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Cnidae sizes in the two morphotypes of the giant Caribbean anemone Condylactis gigantea (Actiniaria: Actiniidae

The sea anemone Condylactis gigantea is an ecologically important member of the benthic community in coral reefs of the tropical Atlantic, and displays two morphotypes with respect to the color in their tentacular tips: the green tip morphotype and
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  1055 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 66(3): 1055-1064, September 2018 Cnidae sizes in the two morphotypes of the giant Caribbean anemone Condylactis gigantea (Actiniaria: Actiniidae) Ricardo González-Muñoz 1 *, Carlos Hernández-Ortiz 2 , Agustín Garese 1 , Nuno Simões 3  & Fabián Horacio Acuña 1 1. Laboratorio de Biología de Cnidarios, Instituto de Investigaciones Marinas y Costeras, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata-CONICET, Rodríguez Peña 4046, 7600 Mar del Plata, Argentina; ricordea.gonzalez@gmail.com, agustingarese@gmail.com, facuna@mdp.edu.ar 2. Departamento de Acuacultura y Biología Marina, Escuela de Ciencias Aplicadas del Mar, Universidad de Oriente,  Núcleo Nueva Esparta, Boca de Río, Isla de Margarita, Venezuela; cehernanort@gmail.com3. Unidad Multidisciplinaria de Docencia e Investigación en Sisal (UMDI-Sisal), Facultad de Ciencias, Universidad  Nacional Autónoma de México (UNAM), Puerto de Abrigo, Sisal, 97356, Yucatán, México; International Chair of Coastal and Marine Studies in Mexico, Harte Research Institute, Texas A&M at Corpus Christi, TX, USA; Laboratorio  Nacional de Resiliencia Costera (LANRESC); ns@ciencias.unam.mxReceived 15-II-2018. Corrected 29-V-2018. Accepted 27-VI-2018. Abstract: The sea anemone Condylactis gigantea  is an ecologically important member of the benthic com-munity in coral reefs of the tropical Atlantic, and displays two morphotypes with respect to the color in their tentacular tips: the green tip morphotype and the pink/purple tip morphotype. Although some molecular and ecological differences have been found between these morphotypes, no other morphological distinctions have  been reported, and currently both are still considered a single taxonomic species. In the present study, we  perform an exploration on the variability in the size of cnidae between these two morphotypes and performed statistical analyses to compare the 10 categories of cnidae from specimens hosted in the Cnidarian Collection of Gulf of Mexico and Mexican Caribbean, of the Universidad Nacional Autónoma de México, which were previ-ously collected in several coral reefs localities of the Yucatán Peninsula. Results reveal no significant variation in cnidae size between the two morphotypes, but significant variations were found within each morphotype. In addition, we update the composition of the cnidom of C. gigantea , and the utility of the size of cnidae to dis-tinguish between morphotypes or closely related species is discussed. Rev. Biol. Trop. 66(3): 1055-1064. Epub 2018 September 01. Key words:  Cnidaria; Anthozoa; cnidom; coral reefs; morphotype; Condylactis gigantea. The giant Caribbean sea anemone Condy-lactis gigantea  (Weinland, 1860) (Actiniaria, Actiniidae) is one of the most common and well-known actiniarian species that inhabits in coastal and coral reefs environments of the Western Atlantic Ocean, and is distributed from Bermuda to southeast Brazil, and along the Gulf of Mexico and the Caribbean Sea (González-Muñoz, Simões, Sánchez-Rodrí-guez, Rodríguez, & Segura-Puertas, 2012). This species is an ecologically important member of the benthic community providing habitat for several species of caridean cleaner shrimps (Silbiger & Childress, 2008; Colom- bara, Quinn, & Chadwick, 2017), as well as symbiotic associations with some species of Caribbean fishes (Hanlon & Kaufman, 1976; Hanlon & Hixon, 1986). Moreover, this spe-cies is also recognized as an important source of biologically active compounds (e.g. Billen, Debaveye, Béress, Garateix, & Tytgat, 2010; Romero et al., 2010; Santos et al., 2013) and, due to its brightly colors and attractive forms, it is much appreciated in the aquarium trade (Chi-appone, Swanson, & Miller, 2001; Sheridan, Fautin, & Garret, 2015).  1056 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 66(3): 1055-1064, September 2018 Condylactis gigantea displays two main morphotypes, particularly with respect to color in the tentacular tips, which can be categorized as the green tip (Fig. 1A) and the pink/purple tip morphotypes (Fig. 1B), although some indi-viduals with whitish, yellowish, or bluish ten-tacular tips can be also rarely found. Previous genetic comparisons with DNA sequence data have found some differences between these two morphotypes from specimens of different depths and reef areas, as well as differences in UV absorbance capacities, suggesting reduced gene flow and ecological differentiation among the green and the pink/purple morphotypes at a small geographic scale (Stoletzki & Schi-erwater, 2005). Other differences between these morphotypes have also been observed on  personality and habitat segregation (Hensley, Cook, Lang, Petelle, & Blumstein, 2012). However, no other morphological differences  between these two morphotypes have been reported and both are currently considered a single taxonomic species.Despite the size of cnidae alone is not necessarily a conclusive taxonomic character to differentiate between species due to its vari-ability within conspecific individuals (Fautin, 2009; Garese, Carrizo, & Acuña, 2016), some studies consider them as an additional specific taxonomic characteristic to distinguish between closely related species, but only when these differences are accompanied by other mor- phological or ecological distinctions (Fautin, 1988). Some studies including quantitative analyses of the size of cnidae to distinguish  between closely related species or between Fig. 1.  Morphotypes of Condylactis gigantea : a.  Green morphotype. b.  Pink/Purple morphotype. Cnidom of C. gigantea   per tissue type. Actinopharynx: c.  small basitrich. d.  large basitrich. Column: e.  small basitrich. f.  large basitrich. Filaments: g.  small basitrich. h.  large basitrich. i.  microbasic b -mastigophore.  j.  microbasic  p -mastigophore. Tentacles: k.   basitrich. l.  spirocysts.  1057 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 66(3): 1055-1064, September 2018 morphotypes suggests results of two opposite sorts. Some studies found significant statistical differences in cnidae sizes comparisons (e.g. Allcock, Watts, & Thorpe, 1998; Watts & Thor- pe, 1998; Manchenko, Dautova, & Latypov, 2000; Watts, Allcock, Lynch, & Thorpe, 2000), while other attempts did not find statistical sup- port to clearly separate species or morphotypes  based on cnidae size differences (e.g. Solé-Cava & Thorpe, 1987; Chintiroglou & Karalis, 2000; González-Muñoz et al., 2015; González-Muñoz, Garese, Tello-Musi, & Acuña, 2017).In the present study, we performed an exploration on the variability in the size of cni-dae and statistically analyze them to compare  between the two morphotypes of C. gigantea , from preserved specimens of the Collection of Cnidarians of the Gulf of Mexico and Mexi-can Caribbean, of the Universidad Nacional Autónoma de México (UNAM). In addition, we update the composition of the cnidom of C.  gigantea , and discuss about the utility of the size of cnidae to distinguish between closely related species or between morphotypes.MATERIALS AND METHODSFive specimens of each of the two mor- photypes were selected from the Collection of Cnidarians of the Gulf of Mexico and Mexican Caribbean Sea (Registration code: YUC-CC-254-11) of the Unidad Multidisci- plinaria de Docencia e Investigación - Sisal (UMDI-Sisal) at the UNAM. Specimens were selected based on the photographs of the living specimens which are included in each record of the collection. All specimens were collected in coastal coral reefs localities along the Yuca-tán Peninsula (Appendix). Pedal disc diam-eter and column height of the samples were measured from living specimens (Appendix); however, comparisons between morphotypes were made regardless the size of the specimens or their reef localities. Four squash prepara-tions were obtained from the main tissue types (~1 mm 3 ) of each specimen. Cnidae capsules were analyzed from tissues from tentacles, actinopharynx, mesenteric filaments, and mid column. Terminology follows Östman (2000). From each of the four squash preparations, the length and width of 30 undischarged capsules (replicates) of each type of cnidae were ran-domly measured using DIC microscopy 1 000x oil immersion (following Williams, 1996). Cni-dae preparations were deposited in the same Cnidarian collection.Cnidae samples were ordered in a bi-dimensional space using principal component analysis (PCA). Differences in ordination given by morphotype and individual specimens within each morphotype were analyzed using a  permutational multivariate analysis of variance (PERMANOVA) procedure (Anderson, 2001). Differences among cnidae size were analyzed for each type of cnidae and tissue separately. The PERMANOVA procedure was applied on resemblance matrices based on the Euclidian distance between samples. Although length and width of the capsules were in the same mea-surement unit, data were normalized prior to analyses. The statistical model used was given  by: Y  ijkl  = M  i +I(M)  j(i) +T  k  +MT  ik  +I(M)T   j(i)k  +e ijkl  , where Y   is the response matrix with n  samples *   P   = 2 variables (number of columns: length and width);  M   is a fixed factor representing mor- photype (with two levels);  I   is a random factor representing individuals nested in  M   (with five levels); T   is the fixed factor representing type of cnidae and is orthogonal to  M   and  I  ;  MT   and  I(M)T   are corresponding interactions terms; and e  is the residual matrix. Permutation pro-cedures were applied to obtain appropriate dis-tributions for the  pseudo-F   statistic under the null hypothesis. All analyses were performed using 999 permutations of residuals under the reduced model. The experimental design was  balanced in every case, and the partitioning of variation was achieved so that the statistic test represents the proportion of the variation in the  bi-dimensional cloud that is explained by the source of variation being tested. All analyses were performed using the software Primer v6 (Clarke & Gorley, 2006).  1058 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 66(3): 1055-1064, September 2018 RESULTSThree hundred cnidae capsules per each specimen were measured, to a total of 3 000 capsules. The same five types of cnidae, dis-tributed in 10 categories regarding the size class and tissue location, were found in all samples of C. gigantea , regardless of morphot-ype. The cnidom of both morphotypes includes  basitrichs (two size categories), microbasic  p -mastigophores, microbasic b -mastigophores, and spirocysts (Fig. 1C, Fig.1D, Fig. 1E, Fig. 1F, Fig. 1G, Fig. 1H, Fig. 1I, Fig. 1J, Fig. 1K and Fig. 1L).The PCA ordination of samples from all tissue types showed that the first principal com- ponent explained a higher percentage of vari-ability in all cases (Table 1). The first principal component represents the cnidae length, while the second principal component is related with the cnidae width (Fig. 2 and Fig. 3). Overall, no significant variation in cnidae size between the green and pink/purple morphotypes was found in any of the comparisons made (Table 1). However, significant variations in cni-dae size were found within each morphotype, in all cases.DISCUSSIONPrevious taxonomic revisions on C. gigan-tea  include only three types of cnidocysts as  part of their cnidom: basitrichs, microbasic  p -mastigophores, and spirocysts (Carlgren, 1949, 1952; González-Muñoz et al., 2012). In the present study, we report the additional find-ing of microbasic b -mastigophores in the mes-enterial filaments of all specimens examined of C. gigantea . Microbasic b -mastigophores have not been previously reported in other spe-cies of the genus Condylactis , but are common in several species classified within the fam-ily Actiniidae and the superfamily Actinioidea Rafinesque, 1815 (Rodríguez et al., 2014). Thus, although its encounter could be expected, also contribute to a better understanding of the cnidae variability within the genus Condylactis  and within Actiniidae.Regarding statistical analyses of the size of cnidae, significant variability was found  between specimens within each morphotype, as have been also observed in other studies (e.g. Allcock et al., 1998; Watts et al., 2000; González-Muñoz et al., 2015, 2017; Garese, Carrizo, & Acuña 2016). However, the com- parison between the green and pink/purple morphotypes reveals no statistical variation, agreeing with previous morphological revi-sions which suggest that there are no other morphological differences between the mor- photypes, besides the variability in the ten-tacular tip coloration (González-Muñoz et al., 2012). In other species of sea anemones the variation between morphotypes occurs also TABLE 1Probability associated with  pseudo -F values obtained through restricted permutations of the residuals of MANOVA models applied to the similarity matrices (Euclidean distance) calculated from cnidae sizes (length and width)TissueCnidae typePC1 %PC2 %  P    (morph)  P    (Ind[Morph])ActinopharynxSmall basitrichs59.740.30.8650.001*Large basitrichs63.136.90.9490.001*ColumnSmall basitrichs56.143.90.8270.001*Large basitrichs67.132.90.7090.001*FilamentsSmall basitrichs59.240.80.2650.001*Large basitrichs53.846.20.6200.001*Microbasic b -mastigophores55.544.50.2700.001*Microbasic  p -mastigophores50.749.30.3010.001*TentaclesBasitrichs56.643.40.4790.001*Spirocysts74.026.00.5830.001** = Significant values.  1059 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 66(3): 1055-1064, September 2018 anatomical structures besides the coloration, such as the tentacular variation of  Phymanthus crucifer   (Le Sueur, 1817) (González-Muñoz et al., 2015); or the variation in the cnidae size range in  Lebrunia coralligens  (Wilson, 1890) (González-Muñoz et al., 2017). Furthermore, although our analyses only focused in the comparison between morphotypes regardless samples body size or reef locality of srcin, results suggest a high degree of stability in the size of cnidae of C. gigantea .Intraspecific variation of cnidae size is a known fact in sea anemones (Garese et al., 2016) and it has been suggested that could be a result of several factors as distinct body sizes or weights (e.g. Chintiroglou & Simsiridou, Fig. 2.  Principal component analyses of cnidae data (length/width) from actinopharynx, column, and filament tissues; data from all specimens examined. Data of size of cnidae of the Green morphotype are represented by unfilled triangles and those of the Pink/Purple morphotype by black triangles.
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