Structural aspects of leg-to-gonopod metamorphosis in male helminthomorph millipedes (Diplopoda)

Abstract

BackgroundIn the adult males of helminthomorph millipedes, one or two pairs of legs in the anterior part of the trunk are strongly modified into sexual appendages (gonopods) used for sperm transfer during the copula. Gonopods differentiate in an advanced phase of post-embryonic development, in most cases as replacement for the walking legs of the seventh trunk ring, as these first regress to tiny primordia, to eventually develop into gonopods at a subsequent stadium. These extremely localized but dramatic changes have been described as a non-systemic metamorphosis. In the present study we describe morphological and anatomical changes of trunk ring VII associated with non-systemic metamorphosis in four helminthomorph species.ResultsAs documented here for the first time by means of traditional histology methods and new techniques based on confocal laser scanning microscopy, the external modifications caused by non-systemic metamorphosis are associated to a huge rearrangement of internal anatomy, mostly due to the development of gonopod apodemes and extrinsic muscles.ConclusionsInternal changes in the seventh trunk ring, locally leading to the dorsal displacement of the ventral nerve cord and the digestive tract, are modulated in a taxon-specific manner, and are very conspicuous in the blaniulids Nopoiulus kochii and Blaniulus guttulatus, with likely major functional consequences.

Something gone awry: unsolved mysteries in the evolution of asymmetric animal genitalia

“…DA/SYM variability has been recorded in Skleroprotopus ramuliferus (Mikhaljova & Korsós 2003), and during development, asymmetry often arises in gonopod promordia, which, however, disappears again upon maturation (Drago et al 2011). Phylum Arthropoda: Branchiopoda Anostraca: males have identical, paired penes (i.e., symmetric); the vagina, which gives entry to the ovisac, is apparently also symmetrically arranged (Dumont & Negrea 2002) Notostraca: copulation takes place, but no intromission (Dumont & Negrea, 2002) Cladocera: copulation takes place; in certain taxa (e.g., Diaphanosoma, Latona, Penilia), paired penes exist; in Leydigia, the penis is single (Dumont & Negrea 2002). No asymmetry appears to be present in either males or females.…”

Sensing linear viscoelastic constitutive parameters with a Timoshenko beam on a multi-layer foundation: Modeling and simulation

“…This reproduces the salient characteristics of the bodies of millipedes [58][59][60] that specifically characterizes their peculiar shape morphing coupled with forward locomotion. In order to retain the independent relative rotational motion between two contiguous elements, it is natural to adapt a Timoshenko beam model that is a one dimensional continuum (axis) with a local Euclidean structure describing the state of cross section [56].…”

Biological Systematics in the Evo-Devo era

“…new pairs of legs are added at each moult. At later stages, however, the eighth pair of legs, often also the ninth, of the male undergo a unique metamorphosis (non-systemic metamorphosis; Drago et al 2008Drago et al , 2011 and are replaced in the adult by specialized sexual appendages (gonopods) used as claspers or to transfer sperm. in most millipede species, these appendages differ dramatically from walking legs, and show up a fantastic diversity of shapes, often too complex to be adequately described in words.…”