No abstract

Red algal parasites are diverse organisms that are unusual due to the fact that many are closely related to their hosts. Parasitism has developed many times within different red algal groups, but the full extent of parasite biodiversity is unknown, as parasites are easily overlooked due to their small size and often low abundance. Additionally, the literature on red algal parasites is dispersed and has not been compiled in over 30 years. Although criteria have been proposed to define what constitutes a red algal parasite, many parasites are poorly described, and the cellular interactions with their host are poorly known. A few studies have demonstrated that parasites transfer organelles to host cells, which can alter the physiology of the host to the benefit of the parasite. Here, we apply a set of defining criteria for parasites to a compiled list of all described red algal parasites. Our results highlight the lack of knowledge of many key parasitic processes including early parasite development, host cell “control”, and parasite origin. Until the biology of more parasites is studied, generalisations on the processes of parasitism in red algae may be premature. We hope this synopsis will stimulate research into this fascinating group.

There are over 120 species of red algal parasites (Florideophyceae) but they are often overlooked due to their small size and patchy distribution. Red algal parasites have mostly been described as independent genera but recent phylogenetic studies have shown that parasites are related to free-living relatives, often their hosts, and have been named in these genera to maintain monophyly. We investigated the morphology, distribution and phylogeny, using diverse molecular markers (mitochondrial, nuclear, plastid), of three new red algal parasites in New Zealand. We describe the parasites using morphological and anatomical observations and estimate their distribution by surveying herbarium vouchers. Analyses of reproductive structures and molecular phylogenies indicate that the closest relative of the parasite Phycodrys novaezelandiaephila sp. nov. is its host, Phycodrys novae-zelandiae. Based on nuclear and mitochondrial markers, the closest relative of the parasite Cladhymenia oblongifoliaphila sp. nov. is its host Cladhymenia oblongifolia but plastid markers group it with Cladhymenia lyallii, suggesting that this species was a past host and the source of parasite plastids. The parasite Judithia parasitica sp. nov. groups with Judithia delicatissima but infects Blastophyllis spp., suggesting that this parasite evolved as a free-living or parasitic Judithia species, and host switching may have occurred. This study adds to our knowledge of New Zealand red algal parasites and highlights contrasting patterns of host-parasite relationships.

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Inter-and intra-specific physiological variations of intertidal macroalgae have been well investigated. However, studies on physiological responses of cryptic algal species have been poorly documented. Bostrychia intricata is a widespread marine red alga in the Southern Hemisphere, and has many cryptic species. We investigated the effect of different salinities and temperatures on the specific growth rate of three cryptic species (N2, N4 and N5) of B. intricata from New Zealand. Our data indicated that all cryptic species grew at the full range of salinities and temperatures tested, but exhibited a significant difference in their specific growth rates. Cryptic species N4 had a higher growth rate than the other two cryptic species under all experimental conditions, whereas cryptic species N2 occasionally showed a higher growth rate than cryptic species N5 at high salinities and lower temperatures. The distinct physiological properties of these cryptic species may explain their distribution pattern (a wider distribution of cryptic species N4 than N2 and N5) in New Zealand. The physiological divergence between the cryptic species could be related to their levels of evolutionary divergence, with more similar physiology between cryptic species, which share a more recent common ancestor (N2 and N5). Our findings underline that morphologically indistinguishable cryptic algal species are different in many other aspects and are truly independent entities.