Biology subjects

Koch, R. E.

Publications and source records attributed to Koch, R. E..

3 recordsLinked to original sources

bioRxiv2025

Mitochondrial genotype interacts with age and sex, but not nuclear background, to shape locomotory performance across mitonuclear strains of fruit flies

The discovery that mitochondrial genomes can harbor functional mutations despite the evolutionarily conserved role of mitochondria has spurred interest in better understanding the ecological and evolutionary consequences of such mitochondrial genetic variation. Because mitochondrial DNA (mtDNA) encodes products that must function in concert with products of the nuclear genome, and because mitochondria are largely maternally inherited, outstanding questions remain as to how, when, and why variation in mtDNA may affect phenotype. In this study, we developed a set of intraspecific "mitonuclear strains" of Drosophila melanogaster fruit flies that vary across 13 mtDNA haplotypes and 3 nuclear genetic backgrounds. We created a new apparatus called the Drop Tower to test the performance of these strains in negative geotaxis, a locomotory trait we predicted to be sensitive to variation at the level of mitochondria, across both sexes and two age classes. We found that both mitochondrial and nuclear genetic variation significantly altered how negative geotaxis performance changed with age and across the sexes, though interactions between mitochondrial and nuclear strains did not affect performance. Across most strains, male flies performed more poorly and suffered a steeper decline with age than did females, and young males appeared to vary more in performance across mitochondrial strains. In addition, we discovered a strong effect of small differences of parental age on negative geotaxis-- and this effect also varied by mitochondrial strain. Collectively, the results of our study reveal that intraspecific variation in both mitochondrial and nuclear DNA can affect age- and sex-related differences in fruit fly locomotory performance. Further exploring the mechanisms linking these subtle genetic differences to locomotory phenotype and creating differences in response between the sexes will be important to understanding the evolutionary forces shaping the patterns we detected.

evolutionary biology↗

bioRxiv2024

Multiple pathways to red carotenoid coloration: House finches(Haemorhous mexicanus) do not use CYP2J19 to produce red plumage

The carotenoid-based colors of birds are a celebrated example of biological diversity and an important system for the study of evolution. Recently, a two-step mechanism, with the enzymes cytochrome P450 2J19 (CYP2J19) and 3-hydroxybutyrate dehydrogenase 1-like (BDH1L), was described for the biosynthesis of red ketocarotenoids from yellow dietary carotenoids in the retina and plumage of birds. A common assumption has been that all birds with ketocarotenoid-based plumage coloration used this CYP2J19/BDH1L mechanism to produce red feathers. We tested this assumption in house finches (Haemorhous mexicanus) by examining the catalytic function of the house finch homologs of these enzymes and tracking their expression in molting birds. We found that CYP2J19 and BDH1L did not catalyze the production of 3-hydroxy-echinenone (3-OH-echinenone), the primary red plumage pigment of house finches, when provided with common dietary carotenoid substrates. Moreover, gene expression analyses revealed little to no expression of CYP2J19 in liver tissue or growing feather follicles, the putative sites of pigment metabolism in molting house finches. Finally, although the hepatic mitochondria of house finches have high concentrations of 3-OH-echinenone, observations using fluorescent markers suggest that both CYP2J19 and BDH1L localize to the endomembrane system rather than the mitochondria. We propose that house finches and other birds that deposit 3-OH-echinenone as their primary red plumage pigment use an alternative enzymatic pathway to produce their characteristic red ketocarotenoid-based coloration.

evolutionary biology↗

bioRxiv2023

Captivity affects mitochondrial aerobic respiration and carotenoid metabolism in the house finch (Haemorhous mexicanus)

In many species of animals, red carotenoid-based coloration is produced by metabolizing yellow dietary pigments, and this red ornamentation is an honest signal of individual quality. However, the physiological basis for associations between organism function and the metabolism of red ornamental carotenoids from yellow dietary carotenoids remains uncertain. A recent hypothesis posits that carotenoid metabolism depends on mitochondrial performance, with diminished red coloration resulting from altered mitochondrial aerobic respiration. To test for an association between mitochondrial respiration and red carotenoids, we held wild-caught, molting male house finches in either small bird cages or large flight cages to create environmental challenges during the period when red ornamental coloration is produced. We predicted that small cages would present a less favorable environment than large flight cages and that captivity would affect both mitochondrial performance and the abundance of red carotenoids. We found no evidence that living in small versus large cages had significant effects on wild-caught house finches; however, birds in cages of any size circulated fewer red carotenoids, showed increased mitochondrial respiratory rates, and had lower complex II respiratory control ratios--a metric associated with mitochondrial efficiency--compared to free-living birds. Moreover, among captive individuals, the birds that circulated the most red carotenoids had the highest mitochondrial respiratory control ratio for complex II substrates. These data support the hypothesis that the metabolism of red carotenoid pigments is linked to mitochondrial aerobic respiration in the house finch, but the mechanisms for this association remain to be established. SUMMARY STATEMENTHolding wild-caught male house finches in cages exposed a relationship between red carotenoid production and mitochondrial respiratory efficiency.

evolutionary biology↗