RESUMEN
Synopsis Siphonophores are free-living predatory colonial hydrozoan cnidarians found in every region of the ocean. Siphonophore tentilla (tentacle side branches) are unique biological structures for prey capture, composed of a complex arrangement of cnidocytes (stinging cells) bearing different types of nematocysts (stinging capsules) and auxiliary structures. Tentilla present an extensive morphological and functional diversity across species. While associations between tentillum form and diet have been reported, the evolutionary history giving rise to this morphological diversity is largely unexplored. Here we examine the evolutionary gains and losses of novel tentillum substructures and nematocyst types on the most recent siphonophore phylogeny. Tentilla have a precisely coordinated high-speed strike mechanism of synchronous unwinding and nematocyst discharge. Here we characterize the kinematic diversity of this prey capture reaction using high-speed video and find relationships with morphological characters. Since tentillum discharge occurs in synchrony across a broad morphological diversity, we evaluate how phenotypic integration is maintaining character correlations across evolutionary time. We found that the tentillum morphospace has low dimensionality, identified instances of heterochrony and morphological convergence, and generated hypotheses on the diets of understudied siphonophore species. Our findings indicate that siphonophore tentilla are phenotypically integrated structures with a complex evolutionary history leading to a phylogenetically-structured diversity of forms that are predictive of kinematic performance and feeding habits.
Los sifonóforos son cnidarios hidrozoos coloniales depredadores que habitan todas las regiones pelágicas del océano. Las téntilas (ramificaciones laterales de los tentáculos) de los sifonóforos son estructuras biológicas dedicadas a la captura de presas. Las téntilas se componen de una matriz compleja de cnidocitos (células urticantes) portadores de diferentes tipos de nematocistes (cápsulas urticantes) y estructuras auxiliares. Las téntilas presenta una extensa diversidad morfológica y funcional en las diferentes especies de sifonóforo. Las relaciones entre la forma de las téntilas y las dietas de los sifonóforos has sido estudiadas previamente, sin embargo, la historia evolutiva que dio lugar a esta diversidad morfológica no ha sido explorada apenas. En este estudio examinamos las adquisiciones y pérdidas evolutivas de las subestructuras de la téntila y los tipos de nematocisto utilizando la filogenia molecular más reciente de los sifonóforos. Las téntilas presentan un mecanismo de disparo a alta velocidad, sincronizando las diferentes subestructuras con gran precisión, durante el cual se la téntila de desenrolla mientras los nematocistes se disparan sobre la presa. En este estudio caracterizamos la diversidad cinemática de estas reacciones para la captura de presas utilizando video de alta velocidad, y describimos su relación con los caracteres morfológicos. Dado que la descarga de las téntilas ocurre en sincronía en toda su diversidad morfológica, hemos evaluado cómo la evolución con integración fenotípica mantiene las correlaciones entre los caracteres morfológicos a través del tiempo. Hallamos que el morfo-espacio de las téntilas tiene baja dimensionalidad, encontramos casos de heterocronía y convergencia morfológica, y generamos hipótesis sobre las dietas de especies de sifonóforo poco estudiadas. Nuestros hallazgos indican que las téntilas de los sifonóforos son estructuras con fenotipos integrados y con una historia evolutiva compleja que ha dado lugar a una diversidad filogenéticamente estructurada de formas asociadas a diferentes rendimientos cinemáticos y hábitos alimenticios.
RESUMEN
Ctenophores, also known as comb jellies, live across extremely broad ranges of temperature and hydrostatic pressure in the ocean. Because various ctenophore lineages adapted independently to similar environmental conditions, Phylum Ctenophora is an ideal system for the study of protein adaptation to extreme environments in a comparative framework. We present such a study here, using a phylogenetically-informed method to compare sequences of four essential metabolic enzymes across gradients of habitat depth and temperature. This method predicts convergent adaptation to these environmental parameters at the amino acid level, providing a novel view of protein adaptation to extreme environments and demonstrating the power and relevance of phylogenetic comparison applied to multi-species transcriptomic datasets from early-diverging metazoa. Across all four enzymes analyzed, 46 amino acid sites were associated with depth-adaptation, 59 with temperature-adaptation, and 56 with both. Sites predicted to be depth- and temperature-adaptive occurred consistently near Rossmann fold cofactor binding motifs and disproportionately in solvent-exposed regions of the protein. These results suggest that the hydrophobic effect and ligand binding may mediate efficient enzyme function at different hydrostatic pressures and temperatures. Using predicted adaptive site maps, such mechanistic hypotheses can now be tested via mutagenesis.
Asunto(s)
Adaptación Biológica/genética , Ctenóforos/química , Ctenóforos/genética , Transcriptoma , Secuencia de Aminoácidos , Distribución Animal , Animales , Ctenóforos/enzimología , Evolución Molecular , Filogenia , Alineación de SecuenciaRESUMEN
A new species of calycophoran siphonophore, Tottonophyes enigmatica gen. nov, sp. nov., is described. It has a unique combination of traits, some shared with prayomorphs (including two rounded nectophores) and some with clausophyid diphyomorphs (the nectophores are dissimilar, with one slightly larger and slightly to the anterior of the other, and both possess a somatocyst). Molecular phylogenetic analyses indicate that the new species is the sister group to all other diphyomorphs. A new family, Tottonophyidae, is established for it. Its phylogenetic position and distinct morphology help clarify diphyomorph evolution. The function and homology of the nectophoral canals and somatocyst is also re-examined and further clarification is given to their nomenclature.
Asunto(s)
Hidrozoos , Filogenia , Animales , ARN Ribosómico 16SRESUMEN
In many oceanic carbon budgets there is a discrepancy between the energetic requirements of deep-sea benthic communities and the supply of organic matter. This suggests that there are unidentified and unmeasured food sources reaching the seafloor. During 11 deep-sea remotely operated vehicle (ROV) surveys in the Gulf of California, the remains (squid carcasses and hatched-out egg sheets) of 64 post-brooding squid were encountered. As many as 36 remains were encountered during a single dive. To our knowledge this is one of the largest numbers of natural food falls of medium-size deep-sea nekton described to date. Various deep-sea scavengers (Ophiuroidea, Holothuroidea, Decapoda, Asteroidea, Enteropneusta) were associated with the remains. Although many of the 80 examined ROV dives did not encounter dead squids or egg sheets (n = 69), and the phenomenon may be geographically and temporally restricted, our results show that dead, sinking squid transport carbon from the water column to the seafloor in the Gulf of California. Based on food fall observations from individual dives, we estimate that annual squid carcass depositions may regionally contribute from 0.05 to 12.07 mg C m-2 d-1 to the seafloor in the areas where we observed the remains. The sinking of squid carcasses may constitute a significant but underestimated carbon vector between the water column and the seafloor worldwide, because squid populations are enormous and are regionally expanding as a result of climate change and pressure on fish stocks. In the future, standardized methods and surveys in geographical regions that have large squid populations will be important for investigating the overall contribution of squid falls to regional carbon budgets.
Asunto(s)
Decapodiformes/fisiología , Cadena Alimentaria , Animales , Organismos Acuáticos/fisiología , Invertebrados/fisiología , México , Océano PacíficoRESUMEN
Feeding strategies and predator-prey interactions of many deep-sea pelagic organisms are still unknown. This is also true for pelagic cephalopods, some of which are very abundant in oceanic ecosystems and which are known for their elaborate behaviors and central role in many foodwebs. We report on the first observations of the giant deep-sea octopus Haliphron atlanticus with prey. Using remotely operated vehicles, we saw these giant octopods holding medusae in their arms. One of the medusae could be identified as Phacellophora camtschatica (the egg-yolk jelly). Stomach content analysis confirmed predation on cnidarians and gelatinous organisms. The relationship between medusae and H. atlanticus is discussed, also in comparison with other species of the Argonautoidea, all of which have close relationships with gelatinous zooplankton.
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Gastrópodos , Octopodiformes/fisiología , Conducta Predatoria , Animales , Organismos Acuáticos , Femenino , Cadena Alimentaria , Masculino , Océanos y MaresRESUMEN
Two new Erenna species, E. insidiator sp. nov. and E. sirena sp. nov., are described from specimens collected in the vicinity of Monterey Bay, California, and also, for E. sirena at the southern end of the Gulf of California, Mexico. Further information on the three extant Erenna species is given, based on specimens collected in the same areas. These have enabled, for instance, the identification of three types of tentilla on the tentacles of E. cornuta Pugh, 2001, rather than the two noted on the single previously known specimen. The genus is remarkable for the presence of bioluminescent lures on the tentilla of all five species. In E. sirena sp. nov. the tentilla are also covered by a red-fluorescent layer, which was briefly described by Haddock et al. (2005), and further details are given herein. Another extraordinary feature of the colonies E. sirena sp. nov. is that the main part of the tentacle, with its tentilla, can be extended away from the siphosomal stem on a long peduncle. This phenomenon also appears to occur in E. laciniata Pugh, 2001, and has not been observed before for other physonect species.
Asunto(s)
Hidrozoos/anatomía & histología , Hidrozoos/clasificación , Distribución Animal , Estructuras Animales/anatomía & histología , Estructuras Animales/crecimiento & desarrollo , Animales , Tamaño Corporal , California , Femenino , Hidrozoos/crecimiento & desarrollo , Masculino , México , Tamaño de los ÓrganosRESUMEN
The traditional view has been that all species of the phylum Ctenophora are capable of producing light. Our inability to elicit luminescence from members of the well-known genus Pleurobrachia, as well as a lack of published documentation, led to an effort to determine whether this genus is truly bioluminescent. Physical and chemical assays of several species from the family Pleurobrachiidae produced no evidence of bioluminescence capability, although all other species of ctenophores tested gave positive results. Some of the historical misperception that Pleurobrachia can produce light might be attributable to confusion with similar luminous genera.