RESUMEN
Medusozoa (Cnidaria) are characterized by diverse life cycles, with different semaphoronts (medusa, medusoid, fixed gonophore, polyp) representing the sexual phase and carrying the gametes. Although egg size is often considered a proxy to understand reproductive and developmental traits of medusozoans, understanding of the processes influencing egg size variation in the group under an evolutionary context is still limited. We carried out a comprehensive review of the variation of egg size in Medusozoa to test whether this variation is related to biological/sexual or environmental traits. Egg size presents a strong phylogenetic signal (λ = 0.79, K = 0.67), explaining why closely related species with different reproductive strategies and different individual sizes have similar egg sizes. However, variation in egg size is influenced by the number of eggs, depth and temperature, with larger eggs frequently present in species with few eggs (1-15), in deep-sea species and in cold-water species. Conversely, the production of small eggs among cold-water species of Staurozoa might be associated with the development of a small benthic larvae in this group. Our study reinforces that egg sizes respond to reproductive and environmental traits, although egg size is highly conserved within medusa classes.
Asunto(s)
Cnidarios , Animales , Filogenia , Reproducción , Evolución Biológica , AguaRESUMEN
The presence of dark pigment spots associated with primary tentacles (or structures derived from them, i.e., rhopalioids) in Staurozoa was recently overlooked in a study on the evolution of cnidarian eyes (defined as a "region made of photoreceptor cells adjacent to pigment cells", irrespective of image formation, i.e., including all photoreceptive organs). Review of old and recent literature on Staurozoa shows that dark pigment spots are present in virtually all species of Manania, as well as some species of Haliclystus, Stylocoronella, and probably Calvadosia. The known ultrastructure of ocelli seems to be compatible with light perception, but no immediate response to changes in light intensity have been observed in the behavior of staurozoans. Therefore, although further studies addressing photic behavior are required, we discuss an earlier hypothesis that the dark spots in some stauromedusae may be related to synchronous spawning, as well as the possible sensorial function of rhopalioids. Observations summarized here suggest a possible ninth independent origin of eyes in Cnidaria, within a lineage of benthic medusae. Alternatively, documented similarity across medusae of Cubozoa, Scyphozoa, and Staurozoa-with eyes being topologically associated with primary tentacles in each of these taxa-could indicate shared ancestry and a single origin of eyes in this clade known as Acraspeda. Information on Staurozoa, one of the least studied groups within Cnidaria, is often neglected in the literature, but correctly recognizing the characters of this class is crucial for understanding cnidarian evolution.
RESUMEN
The collapse of the Fundão tailings dam at Mariana (State of Minas Gerais, Brazil) started a huge human tragedy and likely the most serious environmental disaster in recent Brazilian history. The dam had contained waste from processing iron ore from mines owned by Samarco, a joint venture company of the Brazilian Vale S.A. and the Anglo-Australian BHP Billiton Ltd. Following ineffective attempts to contain the disaster, after 16 days the mud flood reached the sea, where its impact is expected to affect thousands of marine fauna and flora species. Here, we provide an example of one of these species, the cnidarian Kishinouyea corbini Larson 1980 (Staurozoa), emblematic because it is extremely rare, poorly studied, and its known distribution overlaps the threatened area on the Brazilian coast. Based on this case, we discuss the need for efforts to monitor and minimize the possible impacts of this socio-environmental crime, as well as to identify and punish all responsible players in this tragedy, including negligent licensing and supervisory state agencies, in order to prevent future similar tragedies.
O colapso da barragem de rejeitos de Fundão, em Mariana (Minas Gerais, Brasil) iniciou uma enorme tragédia humana e, provavelmente, o mais grave desastre ambiental da história recente do Brasil. A barragem continha rejeitos do processamento de minério de ferro de minas de propriedade da Samarco, uma empresa controlada pela brasileira Vale S.A. e pela anglo-australiana BHP Billiton Ltda. Apesar de tentativas ineficazes para conter o desastre, após 16 dias a lama atingiu o mar, onde provavelmente afetará milhares de espécies da fauna e flora marinhas. Este ponto de vista fornece um exemplo de uma dessas espécies, o cnidário Kishinouyea corbini Larson 1980 (Staurozoa), emblemática pois é extremamente rara, insuficientemente estudada e sua distribuição conhecida para a costa brasileira sobrepõe a área ameaçada pelo desastre. Com base neste caso, discutimos a necessidade de esforços para monitorar e minimizar os possíveis impactos desse crime socioambiental, bem como para identificar e punir todos os responsáveis por esta tragédia, incluindo agências estatais de fiscalização e licenciamento negligentes, a fim de evitar futuras tragédias semelhantes.