Phenotypic plasticity and morphological integration in a marine modular invertebrate

Abstract

BackgroundColonial invertebrates such as corals exhibit nested levels of modularity, imposing a challenge to the depiction of their morphological evolution. Comparisons among diverse Caribbean gorgonian corals suggest decoupling of evolution at the polyp vs. branch/internode levels. Thus, evolutionary change in polyp form or size (the colonial module sensu stricto) does not imply a change in colony form (constructed of modular branches and other emergent features). This study examined the patterns of morphological integration at the intraspecific level. Pseudopterogorgia bipinnata (Verrill) (Octocorallia: Gorgoniidae) is a Caribbean shallow water gorgonian that can colonize most reef habitats (shallow/exposed vs. deep/protected; 1–45 m) and shows great morphological variation.ResultsTo characterize the genotype/environment relationship and phenotypic plasticity in P. bipinnata, two microsatellite loci, mitochondrial (MSH1) and nuclear (ITS) DNA sequences, and (ITS2) DGGE banding patterns were initially compared among the populations present in the coral reefs of Belize (Carrie Bow Cay), Panama (Bocas del Toro), Colombia (Cartagena) and the Bahamas (San Salvador). Despite the large and discrete differentiation of morphotypes, there was no concordant genetic variation (DGGE banding patterns) in the ITS2 genotypes from Belize, Panama and Colombia. ITS1–5.8S-ITS2 phylogenetic analysis afforded evidence for considering the species P. kallos (Bielschowsky) as the shallow-most morphotype of P. bipinnata from exposed environments. The population from Carrie Bow Cay, Belize (1–45 m) was examined to determine the phenotypic integration of modular features such as branch thickness, polyp aperture, inter-polyp distance, internode length and branch length. Third-order partial correlation coefficients suggested significant integration between polypar and colonial traits. Some features did not change at all despite 10-fold differences in other integrated features. More importantly, some colonial features showed dependence on modular features.ConclusionConsequently, module integration in gorgonian corals can be shifted, switched or canalized along lineages. Modular marine organisms such as corals are variations on a single theme: their modules can couple or decouple, allowing them to adapt to all marine benthic environments.

Character lability in deep-sea bamboo corals (Octocorallia, Isididae, Keratoisidinae)

“…ITS2 rDNA-predicted secondary structures showed 5 helices around a central ring, as reported for other octocorals (Aguilar & Sánchez 2007). The most variable sites of ITS2 secondary structures were helices IV and V ( Fig.…”

“…genetic control, Lauter & Doebley 2002), where little variation over the distinctive states is expected due to environmental pressures. Phenotypic plasticity, on the other hand, may be more associated with continuous characters, giving that they can respond to extrinsic controls such as environmental constraints (de Kroon et al 2005, Sánchez et al 2007). This feature may allow the modules to couple or decouple, enhancing the efficiency of resource intake (de Kroon et al 2005) and the adaptation of the octocorals to different benthic habitats (Sánchez et al 2007).…”

“…One of the many reasons why secondary structures from RNA molecules are useful in systematics is because they are relatively well-conserved structures among eukaryotes (Hunter et al 2007, Coleman & van Oppen 2008. Based on the conspicuous homologies, secondary structures facilitate the correct alignment of gene sequences that exhibit a great deal of indels, such as ITS2 (Aguilar & Sánchez 2007). To improve such alignments, ITS2 and 16S RNA secondary structures were reconstructed for 21 bamboo coral sequences and 1 primnoid (Narella nuttingi for 16S and Calyptrophora japonica for ITS2) that was used as an outgroup.…”

“…The first step was to align the primary sequences (MUSCLE, Edgar 2004) with homologous structures already published, e.g. ITS2 in Aguilar & Sánchez (2007) and 16S in , in order to spot conserved sequence fragments comprising important stem and loop structures. Second, the sequences, along with the restrictions and constraints depicted from the alignment, were submitted in MFOLD (Zuker 2003) with default parameters.…”

“…Internal transcribed spacer 2 (ITS2) sequences were obtained using the PCR profile and primers designed by Aguilar & Sánchez (2007). PCR products were run in a denaturing gradient (45 to 80%) polyacrylamide gel under an electrophoresis DGGE at 90 V and 60°C for 14 h. Gels were stained with ethidium bromide and all visualized bands were excised and reamplified Internode width (III) Average (mm) 1.8 3.6 0.3 3.6 7.6 1.8 1.8 1.5 1.8 1.5 1.7 1.6 3.5 1.7 3.8 0.7 2.8 6.7 1.1 1.7 3.4…”