Kayley M. Usher

Vertical transmission of cyanobacterial symbionts in the marine sponge Chondrilla australiensis (Demospongiae)

The cyanobacterial symbionts of the marine sponge Chondrilla australiensis (Demospongiae) were examined using fluorescent microscopy and Transmission Electron Microscopy. Unicellular cyanobacteria with ultrastructure resembling Aphanocapsa feldmannii occur in the cortex and bacterial symbionts are located throughout the mesohyl. In C. australiensis, the developing eggs are distributed throughout the mesohyl and are surrounded by nurse cells attached to them by thin filaments. The nurse cells form cytoplasmic bridges with the eggs, apparently releasing their contents into the egg cytoplasm. The presence of cyanobacterial and bacterial symbionts inside developing eggs and nurse cells in 25% of female Chondrilla australiensiswas established using Transmission Electron Microscopy, suggesting that these symbionts are sometimes passed on to the next generation of sponges via the eggs.

The Biogeography and Phylogeny of Unicellular Cyanobacterial Symbionts in Sponges from Australia and the Mediterranean

The distribution, host associations, and phylogenetic relationships of the unicellular cyanobacterial symbionts of selected marine sponges were investigated with direct 16s rDNA sequencing. The results indicate that the symbionts of the marine sponges Aplysina aerophoba, Ircinia variabilis, and Petrosia ficiformis from the Mediterranean, four Chondrilla species from Australia and the Mediterranean, and Haliclona sp. from Australia support a diversity of symbionts comprising at least four closely related species of Synechococcus. These include the symbionts presently described as Aphanocapsa feldmannii from P. ficiformis and Chondrilla nucula. A fifth symbiont from Cymbastela marshae in Australia is an undescribed symbiont of sponges, related to Oscillatoria rosea. One symbiont, Candidatus Synechococcus spongiarum, was found in diverse sponge genera in the Mediterranean Sea and the Indian, Pacific, and Southern oceans, whereas others were apparently more restricted in host association and distribution. These results are discussed in terms of the biodiversity and biogeographic distributions of cyanobacterial symbionts.

Diversity and abundance of photosynthetic sponges in temperate Western Australia

BackgroundPhotosynthetic sponges are important components of reef ecosystems around the world, but are poorly understood. It is often assumed that temperate regions have low diversity and abundance of photosynthetic sponges, but to date no studies have investigated this question. The aim of this study was to compare the percentages of photosynthetic sponges in temperate Western Australia (WA) with previously published data on tropical regions, and to determine the abundance and diversity of these associations in a range of temperate environments.ResultsWe sampled sponges on 5 m belt transects to determine the percentage of photosynthetic sponges and identified at least one representative of each group of symbionts using 16S rDNA sequencing together with microscopy techniques. Our results demonstrate that photosynthetic sponges are abundant in temperate WA, with an average of 63% of sponge individuals hosting high levels of photosynthetic symbionts and 11% with low to medium levels. These percentages of photosynthetic sponges are comparable to those found on tropical reefs and may have important implications for ecosystem function on temperate reefs in other areas of the world. A diverse range of symbionts sometimes occurred within a small geographic area, including the three big cyanobacterial clades, Oscillatoria spongeliae, Candidatus Synechococcus spongiarum and Synechocystis species, and it appears that these clades all occur in a wide range of sponges. Additionally, spongin-permeating red algae occurred in at least 7 sponge species. This study provides the first investigation of the molecular phylogeny of rhodophyte symbionts in sponges.ConclusionPhotosynthetic sponges are abundant and diverse in temperate WA, with comparable percentages of photosynthetic to non-photosynthetic sponges to tropical zones. It appears that there are three common generalist clades of cyanobacterial symbionts of sponges which occur in a wide range of sponges in a wide range of environmental conditions.

Inter-generational transmission of microbial symbionts in the marine sponge Chondrilla australiensis (Demospongiae)

Mechanisms for the biparental transmission of microbial symbionts to offspring in the marine sponge Chondrilla australiensis are reported. The observation of microbial mutualists in the sperm of C. australiensis is the first report of this kind in any organism, as far as we are aware. The developing eggs were shown by transmission electron microscopy (TEM) to incorporate intercellular cyanobacterial and bacterial symbionts. Nurse cells appeared to transport cyanobacterial symbionts from the surface layers of the sponge to eggs deeper in the matrix, where they were incorporated into the egg cytoplasm prior to spawning. This suggests that a host mechanism exists to actively recognise and incorporate symbionts, ensuring that larvae contain these mutualists before settlement. In addition, an average of 1.64% of mature sperm of C. australiensis contained cyanobacterial symbionts in their cytoplasm. The successful transmission of cyanobacterial symbionts to larvae was demonstrated by autofluorescent microscopy and TEM. The occurrence of organisms with functional mechanisms for transmission of symbionts from both parents to offspring provides the potential for new insights into the nature of host-symbiont interactions.

Sexual reproduction in Chondrilla australiensis (Porifera : Demospongiae)

Increasingly, sponges are being used as models for a wide range of biological systems. However, little is known about the reproductive biology of a group that has been shown to lack gonads or gonadal ducts. The development of gametes in the oviparous demosponge Chondrilla australiensis at Fremantle, Western Australia, was investigated using light microscopy and transmission electron microscopy over 5 years. Results indicate that C. australiensis is gonochoric and oviparous. Egg and sperm development were first apparent inside choanocyte chambers, with both types of gamete apparently developing from choanocytes. During egg development, large numbers of nurse cells appeared attached to eggs, with which they fused at the time of spawning. The origin of the nurse cells remains unclear, but they may also have a choanocyte origin. Eggs took 4 weeks to develop and sperm took approximately 2 weeks, during which time the nucleus condensed and the cytoplasm reduced. Mature sperm could occupy almost the entire matrix of fecund males and were not contained in cysts. Spawning occurred in late summer and autumn over a period of 4-5 days, when the tides were at the maximum height for the month.

Comparative morphology of five species of symbiotic and non-symbiotic coccoid cyanobacteria

The morphology of five unicellular cyanobacterial species from two genera was compared using transmission electron microscopy (TEM) and statistical analyses. Cyanobacteria symbiotic with marine sponges from Australia and the Mediterranean were investigated, together with cyanobacteria from the water column in Western Australia. The aim was to establish whether phenotypic characteristics are useful for distinguishing cyanobacterial species, and to investigate the possible relationships of host species and geographic location on cyanobacterial morphology. Analysis of variance (ANOVA) demonstrated that cell size of the symbionts, Synechococcus spongiarum and Aphanocapsa feldmannii, is directly correlated with the number of turns of the thylakoid, and this must be accounted for in comparative morphological analyses. S. spongiarum cells were approximately one third smaller than those of A. feldmannii, but did not vary significantly in size in Chondrilla australiensis collected from different localities, or in different hosts, including C. nucula and Ircinia variabilis. Other symbionts, including Oscillatoria sp. from Cymbastela marshae, and Aphanocapsa raspaigellae from I. variabilis, were readily distinguished in the sponges examined, both by size and ultrastructural features. While morphological differences appear to be useful in differentiating A. feldmannii from S. spongiarum, morphological similarities are not a reliable indication that coccoid cyanobacteria are the same species.

Larval development, ultrastructure and metamorphosis in Chondrilla australiensis Carter, 1873 (Demospongiae, Chondrosida, Chondrillidae)

Summary This study investigated the cleavage, development and ultrastructure of larvae and settlers in the oviparous sponge Chondrilla australiensis, using electron and light microscopy. Fertilization is internal, and cleavage is total and equal. Swimming coeloblastula larvae are present after 24 h, and are 50–75μm in diameter. They are completely ciliated, spherical or ovoid, with a flattened posterior pole on which longer cilia occur. Larvae are composed only of a monostratified layer consisting of a relatively small number of columnar, monociliated cells. Intercellular junctions join the apical parts of the cells. The small central cavity contains dense populations of bacterial and cyanobacterial symbionts. After a free-swimming period of 24–36 h, larvae settle on the substratum by the anterior pole. Metamorphosis occurs by the dedifferentiation and rearrangement of ciliated cells, which are the source of all adult cells in C. australiensis. Results of our research confirm the monophyly of order Chondrosida.

Isolated microspore culture of chickpea (Cicer arietinum L.): induction of androgenesis and cytological analysis of early haploid divisions

Routine production of haploid plants has not been reported for any legume, despite the major role these species play in sustainable farming systems and human nutrition. It is within this context that we report a protocol for the induction of haploid development in chickpea (Cicer arietinum L.) using isolated microspore culture. The cultivars “Rupali”, “Narayen”, and “Kimberley Large” were identified as responsive to isolated microspore culture. Flower bud length and microspore developmental stage were correlated for these cultivars. Depending on the cultivar, buds 2.85–3.5xa0mm in length contained uninucleate microspores. Microspores from donor plants grown in winter and spring were more responsive than those grown in summer. A cold treatment (4°C) of between 24 and 48xa0h enhanced microspore response in winter- and spring-grown material but was not effective in summer-grown material. A medium developed by the authors was effective for microspore induction and early-stage embryo development. The addition of hormones to this medium was promotive of microspore induction in winter- and spring-grown material, but not in summer-grown material. The initial haploid division predominantly occurred via symmetrical division of the vegetative nucleus. Further research is under way to convert pro-embryos into plants.

First record of photosynthetic cyanobacterial symbionts from mesophotic temperate sponges

Cyanobacterial symbionts may enable sponges to play a critical role in bentho-pelagic coupling, recycling nutrients at the benthic surface and providing a key requirement for ecosystem function. This is the first study to investigate the depths to which these symbioses are viable and the first record of photosynthetic sponges (i.e. sponges having a symbiotic relationship with photosynthetic cyanobacteria) from mesophotic temperate habitats. Sponges with high levels of photosynthetic cyanobacteria occurred at depths of up to 50u2009m, medium levels to 75u2009m and low levels to 150u2009m off south-western Australia. The proportion of sponges that showed no epifluorescence increased greatly with depth. Cyanobacterial symbionts sequenced from sponges at 40 and 50u2009m belonged to the genera Synechococcus and Synechocystis. Our results verify that the domain of photosynthetic sponges is not just tropical or shallow water temperate environments. Sponges made up the highest biomass of biota across all the sites we sampled from depths of 30–150u2009m and we hypothesise that photosynthetic cyanobacterial symbionts may be important in facilitating sponges to dominate habitats at these depths off Australia’s oligotrophic west coast.