Adult plasticity in African cichlids: Rapid changes in opsin expression in response to environmental light differences

Phenotypic plasticity allows organisms to adapt quickly to local environmental conditions and could facilitate adaptive radiations. Cichlids have recently undergone an adaptive radiation in Lake Malawi where they inhabit diverse light environments and tune their visual sensitivity through differences in cone opsin expression. While cichlid opsin expression is known to be plastic over development, whether adults remain plastic is unknown. Adult plasticity in visual tuning could play a role in cichlid radiations by enabling survival in changing environments and facilitating invasion into novel environments. Here we examine the existence of and temporal changes in adult visual plasticity of two closely related species. In complementary experiments, wild adult Metriaclima mbenji from Lake Malawi were moved to the lab under UV‐deficient fluorescent lighting; while lab raised M. benetos were placed under UV‐rich lighting designed to mimic light conditions in the wild. Surprisingly, adult cichlids in both experiments showed significant changes in the expression of the UV‐sensitive single cone opsin, SWS1, in only 3 days. Modeling quantum catches in the light environments revealed a possible link between the light available to the SWS1 visual pigment and SWS1 expression. We conclude that adult cichlids can undergo rapid and significant changes in opsin expression in response to environmental light shifts that are relevant to their habitat and evolutionary history in Lake Malawi. This could have contributed to the rapid divergence characteristic of these fantastic fishes.     

Characterization of opsin gene alleles affecting color vision in a wild population of titi monkeys (Callicebus brunneus)

The color vision of most platyrrhine primates is determined by alleles at the polymorphic X-linked locus coding for the opsin responsible for the middle- to long-wavelength (M/L) cone photopigment. Females who are heterozygous at the locus have trichromatic vision, whereas homozygous females and all males are dichromatic. This study characterized the opsin alleles in a wild population of the socially monogamous platyrrhine monkey Callicebus brunneus (the brown titi monkey), a primate that an earlier study suggests may possess an unusual number of alleles at this locus and thus may be a subject of special interest in the study of primate color vision. Direct sequencing of regions of the M/L opsin gene using feces-, blood-, and saliva-derived DNA obtained from 14 individuals yielded evidence for the presence of three functionally distinct alleles, corresponding to the most common M/L photopigment variants inferred from a physiological study of cone spectral sensitivity in captive Callicebus.     

Demonstration of viability and fertility and development of a molecular tool to identify YY supermales in a fish with both genotypic and environmental sex determination

The pejerrey possesses a genotypic sex determination system driven by the amhy gene and yet shows marked temperature‐dependent sex determination. Sex‐reversed XY females have been found in a naturally breeding population established in Lake Kasumigaura, Japan. These females could mate with normal XY males and generate YY “supermale” individuals that, if viable and fertile, would sire only genotypic male offspring. This study was conducted to verify the viability, gender, and fertility of YY pejerrey and to develop a molecular method for their identification. Production of YY fish was attempted by crossing a thermally sex‐reversed XY female and an XY male, and rearing the progeny until sexual maturation. To identify the presumable YY individuals, we first conducted a PCR analysis using amhy‐specific primers to screen only amhy‐positive (XY and YY) fish. This screening showed that 60.6% of the progeny was amhy‐positive, which suggested the presence of YY fish. We then conducted a second screening by qPCR in order to identify the individuals with two amhy copies in their genome. This screening revealed 13 individuals, all males, with values twice higher than the other 30 amhy‐positive fishes, suggesting they have a YY complement. This assumption as well as the viability, fertility, and “supermale” nature of these individuals was confirmed in progeny tests with XX females that yielded 100% amhy‐positive offspring. These results demonstrate that qPCR can obviate progeny test as a means to identify the genotypic sex and therefore may be useful for the survey of all three possible genotypes in wild populations.     

Shifts in outcrossing rates and changes to floral traits are associated with the evolution of herbicide resistance in the common morning glory

Human‐mediated selection can strongly influence the evolutionary response of natural organisms within ecological timescales. But what traits allow for, or even facilitate, adaptation to the strong selection humans impose on natural systems? Using a combination of laboratory and greenhouse studies of 32 natural populations of the common agricultural weed, Ipomoea purpurea , we show that herbicide‐resistant populations self‐fertilise more than susceptible populations. We likewise show that anther–stigma distance, a floral trait associated with self‐fertilisation in this species, exhibits a nonlinear relationship with resistance such that the most and least resistant populations exhibit lower anther–stigma separation compared to populations with moderate levels of resistance. Overall, our results extend the general finding that plant mating can be impacted by human‐mediated agents of selection to that of the extreme selection of the agricultural system. This work highlights the influence of human‐mediated selection on rapid responses of natural populations that can lead to unexpected long‐term evolutionary consequences.     

Activation of ethylene‐related genes in response to aphid feeding on resistant and susceptible melon and tomato plants

The simple gaseous compound ethylene (ET) has long been recognized as a common component of plant responses to insect feeding and pathogen attack. However, it is presently uncertain whether it plays a role in host–plant resistance to piercing–sucking insects such as aphids. In these experiments, we investigated the expression of key ET‐associated genes in resistant and susceptible interactions in two model systems: the tomato‐Mi‐Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae: Macrosiphini) system and the melon‐virus aphid transmission gene (Vat)‐Aphis gossypii Glover (Hemiptera: Aphididiae: Aphidini) system. We examined expression patterns of genes associated with ET synthesis, perception, signal transduction, and downstream response. When compared with control plants, plants infested with aphids showed marked differences in gene expression. In particular, ET signaling pathway genes and downstream response genes were highly upregulated in the resistant interaction between A. gossypii and Vat⁺, indicating ET may play a role in Vat‐mediated host–plant resistance. A key integrator between the ET and jasmonic acid pathways (Cm‐ERF1) showed the strongest response.