The muscle scar in cavellinids and its importance for the phylogeny of platycope ostracodes

The adductor muscle scars of cavellinids from the Visean (in one case from the Upper Devonian) of the European part of the RSFSR have revealed a significant diversity in their morphology. Aggregate, multiserial with up to five series, bi- to triserial and nearly biserial muscle scars existed simultaneously. The verticaliserial muscle scars were initiated by a biserial larval group which in the course of evolution may have passed, due to neoteny, into the adult stage. Together with Cytherella sp. from Syria, the new data show that the genus Cytherella appeared not in Triassic nor Jurassic time, hut originated among cavellinids possibly in the Early Carboniferous. A new genus is Borovitchella , with the type species B. egorovi n. sp.     

The impact of metamorphosis on the cranial osteology of giant salamanders of the genus Dicamptodon

Pacific giant salamanders (Dicamptodon) rank among the largest terrestrial caudates. Their ontogeny produces two distinct morphs—larval‐neotenic and metamorphosed—which differ in many morphological traits. We identified changes that are initiated by metamorphosis (distinguishing transformed from neotenic specimens) and also recognized age‐related changes occurring irrespective of transformation. During metamorphosis, specimens remodel the palate, rearrange the vomerine dentition, expand the maxilla, broaden the cheek, foreshorten the posterior skull table and develop specific serrated suture patterns in the dermal bones. Instead, large larvae grow a robust pterygoid sutured with a fully ossified trapezoidal vomer and a short maxilla. Small larvae are readily distinguished by tooth count, morphology and arrangement from more advanced larvae. Age‐related features, irrespective of metamorphosis, include pedicellate teeth, morphological differentiation of parasphenoid, enlargement of the orbitosphenoid, distal expansion of columella, and loss of coronoid teeth.     

Neoteny or not? The distribution of the hypophysial duct within the Galaxioidea

The hypophysial duct, a hollow tube of tissue linking the pituitary gland and the buccal cavity, was found in adults of all the galaxiid genera examined except Aplochiton and Paragalaxias . The pituitary structure in these genera, however, indicated that the duct was probably once present and has been subsequently lost. The duct was absent in the other galaxioid families, Retropinnidae and Lepidogalaxiidae. Mapping the distribution of the duct onto a DNA sequence‐based phylogeny suggests that the embryological duct was retained in a galaxiid ancestral to Aplochiton , with subsequent losses in Aplochiton and Paragalaxias .     

Taxonomic notes on Drilus Olivier, 1790 (Elateridae: Agrypninae: Drilini) in Rhodes

I compared the type specimens of Drilus attenuatus Pic, 1914 and D. attenuatus var. subparallelus Pic, 1934 from Rhodes. Both taxa are redescribed and the latter is given the full species status based on the different external morphology and male genitalia. Altogether, four species are currently known from the island of Rhodes: Drilus attenuatus Pic, 1914, D. bleusei (Olivier, 1913), D. rufipes (Baudi di Selve, 1871), and D. subparallelus Pic, 1934 stat. rev. All species but D. rufipes are endemic to the island. An identification key to the males of Drilus species found in Rhodes is provided.     

Why grow up? A perspective on insect strategies to avoid metamorphosis

1. Insects with complete metamorphosis (holometaboly) are extremely successful, constituting over 60% of all described animal species. Complete metamorphosis confers significant advantages because it enables organisms to optimise life‐history components through temporal partitioning, and thereby to exploit multiple ecological niches. Yet holometaboly can also impose costs, and several lineages have evolved life cycle modifications to avoid complete metamorphosis. 2. In this review, we discuss different strategies that have evolved that result in the loss of complete metamorphosis (type I and type II paedomorphosis). In addition, the ecological pressures and developmental modifications that facilitate this avoidance are considered, as well as the importance of life cycle complexity in life‐history evolution. 3. Interestingly, only female holometabolous insects have entirely avoided complete metamorphosis, and it is always the ancestrally juvenile morphology that is retained. These findings point to a strong sex‐biased trade‐off between investment in reproduction and development. While the loss of complete metamorphosis in females has occurred independently on several occasions across holometabolous insects, only a small number of species possessing this ability have been described. 4. Thus, complete metamorphosis, which originated only once in insects, appears to have been almost fully retained. This indicates that significant modifications to the holometabolan metamorphic ground plan are highly constrained, and suggests that the transition to complete metamorphosis is evolutionarily irreversible.     

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

All angiosperms can be arranged along a spectrum from a preponderance of juvenile traits (cambial activity lost) to one of nearly all adult characters (cambium maximally active, mature patterns realized rapidly early in ontogeny). Angiosperms are unique among seed plants in the width of this spectrum. Xylem patterns are considered here to be indicative of contemporary function, not relictual. Nevertheless, most families of early‐divergent angiosperms exhibit paedomorphic xylem structure, a circumstance that is most plausibly explained by the concept that early angiosperms had sympodial growth forms featuring limited accumulation of secondary xylem. Sympodial habits have been retained in various ways not only in early‐divergent angiosperms, but also among eudicots in Ranunculales. The early angiosperm vessel, relatively marginal in conductive abilities, was improved in various ways, with concurrent redesign of parenchyma and fibre systems to enhance conductive, storage and mechanical capabilities. Flexibility in degree of cambial activity and kinds of juvenile/adult expressions has been basic to diversification in eudicots as a whole. Sympodial growth that lacks cambium, such as in monocots, provides advantages by various features, such as organographic compartmentalization of tracheid and vessel types. Woody monopodial eudicots were able to diversify as a result of production of new solutions to embolism prevention and conductive efficiency, particularly in vessel design, but also in parenchyma histology. Criteria for paedomorphosis in wood include slow decrease in length of fusiform cambial initials, predominance of procumbent ray cells and lesser degrees of cambial activity. Retention of ancestral features in primary xylem (the ‘refugium’ effect) is, in effect, a sort of inverse evidence of acceleration of adult patterns in later formed xylem. Xylem heterochrony is analysed not only for all key groups of angiosperms (including monocots), but also for different growth forms, such as lianas, annuals, various types of perennials, rosette trees and stem succulents. Xylary phenomena that potentially could be confused with heterochrony are discussed. Heterochronous xylem features seem at least as important as other often cited factors (pollination biology) because various degrees of paedomorphic xylem are found in so many growth forms that relate in xylary terms to ecological sites. Xylem heterochrony can probably be accessed during evolution by relatively simple gene changes in a wide range of angiosperms and thus represents a current as well as a past source of variation upon which diversification was based. Results discussed here are compatible with both current molecular‐based phylogenetic analyses and all recent physiological work on conduction in xylem and thus represent an integration of these fields. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161 , 26–65.     

Correlated evolution of female neoteny and flightlessness with male spermatophore production in fireflies (Coleoptera: Lampyridae)

The beetle family Lampyridae (fireflies) encompasses ～100 genera worldwide with considerable diversity in life histories and signaling modes. Some lampyrid males use reproductive accessory glands to produce spermatophores, which have been shown to increase female lifetime fecundity. Sexual dimorphism in the form of neotenic and flightless females is also common in this family. A major goal of this study was to test a hypothesized link between female flight ability and male spermatophore production. We examined macroevolutionary patterns to test for correlated evolution among different levels of female neoteny (and associated loss of flight ability), male accessory gland number (and associated spermatophore production), and sexual signaling mode. Trait reconstruction on a molecular phylogeny indicated that flying females and spermatophores were ancestral traits and that female neoteny increased monotonically and led to flightlessness within multiple lineages. In addition, male spermatophore production was lost multiple times. Our evolutionary trait analysis revealed significant correlations between increased female neoteny and male accessory gland number, as well as between flightlessness and spermatophore loss. In addition, female flightlessness was positively correlated with the use of glows as female sexual signal. Transition probability analysis supported an evolutionary sequence of female flightlessness evolving first, followed by loss of male spermatophores. These results contribute to understanding how spermatophores have evolved and how this important class of seminal nuptial gifts is linked to other traits, providing new insights into sexual selection and life-history evolution.     

Leaf anatomy of the genus Psoralea sensu stricto (Psoraleeae, Papilionoideae, Leguminosae)

Leaf anatomy is described from 17 species of Psoralea sensu stricto which includes four species of the genus Hallia Thunberg. Species of the two genera share many characters including the presence of rod-shaped crystals, similar stipule structure and a possible continuum in secretory cavity anatomy ranging from a small and non-trabeculate to a large and trabci ulate form. Hallia species are distinguished b the presence of large tannin cells in the bundle sheaths and a narrow lcngllv.width ratio of palisade cells. In the light of other floral evidence this is considered insufficient to separate the two genera, a view confirmed by cluster analysis. Thus, Salter's proposal of 1939 for their amalgamation is supported. Leaf anatomy of herbaceous species is compared with that of seedlings of Psoralea sp. to assess the possibility that the herbaceous species may have arisen through neoteny from species that are trees or shrubs. Comparative venation studies between stipules and scale leaves suggest that the scale leaf form arose from pinnate-leaved ancestors by leaf reduction.