The effects of climate change on floral anthocyanin polymorphisms

Pigmentation affords resistance to abiotic stressors, and thus can respond adaptively or plastically to drought and extreme temperatures associated with global change. Plants frequently display variability in flower coloration that is underlain by anthocyanin pigmentation. While anthocyanin polymorphisms impact plant–animal interactions, they also impact reproductive performance under abiotic stress. We used descriptions of flower colour from over 1900 herbarium records representing 12 North American species spanning 124 years to test whether anthocyanin-based flower colour has responded to global change. Based on demonstrated abiotic associations with performance of anthocyanin colour morphs, we predicted pigmentation would increase in species experiencing increased aridity, but decline in those experiencing larger increases in temperature. We found that the frequency of reports of pigmented morphs increased temporally in some taxa but displayed subtle declines in others. Pigmentation was negatively associated with temperature and positively associated with vapour pressure deficit (a metric of aridity) across taxa. Species experiencing larger temperature increases over time displayed reductions in pigmentation, while those experiencing increases in aridity displayed increases in pigmentation. Change in anthocyanin-based floral colour was thus linked with climatic change. Altered flower coloration has the strong potential to impact plant–animal interactions and overall plant reproductive performance.

Low-latitude zooplankton pigmentation plasticity in response to multiple threats

Crustacean copepods in high-latitude lakes frequently alter their pigmentation facultatively to defend themselves against prevailing threats, such as solar ultraviolet radiation (UVR) and visually oriented predators. Strong seasonality in those environments promotes phenotypic plasticity. To date, no one has investigated whether low-latitude copepods, experiencing continuous stress from UVR and predation threats, exhibit similar inducible defences. We here investigated the pigmentation levels of Bahamian ‘blue hole’ copepods, addressing this deficit. Examining several populations varying in predation risk, we found the lowest levels of pigmentation in the population experiencing the highest predation pressure. In a laboratory experiment, we found that, in contrast with our predictions, copepods from these relatively constant environments did show some changes in pigmentation subsequent to the removal of UVR; however, exposure to water from different predation regimes induced minor and idiosyncratic pigmentation change. Our findings suggest that low-latitude zooplankton in inland environments may exhibit reduced, but non-zero, levels of phenotypic plasticity compared with their high-latitude counterparts.

Observation of the presence of crypsis in white mullet Mugil curema (Pisces: Mugilidae) juveniles under artificial rearing conditions

This study documents the presence of crypsis in Mugil curema juveniles under laboratory culture. Initially, the juveniles were located in one brown tank (BT1), later almost half of the individuals were placed in a white tank (WT) where they showed a pigmentation change to white. After being moved to another brown tank (BT2), the juveniles changed to their brown original colour, but kept a few small white spots on the dorsal axis of the body. The ventral head melanophore pattern also changed in the white specimens. Temperature (°C), oxygen (mg l−1) and Illuminance light (Lux m−2), total length (mm) and total weight (g) were determined by tank. Chromaticity was measured in L*(relative luminance) a*(measurement relating to the redness or greenness of the light) b*(measurement relating to the yellowness or blueness of the light) coordinates where all three values are required to completely describe an object’s colour. One-way ANOVA showed no differences for temperature, oxygen and illuminance light among tanks. Length and weight were similar for BT1 and WT but both were different from BT2. The white juveniles depicted similar L* as the WT background as well as the dorsal area of the brown pigmentation and converted juveniles to the brown tanks BT1 and BT2, respectively. Therefore, the fish's body relative luminance matches the background. To our knowledge this behaviour has not been reported before for any fish mullet either cultured or living in the wild.

Further evidence of pigmentation change in white sharks, Carcharodon carcharias

Patterns of pigmentation are widely used for the identification of white sharks, with photographic databases often forming the basis for studies of population modelling, site fidelity and movement patterns. The permanence of these identifying markings is assumed to remain constant. Here, we present evidence of melanism resulting in a change in the shape and size of pigmentation markings on the lower caudal lobe of a female white shark. We found a 33% reduction in size of an islet over a 9-month period. The newly melanised region was 10% darker than the adjoining pigmented areas, and did not match the original pattern. Possible causes of the observed melanism are presented, and the implications for the reliability of using caudal-fin pigmentation patterns for identification purposes are discussed, with a combinational matching approach recommended.

Action of light on Micrococcus roseus

Micrococcus roseus is killed by exposure to a continuous spectrum of white light (3000 ft-c (32 292 lm/m2)) in the presence of air and the dye, toluidine blue. Comparison of rates of photodynamic killing for log and stationary phase cells and for two pigmentation mutants indicated that photosensitivity could not be correlated with amount of carotenoid or with carotenoid-chromophore length. Moreover, cells grown in medium containing diphenylamine (DPA) did not contain significant quantities of colored carotenoids; they were not as sensitive to photodynamic killing as fully pigmented cells. Photodynamic killing was accompanied by selective release of magnesium and calcium and by release of UV-absorbing material. In the absence of added photosensitizer, M. roseus, the two mutants, or DPA-inhibited cells were not killed when exposed to white light at intensities as high as 22 000 ft-c (236 806 lm/m2) for as long as 9 h, and cells did not release UV-absorbing material. Under these conditions M. roseus and the yellow mutant did not release as much magnesium or calcium as when subjected to photodynamic killing, but DPA-grown cells leaked sodium, magnesium, and calcium. These observations are consistent with several suggestions: (i) carotenoids do not serve as photochemical buffers in M. roseus; (ii) growth in medium containing DPA or mutations leading to altered pigmentation change membrane organization leading to altered photosensitivity; (iii) M. roseus has an efficient repair mechanism which renders it resistant to photodynamic killing unless an exogenous photosensitizer is present.