Abstract
The special environmental conditions of caves provide habitat for several endemic and relict species, among them terrestrial isopods. The Baradla Cave system (north-eastern Hungary) hosts Mesoniscusgraniger (Frivaldszky, 1865) (Oniscidea, Microcheta, Mesoniscidae), a pygmy, blind, fragile troglophile woodlice species. Its stable environment can be characterised by the lack of light, high relative humidity (96%), low and constant temperature (about 10 °C). We explored the population characteristics (sex ratio, size distribution) and life history traits of the species (e.g. longevity, reproductive strategy, offspring number, and size). Sex ratio and size distribution of the individuals (head-width measurements) were estimated based on a yearly pooled pitfall-trap data set (N = 677). We studied the species’ reproductive strategy under natural conditions (Baradla Cave, Aggtelek National Park). Model populations were set up in the cave and checked monthly between March and October, 2016 (15 replicates, each with 12 randomly chosen adult individuals; ΣN = 180). Digital photos were taken of the live animals and their length was estimated based on the photos by using ImageJ software (average body length: 6.56 ± 0.79 mm). The results showed female dominance in the population [(male:female = 0.43:0.57); p < 0.001 (GLM)]. Female head width (0.87 ± 0.18 mm) was significantly greater than that of males [0.79 ± 0.08 mm; p < 0.001 (t-test)]. Based on our present data we assume that the offspring number per single female is low (3–5), and new-borns have a relatively large size (body length: 4.22 ± 0.53 mm) compared to the adults. The probability of reproduction was continuous by monthly intervals (binomial test) and longevity exceeds one year. Our results suggest that the species follows a stenodynamic life history.
Highlights
Life history strategies in terrestrial isopods were first reviewed and divided into stenodynamic and eurodynamic traits by Sutton et al (1984)
Isopods collected in the pitfall traps were sorted into females, males and juveniles by their sexual characters and size, respectively (Table 1)
Sex ratio was significantly overweighed for females (GLM test, p-value
Summary
Life history strategies in terrestrial isopods were first reviewed and divided into stenodynamic and eurodynamic traits by Sutton et al (1984). A stenodynamic species shows low growth rate, long time to maturity, and produces few and relatively large offspring, while the eurodynamic species have an opposite character They grow faster, mature earlier, reproduce more frequently, and produce more, but smaller offspring (Achouri et al 2008, Sutton et al 1984, Warburg 1994, Brody and Lawlor 1984, Warburg and Cohen 1991, Grundy and Sutton 1989). These strategies are similar to r-K life history strategies (Stearns 1977): stenodynamic species tend to be ‘K’, while eurodynamic species can be best compared to the ‘r’ life history strategy. In reproduction terrestrial isopods show mainly uni-, bi-, or multivoltine iteroparity, sparsely semelparity, and some species are parthenogenetic (Hornung 2011)
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