Biology session

Information on an animal’s fitness can be crucial when it comes to the conservation of a species or a certain population. It’s even more true in the case of endangered species, but more often than not we don’t have the means to directly measure fitness so we have to use other, fitness-related variables to estimate reproductive success, like survival and body size. In insects, the bigger, heavier individuals in average are more fecund and live longer, and the longer they live the more eggs they can lay.

We measured changes in body mass and thorax width over time in individually marked Clouded Apollo butterflies Parnassius mnemosyne and we investigated relationships between body size measured as wing length, proboscis length, thorax width, body mass, and survival.

Our results show that among both females and males, body mass and thorax width decreased with age on the individual and on the population level as well. These results indicate that the difference between the sexes is not fixed, but varied over the years.

Body size has an important role in survival in the case of females, but in some years in males as well. The magnitudes of these relationships are not constant and in the three examined years there were significant differences within both males and females. Survival increased with proboscis length in 2016 and 2017 but decreased in 2018. In 2018 floral composition of the meadow was very different from previous years. These results implies that the effects of body size on survival are influenced by many other environmental factors. These factors and body size determine an individual’s survival probability together and through that – weakening or intensifying each other’s effect – affect reproductive success.