Genetic analysis of body weight in wild populations of medaka fish from different latitudes.

The genetic bases of growth and body weight are of economic and scientific interest, and teleost fish models have proven useful in such investigations. The Oryzias latipes species complex (medaka) is an abundant freshwater fish in Japan and suitable for genetic studies. We compared two wild medaka stocks originating from different latitudes. The Maizuru population from higher latitudes weighed more than the Ginoza population. We investigated the genetic basis of body weight, using quantitative trait locus (QTL) analysis of the F2 offspring of these populations. We detected one statistically significant QTL for body weight on medaka chromosome 4 and identified 12 candidate genes that might be associated with body weight or growth. Nine of these 12 genes had at least one single nucleotide polymorphism that caused amino acid substitutions in protein-coding regions, and we estimated the effects of these substitutions. The present findings might contribute to the marker-assisted selection of economically important aquaculture species.

Acute effects of light and darkness on the activity and temperature rhythms of a subterranean rodent, the Anillaco tuco-tuco.

Tuco-tucos from Anillaco (Ctenomys aff. knighti), are subterranean rodents that run vigorously on laboratory wheels during the night but are active during the day in semi-natural enclosures, where they surface for foraging and burrow maintenance, under intense sunlight. Several studies have shown that light causes opposite, inhibitory and stimulatory, "masking" effects on the activity levels between nocturnal and diurnal species, respectively. Because of the alternating subterranean/surface activity of tuco-tucos in nature during the day and their ability to shift from diurnal to nocturnal patterns in field-to-lab transitions, we assessed the acute effects of light and darkness on running wheel activity, general activity and body temperature. Adult males and females were kept in a LD 12:12 h regimen and exposed to light and dark pulses to verify masking effects in their rhythms. A first experiment consisted in submitting animals to light pulses of different illuminance during the dark phase. Clear inhibition of wheel-running activity occurred, being the response more pronounced as illuminance of the pulse increased, a response typically seen in nocturnal rodents. A second experiment consisted in submitting animals to light pulses during the dark phase, and later to dark pulses during the light phase. This protocol occurred three times in the conditions: 1) without a wheel, 2) with free access to a wheel, and 3) with a blocked wheel. Wheel running was inhibited and body temperature decreased in most animals during the light pulse, with little to no inhibition on general activity. Dark pulses during the light phase had no effect on wheel-running activity nor on general activity but did affect body temperature. Interestingly, there was a single individual that switched from nocturnal to diurnal when kept without a running wheel, offering an opportunity to test nocturnal and diurnal masking patterns to light in the same individual.