Abstracts (first author)
Inter- and intraspecific relationships between performance and temperature in a cryptic-species complex of the rotifer Brachionus plicatilisPDF
The strategy of decreasing size with increasing temperature operates at geographic (Bergmann’s rule) and within-genotype (temperature-size rule) scales and presents a puzzle to researches. The aim of this study was to verify whether differences in the adult size of closely related species coexisting in the same habitat are adaptive. The experiments were conducted on the cryptic species complex of the rotifer Brachionus plicatilis, represented by three species living in the Torrablanca marshes of eastern Spain. A cryptic species complex is a group of species each one satisfying the biological definition of species but having very similar morphologies. It provides an experimental model for testing ecological hypotheses because the species similarity tends to simplify comparisons. The monogonont rotifer species complex Brachionus plicatilis is a good example. Three of the cryptic species co-occur in the same ponds and differ in adult size. Co-occurrence is associated with their different preferences for temperature and salinity, mode of competition and vulnerability to predators. Three aspects of the performance-temperature relationship along a temperature gradient were studied, (i) the population growth rates were compared, (ii) the interspecific phenotypic plasticity of adult size was assessed, and (iii) the pattern of sediment egg bank hatching was explored. The results show that (i) the optimal temperature for population growth is related to species size in a manner foreseen by Bergmanns’ rule, (ii) the temperature-size rule differs between species and may depend on the level of temperature specialization, and that (iii) adult size, as a proxy for resting egg size, is adaptive regarding the hatching pattern. These results broaden the general knowledge on the evolutionary mechanisms behind the body size-temperature relationship and have important consequences for the coexistence and geographic ranges of species, and for species redundancy.