Abstract
SUMMARY: Sponge morphological plasticity has been a long-standing source of taxonomic difficulty. In the Caribbean, several morphotypes of the sponge Callyspongia vaginalis have been observed. To determine the taxonomic status of three of these morphotypes and their relationship with the congeneric species C. plicifera and C. fallax, we compared the spicule composition, spongin fiber skeleton and sequenced fragments of the mitochondrial genes 16S and COI and nuclear genes 28S and 18S ribosomal RNA. Phylogenetic analyses with ribosomal markers 18S and 28S rRNA confirmed the position of our sequences within the Callyspongiidae. None of the genetic markers provided evidence for consistent differentiation among the three morphotypes of C. vaginalis and C. fallax, and only C. plicifera stood as a distinct species. The 16S mtDNA gene was the most variable molecular marker for this group, presenting a nucleotide variability (/ = 0.024) higher than that reported for COI. Unlike recent studies for other sponge genera, our results indicate that species in the genus Callyspongia maintain a high degree of phenotypic plasticity, and that morphological characteristics may not reflect reproductive boundaries in C. vaginalis.
Highlights
Many sessile benthic marine invertebrates exhibit variability in size, shape and color
Two types of spicules were present in oxidized tissue samples: strongyles in Callyspongia plicifera (Fig. 1E) and oxeas in all the other taxa: C. fallax (Fig. 1F), the common grey morph of C. vaginalis (Fig. 1A)
Fig. 2. – Fiber morphology and spicular tracts in Callyspongia spp. (A) Reticulated fiber network of C. fallax highlighting the dense mesh of the ectosomal skeleton and more spaced mesh of the choanosomal skeleton. (B) Dense multispicular fiber tracts in primary and secondary fibers of C. vaginalis grey morph. (C) Pauispicular tracts in primary fibers and unispicular tracts in secondary fibers of C. vaginalis orange morph. (D) Unispicular tracts in C. vaginalis red morph. (E) Paucispicular tracts in primary fibers and unispicular tracts in secondary fibers of C. fallax. (F) Unispicular fiber tract in C. plicifera cored by stronglye spicules
Summary
Many sessile benthic marine invertebrates exhibit variability in size, shape and color. This intra-specific variability has been a long-standing source of taxonomic difficulty and has important implications in associated fields, including ecological research, biodiversity management and the identification of new pharmacologically active substances from invertebrate tissues (Holland, 2000; Miller et al, 2001). Specific morphological diversity is often associated with differences in local environmental conditions or with genetic divergence. Klautau et al, 1999; Miller et al, 2001; López-Legentil and Turon, 2005; Blanquer and Uriz, 2007), often revealing a genetic basis for variable morphology. Studies have uncovered the presence of sibling species in several groups of marine organisms (reviewed in Knowlton, 2000)
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