Organisms can experience conditions that are limiting for growth, survival or reproduction in changing environments. The form and nature of this variability differ among habitats and this led to the evolution of different life histories. A comparative study of some life history traits has been realized under experimental conditions considering lineages of two eutardigrade species: Macrobiotus richtersi (Macrobiotidae) and Hypsibius dujardini (Hypsibiidae). These two species have different habitats, food preferences, reproductive mode, dormancy traits and phylogenetic position. Macrobiotus richtersi is very frequent in leaf litter, feeds on micrometazoans and is able to carry out anhydrobiosis. Hypsibius dujardini mainly colonises freshwater and feeds on algae. Our lineage of H. dujardini never carried out anhydrobiosis under experimental conditions. Both lineages are thelytokous, even though M. richtersi (clone CDMr01) is triploid apomictic, while H. dujardini is diploid automictic. Both species are iteroparous. The lineages were reared under the same laboratory conditions: 14°C temperature and photoperiod of 12h/12h (L/D). Macrobiotus richtersi fed on nematodes, H. dujardini fed on unicellular algae of the genus Selenastrum. The following life history traits were considered: lifespan, age at first oviposition, number of clutches per lifespan, number of eggs per clutch (fertility), number of eggs per lifespan (fecundity), hatching time and hatching percentage.Inter- and intraspecific variability have been observed for most life history traits analysed. Mean number of clutches per lifespan was similar in both species. Females of M. richtersi were characterized by a longer lifespan, and a later age at first oviposition than H. dujardini. Fertility and fecundity of M. richtersi were higher than those of H. dujardini. Lastly, H. dujardini had a lower hatching percentage, and a shorter hatching time than those of M. richtersi. In this last species, an unsynchronized hatching phenology and the presence of resting eggs have been observed. Interspecific variability may be explained by the different habitat colonised that have selected different life history traits. Hypsibius dujardini inhabits substrates normally not subject to desiccation, while M. richtersi inhabits substrates periodically subject to desiccation. In this last condition, strategies to overcome transient and unpredictable environmental conditions are selective such as the well-known capability to enter anhydrobiosis, but also the new finding of a long hatching time.
COMPARATIVE STUDY OF LIFE HISTORY TRAITS IN TERRESTRIAL AND LIMNIC EUTARDIGRADE SPECIES / Altiero, Tiziana; Rebecchi, Lorena. - STAMPA. - volume unico:(2004), pp. 185-185. (Intervento presentato al convegno Twelfth International Maiofauna Conference tenutosi a Ravenna nel 11-16 July 204).