A PHYLOGENETIC STUDY OF PARASITIC GENERA PLACED IN THE FAMILY CHOREOCOLACACEAE (RHODOPHYTA)¹

Abstract

Red algal parasites are common and have a unique type of development in which parasite nuclei are transferred to host cells and “control” host cell development. Previous phylogenetic studies have concentrated on parasites closely related to their hosts, termed adelphoparasites. A second set of parasites, usually classified in a different family or tribe from their host, termed alloparasites, have not been studied phylogenetically. This study concentrates on the wholly parasitic family, the Choreocolacaceae (Gigartinales). Using small subunit rDNA sequence data, we found that all the parasites studied are within the same family as their host. Our data support the placement of Holmsella, species of which parasitize Gracilaria and Gracilariopsis, in the order Gracilariales and suggest that Holmsella is an old parasitic genus. Most other species of the Choreocolacaceae parasitize species of the Rhodomelaceae. The one exception is the hyperparasitism between Harveyella mirabilis (Reinsch) F. Schmitz et Reinke (Rhodomelaceae) and the parasite Gonimophyllum skottsbergii Setchell (Delesseriaceae). The parasites Bostrychiocolax australis Zuccarello et West and Dawsoniocolax bostrychiae (Joly et Yamaguishi‐Tomita) Joly et Yamaguishi‐Tomita are placed within the tribe Bostrychiae as are their hosts. Harveyella mirabilis has a single origin and has switched hosts several times during its passage between the Atlantic and Pacific Oceans. Evidence does not support the continued recognition of the family Choreocolacaceae. Our results also indicate that the distinction between adelphoparasites and alloparasites is unwarranted, with a continuum between newly evolved parasites closely related to their hosts and parasites less closely related to their hosts.

What's in a name? Monophyly of genera in the red algae: Rhodophyllis parasitica sp. nov. (Gigartinales, Rhodophyta); a new red algal parasite from New Zealand

“…This Rhodophyllis parasite also produces 2nd PC between host and parasite cells, which have been observed in all described red algal parasites to date (Goff andZuccarello 1994, Kraft andAbbott 2002). This suggests that 2nd pit connections are an essential feature not only of the early developmental stages of the parasite (Zuccarello et al 2004) but are also essential for parasite-host development (Goff andColeman 1985, Zuccarello andWest 1994). 2nd pit connections allow the parasite to transfer nuclei and cytoplasmic organelles to host cells (Goff and Coleman 1984) and appear to give the parasite control over the host cells (Goff and Coleman 1987); the parasite changes the metabolism within the infected host cells and transforms the morphology of host cells (Goff and Zuccarello 1994).…”

“…The incorporation of the parasites into the host genus also changes the morphological circumscription of the host genus. We feel that this is not a serious issue as the genus can be amended to include "and the parasites derived from it," but this needs to be tested as some parasites are not so closely related to their hosts (Zuccarello et al 2004). The first example to follow this practice is the transfer of Congracilaria babae Yamamoto to Gracilaria babae (Yamamoto) P. -K. Ng et al as it is nested in the host genus (Ng et al 2014).…”

“…Molecular studies are helpful in determining the evolutionary relationship between host and parasite (Zuccarello et al 2004). Gene sequences of plastid DNA have shown that they are mostly identical between hosts and parasites, which suggests that red algal parasite retain the host plastids (Goff and Coleman 1995).…”

“…Red algal parasites are common on other red algae and have been described from several orders within the Florideophyceae (Goff 1982), a few molecular-based phylogenetic studies have focused on a handful of species (Goff et al 1997, Zuccarello et al 2004, Ng et al 2013, with new species still being described (Kim and Cho 2010).…”

Are all red algal parasites cut from the same cloth?

“…Therefore, understanding the evolutionary trajectory between photosynthesis and abandoning autotrophy for a parasitic strategy, is of particular importance. Red algal parasites are uniquely valuable to study this path because they have independently evolved many times, providing literally dozens of discrete events to compare [4][5][6][7]. This system may provide novel insights into the evolution of parasitism, especially with regard to the early stages of transitioning from a photosynthetic past.…”