The telotrophic ovary known from Neuropterida exists also in the myxophagan beetle Hydroscapha natans

Abstract

The ovary structure of the myxophagan beetle, Hycdoscapha natans, was investigated by means of light and electron microscopy for the first time. Each of the two ovaries consists of three ovarioles, the functional units of insect oogenesis. The ovary type is telotrophic meroistic but differs strongly from the telotrophic ovary found among all polyphagous beetles investigated so far. All characters found here are typical of telotrophic ovaries of Sialidae and Raphidioptera. Both taxa belong to the Neuropterida. As in all telotrophic ovaries, all nurse cells are combined in an anterior chamber, the tropharium. The tropharium houses two subsets of germ cells: numerous nurse cell nuclei are combined in a central syncytium without any cell membranes in between, surrounded by a monolayer of single-germ cells, the tapetum cells. Each tapetum cell is connected to the central syncytium via an intercellular bridge. Tapetum cells of the posterior zone, which sufficiently contact prefollicular cells, are able to grow into the vitellarium and develop as oocytes. During previtellogenic and early vitellogenic growth, oocytes remain connected with the central syncytium of the tropharium via their anterior elongations, the nutritive cords. The morphological data are discussed in the light of those derived from ovaries of other Coleoptera and from the proposed sister group, the Neuropterida. The data strongly support a sister group relationship between Coleoptera and Neuropterida. Furthermore, several switches between polytrophic and telotrophic ovaries must have occurred during the radiation of ancient insect taxa.

Germ-cell cluster formation in the telotrophic meroistic ovary of Tribolium castaneum (Coleoptera, Polyphaga, Tenebrionidae) and its implication on insect phylogeny

“…These cells, the tapetum cells, open into the central syncytium with an intercellular bridge. Only posterior tapetum cells can develop successfully into oocytes (=the Sialis type; Büning 1979cBüning , 1980Büning , 2005. Recent investigations on ovaries of larvae and pupae of Raphidia species confirm previous results on Sialis (Jedrzejowska and Kubrakiewicz 2004).…”

“…The new results we have now added, together with the recent discovery of the Sialis type of telotrophic ovaries in myxophagan beetles (Büning 2005), allow us to reconceive the evolution of the polyphagan ovary type.…”

“…In both subtaxa (Neuropterida and Coleoptera), all types of insect ovaries are present: panoistic (different green colors, indicating independent origin), polytrophic meroistic [orange and subfigure (a), red and subfigure (b)], and telotrophic meroistic (blue, magenta). The analysis of the developmental pathways leading to these types is strong evidence in favor of the above diagram (this investigation and Büning 2005). While ancient ancestors had polytrophic meroistic ovaries (main type in Acercaria and Holometabola; Büning 1998), the direct ancestors of Neuropterida and Coleoptera developed the telotrophic ovary of the Sialis type.…”

“…These data gained on the Tribolium ovary, together with the discovery of a Sialis type telotrophic ovary in another suborder of Coleoptera (Büning 2005), shed new light on the phylogeny of the supraorder Neuropterida/ Coleoptera. The given interpretation shows that switches between ovary types must have happened in common ancestors during the radiation period of insect taxa.…”

Two distinct but convergent groups of cells trigger Torso receptor tyrosine kinase activation by independently expressing torso-like

“…Conversely, in more evolved insects, a group of nurse cells are clustered at the anterior end of the oocyte and it is only later that the anterior side of the oocyte is separated from the nurse cells and contacts the follicle cells (for a description, see ref. 26). In Tribolium, an insect with a more primitive ovary in which tsl expression has been examined, tsl is precisely expressed in the follicle cells overlying both edges of the oocyte (27).…”