Sexual reproductive biology of a colonial rotifer Sinantherina socialis (Rotifera: Monogononta): do mating strategies vary between colonial and solitary rotifer species?

Abstract

In many aquatic invertebrates including monogonont rotifers, sex provides genetic variation and dormant stages that allow for dispersal in time and space. While the reproductive biology of some solitary monogonont rotifer species is known, little is known concerning mating behaviors in colonial rotifers. Coloniality poses unique challenges to the typical mating behavior of solitary rotifers. For instance, most species engage in circling behavior, where the male swims in close proximity to the female. In colonial forms, access to a particular female may be hindered by nearby colony mates. Here, we provide descriptions of (1) male morphology, (2) mating behavior, and (3) types of eggs of the widespread colonial rotifer Sinantherina socialis, and discuss modifications in mating strategies as a consequence of coloniality. Two important differences from mating patterns documented in solitary rotifers were found in S. socialis. First, duration of circling phase of mating is protracted for males encountering small colonies of females as compared to solitary females. Males encountering single females removed from their colonies behave similarly to those of solitary species. Second, duration of copulation in S. socialis is the shortest reported for any rotifer species. Endogamy might occur in this species as sons copulate with their sisters and mothers, at least under laboratory conditions. Examples of behaviors are available in linked video clips.

Keywords:

• invertebrate reproduction
• amphoteric mixis
• male morphology
• mating
• behavior
• video analysis

Acknowledgments

The authors thank Dr. Robert Lee Wallace of Ripon College, Wisconsin, for his comments and suggestions as well as two anonymous reviewers. Rotifers were collected under permit BIBE-2001-SCI-0058 to E. J. Walsh at Big Bend National Park.