Abstract
Seasonal variation of liver glycogen, lipids and melanomacrophages were investigated in a non-hibernating population of Pelophylax kl. esculentus from Calabria by histochemical methods and computer-assisted image analysis. Twenty individuals of both sexes were sampled in a tank in Roseto Capo Spulico (Cosenza, Calabria) in four periods of the year 2016 (February, May, July, October). Portions of liver from each individual were included in paraffin for glycogen and melanomacrophages, and epoxydic resin-araldite for lipid analysis. Sections were stained with periodic acid-Schiff (PAS) for glycogen (with diastase-PAS as control) or osmium-tetroxide for lipids, or left unstained for melanomacrophages (appearing naturally black due to melanin). Image analyses were performed on 9–12 grayscale converted pictures per individual. Total areas per µm2 of glycogen, lipids and melanomacrophages, as well as counts of lipid droplets and melanomacrophages and mean area of single lipid droplets and melanomacrophages, were measured. Statistical analyses were performed by analysis of variance (ANOVA) with bootstrap resampling. Significant variation among sampling periods was found for each variable. Glycogen and lipids co-vary, with higher values observed in October–February and lower values in May–July, whereas melanomacrophages reach a peak in May and have much lower values in the other months. It is concluded that, in the absence of a hibernating period, reproduction is the main force regulating the annual cycles of reserve storing and melanin production.
Highlights
The liver performs several essential functions in the adaptation to the environmental changes that Anura face during their life cycle
The liver mass varies during the annual cycle up to three times and this variation is related to body shape and mass, environmental variables, reproduction, dormancy and even phylogenetic history (Withers & Hillman 2001)
Lipid droplets and melanomacrophages showed significant variation among the four periods sampled, as shown in the results from the statistical analyses summarized in Tables I and II
Summary
The liver performs several essential functions in the adaptation to the environmental changes that Anura face during their life cycle. Crawshaw & Weinkle 2000) For both substances, seasonal variation in accumulation by the liver is reported, in particular in those species from temperate climates that undergo dormancy Reserves of glycogen and lipids increase in the period following reproduction and preceding dormancy. The increase of reserves between the emergence from dormancy and the starting of the breeding period depends on the reproductive strategy. From this point of view, anurans can be divided into two main categories, i.e. income and capital breeders. Income breeders feed after emergence and their reserves increase prior to breeding, whereas capital breeders do not feed and depend on the reserves accumulated prior to dormancy that further decrease after emergence Income breeders feed after emergence and their reserves increase prior to breeding, whereas capital breeders do not feed and depend on the reserves accumulated prior to dormancy that further decrease after emergence (i.e. Chen et al 2011)
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