Molecular phylogeny of the Volvocine flagellates

Evolution of complexity in the volvocine algae: transitions in individuality ..

19/12/2017 · Molecular phylogeny of the Volvocine ..

It has been argued that for certain lineages, noncoding DNA expansion is a consequence of the increased random genetic drift associated with long-term escalations in organism size. But a lack of data has prevented the investigation of this hypothesis in most plastid-bearing protists. Here, using newly sequenced mitochondrial and plastid genomes, we explore the relationship between organelle DNA noncoding content and organism size within volvocine green algae. By looking at unicellular, colonial, and differentiated multicellular algae, we show that organelle DNA complexity scales positively with species size and cell number across the volvocine lineage. Moreover, silent-site genetic diversity data suggest that the volvocine species with the largest cell numbers and most bloated organelle genomes have the smallest effective population sizes. Together, these findings support the view that nonadaptive processes, like random genetic drift, promote the expansion of noncoding regions in organelle genomes.

16/09/2017 · less, we now know that the volvocine lineage hypothesis is an oversimplification

Pandorina - an overview | ScienceDirect Topics

N2 - It has been argued that for certain lineages, noncoding DNA expansion is a consequence of the increased random genetic drift associated with long-term escalations in organism size. But a lack of data has prevented the investigation of this hypothesis in most plastid-bearing protists. Here, using newly sequenced mitochondrial and plastid genomes, we explore the relationship between organelle DNA noncoding content and organism size within volvocine green algae. By looking at unicellular, colonial, and differentiated multicellular algae, we show that organelle DNA complexity scales positively with species size and cell number across the volvocine lineage. Moreover, silent-site genetic diversity data suggest that the volvocine species with the largest cell numbers and most bloated organelle genomes have the smallest effective population sizes. Together, these findings support the view that nonadaptive processes, like random genetic drift, promote the expansion of noncoding regions in organelle genomes.

The remaining genera include Pandorina that ..

Chlorophyceae apparently arose during the later stages of green algal evolution and are not an early branching lineage (). This group includes a predominance of freshwater taxa such as Sphaeropleales (= Chlorococcales; e.g. Scenedesmus), and many of the familiar flagellates such as Volvox and Chlamydomonas (Volvocales). Recently, molecular techniques were used to re-examine phylogenetic relationships in Volvocales (, , ) as previously deduced by morphological and gene sequence data (; ). Volvox has been considered to be the limit of the colonial development in the volvocine series, in which Gonium and unicellular forms such as Chlamydomonas are early branching lineages (). Although much of the evolution in the colonial Volvocales superficially appears to constitute a gradual progression in colonial complexity and in types of sexual reproduction, as in the traditional volvocine lineage hypothesis, reverse evolution must be considered for the origin of certain species of Pleodorina (). Apparently, both colonial and unicellular morphotypes have evolved independently in several clades (, ; ). Thus, the traditional view of a unidirectional, monophyletic progression from unicellular, through colonial, to multicellular forms, represented by the sequence Chlamydomonas, Gonium, Pandorina, Eudorina, Pleodorina and Volvox, is not supported by gene sequence analyses (; ).

Molecular phylogeny of the volvocine flagellates | Read …