Echinodermata: Asteroidea) As Affected by Population Density Ken A

This article was downloaded by: [Sterling, Ken A.] On: 24 February 2011 Access details: Access Details: [subscription number 933992417] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK Invertebrate Reproduction & Development Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t926968007 Rates of fission in Aquilonastra corallicola Marsh (Echinodermata: Asteroidea) as affected by population density Ken A. Sterlinga; Stephen M. Shustera a Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011-5640, USA First published on: 24 January 2011 To cite this Article Sterling, Ken A. and Shuster, Stephen M.(2011) 'Rates of fission in Aquilonastra corallicola Marsh (Echinodermata: Asteroidea) as affected by population density', Invertebrate Reproduction & Development, 55: 1, 1 — 5, First published on: 24 January 2011 (iFirst) To link to this Article: DOI: 10.1080/07924259.2010.548631 URL: http://dx.doi.org/10.1080/07924259.2010.548631 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Invertebrate Reproduction & Development Vol. 55, No. 1, March 2011, 1–5 Rates of fission in Aquilonastra corallicola Marsh (Echinodermata: Asteroidea) as affected by population density Ken A. Sterling* and Stephen M. Shuster Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011-5640, USA (Received 12 February 2010; final version received 10 August 2010) The sea star Aquilonastra corallicola reproduces asexually by splitting across the central disc, a process known as fission. Although photoperiod and body mass are known to influence the rate of reproduction in fissiparous asteroid species, to our knowledge, the effects of population density have not been experimentally measured in asteroids. We tested the effects of three population densities on the rate of fission in laboratory populations maintained for 4 months at low, medium, and high (n ¼ 5, 15, and 30 per treatment replicate, respectively) population densities. Our results show that population density has a significant, inverse effect upon rate of reproduction in this species. This suggests that density-dependent regulation of asexual reproduction is a significant factor in explaining the observed patterns of population structure in marine clonal invertebrates. Keywords: asexual reproduction; clonal invertebrates; density-dependent affects; fissiparous asteroid; metapopulation Introduction Mladenov 1996; Lawrence and Herrera 2000). Fissiparous sea stars are capable of reproducing Mladenov’s (1996) model illustrated various endoge- asexually by dividing across the central disc, usually nous and exogenous conditions that may lead to either resulting in two approximately equal halves that then the sexual or the asexual phase and its associated body regenerate into two complete animals (Emson and form. There is also evidence that similar exogenous and Wilkie 1980). This tendency is distinguished from other endogenous factors regulate rates of fission. asteroids capable of reproducing through ray autot- Rates of fission in the sea star Stephanasterias omy where one or more rays can be detached from the albula reach their peak in the spring and summer animal, sometimes as a defense mechanism, and the (Mladenov et al. 1986) when daylight is longest in the individual rays then regenerate into a complete animal northern hemisphere. Photoperiod, tidal influences, (Emson and Wilkie 1980). and temperature were all positively correlated with Fissiparous sea stars are generally thought to be higher rates of fission in Coscinasterias tenuispina heterogonic, able to reproduce both asexually and (Alves et al. 2002), while temperature and photoperiod Downloaded By: [Sterling, Ken A.] At: 20:52 24 February 2011 sexually (Emson and Wilkie 1980). Sexual reproduc- were positively correlated with higher rates of fission in tion seems to appear in favorable habitats and under Allostichaster capensis (Rubilar et al. 2005). Higher stable environmental conditions while asexual repro- temperature was also found to be a factor regulating duction appears to be favored in marginal habitat and fission in Coscinasterias acutispina (Haramoto et al. unstable environmental conditions (Crump and Barker 2007). Body mass has been shown to affect the rate of 1985; Achituv and Sher 1991; Mladenov 1996). This fission in Allostichaster insignis and Coscinasterias pattern of reproduction is expected to generate con- muricata, with smaller animals having a higher rate siderable local population structure, as is now well- of fission (Crump and Barker 1985; Barker and documented among clonal marine species exhibiting Scheibling 2008). The availability of food has also metapopulations (Okamura et al. 2002). been shown to influence relative rates of fission Other factors such as photoperiod, temperature, (Crump 1971; Skold et al. 2002; Haramoto et al. availability of food, salinity, pH, oxygen, and overall 2007; Barker and Scheibling 2008). stability of the habitat may influence the ratio of asexual Another factor that has been mentioned as a to sexual reproduction in a population of fissiparous sea potential cause of fluctuations in rates of fission in stars at any point in time (Emson and Wilkie 1980; sea stars is population density (Mladenov 1996); *Corresponding author. Email: [email protected] ISSN 0792–4259 print/ISSN 2157–0272 online ß 2011 Taylor & Francis DOI: 10.1080/07924259.2010.548631 http://www.informaworld.com 2 K.A. Sterling and S.M. Shuster although to our knowledge there have been no temperature to 25C. Light was provided by standard experimental publications upon this topic in asteroids. 40-W fluorescent fixtures and pH was maintained Evidence that population density has an effect upon between 8.2 and 8.3. The buffering capacity of the rates of asexual reproduction has been found in other water was 10–12 dKH (degrees carbonate hardness). invertebrates such as holothurians (Lee et al. 2008), We dissolved a commercially available synthetic sea zoanthids (Tanner 1999), rotifers (Hagiwara et al. water mix in distilled water to achieve a specific gravity 1994), Hydra pseudoligactis (Bell and Wolfe 1985), soft of 1.023. Shelter was provided by artificial rocks made corals (Karlson et al. 1996), and the polychaete worm from Portland cement that we poured into molds so Pygiospio elegans (Wilson 1983). that the rocks in each aquarium were identical. Three The sea star genus Aquilonastra was established of these rocks were placed in each aquarium. A small by O’Loughlin and Waters’s (2004) revision pump was placed in each aquarium to provide water of Asterinidae, who subsequently reorganized circulation and a 6 cm thick layer of dark gray calcite Aquilonastra species based on morphological charac- gravel provided the substrate. The sea stars fed on ters resulting in 13 new species and the recognition of diatoms and green algae growing on the rocks and several undescribed species (O’Loughlin and Rowe glass walls of the aquarium. As the glass walls and 2006). O’Loughlin and Rowe (2006) further state that rocks had identical surface areas in each aquarium, it it is likely that extant species with large geographical was assumed that food resources were identical in each ranges could prove to be more than one species. aquarium. Described species are also known to show great Sea stars were obtained through a retail reef morphological variation across their range aquarium supplier and the exact location of the (O’Loughlin and Rowe 2006). Current taxonomic source of the animals is unknown. Animals were relationships within the genus Aquilonastra are at divided into four size classes (54 mm, 4–5 mm, 5–6 mm, best provisional and as no molecular phylogenies have and 46 mm) and animals from each size class were been performed, we will use the species name haphazardly placed into replicates so that the mean Aquilonastra corallicola for the animal used in our size of the animals was roughly the same in each experiment though we recognize that it may be an replicate. We did not place the animals into the aquaria undescribed form of Aquilonastra. This species desig- until 6 weeks, after we had set them up to allow the nation was based on morphological characters from growth of diatoms and green algae as a food resource. published descriptions (Marsh 1977; Oguro 1983; We did not start collecting data until after the animals O’Loughlin and Rowe 2006). A. corallicola is a small, had been in the aquaria for 6 more weeks, enabling us cryptic sea star, the longest ray averaging only 4.33

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