acoustical methods suggested that cisco had frequent metalimnetic forays. Additionally, including years 2000-2004, the previous correlation between mean Bythotrephes abundance and refuge thickness no longer held. The refuge hypothesis appears to fail, as the amount of metalimnetic illumination was always above the level at which cisco reaction distance to prey is maximal. Selection of Bythotrephes by cisco instead appeared to increase once Bythotrephes became abundant, remaining consistent and nontrivial even after Bythotrephes population declined. Resume : Depuis son introduction au lac Harp, Ontario, Canada, l'abondance en ete du cladocere Bythotrephes longimanus, consommateur de zooplancton, a varie considerablement, tant dune annee a fautre qu'au tours dune meme annee. Le principal poison planctonophage au lac Harp est le cisco de lac, Coregonus artedi, qui vit en eau froide. Des etudes anterieures ont emis l'hypothese selon laquelle l'abondance de Bythotrephes est affectee par l'epaisseur durant le jour dune zone ephemere et sombre de refuge a fabri des ciscos qui pourrait se former au bas du metalimnion. Durant l'ete 2003, nous avons estime l'epaisseur maximale de ce refuge de jour en simulant l'energie lumineuse visible aux ciscos et avons trouve qu'elle etait toujours negative et sans correlation avec les taux de mortalite des Bythotrephes. Des observations directes avec des filets maillants et des methodes acoustiques indiquent que les ciscos font des incursions frequentes dans le metalimnion. De plus, lorsqu'on bent compte des annees 2000-2004, la correlation anterieure entre l'abondance moyenne de Bythotrephes et l'epaisseur du refuge ne bent plus. L'hypothese du refuge semble donc ne pas s'appliquer, puisque fintensite lumineuse dans le metalimnion est toujours superieure au niveau auquel la distance de reaction des ciscos a leur proie est maximale. La selection des Bythotrephes par les ciscos semble augmenter lorsque l'abondance des Bythotrephes est elevee et elle demeure soutenue et non negligeable meme apres le declin de la population de Bythotrephes. [Traduit par la Redaction], Introduction Bythotrephes longimanus is a large (~ 3 mm) Palaearctic cladoceran that was introduced to North America prior to 1982 (Johannsson et al. 1991), and since has spread to more [...]

Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis relicta. We monitored the vertical movements and depth selection behavior of mysids exposed to different light intensities and light-temperature gradients in the laboratory and derived a mysid light preference function in units relevant to mysid vision: 'mylux'. Mysids preferred light levels between [10.sup.-8] and [10.sup.-7] mylux (~[10.sup.-6] to [10.sup.-5] lux) and rarely moved into waters of [10.sup.-3] mylux (~0.1 lux) and greater. A model that assumed equal weight and independence of mysid light and temperature preference functions successfully predicted the proportion of mysids found in two different temperature-light combinations in the laboratory. This model also predicted the depth of maximum mysid density to within 2 m on two spring nights and within 5 m on two summer nights of varying moon phase and thermal conditions in Lake Ontario. This study provides novel insights into how temperature and light interact to influence the vertical distribution of mysids. Our model may be used to predict mysid vertical distribution in any deepwater system inhabited by mysids in which the primary mysid predators are visual feeders. La lumiere et la temperature influencent fortement la repartition verticale des mysis, Mysis relicta. Nous avons note les deplacements verticaux et le comportement de selection de profondeur de mysis exposes a differentes intensites lumineuses et a des gradients de lumiere-temperature en laboratoire et avons mis au point une fonction de preference lumineuse des mysis en unites [much less than] mylux [much greater than] qui sont compatibles avec la vision des mysis. Les mysis preferent des intensites lumineuses de [10.sup.-8] a [10.sup.-7] mylux (~[10.sup.-6] a [10.sup.-5] lux) et penetrent rarement dans des eaux de [10.sup.-3] mylux (~0,1 lux) ou plus. Un modele qui presume un poids egal et une independance des fonctions de preference de lumiere et de temperature des mysis predit avec succes les proportions de mysis retrouvees dans deux combinaisons differentes de temperature-lumiere en laboratoire. Ce modele predit aussi la profondeur de densite maximale des mysis avec une precision de 2 m lors de deux nuits de printemps et une precision de 5 m lors de deux nuits d'ete de phase lunaire et de conditions thermiques differentes au lac Ontario. Notre etude ouvre des perspectives nouvelles sur l'influence de l'interaction de la temperature et de la lumiere sur la repartition verticale des mysis. Notre modele peut servir a predire la repartition verticale des mysis dans n'importe quel systeme d'eau profonde habite par les mysis et dans lequel les principaux predateurs des mysis se nourrissent a vue. [Traduit par la Redaction], Introduction Zooplankton diel vertical migration (DVM) is a widely occurring and well-documented phenomenon in both marine and freshwater ecosystems (Hamner 1988; Haney 1988). Although a vast literature exists on the [...]