سایت آناتومی بی مهرگان
نمونه متن برای ترجمه
Preface
This is one of many exercises available from Invertebrate Anatomy OnLine , an Internet laboratory manual for courses in Invertebrate Zoology. Additional exercises can be accessed by clicking on the links to the left. A glossary and chapters on supplies and laboratory techniques are also available. Terminology and phylogeny used in these exercises correspond to usage in the Invertebrate Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated figure callouts refer to figures in the textbook. Callouts that are not hyphenated refer to figures embedded in the exercise. The glossary includes terms from this textbook as well as the laboratory exercises.
Systematics
Arthropoda P, Mandibulata, Tracheata, Hexapoda SC, Insecta C, Dicondylia, Pterygota, Metapterygota, Neoptera, Orthopterodea SO, Orthoptera O, Caelifera sO, Acrididea iO, Acridoidea SF, Romaleidae F, Romaleini T, (Fig 16-15, 20-14, 20-15, 21-23)
Arthropoda
Arthropoda, by far the largest and most diverse animal taxon, includes chelicerates, insects, myriapods, and crustaceans as well as many extinct taxa. The body is segmented and primitively bears a pair of jointed appendages on each segment. The epidermis secretes a complex cuticular exoskeleton which must be molted to permit increase in size. Extant arthropods exhibit regional specialization in the structure and function of segments and appendages. The body is typically divided into a head and trunk, of which the trunk is often itself divided into thorax and abdomen.
The gut consists of foregut, midgut, and hindgut and extends the length of the body from anterior mouth to posterior anus. Foregut and hindgut are epidermal invaginations, being derived from the embryonic stomodeum and proctodeum respectively, and are lined by cuticle, as are all epidermal surfaces. The midgut is endodermal and is responsible for most enzyme secretion, hydrolysis, and absorption.
The coelom is reduced to small spaces associated with the gonads and kidney. The functional body cavity is a spacious hemocoel divided by a horizontal diaphragm into a dorsal pericardial sinus and a much larger perivisceral sinus. Sometimes there is a small ventral perineural sinus surrounding the ventral nerve cord.
The hemal system includes a dorsal, contractile, tubular, ostiate heart that pumps blood to and from the hemocoel. Excretory organs vary with taxon and include Malpighian tubules, saccate nephridia, and nephrocytes. Respiratory organs also vary with taxon and include many types of gills, book lungs, and tracheae.
The nervous system consists of a dorsal, anterior brain of two or three pairs of ganglia, circumenteric connectives, and a paired ventral nerve cord with segmental ganglia and segmental peripheral nerves. Various degrees of condensation and cephalization are found in different taxa.
Development is derived with centrolecithal eggs and superficial cleavage. There is frequently a larva although development is direct in many. Juveniles pass through a series of instars separated by molts until reaching the adult size and reproductive condition. At this time molting and growth may cease or continue, depending on taxon.
Mandibulata
Mandibulata includes arthropods in which the third head segment bears a pair of mandibles. As currently conceived this taxon includes myriapods, hexapods, and crustaceans. Appendages may be uni- or biramous and habitats include marine, freshwater, terrestrial, and aerial.
Tracheata
Myriapods and hexapods share tracheae and a single pair of antennae and are sister taxa in Tracheata. Crustaceans, which have gills and lack tracheae, are excluded and form the sister group.
Hexapoda
The body is divided into three tagmata; head, thorax, and abdomen. Appendages are uniramous and a single pair of antennae is present. Three pairs of legs and two pairs of wings are found on the thorax of most adults. Hexapod legs are uniramous although there is increasing evidence that they evolved from multiramous appendages of their ancestors. Gas exchange is accomplished by trachea. Excretory organs are Malpighian tubules and the end product of nitrogen metabolism is uric acid. There is relatively little cephalization of the nervous system. Insects are gonochoric with copulation and internal fertilization.
Insecta
Most hexapods are insects. A few hexapod taxa (orders) lack wings and have primitive mouthparts recessed into the head and belong to Entognatha, the sister taxon of Insecta. Insects have ectognath mouthparts and the adults (imagoes) of most taxa have wings.
Pterygota
Pterygotes are the winged insects. These insects are derived from a winged common ancestor. Adults of most taxa have wings although they have been lost in some.
Orthoptera
Orthoptera includes 20,000 species of grasshoppers, crickets, locusts, katydids, and their relatives. These are mostly large insects with an enlarged pronotum. The hind femora are large and adapted for jumping. Females have a large ovipositor but male genitalia are not visible externally. Most are herbivores.
Natural History
Lubbers are tropical short-horned grasshoppers of the family Romaleidae. The family is largely restricted to Central and South America but one species, Romalea microptera (= R. guttata), occurs in the southeastern United States where its range once extended from Florida to Texas and north to Tennessee and the Carolinas. Several other lubber species are confined to arid regions of the western United States but R. microptera is adapted to moister habitats and is the only species in the east.
Until recently, isolated populations of R. microptera were present in Tennessee, Arkansas, South Carolina, Florida, and Louisiana. Eastern lubbers remain abundant in Florida, especially in the Everglades, but at present the only confirmed population remaining outside of Florida is in South Carolina. Anyone having knowledge of extant R. microptera populations, other than those in Florida, may communicate that information to Dr. Doug Whitman of Illinois State University at dwwhitm@ilstu.edu . Habitat destruction and pesticides are probably responsible for the decline of this species. Although its distribution is patchy, where present the eastern lubber can be very common in the summer.
The lubber family (Romaleidae) is characterized by the presence of a pair of strong spines at the tip of the hind tibia. One spine is medial, the other lateral. Lubbers (and some other grasshoppers) also have a prominent midventral tooth-like process on the first thoracic segment, between the first pair of legs. The common name “lubber” alludes to the stocky, heavy-bodied appearance of members of this family. The Merriam-Webster Collegiate Dictionary defines lubber as a “big clumsy fellow”.
The wings of most lubber grasshoppers are rudimentary and incapable of flight. Romalea microptera has reduced, non-functional wings and is flightless (microptera = small wing). Consequently its dispersive ability is weak and there is little gene flow between populations. Grasshoppers have chewing mouthparts and lubbers use theirs to feed on almost any green vegetation but they prefer lilies (in the family Lilaceae). Members of this plant family synthesize allelochemicals to protect themselves from herbivores but these compounds are ineffective against lubbers. Instead, lubber grasshoppers save toxins from the lilies they ingest and use them in their own defense.
Like many chemically protected organisms lubbers are aposematically colored to discourage predation. Nymphs are usually jet black with bright orange, yellow, or red markings, including a distinct middorsal red stripe. (A few individuals may be pale pinkish orange with darker red markings.) In contrast, adults are cryptic with black, yellow, and brown markings. The hind wings, however, are hot pink with a black border but they are normally hidden by the forewings, which have a faint pink blush. (An uncommon black color morph is found on the Gulf of Mexico coast. Adults of this morph are black with yellow markings.)
When threatened, an adult lifts the forewings and spreads the hindwings to display its startling pink and black pattern which may resemble an eye to a would-be predator. It also hisses and releases a repugnatorial substance from glands in the thorax. Like other grasshoppers it releases a repellant oral secretion (known to children as “tobacco juice” that also contains toxins from its diet. It has other toxins in the blood. A single bad experience with a protected lubber is sufficient to cause a predator to avoid all lubbers in the future.
Romalea is gonochoric but with little sexual dimorphism other than a marked disparity in size. Females (about 75 mm) are larger than males (about 55 mm) and have a short ovipositor which is lacking in males.
Like other orthopterans lubbers are paurometabolous (Fig 21-13). Juveniles resemble adults and undergo a gradual increase in size, but not shape, from juvenile to imago. Lubbers have an annual life cycle and females inject eggs into the ground in late summer. During mating and until oviposition the smaller male rides the female to guard against insemination by rival males. Adults die after oviposition. Eggs enter diapause, overwintering in the ground to hatch in the spring. First instar nymphs appear in April in South Carolina and are black and red as described above. In Florida nymphs may appear as early as February. Lubbers have four nymphal instars, all with similar pigmentation and appearance except that they become progressively larger as spring and summer progress. The final molt, in summer, transforms the final juvenile instar into the winged and sexually mature imago (adult). In 2006, in Greenwood, South Carolina, the first imagoes were recorded on 24jun. None was seen after 10sep.
Early instar nymphs remain together in sibling groups consisting of the individuals from a single oviposition. Later instars and imagoes, however, leave these aggregations and go their separate ways.
Natural history information is from Whitman (2006), Eisner (2003), and from observations of the Greenwood, South Carolina population.
Laboratory Specimens
Because they are relatively primitive, more or less typical insects, grasshoppers are often used in introductory biology laboratories as an introduction to insect or arthropod anatomy. In North America, the eastern lubber grasshopper, Romalea microptera (= R. guttata), is the species usually employed for this purpose because it is large and readily available. Adults are 50-75 mm in length and are easily dissected and provide a good example of general, relatively unspecialized insect anatomy. This is usually the species provided by biological supply companies although other grasshoppers are sometimes found in their shipments. (Any specimens with large wings are not Romalea.)
Romalea, like most animals, is best studied using anesthetized living, or freshly sacrificed specimens. Preserved animals are less satisfactory. Unfortunately, the lubber life cycle is such that living adults are not usually available during the academic year when they are needed by most invertebrate zoology courses and consequently it is almost always studied using commercially provided preserved material. The cricket, Acheta domestica, in contrast, is available alive and inexpensively at bait shops throughout the year and is recommended as a substitute. Dissection instructions for Acheta are available at Invertebrate Anatomy OnLine.
Conduct the study using a dissecting microscope. Living or preserved specimens can be used. This description is based on fresh, unpreserved specimens. References to color usually are not applicable to preserved material. Anesthetization of living specimens is optional for the study of external anatomy. Anesthetization can be accomplished with carbon dioxide or chloroform. For the study of internal anatomy, living specimens can be anesthetized as above or killed by exposure to fumes from a cotton ball dampened with ethyl acetate in a covered culture dish.
External Anatomy
Tagmata
Examine a male or female Romalea under magnification. The arthropod body is composed of a linear series of segments, some or all of which bear paired jointed segmental appendages. Most arthropods, including insects, are heteronomous, with their segments and their appendages variously modified and grouped in regions, or tagmata, specialized for different functions. The alternative homonomous condition, with all segments and appendages alike over the length of the body, is primitive but, among Recent taxa, is approached only by a few crustaceans.
Figure 1. Lateral view of an adult male lubber grasshopper from Greenwood, South Carolina. Orthop19La.gif
The three tagmata of the insect body are the anterior head, middle thorax, and posterior abdomen (Fig 1, 21-1C). The head, which shows few external signs of segmentation, bears the eyes, antennae, mouth, and mouthparts. Its major functions are sensory reception and feeding. The thorax, whose primary function is locomotion, is larger and bears three pairs of legs and, typically, two pairs of wings. The abdomen is the largest tagma and is conspicuously segmented. It houses most of the digestive, excretory, and reproductive viscera and its appendages, when present, are specialized for copulation or oviposition. Most abdominal segments lack appendages and those present are highly modified. The external genitalia, at the posterior end of the abdomen, are highly modified segmental appendages.
Head
The head is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium. The mouthparts are attached ventrally to the capsule, a condition known as hypognathus. The mouth, which you will see later, is located on the ventral surface of the head and is surrounded by the mouthparts. These mouthparts enclose a space, the preoral cavity (Fig 21-7), from which the mouth opens. The head is more or less ovoid in shape with a nearly vertical anterior surface.
Figure 2. En face view of Romalea. Orthop20L.gif
