Biology session

The special environmental conditions of caves (lack of light, high relative humidity, low and constant temperature) ensure habitat for several endemic and relict species. János Frivaldszky is considered to be the founder of cave biology in Hungary in the middle of 19th century. He described Mesoniscus graniger, a blind terrestrial isopod species from the Baradla Cave. From 1920, his work was continued by Endre Dudich who established there a laboratory for cave biology. There are publications on the distribution area, environmental tolerance and food sources of the species. Its population characteristics (sex ratio, possible morphological differences between sexes) and life history strategies (e.g. longevity, reproductive strategy, offspring number and size) are not known yet. We aimed to explore these features.

Sex ratio and size distribution of the individuals (based on head-width measurements) were estimated based on pitfall-trap data (N = 677). We studied the species’ reproductive strategy under natural (Baradla Cave, Aggtelek National Park) and laboratory conditions (Dept. of Ecology, UVM). We checked the cave model population (15 parallels, each with 12 individuals; N = 180) monthly between March and September, 2016. Digital photos were taken on the small sized (6:56 ± 0.79 mm), fragile animals and their length was estimated on these photos using the ImageJ software. The external morphology of the species was studied by light and scanning electron microscopic methods.

Our results proved female dominance in the population (male:female = 0.43: 0.57). Female head width (0.87 ±0.18 mm) was significantly higher than that of males (0.79 ± 0.08 mm) [p<0.001 (t-test)]. The thickness of cuticle was found to be 4.29 ±1.26 µm. The external morphology of sexes did not differ but we found sexual dimorphism in their size. Statistical analyses of the timing in reproduction, offspring number per female, and offspring size need further data. Based on our present knowledge we might assume that the offspring number per single females is low (3-4), and newborns have a relatively large size (2.55 ±0.88 mm mm). That is a typical feature of animals with 'K' life-history strategies. During the investigated period new offsprings appeared continuously in the model populations. The probability of reproduction on a monthly basis proved to be around 30-40% [(binomial test)].