Feeding, Reproduction, and Sexuality in Pfiesteria spp. and Cryptoperidiniopsoid Estuarine Heterotrophic Dinoflagellates

Abstract

Dinoflagellates are an ancient, adaptively diverse group of protists that are important primary producers and/or consumers in many aquatic habitats. Most species are known only from drawings, photographs, or written descriptions. Comparatively few have been cultured for experimentation because of unknown nutritional requirements. Thus, studies on the behavior and reproduction of most dinoflagellates are still at the level of observational science.

Pfiesteria spp. and cryptoperidiniopsoids are closely related thecate, omnivorous dinoflagellates in temperate-subtropical estuaries. These species are relatively easy to culture, which has allowed knowledge of their range and impacts to progress quickly. This research investigated feeding, reproduction, and sexuality of these ecologically significant dinoflagellates in several studies, including: (i) asexual reproduction in Pfiesteria spp., and sexuality in P. piscicida were examined. Cell division was described in nonmotile cysts, supported by photography and flow cytometric DNA measurements. Sexuality — including nuclear cyclosis, a precursor to meiosis — was documented in P. piscicida clonal cultures. Taxonomic placement of Pfiesteria spp. within the order Peridiniales was suggested. (ii) Aspects of the life history and nutritional ecology of cryptoperidiniopsoids were investigated. The DNA content and population DNA profiles of synchronized populations from different cryptoperidiniopsoid isolates were measured and related to their life history. (iii) A method was developed to obtain dense, synchronous populations of Pfiesteria spp. and cryptoperidiniopsoids, with minimal cytoplasmic DNA contamination. The technique will be useful in ecological, biochemical, and molecular investigations. (iv) Asexual and sexual reproductive pathways of P. shumwayae were examined. Full evidence of sexuality was only found when clonal isolates were mixed; thus, self-sterility factors apparently influenced sexuality.

These investigations provided new information on nutrition, reproduction, and sexuality in these species. Detailed accounts of dinoflagellate reproduction are rare, especially for heterotrophic species, and observations on nuclear cyclosis and meiosis are extremely rare. This research was also among the first to provide DNA measurements in support of ploidy assumptions for phagotrophic dinoflagellates. The findings are fundamentally relevant to the behavior, ecology, and phylogeny of these ecologically significant dinoflagellates.