Maternal investment decreases under stressful environments in 11 plateau brown frog (Rana kukunoris) populations

Geographic variation in reproductive investment of seven populations of male Brown frog (Rana kukunoris), endemic to the eastern Tibetan Plateau

Life-history theory suggests that male anurans living in harsh and unpredictable environmental conditions (e.g., low temperature and/or high seasonality) should decrease reproductive investment because of short periods of activity and poor productivity. Although geographic variations in female life-history traits have been investigated intensively across a wide range of taxa, similar studies in males have been scarce. Here, we examined geographic variation in male testis mass of the brown frog (Rana kukunoris) across seven different altitudes on the eastern Tibetan plateau, and tested the hypothesis that relative size of testis mass should increase with increasing temperature and/or decreasing seasonality. In this study, we found male body condition, age and testis mass did not increase with temperature and temperature seasonality, which do not conform to our previous hypothesis, revealing that differences in temperature and temperature seasonality across populations could not drive the evolution of testis size. However, we found a positive correlation between testis mass and body condition or age when controlling for population and the effect of temperature and temperature seasonality, indicative of a condition-dependent expression of testis size. In addition, a correlation between testis mass and operational sex ratio was not significant, suggesting that male–male competition did not lead to increasing levels of sperm competition.

Early swelling response to phytohemagglutinin is lower in older toads

The effects of age on performance of life-history traits are diverse, but a common outcome is senescence, an irreversible deterioration of physical and physiological capabilities of older individuals. Immune response is potentially bound to senescence. However, little is known about immune response ageing in amphibians. In this work, we test the hypothesis that amphibian early immune response is reduced in older individuals. To this end, we captured adult natterjack toads (Epidalea calamita) and inoculated them with phytohemagglutinin, an innocuous protein that triggers a skin-swelling immune response whose magnitude is directly proportional to the ability of the individual to mount an immune response. We measured early swelling immune response (corresponding to an innate-response stage) hourly, for six hours, and we calculated the area under the curve (AUC) for each individual's time series, as a measure of immune response magnitude incorporating time. We estimated toad age by means of phalanx skeletochronology. Swelling and AUC decreased with age. Therefore, in accordance with our predictions, early immune response seems subject to senescence in these toads. Reduced ability to get over infections due to senescence of immune respose might be-together with a worse functioning of other organs and systems-among the causes of lower survival of older specimens.