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Department of Biological Science, Florida State University, Tallahassee, Florida 32306-1100
*To whom correspondence should be addressed. E-mail: Wulff{at}bio.fsu.edu
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionLiterature Cited |
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionLiterature Cited |
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Sponges are among the most abundant and diverse sessile animals in many hard substratum marine habitats, including coral reefs, mangrove roots, rock walls, and caves. Their conspicuous diversity of colors and growth forms superficially make identification seem clear-cut, but the relative paucity of quantifiable morphological characters, and the malleability of overall form, makes sponge systematics particularly challenging. Many sponge species have gone through series of name changes and movement among families and even orders of Demospongiae (e.g., Hooper and van Soest, 2002). Measurements and descriptions of skeletal elements have been the mainstay of species distinctions, but closer scrutiny with information derived from microscopy, chemistry, and molecular techniques has demonstrated that some species that had long been considered to be cosmopolitan, or morphologically variable, are actually more than one species (e.g., Boury-Esnault et al., 1992, 1993, 1999; Solé-Cava et al., 1992; Klautau et al., 1994; Solé-Cava and Boury-Esnault, 1999; Boury-Esnault and Solé-Cava, 2004).
A few species have distinctive characteristics that have allowed apparently unambiguous identification for more than a century. Tedania ignis (Duchassaing and Michelotti), the common Caribbean fire sponge, is one of these species. The genus Tedania, which is distributed worldwide, has recently received much attention in the systematics literature. It has been placed in a separate family (Tedaniidae) within the Order Poecilosclerida (Bergquist and Fromont, 1988; Hooper and Wiedenmayer, 1994; Desqueroux-Faúndez and van Soest, 1996), and recent descriptions of new species have provided impetus for reinterpretation of previous species assignments in Brazil (Mothes et al., 2000), the southeastern Pacific (Desqueyroux-Faúndez and van Soest, 1996), the western Pacific (Kennedy and Hooper, 2000), and the Iberian Peninsula (Cristobo, 2002). Throughout this period of scrutiny, T. ignis has remained undisturbed, although a number of specimens previously regarded as other species are now considered to be T. ignis (e.g., Mothes et al., 2000). T. ignis was described as Thalysias ignis by Duchassaing and Michelotti in 1864 and was moved to Tedania by Verrill (1907). It is a conspiciuous sponge, with a bright saturated orange color and a characteristic spicule complement and growth form, and it causes contact dermatitis in humans. As one of the most common, readily collected, and easily manipulated species in the tropical western Atlantic, it has provided fertile material for chemistry (e.g., Schmitz et al., 1984; Garson, 1993; Monks et al., 2002), larval biology (e.g., Jaeckle, 1995; Maldonado and Young, 1996; Maldonado, 1998), and ecology (e.g., Sutherland, 1980; Bingham and Young, 1991; Wulff, 1995, 2005; Ellison et al., 1996; Dunlap and Pawlik, 1996; Nunez et al., 1999).
In June 2001 I first noticed sponges similar to T. ignis, and with the same spicule complement, living in seagrass meadows near Twin Cays, Belize. Their subtle differences in morphology and coloration could have been attributed to environmental differences in the seagrass meadow, relative to the nearby mangrove roots on which T. ignis is abundant, but for one observation: experiments investigating sponge feeding by the large, common, seagrass-dwelling starfish Oreaster reticulatus had demonstrated that it readily consumes T. ignis collected from mangrove roots, but consistently rejects most seagrass-dwelling sponge species (Wulff, 1995). The starfish rapidly find and consume edible sponges that wash into seagrass beds from reefs or that fall off of mangrove roots (Wulff, 1995, 2000). Thus T. ignis in a seagrass bed inhabited by Oreaster was a clear anomaly. Once the possibility of a cryptic Tedania species was raised, individuals of the unusual form were also readily distinguishable among individuals of the normal T. ignis on nearby mangroves. In January 2002, I also noticed the unusual form growing on mangrove roots, along with T. ignis, sensu stricto, in Bocas del Toro, Panama.
Spicules of the two forms are indistinguishable by shape and overlap in sizes, so molecular characters and ecological attributes were analyzed as well. Experimental manipulations evaluated "common garden" growth rates, survival of transplantation among habitats, and consumption by starfish, angelfish, and parrotfish. Field experiments and other analyses were duplicated, as much as possible, in Twin Cays, Belize, and Bocas del Toro, Panama, providing a biogeographic perspective on ecological as well as molecular and morphological attributes.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionLiterature Cited |
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Habitat distribution patterns were quantified in the course of complete censuses of 10 mangrove roots or root clusters at each of three sites: Sponge Haven and Hidden Creek, both in Twin Cays, Belize; and across the bay from the Smithsonian Tropical Research Institute marine station in Bocas del Toro, Panama. Seagrass meadows and coral reefs in Bocas del Toro and Belize were also surveyed for the two forms.
Growth rates and development of the overall growth form of Tedania ignis from mangrove roots (n = 10), and the unusual form from both mangroves (n = 10) and seagrass meadows (n = 10), were compared by attaching small pieces (6–13 cm3, all cut to the same oblong shape, with length approximately twice the width) with cable ties to lengths of pre-conditioned PVC pipe suspended among mangrove roots at Sponge Haven, Twin Cays, Belize. The volume of each piece was recorded at the start and after 6 months.
To determine if absence from a habitat indicated inability to live there rather than lack of colonization, in Belize transplants were made to habitats in which one or the other form was not found. Tedania ignis, sensu stricto, which was only found on mangroves, was transplanted from mangrove roots to seagrass, 250 m away (n = 12); and the unusual form was transplanted from mangrove roots at one site where it was abundant (Sponge Haven) to mangrove roots at another site, 330 m away (Hidden Creek), from which it was absent (n = 12). Controls for manipulation effects (i.e., cutting, transporting by boat, and reattaching with cable ties) were transplantation of T. ignis from mangroves at Sponge Haven to mangroves at Hidden Creek, where it is common (n = 12), and of the unusual form from mangroves at Sponge Haven to the seagrass meadow, where it is common (n = 10). Transplants to the seagrass meadow were randomly spaced along three transect lines, and transplants to mangrove roots were placed wherever they would not be in immediate contact with prior residents.
Morphological distinction between forms
Spicule preparations were made from specimens of each Tedania form from both Panama and Belize. Individuals of the unusual form were collected on mangrove roots at both locations, and also in seagrass beds in Belize. Individuals of T. ignis were collected on mangrove roots in Panama and Belize, and also at geographically distant sites where the unusual form was not found: on mangrove roots in the Florida Keys (Zane Grey Creek, Long Key), and on very low intertidal rocks on the coast of Brazil near Recife. For each spicule type, 25 length measurements and 10 width measurements were made for each individual.
Whole skeletons were cleaned for examination by macerating the tissue. Architectural features were compared by light microscopy. In the field, overall growth form was quantified by measuring heights and widths of individual volcano-shaped mounds.
Molecular distinction between forms
Comparisons of the DNA sequence of the mitochondrial cytochrome c oxidase subunit I gene (COI) between each form of Tedania and other genera representing the order Poecilosclerida that were available in GenBank were made to determine if the unusual form of Tedania could be genetically distinguished from T. ignis. COI sequences from four other poecilosclerid species were used: Iotrochota birotulata (AY561963), Diacarnus spinipoculum (AY561975), Crambe crambe (AF526297 and AF526298), and Microciona prolifera (AJ704978). Small samples (3 x 4 mm) were excised from three individuals of each form of Tedania from mangroves, from two individuals of the unusual form from seagrass, in Belize, and from one individual of each form from mangroves in Bocas del Toro, Panama. Samples were preserved in 100% ethanol and, after several changes of the ethanol to relieve dilution, transported to the laboratory and stored at –80 °C.
Total nucleic acid was extracted from small subsamples using a cetyl-trimethyl-ammonium bromide extraction technique (Doyle and Doyle, 1987) and amplified by PCR using the primers and protocols of Folmer et al. (1994). PCR products were purified using the ExoSAP-IT kit (USB Corporation, Cleveland, OH) and were directly sequenced in both the forward and reverse directions using the amplification primers. Forward and reverse sequences were edited and assembled using Sequencher 4.0.5 (Gene Codes Co., Ann Arbor, MI). PCR products yielding ambiguous sequences were amplified and sequenced for a second time from the original extraction and used to create a majority consensus sequence using all four sequences (two forward and two reverse). In cases where no clear consensus could be reached, the International Union of Pure and Applied Chemistry (IUPAC) ambiguity codes were applied. An alignment of all sequences was made using the default settings in Clustal x 1.81 (Thompson et al., 1997) and adjusted manually in Bioedit 5.0.9 (Hall, 1999). Pairwise genetic distances were calculated with the DNADIST 3.5c accessory application in Bioedit, using the default settings.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionLiterature Cited |
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Growth rates and development of overall form.
Growth rates of the two forms were similar on PVC pipes suspended among mangrove roots, with mean specific growth rates (i.e., size increase/original size) over 6 months of 4.51 (SE = 0.74), for T. ignis of 5.41 (SE = 0.63) for the unusual form from mangroves, and of 4.28 (SE = 0.46) for the unusual form from seagrass. Sample sizes were, respectively, 5, 7, and 6, as only individuals that increased in size were included in these growth rate estimates.
Overall morphologies that developed during the 6 months were strikingly different for the two forms. All individuals of T. ignis grew as low mounds, extending evenly in all lateral directions. By contrast, all individuals of the unusual form, from both the mangroves and seagrass, developed one to three (in most cases two) tall and relatively narrow, volcano-shaped mounds (dimensions of the four largest mounds, as height by width [midway between base and peak], were 4.5 x 2.4 cm, 5.2 x 2.0 cm, 8.0 x 2.1 cm, 5.8 x 2.9 cm), each surmounted by a single osculum. Three of the 10 individuals of T. ignis did not survive, while all 10 individuals of the unusual form from the mangroves and all 10 from the seagrass survived. The basis for this distinction may lie in differences in initial attachment to the PVC pipes. Within 2 days, all individuals of the unusual form had started to spread in a thin crust over the pipes, creating a very stable attachment. All individuals of both forms were firmly attached after 10 days, but individuals of T. ignis had not spread over the PVC, so their grip was not as resistant to being dislodged.
Transplantation among habitats.
Transplants of all 10 individuals of the unusual form from the seagrass to mangroves at Sponge Haven survived. Of 12 individuals of the unusual form transplanted from mangroves at Sponge Haven to mangroves at Hidden Creek, a distance of only 330 m, no individuals survived (previously reported in Wulff, 2004). The transplanted sponges had readily reattached and appeared to be thriving at the end of 10 days, so their disappearance during the subsequent 12 months suggested that this tidal creek had episodes of abiotic conditions that were intolerable to the unusual form but not to T. ignis. All 12 transplants of T. ignis from Sponge Haven to Hidden Creek (i.e., the controls for manipulation and transportation effects) survived (Table 1). When T. ignis was transplanted into seagrass meadows at Twin Cays (n = 12 individuals), 250 m from their home mangrove roots at Sponge Haven, all individuals were consumed by the starfish Oreaster reticulatus within 5 days. All 10 individuals of the unusual form transplanted from Sponge Haven mangroves to the seagrass (i.e., the controls for manipulation and transportation effects) survived (Table 1).
Morphological distinction among forms
Spicule types did not differ between the forms. Both had smooth, slightly curved styles; straight tylotes with microspined ends; and two classes of very thin, straight onychaetes, microspined along their entire lengths (e.g., Wiedenmayer, 1977; van Soest, 1984; Zea, 1987). Dimensions of each of the four spicule types overlap between the two forms, although styles of the unusual form tend to be slightly shorter (Table 2). To ensure that spicule size comparisons were not confounded by possible mixtures of the two forms in previous literature reports, I compared the spicule dimensions of sponges I had collected since I became aware of the possibility of a cryptic Tedania species. For all of these samples, spicule lengths of individuals of T. ignis did not differ among sponges collected in Belize, Panama, Brazil, and the Florida Keys (Table 2).
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Although the lengths of spicules per se do not differentiate these species unambiguously, the ratios of lengths of spicules of different types do. Within individual specimens of the unusual form, the tylotes and styles were consistently very similar in size; in T. ignis the styles were longer than the tylotes in every specimen (Table 2). The mean percent difference in length between tylotes and styles for the 8 specimens of T. ignis represented in Table 2 is 12.8% (range 8.3%–16.1%), contrasting with the mean percent difference in length between tylotes and styles for the 12 specimens of the unusual form of only 1.6% (range 0.6%–2.8%). The difference between the forms in the relative sizes of tylotes and styles is significant by the Wilcoxon two-sample test (P < 0.001), and this clear morphospace separation between the forms is depicted in Figure 1.
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The genetic distance between individuals of the same Tedania form is due to nucleotide substitutions that are not shared among all individuals, while the genetic distance between forms is mostly due to mutations shared among all individuals sampled of each form. There are 8 single nucleotide mutations dispersed throughout the alignment that are specific to each form of Tedania and are present in all individuals of that form sequenced, regardless of site or habitat, creating a genetic signature of each form (Table 3).
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Description.
Large specimens are clusters of tall volcano-shaped mounds, each mound surmounted by a single osculum; smaller specimens consist of a single tall, narrow, volcano-shaped mound rising from a wider base. In mangrove specimens, the mounds tend to be at least twice as tall as they are wide (Fig. 2A, B), and in seagrass specimens adjacent mounds may become partially fused (Fig. 2C). Skeletal construction is very focused on narrow ridges running up the sides of the mounds. The crevices between the ridges are 3–8 mm wide, when measured midway between the base and peak of each mound, and at least as deep. In life this imparts a vertically striped appearance to the mounds, as the dermal membrane covering the canals between the ridges is almost translucent and is clearly inflated when the sponge is pumping (Fig. 2A). The dermal membrane also provides a rim (1–3 mm wide) around the edge of each osculum (Fig. 2). During lulls in pumping, the membrane collapses, closing the osculum and making the vertical ridges sharply evident (Fig. 2D). The consistency is highly compressible, and the color is orange, with a slightly pink tint. White flecks are often scattered in the ectosome (Fig. 2).
Spicules.
Ectosomal tylotes are terminally microspined, with the shafts very straight and the ends slightly inflated. Choanosomal styles are smooth and slightly curved, with the curved portion about a third of the way from the head to the pointed end. Onychaetes are very narrow, microspined along their entire lengths, and of two distinct size classes. Spicule dimensions are given as minimum –mean –maximum for lengths (n = 25) and widths (n = 10) in each category. Type specimen (mangrove root): tylotes 218 –230.4 –240 µm x 3.2 –3.6 –4.0 µm; styles 214 –237.1 –250 µm x 4.8 –5.0 –5.3 µm; large onychaetes 126 –155.6 –172 µm x 1.4 –1.6 –1.8 µm; small onychaetes 45 –60.3 –78 µm x 0.6 –0.9 –1.0 µm. Paratype specimen (seagrass meadow) tylotes 230 –253.8 –266 µm x 3.2 –3.4 –3.8 µm; styles 252 –259.5 –272 µm x 4.8 –5.3 –6.4 µm; large onychaetes 124 –168.6 –195 µm x 1.5 –1.6 –1.8 µm; small onychaetes 48 –63.8 –99 µm x 0.5 –0.7 –0.8 µm. Within individual specimens styles and tylotes were always very similar in length (within 0.6%–2.8%). Spicule dimensions were very similar in mangrove specimens from Belize and Panama (Table 2). Spicules were slightly longer in seagrass specimens.
Distribution.
To date, T. klausi has been identified only in Panama and Belize. In Panama it inhabits mangrove roots in Bocas del Toro; and in Twin Cays, Belize, it inhabits both seagrass meadows and mangrove roots. Although it was searched for on mangroves in the Pelican Cays in Belize, and in the Florida Keys, where the similar T. ignis can be common, it was not found at these sites. If some of the seagrass meadow and lagoon specimens referred to T. ignis in previous literature reports and guidebooks represent this newly described species, its geographic distribution is greater than recognized here.
Etymology.
The species name honors Klaus Rützler of the U.S. National Museum of Natural History, Smithsonian Institution, for his many years of creative and path-making contributions to sponge science, bridging the fields of ecology, systematics, functional morphology, and cell biology; and for his generous encouragement of colleagues; and—through development and maintenance of the Caribbean Coral Reef Ecosystem Program and the Carrie Bow Cay field station on the Belize Barrier Reef—for his facilitation of studies of sponges and all other groups of organisms inhabiting the coral reefs, mangroves, and seagrass meadows of Belize.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionLiterature Cited |
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Consequences of ecological differences between cryptic species
Distinguishing cryptic species has ramifications beyond systematics. Differences between Tedania ignis and T. klausi in palatability to potential predators and in susceptibility to abiotic extremes and disease have consequences for habitat distributions, potential invasiveness, and disease dynamics. Ready consumption of T. ignis by the large (up to 19 cm in radius), common, seagrass-dwelling starfish Oreaster reticulatus suggests that some seagrass meadow specimens referred to T. ignis (e.g., Wiedenmayer, 1977; Humann, 1992) may actually be T. klausi. Ecological conclusions based on designation of T. ignis as a habitat generalist (e.g., Diaz et al., 2004) may require reevaluation, although it is possible that continued loss of predators from seagrass meadows and coral reefs could allow T. ignis to expand its habitat distribution. T. ignis is one of two mangrove species most readily consumed by reef-dwelling angelfishes (Dunlap and Pawlik, 1996; Wulff, 2005). Unusually great palatability to reef and seagrass-dwelling predators appears to constrain T. ignis to living on mangrove roots or in intertidal or cryptic spaces, raising the possibility that ecological speciation within the Caribbean has generated a seagrass meadow version, T. klausi.
The possibility that a species might become invasive if introduced outside its normal range is of increasing importance in marine systems, and differences in susceptibility to predators and abiotic factors are relevant to this concern. Because it is unusually palatable, T. ignis would not be predicted to be invasive, but T. klausi, which might be mistaken by humans for its more edible congener, would be less likely to be kept in check by predators. On the other hand, T. klausi may be more constrained by abiotic factors, as evidenced by its inability to inhabit Hidden Creek in Belize, where T. ignis is abundant.
Disease influenced these similar-looking species differently in Bocas del Toro, Panama, in early summer 2004. Many T. klausi individuals were lost, with no effect on T. ignis individuals growing immediately adjacent to them. Disease in sponges has generally been reported to influence only one or a few of the species in diverse communities (e.g., Smith, 1941; Reiswig, 1973; Rützler, 1988; Wulff, 1997, 2006; Goreau et al., 1998; Pansini and Pronzato, 1990; Pronzato et al., 1999; Nagelkerken et al., 2000; Williams and Bunkley-Williams, 2000). The possibility that disease is caused by species-specific pathogens provides additional impetus for distinguishing cryptic species. If pathogen transmission is density-dependent, spread of disease would be predicted to be more rapid for a large population of a single common species than for sparser populations of two species, only one of which is vulnerable.
Morphological and molecular distinction among sponge species
Heavy reliance on morphological characters in sponge systematics may reflect what characters are readily available rather than confidence in their reliability. The possibility that simple comparisons of spicule measurements and shapes cannot be used for definitive species identification has been raised for T. ignis before (e.g., de Laubenfels, 1950a,b; Lehnert and van Soest, 1996; Kennedy and Hooper, 2000), and for sponges generally (e.g., Klautau et al., 1999). When de Laubenfels (1950a) wondered if Bermuda Tedania specimens that he could consistently distinguish from T. ignis by subtle differences in the field, and by smaller spicules and tylostyles rather than styles, represented a different species, he opted to provide a new name (T. tora), but remarked "We may grant that tora is distinctly different from the abundant Tedanias that surround it, but argue that it represents some pathological modification, like finding a few hunchbacks among a crowd of people, all the others being normal as to spine."
The spicule complement of T. ignis is shared by Tedania anhelans, the type species of the genus, with the exception of the two classes of onychaetes in T. ignis. Many specimens throughout the tropical world oceans have been referred to T. anhelans, but reexamination of those collected in Brazil (Hechtel, 1976; van Soest, 1987; Mothes et al., 2000) placed them in T. ignis, and questions have been raised about other specimens as well (e.g., de Laubenfels 1950a, b). The spicule dimensions of specimens of T. ignis that I have collected since I became aware of the possibility of a cryptic Tedania species show very little difference over a large geographic range (from Brazil, the Florida Keys, Panama, and Belize) and between mangrove roots or intertidal rocks (Table 2). Perhaps some of the more varied dimensions reported in the literature reflect mixtures of specimens of T. ignis and T. klausi, which could easily be confounded because they share the same spicule types, and lengths of spicules of each type overlap. New ways of using measurements of skeletal elements for species distinction are suggested by the clear distinction between T. ignis and T. klausi in the relative lengths of two categories of spicules within individual sponges (Fig. 1).
What molecular tools will be most useful in helping to distinguish among sponge taxa at different levels, and in different groups of sponges, is still being determined. An analysis of studies in which allozymes have been used to distinguish cryptic species revealed the intriguing pattern that genetic identities for some sponge genera are unusually large between species, in others they are similar to those in other invertebrate taxa, and in still others both patterns are present (Solé-Cava and Boury-Esnault, 1999). Analysis of COI sequences has been successfully applied on the interspecific level, to test hypothesized cospeciation of sponge species in the order Halichondrida with bacterial symbionts (Erpenbeck et al., 2002), but COI sequences for four species in two genera of freshwater sponges in Lake Baikal were found to be identical (Schröder et al., 2003). Although COI variability was found to be low for Crambe crambe in the western Mediterranean and eastern Atlantic, it has provided evidence for intraspecific population structure over distances ranging from 20 to 3000 km (Duran et al., 2004). In the present study, COI variability was also low, but the same eight nucleotides distinguished T. ignis and T. klausi regardless of habitat and over a geographic distance of at least 1200 km—a pattern congruent with all of the ecological and morphological data collected.
Biogeographic aspects of Tedania klausi and Tedania ignis
T. ignis has been reported from much of the coast of Brazil (Mothes et al., 2000), and throughout the wider Caribbean region: from Venezuela (Sutherland, 1980; Diaz et al., 1985), Colombia (Zea, 1987), and Panama (Wulff, 1994), to Belize (Ellison et al., 1996; Rützler et al., 2000; Wulff, 2005), Jamaica (Hechtel, 1965), Cuba (Alcolado, 1980), and the Bahamas (Wiedenmayer, 1977), to the Indian River Lagoon (Maldonado and Young, 1996), northern Gulf of Mexico (Storr, 1976; pers. obs.), and Bermuda (de Laubenfels, 1950a; Rützler, 1986).
Reports have not been confined to the tropical western Atlantic. De Laubenfels (1950b) collected what he referred, with some qualms, to T. ignis, in Kaneohe Bay in Hawaii. Re-examination of his specimen USNM 22744 confirmed that the spicules are shorter than those of Caribbean Tedania examined for this study (Table 2), and the lengths of tylotes and styles are similar to each other. These characteristics are reminiscent of T. ignis identified by de Laubenfels (1950a) in Bermuda, raising questions about possible spicule differences in northern extremes of the range, as well as of geographic distributions and cryptic species. Spicule dimensions of an Iwayama Bay, Koror, Palau specimen, referred by de Laubenfels (1954) to T. ignis (USNM 22921), are remarkably similar to those of Caribbean T. ignis (Table 2). His chief concern about the Palau specimen was that it was tucked into a semi-cryptic space instead of living exposed; but this might be expected for a sponge species that is as readily consumed as T. ignis (e.g., Dunlap and Pawlik, 1996; Wulff, 2005). The misgivings that de Laubenfels had were significant enough for him to suggest that his specimens from both Hawaii and Palau be regarded as belonging to a subspecies, T. ignis pacifica (de Laubenfels, 1954).
These are not the only Tedania specimens raising Caribbean-tropical Pacific biogeography questions that merit further study. Like the Hawaii specimen of de Laubenfels, a sponge recently collected in Guam and identified as T. ignis (pers. comm.; G. Pauly, Florida Museum of Natural History) has small spicules (Table 2) relative to Caribbean Tedania; but further exploration of ecological and molecular characters may tell an interesting biogeography story of this genus. The volcano-shaped mounds, transluscent inflated vertical canals, and white flecks in the ectosome of this navigation-buoy-dwelling sponge from Guam match the external characteristics of T. klausi, raising the contrasting possibilities that this previously undescribed species may have recently colonized the Caribbean from the tropical Pacific; or vice versa.
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Acknowledgments |
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Footnotes |
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Literature Cited |
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