Sexual Plasticity and Self-Fertilization in the Sea Anemone Aiptasia diaphana

Traits that influence reproductive success and contribute to reproductive isolation in animal and plant populations are a central focus of evolutionary biology. In the present study we used an experimental approach to demonstrate the occurrence of environmental effects on sexual and asexual reproduction, and provide evidence for sexual plasticity and inter-clonal fertilization in laboratory-cultured lines of the sea anemone Aiptasia diaphana. We showed that in A. diaphana, both asexual reproduction by pedal laceration, and sexual reproduction have seasonal components. The rate of pedal laceration was ten-fold higher under summer photoperiod and water temperature conditions than under winter conditions. The onset of gametogenesis coincided with the rising water temperatures occurring in spring, and spawning occurred under parameters that emulated summer photoperiod and temperature conditions. In addition, we showed that under laboratory conditions, asexually produced clones derived from a single founder individual exhibit sexual plasticity, resulting in the development of both male and female individuals. Moreover, a single female founder produced not only males and females but also hermaphrodite individuals. We further demonstrated that A. diaphana can fertilize within and between clone lines, producing swimming planula larvae. These diverse reproductive strategies may explain the species success as invader of artificial marine substrates. We suggest that these diverse reproductive strategies, together with their unique evolutionary position, make Aiptasia diaphana an excellent model for studying the evolution of sex

The effect of temperature on larval pre-settlement duration and metamorphosis for the sponge, Rhopaloeides odorabile

Rising sea temperatures may potentially affect the dispersive larval phase of sessile marine invertebrates with consequences for the viability of adult populations. This study demonstrated that the planktonic larvae of Rhopaloeides odorabile, a common Great Barrier Reef sponge, survived and metamorphosed when exposed to temperatures up to 9°C above the annual maximum (~29°C). Planktonic larval duration of 54 h, at ambient temperatures (~28°C), were reduced to 18 h for larvae exposed to elevated temperatures (32–36°C). Moreover, at ambient temperatures larvae began metamorphosing after 12 h, but at 32–36°C this reduced to only 2 h. Larvae survived and could still metamorphose at temperatures as high as 38°C, but were no longer functional at 40°C. These results imply that predicted increases in sea surface temperature may reduce planktonic larval duration and dispersal capabilities, thereby contributing to population subdivision of the species

Roundtable Discussion Groups Summary Papers: Environmental Bio-Indicators in Coral Reef Ecosystems: the Need to Align Research, Monitoring, and Environmental Regulation

Editors\u27 Note: At the 14th International Conference on Environmental Bioindicators (14th ICEBI) held in Linthicum Heights, Maryland, USA on 24–26 April 2006, the Conference Chairs and Program Committee initiated the Roundtable Discussion Groups as a regular feature of this and future conferences. The Discussions are designed to generate focused debate around key topic areas, led by academic, government and industry experts, and are structured to produce definitive papers for peer review and publication in EBI\u27s first-quarter issue of each publication year, albeit this year the papers will be published over the first two issues of 2007. The three Roundtables of the 14th ICEBI posed questions revolving around the chosen topic areas of Mercury Bioindicators, Marine Ecosystem-level Indicators, and Regulatory and Policy Uses of Bioindicators, and moved from “what we know” to “where we need to go” and “what are the policy implications from our discussions and conclusions.” The following paper on coral reef indicators is the first product of this undertaking. The second Roundtable paper on Mercury Bioindicators, along with a summary of the third Roundtable on Regulatory and Policy Uses of Bioindicators, will occur in our next issue. A roundtable workshop was held on 24–26 April 2006 at the 14th International Conference on Environmental Bioindicators (14th ICEBI) to discuss environmental bioindicators as they apply to the coral reefs. Participants discussed procedures and potential bioindicators currently being used to monitor these ecosystems, those showing promise for future use, and candidates for future research and development. Attendees represented research and educational institutions, environmental consulting firms, and US federal government regulatory agencies. Despite the fact that these three interest-groups have similar ultimate objectives of protecting coral reef ecosystems, they are engaged in different activities, using different jargon and techniques, and are pursuing different proximal objectives. Their different perspectives presented challenges for information transfer among the groups. Coral reef scientists, both descriptive and experimental, are attempting to explain the underlying processes controlling reef health, and assign functional relationships within that system, making it possible to predict effects of natural or anthropogenic perturbations. Individuals involved in monitoring are attempting to document components of the ecosystem and their characters that might indicate the state of reef health through time, generally at the macro-scale. Such monitoring generally utilizes at least some of the basic ecological, geological, chemical, or physical relationships defined by the first group. The third group – the environmental regulators and resource managers – is attempting to set limits for defining methods that will defensively document transgressions by parties causing damage to the environment. They also provide guidance for remediation. Management objectives almost universally require “reference points” or “bands” or standards against which alleged violations can be compared and which can be confidently and demonstrably traced to some anthropogenic source, within the guidelines of the law. One of the problems recognized in the workshop was that differences in their respective objectives created communication and information gaps. Each group is encouraged to become conversant with the terminology and objectives of the other groups to provide a legal framework to effect environmental protection. Thus, for research and monitoring groups, reviewing the effectiveness of one bioindicator over another for predicting anthropogenic effects, although important, may be premature. Rather, it is more important to first understand the ultimate requirements of local, state, and federal governments, understand the staff and funding limitations of the resource management agencies, and become conversant with resource management terminology and needs. Then specific and relevant information can be channeled to the responsible regulatory bodies that will assist in achieving the common ultimate goal of environmental protection of coral reefs. A clear conclusion from this workshop is that a bioindicator review process must “start with the end in mind.

The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides

Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14-20 m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1 degrees-30.0 degrees C in mean increments of 0.4 +/- 0.1 degrees C (+/- SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5 degrees C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4 degrees-27.7 degrees C, and were smallest and had the lowest population densities at 25.8 degrees C and 28.8 degrees C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1 degrees C and 30 degrees C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatio-temporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase