摘要:

The functional anatomy of avian ciliary muscles has been difficult to describe, due to the muscle's inaccessible location inside the eye. The ciliary muscle of the chicken (Gallas gallus domesticus), the pigeon (Columbia livia), the kestrel (Falco sparverius), and the hooded merganser (Margus cucullatus) (four species with differing accommodative needs) was examined histologically in both the relaxed and contracted states. The ciliary muscle of all four species can be divided into three main muscle fibre groups based on insertion and origin: anterior, posterior and internal. The anterior muscle fibre group originates at the sclera under the scleral ossicles and inserts into the inner lamellae of the cornea. During accommodation these fibres pull the cornea posteriorly, changing the curvature of the cornea. The posterior muscle fibre group originates on the sclera and inserts posteriorly onto the baseplate of the ciliary body. The posterior fibre group acts on the baseplate of the ciliary body, pulling it forward to change the curvature of the lens during accommodation. The internal muscle fibre group extends from the baseplate of the ciliary body to the inner lamellae of the cornea and thus has a role in both corneal and lenticular accommodation. Species differences do exist, as seen in subgroups determined by the orientation of the fibres between the relaxed and contracted states and the percentage of fibres within the main muscle fibre groups. In general, the majority of ciliary muscle fibres in chickens, pigeons, and kestrels are in the anterior muscle fibre group, suggesting an emphasis on corneal accommodation; in the ciliary muscle of the hooded merganser, the majority of fibres are in the internal and posterior muscle fibre groups, indicating that lenticular accommodation is the predominant form of accommodation.

ISSN:0006-8977    

DOI:10.1159/000112999

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The functional anatomy of avian ciliary muscles has been difficult to describe, due to the muscle's inaccessible location inside the eye. The ciliary muscle of the chicken (Gallas gallus domesticus), the pigeon (Columbia livia), the kestrel (Falco sparverius), and the hooded merganser (Margus cucullatus) (four species with differing accommodative needs) was examined histologically in both the relaxed and contracted states. The ciliary muscle of all four species can be divided into three main muscle fibre groups based on insertion and origin: anterior, posterior and internal. The anterior muscle fibre group originates at the sclera under the scleral ossicles and inserts into the inner lamellae of the cornea. During accommodation these fibres pull the cornea posteriorly, changing the curvature of the cornea. The posterior muscle fibre group originates on the sclera and inserts posteriorly onto the baseplate of the ciliary body. The posterior fibre group acts on the baseplate of the ciliary body, pulling it forward to change the curvature of the lens during accommodation. The internal muscle fibre group extends from the baseplate of the ciliary body to the inner lamellae of the cornea and thus has a role in both corneal and lenticular accommodation. Species differences do exist, as seen in subgroups determined by the orientation of the fibres between the relaxed and contracted states and the percentage of fibres within the main muscle fibre groups. In general, the majority of ciliary muscle fibres in chickens, pigeons, and kestrels are in the anterior muscle fibre group, suggesting an emphasis on corneal accommodation; in the ciliary muscle of the hooded merganser, the majority of fibres are in the internal and posterior muscle fibre groups, indicating that lenticular accommodation is the predominant form of accommodation.

ISSN:0006-8977    

DOI:10.1159/000316289

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Weakly electric fish have parallel electrosensory systems, the phylogenetically older ampullary system and the novel tuberous system. The tuberous system is an adaptation related to the evolution of active electrolocation. To examine the evolutionary relationship of the ampullary and tuberous systems, the temporal filtering properties of ampullary neurons in the dorsal torus semicircularis of Eigenmannia were studied. 'Whole-cell' recordings were made in vivo using patch type pipettes. The responses of 19 neurons to sinusoidal electric signals (<40 Hz) were recorded and the anatomy of these neurons demonstrated by injection of biocytin. All eight low-pass ampullary neurons had broad, relatively smooth post-synaptic potentials (psps) that at low frequencies nicely reflected the sinusoidal stimuli. These neurons had somata of 10–14 μm diameter and thick, spiny dendrites. Eight high-pass neurons were recorded, representing three physiological classes. The first class (3 neurons) had psps that roughly followed the sinusoidal time course of the stimulus; the psp morphology was similar to low-pass neurons. The second class had many small, fast, individual psps; their rate of occurrence varied with the stimulus. Finally, four neurons showed psps that were of constant width across stimulus frequencies. All three classes of high-pass neurons had small somata (8–10 μm diameter) with thin dendrites and either few or no spines. Some of these neurons had large varicosities on the dendrites. Three neurons had band-pass filtering properties: neurons that showed strong band-pass properties were morphologically similar to low-pass neurons. Comparisons of the temporal filtering, shapes of post-synaptic potentials, and anatomy of ampullary and tuberous neurons in the torus suggest that the circuitry for tuberous processing in the torus may have evolved as an elaboration or duplication of the ampullary system. The mechanisms underlying the low-pass filtering characteristics of tuberous neurons therefore appear to have predated the evolution of the tuberous system and to have served as a pre-adaptation for the evolution of the jamming avoidance response. In addition, these data support the hypothesis that spine density influences the temporal filtering properties of neurons.

ISSN:0006-8977    

DOI:10.1159/000113000

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

ISSN:0006-8977    

DOI:10.1159/000113001

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

ISSN:0006-8977    

DOI:10.1159/000316290

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

ISSN:0006-8977    

DOI:10.1159/000113223

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

ISSN:0006-8977    

DOI:10.1159/000316291

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113002

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113003

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113004

出版商:S. Karger AG    

年代:1997

数据来源: Karger