Variations of reproductive traits of two semi-terrestrial isopods, Ligia exotica and L-taiwanensis (Crustacea: Ligiidae), in southern Taiwan

Both inter- and intraspecific reproductive traits of 2 semiterrestrial isopods were examined and compared in an attempt to provide insights into the adaptive strategies of reproduction. Gravid females of Ligia exotica (Roux) from the littoral zone and Ligia taiwanensis (Lee) from mountain brooks show differences in reproductive allocation per brood (F-1,F-198 = 706, p < 0.001), weight-specific egg weight (F-1,F-198 = 166, p < 0.001), and weight-specific fecundity (F-1,F-198 = 120, p < 0.001), but they also display similarities in the interrelationships between reproductive traits. The reproductive traits of L. taiwanensis, such as larger weight-specific egg size and lower reproductive allocation, seem more in accordance with theoretical predictions for K-selected traits than those of L. exotica. When the effects of body size are removed, both species show a significant positive correlation between fecundity and brood weight (L. exotica: r = + 0.49, t = 5.50, p < 0.001; L. taiwanensis: r = + 0.96, t = 36.09, p < 0.001), and a negative correlation between fecundity and egg size (L. exotica: r = - 0.77, t = 11.78, p < 0.001; L. taiwanensis: r = - 0.32, t = 3.41, p < 0.001) intraspecifically. The reciprocal relationships between egg size and fecunidity in L. exotica and L. taiwanensis seem to match the assumption of optimality theories of life-history evolution.