Intertidal benthic communities associated with the macroalgae <Emphasis Type="Italic">Iridaea cordata</Emphasis> and <Emphasis Type="Italic">Adenocystis utricularis</Emphasis> in King George Island,Antarctica

Antarctic benthos has been a main target in Antarctic research, but very few quantitative studies have been carried out in the littoral zone, which may be seasonally covered by macroalgae. In this work, we studied (1) cover and biomass of the macroalgae Iridaea cordata and Adenocystis utricularis, and (2) composition of macrobenthic assemblage associated with these macroalgal species at three locations at King George Island: Mareograph Beach (1 M), Tank’s Bay (2R) and Ardley Bay (3R). Iridaea cordata was collected by completely detaching the algae from the substrate, while A. utricularis was scraped. Adenocystis utricularis covered more than 80 % of the substrate at all locations, while coverage of Iridaea cordata was below 53 % or absent (3R). Fresh biomass of I. cordata was 0.8–61.4 g/individual and 4.7–93.0 g/100 cm² for A. utricularis. The assemblage associated with both macroalgae differed significantly between sites. The studied fauna was composed mainly of amphipods, gastropods and bivalves. Species diversity was higher in the community associated with A. utricularis. A total of ~27 ind/g DW were found associated with I. cordata, while ~112 ind/g DW were found associated with A. utricularis. The most abundant groups associated with I. cordata were amphipods at 1 M (57 %) and gastropods at 2R (46 %). Both groups were responsible for the dissimilarity between localities (62.50 %). The most abundant groups associated with A. utricularis were the gastropods at all localities reaching up to 82 % at 1 M. This study provides a first baseline on the diversity and abundance of benthic assemblages associated with intertidal macroalgae in the southwest of King George Island.     

Phylogenetic distribution of regeneration and asexual reproduction in Annelida: regeneration is ancestral and fission evolves in regenerative clades

Regeneration, the ability to replace lost body structures, and agametic asexual reproduction, such as fission and budding, are post‐embryonic developmental capabilities widely distributed yet highly variable across animals. Regeneration capabilities vary dramatically both within and across phyla, but the evolution of regeneration ability has rarely been reconstructed in an explicitly phylogenetic context. Agametic reproduction appears strongly associated with high regenerative abilities, and there are also extensive developmental similarities between these two processes, suggesting that the two are evolutionarily related. However, the directionality leading to this relationship remains unclear: while it has been proposed that regeneration precedes asexual reproduction, the reverse hypothesis has also been put forward. Here, we use phylogenetically explicit methods to reconstruct broad patterns of regeneration evolution and formally test these hypotheses about the evolution of fission in the phylum Annelida (segmented worms). We compiled from the literature a large dataset of information on anterior regeneration, posterior regeneration, and fission abilities for 401 species and mapped this information onto a phylogenetic tree based on recent molecular studies. We used Markovian maximum likelihood and Bayesian MCMC methods to evaluate different models for the evolution of regeneration and fission and to estimate the likelihood of each of these traits being present at each node of the tree. Our results strongly support anterior and posterior regeneration ability being present at the basal node of the annelid tree and being lost 18 and 5 times, respectively, but never regained. By contrast, the ability to fission is reconstructed as being absent at the basal node and being gained at least 19 times, with several possible losses. Models assuming independent evolution of regeneration and fission yield significantly lower likelihoods. Our findings suggest that anterior and posterior regeneration are ancestral for Annelida and are consistent with the hypothesis that regenerative ability is required to evolve fission.