The developmental and genetic trajectory of coloration in the guppy (Poecilia reticulata)

Correlation of skin color and plasma carotenoid-related metabolites of ornamental koi carp under temperature fluctuations

The skin color of koi carp (Cyprinus carpio L.) is one of the traits that most influence their ornamental and economic values. The present study suggested the effects of temperature fluctuation on koi carp in terms of skin color and plasma carotenoids and related-metabolites. The main results were as follows. (1) The vulnerability of koi skin color to acute temperature stress was in the order of white koi> black koi> yellow koi. Both high- (25°C-30°C-25°C) and low-temperature (25°C-20°C-25°C) fluctuations tended to decrease the saturation of white koi. The temperature fluctuation had little effects on the skin color of black and yellow koi. (2) Targeted metabolomics analysis indicated that the effects of cooling stress on oxycarotenoids of all five koi varieties were reversible. The plasma oxycarotenoids in mirror koi with all colors were insensitive to acute heat stress. However, the cooling process from a high temperature (30°C-25°C) still made contributions to the increase of oxycarotenoids. (3) The principal component analysis confirmed the deviation of carotenoid-related metabolites after high temperature fluctuation and the reversibility after low temperature fluctuation. Finally, the correlation analysis revealed that koi skin brightness was negatively correlated with the plasma guanine content and that temperature fluctuations might change koi skin brightness via the L(-)-epinephrine-guanine pathway. The red hue and yellow hue were negatively correlated with the oxycarotenoids in plasma, suggesting that oxycarotenoids were favorable for enhancing koi skin color saturation. Overall, this study revealed the direct action of temperature fluctuations on the skin color and carotenoid-related metabolites of koi.

Triphenyltin exposure induced abnormal morphological colouration in adult male guppies (Poecilia reticulata)

Fish morphological colouration is essential for their survival and reproduction success; however, it is vulnerable to environmental factors, such as pollutants. Triphenyltin (TPT) is widespread in aquatic ecosystems, and its impacts on fish have been problematic. Therefore, the purpose of this study was to investigate the effects of TPT at environment-related concentrations (0, 1, 10 and 100 ng Sn/L) on morphological colouration in male guppies (Poecilia reticulata). The results showed that TPT exposure affected both orange/red and dark morphological colouration in guppies. The faded orange/red colouration might be related to the decrease of coloured pteridine and Pts (6-Pyruvoyltetrahydropterin Synthase) expression. In addition, TPT exposure induced melanogenesis, however, much melanin was distributed diffusely in the skin and did not seem to form a spot pattern, giving the fish a dull appearance. According to the skin transcriptional profiles, the changes of dark morphological colouration might be related to the changes in genes related to the functions of melanosome components (Gpnmb, Slc45a2 and Tyr), construction (Ap3d1, Fig4, Hps3, Hps5, Lyst, Rabggta, Txndc5 and Vps33a), and transport (Rab27a). Additionally, genes related to the regulation of melanogenesis (Atrn and Pomc) and system effects (Atox1, Atp6ap2, Atp6v1f, Atp6v1h, Rpl24, Rps19 and Rps20) might also be involved in the molecular mechanisms of abnormal morphological colouration induced by TPT. The present study provides crucial data on the molecular basis of abnormal morphological colouration in fish exposed to TPT and underscores the importance of toxicological studies of the effects of pollutants in aquatic environments on fish morphological colouration.

Variation on a theme: pigmentation variants and mutants of anemonefish

Pigmentation patterning systems are of great interest to understand how changes in developmental mechanisms can lead to a wide variety of patterns. These patterns are often conspicuous, but their origins remain elusive for many marine fish species. Dismantling a biological system allows a better understanding of the required components and the deciphering of how such complex systems are established and function. Valuable information can be obtained from detailed analyses and comparisons of pigmentation patterns of mutants and/or variants from normal patterns. Anemonefishes have been popular marine fish in aquaculture for many years, which has led to the isolation of several mutant lines, and in particular color alterations, that have become very popular in the pet trade. Additionally, scattered information about naturally occurring aberrant anemonefish is available on various websites and image platforms. In this review, the available information on anemonefish color pattern alterations has been gathered and compiled in order to characterize and compare different mutations. With the global picture of anemonefish mutants and variants emerging from this, such as presence or absence of certain phenotypes, information on the patterning system itself can be gained.

Gene expression trajectories during male and female reproductive development in balsam poplar (Populus balsamifera L.)

Plant reproductive development from the first appearance of reproductively committed axes through to floral maturation requires massive and rapid remarshalling of gene expression. In dioecious species such as poplar this is further complicated by divergent male and female developmental programs. We used seven time points in male and female balsam poplar (Populus balsamifera L.) buds and catkins representing the full annual flowering cycle, to elucidate the effects of time and sex on gene expression during reproductive development. Time (developmental stage) is dominant in patterning gene expression with the effect of sex nested within this. Here, we find (1) evidence for five successive waves of alterations to the chromatin landscape which may be important in setting the overall reproductive trajectory, regardless of sex. (2) Each individual developmental stage is further characterized by marked sex-differential gene expression. (3) Consistent sexually differentiated gene expression regardless of developmental stage reveal candidates for high-level regulators of sex and include the female-specific poplar ARR17 homologue. There is also consistent male-biased expression of the MADS-box genes PISTILLATA and APETALA3. Our work provides insights into expression trajectories shaping reproductive development, its potential underlying mechanisms, and sex-specific translation of the genome information into reproductive structures in balsam poplar.

Sex-biased expression between guppies varying in the presence of ornamental coloration

Sex-biased gene expression provides a means to achieve sexual dimorphism across a genome largely shared by both sexes. Trinidadian guppies are ideal to examine questions of sex-bias as they exhibit sexual dimorphism in ornamental coloration with male only expression. Here we use RNA-sequencing to quantify whole transcriptome gene expression differences, with a focus on differential expression of color genes between the sexes. We determine whether males express genes positively correlated with coloration at higher levels than females. We find that all the differentially expressed color genes were more highly expressed by males. Males also expressed all known black melanin synthesis genes at higher levels than females, regardless of whether the gene was significantly differentially expressed in the analysis. These differences correlated with the visual color differences between sexes at the stage sampled, as all males had ornamental black coloration apparent. We propose that sexual dimorphism in ornamental coloration is caused by male-biased expression of color genes.

Convergent evolution of coloration in experimental introductions of the guppy (Poecilia reticulata)

Despite the multitude of examples of evolution in action, relatively fewer studies have taken a replicated approach to understand the repeatability of evolution. Here, we examine the convergent evolution of adaptive coloration in experimental introductions of guppies from a high-predation (HP) environment into four low-predation (LP) environments. LP introductions were replicated across 2 years and in two different forest canopy cover types. We take a complementary approach by examining both phenotypes and genetics. For phenotypes, we categorize the whole color pattern on the tail fin of male guppies and analyze evolution using a correspondence analysis. We find that coloration in the introduction sites diverged from the founding Guanapo HP site. Sites group together based on canopy cover, indicating convergence in response to light environment. However, the axis that explains the most variation indicates a lack of convergence. Therefore, evolution may proceed along similar phenotypic trajectories, but still maintain unique variation within sites. For the genetics underlying the divergent phenotypes, we examine expression levels of color genes. We find no evidence for differential expression, indicating that the genetic basis for the color changes remains undetermined.