Chloé A.-F. Bourmaud

Molecular species delimitation methods and population genetics data reveal extensive lineage diversity and cryptic species in Aglaopheniidae (Hydrozoa)

A comprehensive inventory of global biodiversity would be greatly improved by automating methods for species delimitation. The Automatic Barcode Gap Discovery method, the Poisson tree processes algorithm and the Generalized mixed Yule-coalescent model have been proposed as means of increasing the rate of biodiversity description using single locus data. We applied these methods to explore the diversity within the Aglaopheniidae, a hydrozoan family with many species widely distributed across tropical and temperate oceans. Our analyses revealed widespread cryptic diversity in this family, almost half of the morpho-species presenting several independent evolutionary lineages, as well as support for cases of synonymy. For two common species of this family, Lytocarpia brevirostris and Macrorhynchia phoenicea, we compared the outputs to clustering analyses based on microsatellite data and to nuclear gene phylogenies. For L. brevirostris, microsatellite data were congruent with results of the species delimitation methods, revealing the existence of two cryptic species with Indo-Pacific distribution. For M. phoenicea, all analyses confirmed the presence of two cryptic species within the South-Western Indian Ocean. Our study suggests that the diversity of Aglaopheniidae might be much higher than assumed, likely related to low dispersal capacities. Sequence-based species delimitation methods seem highly valuable to reveal cryptic diversity in hydrozoans; their application in an integrative framework will be very useful in describing the phyletic diversity of these organisms.

Phylogenetic relationships within Aglaopheniidae (Cnidaria, Hydrozoa) reveal unexpected generic diversity

Morphology can be misleading in the representation of phylogenetic relationships, especially in simple organisms like cnidarians and particularly in hydrozoans. These suspension feeders are widely distributed in many marine ecosystems, and the family Aglaopheniidae Marktanner‐Turneretscher, 1890 is among the most diverse and visible, especially on tropical coral reefs. The taxonomy of this family is based on morphological characters with emphasis on reproductive structures for the identification of genera. This study is the most comprehensive molecular phylogeny of the Aglaopheniidae to date, including six genera and 38 species, of which 13 were investigated for the first time and sampled on tropical coral reefs throughout the Indo‐Pacific region. For newly sampled individuals, we sequenced the 16S rRNA, the nuclear locus comprising the complete ITS1‐5.8S rRNA gene‐ITS2 and the first intron of the calmodulin nuclear gene. Phylogenetic analyses of the data revealed and confirmed a general polyphyly, or doubtful monophyly, of all sampled genera in tropical regions based on both the mitochondrial and nuclear markers. Our results revealed that several morphological characters used today are unsuited to resolve phylogenetic relationships between species and genera, as well as the high phyletic diversity within this family. Future revision of the classification of this family will require extensive geographic sampling and the use of an integrative approach.

Medusoid release and spawning of Macrorynchia philippina Kirchenpauer, 1872 (Cnidaria, Hydrozoa, Aglaopheniidae)

The life cycle of the aglaopheniid Macrorynchia philippina Kirchenpauer, 1872, is re-described from examination of live specimens collected from Reunion Island, Indian Ocean. Fertile colonies were collected on the outer slope of the coral reef and medusoid release happened a few hours later. Video sequences were recorded. Colonies were hermaphroditic: each phylactocarp contained one female and one male gonotheca. Sexual dimorphism was remarkable: sex could be recognized by colour, the female being red ochre, including about 40 oocytes disposed in a mosaic feature, and the male yellow ochre, having a homogeneous mass of spermatozoa. The blastostyle ran all around the gonangium near the closure of the two valves of the gonotheca, forming gubernacula. A ring of refringent corpuscles was clearly visible near the apex. Medusoids were indistinguishable inside the gonotheca. Male and female medusoids were released simultaneously at gamete maturity. Medusoid release involved the basal rupture of the blastostyle and the rupture of the links between the ectoderm surrounded the medusoid (the mantle), including the blastostyle (the mantle), and the gonothecal perisarc. While the two valves of the gonotheca were pushed and drew aside, the medusoid emerged by slipping out of the mantle that ruptured distally, forming a sheath; the bell of the medusoid did not contract. Immediately after emergence, quick and strong contractions of the bell allowed the medusoid to swim and induced spawning by breaking the ectoderm surrounding the gametic mass around the spadix. Spawning lasted only a few minutes: both oocytes and spermatozoa were expelled at each contraction. Spent medusoids remained alive only about 2 h. External fertilization gave rise to planulae 1 day later.

Isolation and characterisation of 16 microsatellite loci from a widespread tropical hydrozoan, Lytocarpia brevirostris (Busk, 1852)

We isolated and characterized 16 polymorphic microsatellite loci for Lytocarpia brevirostris (Aglaopheniidae), a hydrozoan common in the tropical Indo-Pacific region. Four to 34 alleles per locus were detected at the Indo-Pacific scale. At the population level, observed (Ho) and expected (He) heterozygosities ranged across 0.100–0.625 and 0.097–0.597, respectively. Three markers showed significant deviation from Hardy–Weinberg equilibrium, all of them presenting null alleles. Linkage disequilibrium was detected in three pairs of loci among 120. These primers provide powerful tools for studying population genetic diversity and the implication of life cycle strategies on population differentiation in tropical hydrozoans. This will be valuable for the conservation of coral reefs biodiversity and the design of marine protected areas.

Cloning by releasing specialized frustules in a successful epiphytic zooxanthellate haleciid (Cnidaria, Hydrozoa, Haleciidae), with comments on stolonization and frustulation

Summary Investigations on the hydroid biodiversity of the Îles Glorieuses (Indian Ocean) were carried out during a 2-week field trip in November 2003. The coral reef flats were prospected by foot and by snorkelling at low tide from the beach to the outer reef front. Two brown algae, Turbinaria ornata and T. decurrens, were among the main seaweeds on both sides of the reef front. They were frequently covered by a zooxanthellate Halecium species, still unidentified but closely related to the Atlantic species Halecium nanum. Gonothecae of this haleciid were found only twice, but the colonies exhibited a large number of specialized frustules of a previously undescribed type, produced by budding. These propagules were located underneath the hydrothecae. They exhibited a special shape, boomerang- or tetrapod-like, with three to four branches provided with a thick ectoderm, and they detached from the parent colony. Settlement was facilitated by sticky secretions of the ectoderm around the frustule. This cloning process, occurring together with both the spreading of colonies by budding new hydranths and the occurrence of sexual reproduction, appeared to be an efficient reproductive strategy, giving rise to a large population and ensuring the success of Halecium sp. at the time of the study. Zooxanthellae are probably important to such success. Asexual reproduction by stolonization is commonly used among hydroids, whereas asexual reproduction by frustulation is scarcer. Species provided with much more specialized propagules, such as stolons in several epiphytic species, or with frustules as here described, are rare. Planktonic complex propagules, which differ in shape by including a hydranth and stolons and which are here considered a consequence of stolonization instead of frustulation, were previously described for Halecium pusillum as a reproductive process independent of environmental conditions. Specialized frustules as described here are certainly a feature of the life cycle of Halecium sp., but further investigations are needed to determine if their production is seasonally linked and if they are responsible for other than local dispersal.

Modern alongside traditional taxonomy—Integrative systematics of the genera Gymnangium Hincks, 1874 and Taxella Allman, 1874 (Hydrozoa, Aglaopheniidae)

We studied the diversity within the former genus Gymnangium in the South West Indian Ocean by using an integrative approach of both traditional (morphology-based) and modern molecular taxonomy. Nine species were recorded in the material collected. A total of 97 16S mitochondrial DNA sequences and 54 Calmodulin nuclear sequences from eight Gymnangium/Taxella species were analyzed. We found both morphological and molecular differences in the studied Gymnangium species that make it necessary to split the genus. It is proposed to revalidate the genus Taxella which is currently regarded as a synonym of Gymnangium. Two species of the genus Taxella (T. eximia and T. gracilicaulis), until now regarded as distinct species based on morphological characteristics, cluster together in one phylogenetic clade. Possible explanations are discussed. Two species from Madagascar new to science are herein described and rare species from the Indian Ocean islands are re-described.

Non-released cryptomedusoid in the life cycle of Antennella sp. (Cnidaria, Hydrozoa, Halopterididae) from La Réunion, Indian Ocean

Summary Specimens of Antennella sp. were collected by scuba diving during the austral summer on the outer slope of the fringing reefs located on the western coast of La Réunion (55°30′E, 21°50′S) where the species forms microscopic colonies on red algae. A fertile colony was kept alive in a closed system in the laboratory. Like other Antennella species, it exhibits hermaproditism and sexual dimorphism: gonangia of both sexes are on the same stem, with female gonothecae being clearly bigger than male. In both sexes we observed cryptomedusoids with a subumbrellar cavity, an eccentric spadix surrounded by the gametes and a ring of refringent corpuscles on top. Male gonothecae have a compact blue-grey homogeneous mass of spermatozoa while females contain circa five white-opaque oocytes with a clearly visible darker nucleus. When the gametes were mature, one day after collection, medusoid tissues slid towards the base of the gonotheca in both sexes. Female gametes remained free inside the gonotheca while spermatozoa were liberated in the aquarium and fertilized oocytes. Several embryos at different stages of embryonic development (from morula to blastula) were incubated in a single gonotheca. The planula was not observed. This study revealed a previously undescribed pattern of sexual reproduction in the family Halopterididae involving unreleased cryptomedusoids instead of fixed sporosacs. This may be a more advanced regression stage of the medusa than free cryptomedusoids encountered in related families.