Peculiarities of the brain organization and fine structure in small insects related to miniaturization. 1. The smallest Coleoptera (Ptiliidae)

Makarova, Anastasia A.; Polilov, Alexey A.

doi:10.1134/s0013873813060043

Cited by 18 publications

(24 citation statements)

References 20 publications

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“…In microcoleopterans all ganglia (including those of the head and metasoma) are more strongly fused or concentrated and partly or completely shifted into the mesosoma [31, 35]. The number of neurons in Megaphragma is strongly reduced, as in all other studied microinsects [15, 39]. Adults of the two studied species of Megaphragma display the unique phenomenon of reduced number of nuclei and cell bodies of neurons, as a result of lysis at later stages of pupal development.…”

Section: Discussionmentioning

confidence: 99%

Anatomy of adult Megaphragma (Hymenoptera: Trichogrammatidae), one of the smallest insects, and new insight into insect miniaturization

Polilov

2017

PLoS ONE

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The body size, especially in cases of extreme reduction, is an important characteristic that strongly determines the morphology, physiology, and biology of animals. Miniaturization is a widespread trend in animal evolution and one of the principal directions of evolution in insects. Miniaturization-related features of insect morphology have been subject to intensive studies during the last few years, but the structure of the smallest insects remains insufficiently known. It is especially important to study hymenopterans of the genus Megaphragma, which include the smallest flying insects and a species in which an almost anucleate nervous system was recently discovered. This article is the first detailed study of the external and internal morphology of adults of Megaphragma mymaripenne and M. amalphitanum using histological methods, 3D computer modeling and other techniques. It is shown that in spite of the extremely small size the organization of Megaphragma retains a considerkable level of structural complexity. On the other hand, miniaturization leads to re-organizations of several organ systems. Unique structural features related to miniaturization have been found in both species: lysis of cell bodies and nuclei of neurons at late stages of pupal development, absence of the heart, and considerable reductions in the set of muscles. Comparative analysis of structure in the smallest insects representing different taxa has revealed common features of the evolutionary process of miniaturization in insects.

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Section: Discussionmentioning

confidence: 99%

Anatomy of adult Megaphragma (Hymenoptera: Trichogrammatidae), one of the smallest insects, and new insight into insect miniaturization

Polilov

2017

PLoS ONE

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“…Rather, in very small insects the brain is disproportionately large and, together with the subesophageal ganglion, can extend into the thorax (77,79), much as the brain extends even into the proximal parts of the legs in some miniature spiders (17,18). There is also an extreme reduction in cell number in the central nervous system, as well as a reduction in the size of the cell bodies of neurons; cell body size seems to be limited by the size of the nucleus, which occupies most of the cell body volume in neurons of very small insects (45,77). In the extreme case, neurons lose their nuclei altogether (78).…”

Section: The Sizes Of Insectsmentioning

confidence: 97%

Developmental Mechanisms of Body Size and Wing-Body Scaling in Insects

Nijhout

Callier

2015

Annu. Rev. Entomol.

111

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The developmental mechanisms that control body size and the relative sizes of body parts are today best understood in insects. Size is controlled by the mechanisms that cause growth to stop when a size characteristic of the species has been achieved. This requires the mechanisms to assess size and respond by stopping the process that controls growth. Growth is controlled by two hormones, insulin and ecdysone, that act synergistically by controlling cell growth and cell division. Ecdysone has two distinct functions: At low concentration it controls growth, and at high levels it causes molting and tissue differentiation. Growth is stopped by the pulse of ecdysone that initiates the metamorphic molt. Body size is sensed by either stretch receptors or oxygen restriction, depending on the species, which stimulate the high level of ecdysone secretion that induces a molt. Wing growth occurs mostly after the body has stopped growing. Wing size is adjusted to body size by variation in both the duration and level of ecdysone secretion.

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“…A considerable number of studies have been published on effects of miniaturization in beetles. However, almost all of them deal exclusively with representatives of the suborder Polyphaga (Grebennikov & Beutel, ; Polilov, , ; Polilov & Beutel, , ; Makarova & Polilov, ; Yavorskaya et al ., , ; Yavorskaya & Polilov, ). In contrast, in the suborder Myxophaga, which also includes some very small species, only the larval head structures of Hydroscapha natans have been discussed in this context (Beutel & Haas, ).…”

Section: Discussionmentioning

confidence: 99%

“…In Sphaerius , a considerable part of the posteriorly inclined protocerebrum reaches into the prothorax, a rare feature in adult beetles. In Ptiliidae, for instance, most of the brain is still located in the cephalic lumen, with only a small portion of it reaching the anterior prothorax (Makarova & Polilov, ). As far as is known at present, Corylophidae is the only group where the entire adult brain is shifted into the thorax (Polilov & Beutel, ; Yavorskaya & Polilov, ) (Fig.…”

Section: Discussionmentioning

confidence: 99%

Cephalic anatomy of Sphaeriusidae and a morphology‐based phylogeny of the suborder Myxophaga (Coleoptera)

Yavorskaya

Anton

Jałoszyński

et al. 2018

Systematic Entomology

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Myxophaga are a small group of beetles, but phylogenetically crucial as one of the four coleopteran suborders. The monogeneric Sphaeriusidae, one of four myxophagan families, comprise about 20 species, most of them living in moist substrate at river edges. The morphology of the minute hemispherical adult is very insufficiently known. Consequently, we document external and internal head structures using scanning electron microscopy, microtome sections and three-dimensional reconstructions. The results are discussed with respect to effects of miniaturization and also functional aspects, especially microphagous feeding habits. The head of Sphaerius is less affected by size reduction compared with other beetles of the same size class (e.g. larger Ptiliidae, Corylophidae). Features related to very small size are the absence of externally visible ridges and a partial shift of the brain into the prothorax. The cephalic musculature is apparently not affected. The feeding apparatus is similar to what is found in microphagous species of Polyphaga, especially in Scirtoidea and Staphyliniformia. However, in contrast to polyphagans with similar feeding habits, the hypopharyngeal longitudinal ridge (or process) of Sphaerius is strongly reduced and a fimbriate galea is lacking. The observed features are also evaluated in a cladistic analysis of larval and adult characters. The results are distinctly in conflict with branching patterns suggested by analyses of molecular data, but in agreement with previous morphological studies. In contrast to a pattern obtained in a recent molecular study -(Hydroscaphidae + (Torridincolidae + (Sphaeriusidae + Lepiceridae))) -our analyses yielded Lepiceridae as sister to the remaining Myxophaga (branch support 9), and Sphaerius as sister taxon of Hydroscaphidae (branch support 5). The monophyletic origin of the latter two taxa is supported by unusual synapomorphies of adults and larvae. Sphaerius is characterized by numerous autapomorphies of the head: a labro-mandibular locking device, a bipartite M. frontoepipharyngalis (M9) with subcomponents oriented in the opposite direction, a deep antennal furrow, an intercalary antennomere with a structure resembling a sucking disc, a strongly elongated flagellomere 1, a compact three-segmented antennal club, strong bundles of M. tentorioscapalis (M4) originating on the posterior head capsule, a concave anterior side of maxillary palpomere 2, and an elongated second pair of tormae posteriorly connected with a process of the hypopharyngeal suspensorium.

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Peculiarities of the brain organization and fine structure in small insects related to miniaturization. 1. The smallest Coleoptera (Ptiliidae)

Cited by 18 publications

References 20 publications

Anatomy of adult Megaphragma (Hymenoptera: Trichogrammatidae), one of the smallest insects, and new insight into insect miniaturization

Anatomy of adult Megaphragma (Hymenoptera: Trichogrammatidae), one of the smallest insects, and new insight into insect miniaturization

Developmental Mechanisms of Body Size and Wing-Body Scaling in Insects

Cephalic anatomy of Sphaeriusidae and a morphology‐based phylogeny of the suborder Myxophaga (Coleoptera)

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