Abstract:Speciation problems are reviewed in the context of biogeography of fresh-water algae. Currently accepted species concept in phycology is based on morphological characters, and according to this concept, most freshwater algal species are considered cosmopolitan. This implies whether they have a highly efficient means of dispersal or their morphological characters are very static through a long evolutionary time. Recent studies of reproductive isolation show that some biological species of fresh-water algae are … Show more
“…For example, closely related members of the same planktonic genera having very similar morphologies are known to occur in similar habitats worldwide (14), suggesting extremely rapid and effective dispersal. Many species of phytoplankton thus can be considered to be cosmopolitan (15), and the same floras and keys can be used in Europe, Asia, and the Americas (16). However, other potentially cosmopolitan microbial taxa with a similarly small body size do nonetheless exhibit significant species-area relationships (soil fungi, ref.…”
Species-area relationships have been observed for virtually all major groups of macroorganisms that have been studied to date but have not been explored for microscopic phytoplankton algae, which are the dominant producers in many freshwater and marine ecosystems. Our analyses of data from 142 different natural ponds, lakes, and oceans and 239 experimental ecosystems reveal a strong species-area relationship with an exponent that is invariant across ecosystems that span >15 orders of magnitude in spatial extent. A striking result is that the species-area relationship derived from small-scale experimental studies correctly scales up to natural aquatic ecosystems. These results significantly broaden our knowledge of the effects of island size on biodiversity and also confirm the relevance of experimentally derived data to the analysis and understanding of larger-scale ecological patterns. In addition, they confirm that patterns in microbial diversity are strongly consistent with those that have been repeatedly reported in the literature for macroorganisms.biodiversity ͉ island biogeography ͉ species-area ͉ scale-invariance
“…For example, closely related members of the same planktonic genera having very similar morphologies are known to occur in similar habitats worldwide (14), suggesting extremely rapid and effective dispersal. Many species of phytoplankton thus can be considered to be cosmopolitan (15), and the same floras and keys can be used in Europe, Asia, and the Americas (16). However, other potentially cosmopolitan microbial taxa with a similarly small body size do nonetheless exhibit significant species-area relationships (soil fungi, ref.…”
Species-area relationships have been observed for virtually all major groups of macroorganisms that have been studied to date but have not been explored for microscopic phytoplankton algae, which are the dominant producers in many freshwater and marine ecosystems. Our analyses of data from 142 different natural ponds, lakes, and oceans and 239 experimental ecosystems reveal a strong species-area relationship with an exponent that is invariant across ecosystems that span >15 orders of magnitude in spatial extent. A striking result is that the species-area relationship derived from small-scale experimental studies correctly scales up to natural aquatic ecosystems. These results significantly broaden our knowledge of the effects of island size on biodiversity and also confirm the relevance of experimentally derived data to the analysis and understanding of larger-scale ecological patterns. In addition, they confirm that patterns in microbial diversity are strongly consistent with those that have been repeatedly reported in the literature for macroorganisms.biodiversity ͉ island biogeography ͉ species-area ͉ scale-invariance
Mating affinity, nuclear rDNA internal transcribed spacer (ITS) sequence, and geographic distribution of more than 100 isolates of Pandorina , Volvulina , and Yamagishiella were determined. Comparative analysis of ITS sequences reaffirmed the unity of Pandorina morum and its separation from all other species of Volvocaceae except those of Volvulina. This latter genus, represented by four species, appears to represent only morphological variants of several P. morum subclades. The P. morum clade (including also additional species such as P. smithii and P. colemaniae ) encompasses an evolutionary span, as determined by comparison of ITS, greater than either of the multispecies genera Gonium or Eudorina. There are at least 30 Pandorina / Volvulina syngens, sexually isolated groups, so far as can be determined, among the current collection of strains. In addition, as in other volvocacaean genera, two clones are homothallic, capable of forming zygotes within a genetic clone. The existence of so many syngens suggests that considerable evolutionary diversification of the genes controlling gamete compatibility and intercross survival has occurred, unaccompanied by significant morphological change. Within each syngen, genetic distance increases with geographic distance between collection sites. At least half of the isolates studied must have been introduced northward since the Pleistocene. Although we probably know more about characters in this group of algae than any other algal group, in part because they are so easy to culture, we are still largely ignorant of what circumscribes their niche in nature. The study of all these organisms, distributed throughout the world presumably by the activities of shorebirds, emphasizes the evolutionary role of mating genes in the inevitable formation of new genetically isolated subclades in these eukaryotes and provides initial data on their rate of appearance versus their rate of distribution over the earth.
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