Testing the potential mechanisms for the maintenance of a genetic color polymorphism in bluefin killifish populations.

The maintenance of genetic variation in the face of natural selection is a long-standing question in evolutionary biology. In the bluefin killifish Lucania goodei, male coloration is polymorphic. Males can produce either red or yellow coloration in their anal fins, and both color morphs are present in all springs. These 2 morphs are heritable and how they are maintained in nature is unknown. Here, we tested 2 mechanisms for the maintenance of the red/yellow color morphs. Negative frequency-dependent mating success predicts that rare males have a mating advantage over common males. Spatial variation in fitness predicts that different color morphs have an advantage in different microhabitat types. Using a breeding experiment, we tested these hypotheses by creating populations with different ratios of red to yellow males (5 red:1 yellow; 1 red:5 yellow) and determining male mating success on shallow and deep spawning substrates. We found no evidence of negative frequency-dependent mating success. Common morphs tended to have higher mating success, and this was particularly so on shallow spawning substrates. However, on deep substrates, red males enjoyed higher mating success than yellow males, particularly so when red males were rare. However, yellow males did not have an advantage at either depth nor when rare. We suggest that preference for red males is expressed in deeper water, possibly due to alterations in the lighting environment. Finally, male pigment levels were correlated with one another and predicted male mating success. Hence, pigmentation plays an important role in male mating success.

Lower Extremity Problem-Solving: Challenging Cases.

Lower limb dysfunction associated with upper motor neuron syndrome can be complex due to interaction of muscle overactivity, weakness, impaired motor control, and contracture. Treatment should be goal-directed and address the patient's passive and active functional impairments in addition to their symptoms. Therefore, a comprehensive, multidisciplinary team approach tailored to each patient's unique needs and functional goals is warranted. This article reviews the evaluation and management of issues related to lower limb muscle overactivity and how this approach was applied to 3 challenging cases.

Exploring visual plasticity: dietary carotenoids can change color vision in guppies (Poecilia reticulata).

Differences in color vision can play a key role in an organism's ability to perceive and interact with the environment across a broad range of taxa. Recently, species have been shown to vary in color vision across populations as a result of differences in regulatory sequence and/or plasticity of opsin gene expression. For decades, biologists have been intrigued by among-population variation in color-based mate preferences of female Trinidadian guppies. We proposed that some of this variation results from variation in color vision caused by plasticity in opsin expression. Specifically, we asked about the role of dietary carotenoid availability, because carotenoids (1) are the precursors for vitamin A, which is essential for the creation of photopigments and (2) have been linked to variation in female mate choice. We raised guppies on different carotenoid-level diets and measured opsin expression. Guppies raised on high-carotenoid diets expressed higher levels of long wavelength sensitive opsin (LWS) opsins than those raised on lower levels of carotenoids. These results suggest that dietary effects on opsin expression represent a previously unaccounted for mechanism by which ecological differences across populations could lead to mate choice differences.

Diurnal lighting patterns and habitat alter opsin expression and colour preferences in a killifish.

Spatial variation in lighting environments frequently leads to population variation in colour patterns, colour preferences and visual systems. Yet lighting conditions also vary diurnally, and many aspects of visual systems and behaviour vary over this time scale. Here, we use the bluefin killifish (Lucania goodei) to compare how diurnal variation and habitat variation (clear versus tannin-stained water) affect opsin expression and the preference to peck at different-coloured objects. Opsin expression was generally lowest at midnight and dawn, and highest at midday and dusk, and this diurnal variation was many times greater than variation between habitats. Pecking preference was affected by both diurnal and habitat variation but did not correlate with opsin expression. Rather, pecking preference matched lighting conditions, with higher preferences for blue at noon and for red at dawn/dusk, when these wavelengths are comparatively scarce. Similarly, blue pecking preference was higher in tannin-stained water where blue wavelengths are reduced. In conclusion, L. goodei exhibits strong diurnal cycles of opsin expression, but these are not tightly correlated with light intensity or colour. Temporally variable pecking preferences probably result from lighting environment rather than from opsin production. These results may have implications for the colour pattern diversity observed in these fish.

Poly(L-cysteine) as an electrochemically modifiable ligand for trace metal chelation.

The short-chain (n approximately equal to 50) homopolymer poly(L-cysteine) (PLC) has been previously studied for use as a novel metal chelator. PLC exhibits reversible oxidation-reduction chemistry involving the thiol groups of the cysteine (Cys) residues. Previously, chemical oxidation of the PLC immobilized on silica showed that metal binding capacity was minimal in the oxidized state. In this study, Cys and PLC are immobilized on a glassy carbon disk electrode (GCE) to study these redox processes and how they impact metal binding and release. Voltammetric and chronoamperometric methods were employed to demonstrate nearly monolayer coverage of both immobilized Cys monomer and immobilized PLC on GCE. The PLC-GCE exhibited a maximum metal binding capacity for Cd2+ of approximately 11 Cd2+ ions/chain. No detectable metal binding capacity was observed for oxidized PLC. The bound metals were capable of being efficiently released through disulfide bond formation and tertiary structure changes by means of repetitive oxidative pulses. The Cys-modified electrode exhibited a metal binding capacity for Cd2+ of approximately 1 Cd2+/Cys. Oxidized Cys did retain a significant capacity following oxidation, likely as a result of complexation with the terminal carboxylate site and unoxidized thiols. A glycine (Gly)-modified electrode was also evaluated as an amino acid control. Minimal Cd2+ binding was observed. Further metal binding studies were conducted using PLC-GCE with single metal solutions of Co2+, Cu2+, Ni2+, and Pb2+, as well as a multimetal solution composed of equal concentrations of all five target metals. The observed metal binding trend was as follows: Cu2+ > Cd2+ > Ni2+ > Pb2+ > Co2+. All metals were quantitatively released upon oxidation of PLC using the same anodic potential, 600 mV vs Ag/AgCl.