Juvenile Sphaeroma quadridentatum invading female-offspring groups of Sphaeroma terebrans

Abstract

Female isopods Sphaeroma terebrans Bate 1866 are known to host their offspring in family burrows in aerial roots of the red mangrove Rhizophora mangle. During a study on the reproductive biology of S. terebrans in the Indian River Lagoon, Florida, USA, juvenile S. quadridentatum were found in family burrows of S. terebrans. Between September 1997 and August 1998, each month at least one female S. terebrans was found with juvenile S. quadridentatum in its burrow. The percentage of S. terebrans family burrows that contained juvenile S. quadridentatum was high during fall 1997, decreased during the winter, and reached high values again in late spring/early summer 1998, corresponding with the percentage of parental female S. terebrans (i.e. hosting their own juveniles). Most juvenile S. quadridentatum were found with parental female S. terebrans, but a few were also found with reproductive females that were not hosting their own offspring. Non-reproductive S. terebrans (single males, subadults, non-reproductive females) were never found with S. quadridentatum in their burrows. The numbers of S. quadridentatum found in burrows of S. terebrans ranged between one and eight individuals per burrow. No significant correlation between the number of juvenile S. quadridentatum and the numbers of juvenile S. terebrans in a family burrow existed. However, burrows with high numbers of juvenile S. quadridentatum often contained relatively few juvenile S. terebrans. The majority of juvenile S. quadridentatum found in family burrows of S. terebrans were smaller than the juvenile S. terebrans that were cared for by their mothers. The results indicate that the presence of S. quadridentatum in S. terebrans family burrows may negatively affect the duration of extended parental care in S. terebrans. It is not known why parental female S. terebrans are not able to discriminate against juvenile S. quadridentatum. Possibly, the fact that the two species are closely related facilitates S. quadridentatum sneaking into S. terebrans family burrows.

Keywords:

• Reproduction Extended Parental Care Isopoda Peracarida Burrow Invasion