Notheia is believed to be an
obligateepiphyte of Hormosira banksii, although there is a single unconfirmed observation of Notheia attached to
Xiphophora chondrophylla).[2][4][5]Hormosira is also from the order
Fucales - and it is rare to have an
epiphyte so closely related to its host.[citation needed]Notheia growth appears to be entirely dependent upon its host. Attempts to grow Notheia in culture were unsuccessful until Hormosira extracts were included.[1]
The costs to Hormosira in this relationship are still unclear. Although the tissues of Hormosira are pushed up tightly against the
thallus of Notheia, which gives the impression that Notheia emerges from deep within the host, there are no
plasmodesmata observed between adjacent Notheia and Hormosira cells.[1] Similarly, the benefits that Notheia obtains from attaching to Hormosira are also unclear. The fronds of Hormosira are weakly attached to the substratum and there is frequent dislodgement in storm events or periods of high wave energy – therefore the fronds that drift may offer long-distance dispersal to Notheia which could be a key mechanism for the distributional success of this species[6] Capon et al. (1998) [7] highlighted for the first time that
tetrahydrofurans from Notheia act as potent and selective inhibitors of the
larval development of
parasiticnematodes, which may be a positive effect that Hormosira receives from this
symbiotic relationship. Notheia has a higher
photosynthetic capacity than its host Hormosira, probably because of its greater surface area or smaller allocation to chemical defences.[8]
In natural populations of Hormosira in Australia, tide pools have a consistently higher proportion of infected plants with Notheia than the low shore reef populations.[1] This pattern suggests that Notheia has narrower environmental tolerances than its host. Sexually mature Hormosira have been observed to carry more infections and that infections were usually most abundant on the conceptacles - usually next to the osteoles (conceptacles openings). Although Hormosira is
dioecious, Nothiea does not appear to exhibit any preference towards settlement on male or female plants.[1]
Analyses of Notheiabiomass have shown a strong positive effect on
invertebratebiodiversity.[4]Notheia provides food, protection, and niche space for a large range of small
invertebrates, which in turn are an important source of food for higher
trophic levels.[4]
Images of Notheia anomala
Notheia growing on Hormosira in a tide pool at
Kaikōura, New Zealand
Notheia growing on Hormosira
A thallus of Hormosira covered in Notheia
Base of a Notheia plant attached to Hormosira tissue
Notheia conceptacles. Photo taken from an embedded wax block during histology studies
Notheia is
monoecious and produces male and female
gametangia in the same
conceptacle.[1][2] Female gametangia are present throughout the year, and they develop either on branched or unbranched stalks within the
conceptacle, or directly from the walls of
conceptacles. They contain 8
zooids each 10-12 μm long by 5-6 μm wide. About 4 hours after release via
paraphyses, female gametes begin to settle. Male
gametangia have been observed only between April and July (
Southern Hemisphere,
Australia). They are borne in a similar manner to the female
gametangia, and contain 64
zooids, each 5 μm long by 2-3 μm wide.
Both
gametes are pyriform in shape (pear form) with two laterally inserted
flagella (the anterior one longer than the posterior). They each possess one
eyespot - and have never been observed to contain two or more. Male and female
gametes freely intermingle within a
conceptacle, but as long as female gametes are motile, males are not attracted to them. About 4 h after release, female
gametes settle on surrounding
Hormosira tissue, and once that has occurred, the male
gametes are then attracted to the settled female
gametes.
References
^
abcdefghiHallam, N. D., Clayton, M. N., & Parish, D. (1980). Studies on the association between Notheia anomala and Hormosira banksii (Phaeophyta). Australian Journal of Botany, 28(2), 239-248.
^
abcdeGibson, G., & Clayton, M. N. (1987). Sexual reproduction, early development and branching in Notheia anomala (phaeophyta) and its classification in the Fucales. Phycologia, 26(3), 363-373.
^
abcMetcalfe, Iris Hayrunisa (2017). Phenological, physiological, and ecological factors affecting the epiphyte Notheia anomala and its obligate host Hormosira banksii (Master of Science in Biology thesis). University of Canterbury.
hdl:
10092/13428.
^
abcThomsen, M. S., Metcalfe, I., South, P., & Schiel, D. R. (2016). A host-specific habitat former controls biodiversity across ecological transitions in a rocky intertidal facilitation cascade. Marine and Freshwater Research, 67(1), 144-152.
^Raven, J. A., Beardall, J., Johnston, A. M., Kuebler, J. E., & McInroy, S. G. (1996). Inorganic carbon acquisition by Xiphophora chondrophylla (Phaeophyta, Fucales). Phycologia, 35(2), 83-89.
^McKenzie, P. F., & Bellgrove, A. (2009). Dislodgment and attachment strength of the intertidal macroalga Hormosira banksii (Fucales, Phaeophyceae). Phycologia, 48(5), 335-343.
^Capon, R. J., Barrow, R. A., Rochfort, S., Jobling, M., Skene, C., Lacey, E., Gill, J. H., Friedel, T., & Wadsworth, D. (1998). Marine nematocides: tetrahydrofurans from a southern Australian brown alga, Notheia anomala. Tetrahedron, 54(10), 2227-2242.
^Raven, J., Beardall, J., Johnston, A., Kübler, J., & Geoghegan, I. (1995). Inorganic carbon acquisition by Hormosira banksii (Phaeophyta: Fucales) and its epiphyte Notheia anomala (Phaeophyta: Fucales). Phycologia, 34(4), 267-277.