Estrutura e funcionamento dos espermatóforos de Doryteuthis plei (Mollusca: Cephalopoda) e reavaliação da reação espermatofórica dos cefalópodes / Spermatophore structure and functioning in Doryteuthis plei (Mollusca: Cephalopoda), and a reappraisal of the cephalopod spermatophoric reaction

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Male coleoid cephalopods produce elaborate spermatophores, which are transferred to the female during mating. These spermatophores are capable of functioning autonomously and extracorporeally, undergoing complicated changes during the so-called spermatophoric reaction, i.e., a complex process of evagination of the spermatophoric tunics and membranes that, ultimately, leads to the extrusion and attachment of the sperm mass on the females body. Few detailed morphological studies regarding this structure have yet been conducted, and much of the knowledge on the coleoid spermatophore was generated by classical studies of the 19th and early 20th centuries; furthermore, investigations on the functioning of this structure are even rarer. Since the extracorporeal functioning of coleoid spermatophores must rely entirely on the intricate structure and organization of the tunics, membranes, and other structures composing the spermatophore, only detailed investigations of these components would provide the basis for comprehending its mechanics. On these grounds, the present five-chapter Thesis aimed to provide solid evidence that could allow for postulating hypothesis on the functioning and evolution of this unique structure. In the first chapter, an investigation of the morphology of the spermatophore of Doryteuthis plei (Blainville, 1823) applying several microscopy techniques was carried on. A much more complex structural arrangement was revealed for the loliginid spermatophore, the most striking findings being: 1) the complex, layered structure of the middle membrane, which bears an additional, chemically distinct segment surrounding part of the cement body; 2) the presence of a space between the inner tunic and middle membrane filled with a fine reticulated material, presumably a viscous fluid in the fresh state; 3) the presence of stellate particles not only embedded in the spiral filament, but also closely applied to the inner membrane at the level of the cement body; 4) the presence of a pre-oral chamber in the cap region; and 5) the complex organization of the cement body, formed by two distinct layers encompassing contents of different chemical and textural properties. Careful literature reassessment suggests several of these features are common to loliginids, and to some extent to other squids. Their possible functional implications are discussed in light of our knowledge on the spermatophoric reaction mechanics. As part of the investigation on the spermatophoric reaction, and the mechanisms involved in the attachment of the sperm mass on the females body, it was found that the everting spermatophore, when directed towards the incised region of an experimental tissue sample, was able to readily penetrate the artificially exposed musculature, almost resembling natural deep implantation observed in some oceanic and deep-sea squids; this finding is reported in the second chapter, where it was hypothesized that the mechanism involved in deep implantation could be inherent to the 215 spermatophore structure of all squids. The third chapter investigated the functional morphology of the spermatophore of the squid D. plei applying in vitro analysis of the reaction, as well as light and electron microscopy investigation of spermatangia (everted spermatophores containing the sperm mass) obtained either in vitro or naturally attached on the female. Hitherto unnoticed functional features of the loliginid spermatophore revealed herein required a reappraisal of some important processes involved in the spermatophoric reaction, as well as the proposal of new hypotheses to explain their mechanics. The most striking findings concern to the attachment mechanism, which is not carried out solely by cement adhesive material, as previously believed, but rather by a complex process performed by multiple structures that lead to the implantation of the base of the spermatangium into the female body. Firstly, the everting ejaculatory apparatus is presumably able to superficially puncture the female tissue. Subsequently to this process, the cement body passes through a complex structural rearrangement, which leads to the injection of both its viscid cement contents and pointed oral region through the puncture into the female tissue. When the inner membrane at the oral region of the cement body is everted, its sharp stellate particles are exposed, presumptively adhering to the scarified tissue and augmenting attachment by assuring the injection of the cement material inside the superficial hole. The functioning of the loliginid spermatophore is revisited in light of these findings. The forth chapter, building upon evidence from the literature along with evidence from these experiments, proposes a theoretical model to explain how the everting ejaculatory apparatus would be able to mechanically perforate, and concomitantly implant the spermatophore into the female body during the spermatophoric reaction. It is proposed that this process is achieved chiefly through the combination of 1) an "evaginating-helix" mechanism performed by the everting ejaculatory apparatusspiral filament, and 2) the anchorage provided by its numerous, minute sharp stellate particles. Finally, the fifth chapter reviews the literature concerning the phenomenon of implantation of spermatophores in decapodiforms, and presents evidence corroborating the proposed theoretical model ascribing the role of implantation to the mechanical perforation performed by the spiral filament. The mechanisms of spermatophore transfer are also reviewed for octopodiforms, and a reinterpretation of the function of the spermatophoric reaction in this case is provided. In light of parsimonious character optimizations performed onto recently published phylogenetic trees, a complete ejaculatory apparatus with a spiral filament, as well as the spermatophoric reaction, apparently emerged once and early in the evolution of the Coleoidea. This novelty possibly provided an efficient attachment mechanism and presumably countered the changes associated with the adoption of an active mode of life by coleoids, augmenting fertilization success. Two main hypotheses for the evolution of the complex spermatophore within Coleoidea and Decapodiformes are proposed.

ASSUNTO(S)

spermatophoric reaction cephalopoda - morfologia reação espermatofórica spermatophore cephalopoda - reprodução cephalopoda - morfology loliginidae 6. mollusca cephalopoda - reproduction mollusca loliginidae espermatóforo

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