Structure and Development of the Parotoid Gland in
Transcription
Structure and Development of the Parotoid Gland in
Structure and Development of the Parotoid Gland in Metamorphosed and Neotenic Ambystoma gracile Author(s): Lawrence E. Licht and David M. Sever Source: Copeia, Vol. 1993, No. 1 (Feb. 11, 1993), pp. 116-123 Published by: American Society of Ichthyologists and Herpetologists (ASIH) Stable URL: http://www.jstor.org/stable/1446302 Accessed: 30-06-2015 16:06 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/ info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Society of Ichthyologists and Herpetologists (ASIH) is collaborating with JSTOR to digitize, preserve and extend access to Copeia. http://www.jstor.org This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions COPEIA, 1993, NO. 1 116 S. H. Weitzman for their critiques of an earlier draft; D. J. Stewart for contributing literature and information concerning Neolebias; and G. G. Teugels and D. A. Hendrickson for the loan of museum specimens. Funding for field research was furnished by the United States Center for International Exchange of Scholars and the United States Information Service in the form of a Fulbright Research Grant to the first author. gique de l'Angola. PublicationCulturaisCompanhia de Diamantesde Angola 75:1-381. ANDJ. P. GOSSE. 1963. Revision des genres Nannaethiops Giinther, 1871 et Neolebias Steindach- __---, ner, 1894 et descriptuionde troisespeciesnouvelles (Pisces; Citharinidae).Annls. Mus. R. Afr. Centr. 116:5-40. AND. 1982. Rehabilitation des genres ---, Congocharax Matthes, 1964 et Dundocharax Poll, 1967 (Pisces, Distichodontidae)mis en synonymie par R. P. Vari, 1979 avec NeolebiasSteindachner. Bull. Inst. R. Sci. Nat. Belg. 54:1-8. TEUGELS, LITERATURE CITED BELL-CROSS, G., ANDJ. L. MINSHULL.1988. The fish- es of Zimbabwe. National Museums and Monuments of Zimbabwe,Harare, Zimbabwe. HUBBS, C. L., AND K. F. LAGLER. 1958. Fishes of the Great Lakes region. Cranbrook Institute of Science, Bloomfield, Michigan. KELLEY, D. W. 1968. Fishery development in the central Barotseflood plain. FAO Fish. UNDP(TA) Rep. FRi/UNDP(TA): 1-151. LEVITON, A. E., R. H. GIBBS, JR., E. HEAL, AND C. E. DAWSON. 1985. Standardsin herpetology and ichthyology: Part 1. Standardsymbolic codes for institutionalresource collections in herpetology and ichthyology. Copeia 1985:802-832. POLL,M. 1967. Contributiona la faune ichthyolo- G. G., ANDT. R. ROBERTS.1990. Descrip- tion of a smalldistinctivelycoloured new species of the characoidgenusNeolebiasfrom the Niger delta, West Africa(Pisces;Distichodontidae).J.Afr. Zool. 104:61-67. VARI,R. P. 1979. Anatomy, relationshipsand classificationof the familiesCitharinidaeand Distichodontidae (Pisces,Characoidea).Bull. Br. Mus. Nat. Hist. (Zool.) 36:261-344. WINEMILLER, K. 0. 1991. Comparativeecology of Serranochromis species (Teleostei: Cichlidae)in the Upper ZambeziRiver.J. Fish Biol. 39:617-639. DEPARTMENT OF WILDLIFE AND FISHERIES SCI- ENCES, TEXAS A&M UNIVERSITY, STATION, TEXAS 77843-2258. COLLEGE Submitted 22 Nov. 1991. Accepted 12 Feb. 1992. Section editor: R. Winterbottom. Copeia, 1993(1), pp. 116-123 Structure and Development of the Parotoid Gland in Metamorphosed and Neotenic Ambystomagracile LAWRENCEE. LICHT AND DAVID M. SEVER Structure and development of the parotoid gland were examined in larval, metamorphosed, and neotenic Ambystoma gracile. Larvae first show gland enlargement when they are near 50 mm SVL, the size at metamorphosis. The gland is well developed in metamorphs and only partially developed in neotenes. In neotenes, gland height is reduced but histology and histochemistry do not differ from that in metamorphosed individuals. Lowering the head and positioning of the gland as part of defensive behavior first appears at metamorphosis, and such behavior is readily shown by most metamorphs. Larvae and neotenes do not show the same defensive behavior as metamorphs. metamorphosis, larval salamanders undergo numerous morphological changes involving skin texture, skull shape, tongue appearance, hyobranchial apparatus, and gill slit closure and loss (Lauder and Shaffer, 1986; Reilly, 1987; Reilly and Lauder, 1988). Some salamanders, however, may not metamorphose, AT and neoteny, the attainment of sexual maturity with the retention of larval morphology, occurs in all families (Dent, 1968; Duellman and Trueb, 1986). Neoteny can be either complete or incomplete (Reilly, 1986, 1987). For example, in the family Salamandridae, neoteny is incomplete, and many features such as gill structures @ 1993 by the American Society of Ichthyologists and Herpetologists This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions LICHT AND SEVER-PAROTOID remain larval, but skull morphology becomes adult. In the Ambystomatidae, there is complete larval morphology in these characters (Reilly, 1986, 1987), although at sexual maturity, the cloacal glands in neotenes become adult (Licht and Sever, 1991). Facultatively neotenic species are those in which some individuals of a population undergo metamorphosis and others remain larval (Duellman and Trueb, 1986). The Northwestern Salamander, Ambystomagracile, is unique among such species in having enlarged, raised parotoid glands on the head behind the eyes (Bishop, 1943; Stebbins, 1951). The general morphology of the gland, effects of glandular secretions, and use of the gland in defensive behavior in metamorphosed A. gracile have been described by Brodie and Gibson (1969) and Williams (1983). Neither the ontogeny of gland development in metamorphs nor the extent of gland development in neotenic individuals has been studied in detail. Thus, we examined a series of A. gracile including larval, neotenic, and metamorphosed individuals to describe histological details of gland structure and to determine the extent of gland development in all life-history forms of the species. Moreover, because most morphological features in neotenic A. gracile remain larval (Reilly, 1987), the comparative development of the parotoid gland in neotenes and metamorphs represents a useful character to establish a more complete description of heterochronic characters in this species. MATERIALS AND METHODS Ambystomagracile were collected from the Little Campbell River in Langley, British Columbia, and Hollyburn Mountain in West Vancouver, British Columbia. Some specimens, collected in 1969, 1984, or 1988, were used in other studies (Licht, 1975; Lowcock and Licht, 1990; Licht and Sever, 1991) and were preserved in 5% formalin. Voucher specimens are deposited in the Canadian Museum of Nature, NMC 33903-1 to 33903-7. Three types of individuals were examined: juvenile larvae, metamorphs, and neotenes. Sexual maturity was established by the presence of enlarged testes and coiled, pigmented vasa deferentia in males and yolk-filled, pigmented ova in females (Semlitsch, 1985; Lowcock and Licht, 1990). Parotoid gland dimensions.-The parotoid gland is visible as a dorsal swelling on either side of the head and extends from the neck to the eye. Gland length through its midline was measured in the metamorphs from the posterior margin DEVELOPMENT IN AMBYSTOMA 117 of the gland on the neck to the anterior margin at the eye. In branchiate individuals, because the gland was not conspicuously enlarged, this measurement was made at a point from the third gill arch to the eye. The snout-vent length (SVL to nearest 1 mm) and length of gland site (nearest 0.5 mm) were measured in larvae, metamorphs, and neotenes. For visibly enlarged glands, gland height and width (at midpoint of the gland to nearest 0.5 mm) were measured by use of a dissecting microscope. All measurements were log transformed, and the relationship between SVL and gland dimensions was analyzed by least-squares regression. Males and females (excluding juvenile larvae) were analyzed separately to test for sexual dimorphism in gland length. Measurements for metamorphs and neotenes were compared by analysis of covariance (Zar, 1984). All statistical analyses were run on Statistical Analysis System computer programs (SAS, 1985). Histology.-For histological studies, six metamorphs (three females, 71-80 mm, and three males, 74-79 mm SVL) and seven neotenes (three females, 63-76 mm, and four males, 6577 mm SVL) were examined. All specimens were laboratory-reared individuals of the same age (13 months' posthatching). The parotoid gland region for three larvae (35-48 mm SVL) was also examined histologically. Parotoid glands were excised from specimens preserved in 5% formalin, rinsed in water, dehydrated in a graded series of alcohol, cleared in toluene, and embedded in paraffin. Sections 10 ,m thick were cut on a rotary microtome and affixed to albuminized slides. Some slides from each specimen were stained in hematoxylin-eosin whereas others were treated with the "histochemical quad stain" (Floyd, 1990), which contains stains and reactions diagnostic for proteins (naphthol yellow S), neutral carbohydrates (periodic acid/ base fuchsin Schiff-PAS), and acidic mucosubstances (Alcian blue at pH 2.0). The heights of 11 gland tubules selected at random from the midline of the parotoid gland cluster were measured to the nearest 0.01 mm with an ocular micrometer in a microscope at 100 x magnification. Behavior.-As part of another study (Licht, 1992), a series of larvae of A. gracile were raised in the laboratory under constant temperature (19.5 ? 1 C) and food levels. After a number of months, some larvae metamorphosed, and other remained branchiate as neotenes. The neotenes were kept separately in glass bowls with one liter of dechlorinated water, and meta- This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions COPEIA, 1993, NO. 1 118 .'043 CB7 0 Fig. 1. Parotoid gland in Ambystomagracile: (A) Gland enlargement in metamorphic (on left) compared to neotenic individual, each 65 mm SVL; (B) cut parotoid gland showing depth (2 mm); (C) newly metamorphosed individual showing defensive behavior and parotoid gland directed toward probe. This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions LICHT AND SEVER-PAROTOID morphs were held individually in plastic boxes lined with wet paper towels. All were kept at 19.5 (+1) C. To assess salamander defensive behavior, especially as it related to the use of the head and parotoid gland area, 23 neotenes and 27 metamorphs were each touched with a glass probe on the tip of the snout or the gland. Twelve other individuals were tested as they completed metamorphosis and still retained gill stubs. All neotenic and metamorphosed individuals were over 55 mm SVL. Observations were made on the immediate response and general behavior of each individual, but results were not quantified. RESULTS Parotoid gland dimensions.-The gland is a kidney-shaped swelling on the head behind the eye (Fig. 1). Gland length, or the site for gland location, did not differ between metamorphosed males (n = 26) and females (n = 23) {F = 2.15, P > 0.20}, nor between neotenic males (n = 22) and females (n = 31) {F = 1.21, P > 0.20}. Gland length varied directly with SVL in larvae, metamorphosed and neotenic individuals [sexes combined (Table 1)]. The regression lines for gland length and SVL for metamorphosed and neotenic groups differ significantly (ANCOVA, = 60.25, P < 0.001). F[1,981 The gland is conspicuously raised in metamorphosed individuals but not in either larvae or neotenes (Fig. 1A-B). Mean gland height for 20 metamorphosed individuals (56-80 mm SVL) was 1.90 mm (SD = 0.20), and mean width was 6.15 mm (SD = 0.56). Gland width was significantly correlated with SVL (r = 0.868, df = 18, P < 0.001), but gland height was not (r = 0.222, df = 18, P > 0.20). Swelling of the gland was barely perceptible in neotenes, and neither height nor width was measured. The gland first became visibly enlarged as larvae, from 50-55 SVL, began to metamorphose. By the time gills are resorbed, the gland was fully enlarged in length from neck to eye and was 1.5-2.0 mm high (n = 12). An individual (55 mm SVL) with gill stubs had enlarged glands (Fig. 1C). Histology.-The parotoid gland is composed of numerous granular glands in the dermis (Williams, 1983). No sexual dimorphism in gland cytology was observed. In metamorphosed individuals, the granular glands are tightly packed, columnar, and filled with granules of two sorts (Fig. 2A). The most numerous granules are eoin diameter. These sinophilic and about 5 tsm DEVELOPMENT IN AMBYSTOMA 119 are separatefromsmallgroupsof largergran- ules, about 20 Ctmin diameter, that vary from basophilic to eosinophilic. Both types of granules stain positively for proteins and give a slightly positive PAS reaction for neutral carbohydrates. Nuclei are flattened and are limited to the periphery of the gland. Usually a distinction between cytoplasm and luminal contents was not resolved, especially in the most full glands. Where the luminal-epithelial borders are apparent, the epithelial layer is a narrow, simple band of cells, cuboidal toward the epidermis and squamous distally. Thus, the bulk of each gland is composed of granules in the lumen. At the junction between each gland and the basal surface of the epidermis is a narrow duct that leads from the granular gland lumen to the surface of the epidermis (Fig. 2B). A demilune containing PAS-positive granules is near the base of the duct. Superficial to the epithelial cells is a thick sheath that contains melanin and PAS+ collagen fibers. As noted by Williams (1983), a superficial collar of smooth muscle surrounds the base of the excretory duct. Alcian blue-positive mucous glands also occur in the dermis, and the epidermis is composed of three layers of cuboidal epithelial cells covered by a superficial squamous keratinized layer. The main difference between the granular glands in metamorphosed compared to neotenic individuals is gland height. In metamorphosed individuals, mean gland height is 1.11 mm (SD = 0.19); in neotenes, mean gland height is 0.54 mm (SD = 0.19). No difference in gland height exists between sexes of either neotenes or metamorphs. Otherwise, metamorphosed and neotenic individuals differ only in skin anatomy (Fig. 2C). In the neotenes, the outer keratinized layer of the epidermis is absent, and Leydig cells, containing PAS-positive and naphthol yellow-positive granules, are numerous in the epidermis. As in metamorphs, mucous glands are abundant in the dermis of neotenes. Evidence of dermal gland development was seen in only one immature larval specimen, 47 mm SVL, that possessed flattened granular glands 0.10-0.18 mm in diameter (Fig. 2D). These glands contain small granules that give slightly positive reactions to PAS and naphthol yellow and large vacuoles containing a flocculent substance that reacts positively to naphthol yellow. Mucous glands are absent in this individual. No glands occur in the dermis in the other immature larvae. Behavior.-Larvae and neotenes responded to a touch on their snout or neck from a glass This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions COPEIA, 1993, NO. 1 120 Ai? , '"-,. ? .7 . A, . -j•: . ." ?-.,: .H.. . .• . Sg Nu _ r1* . .: . ... - .L.g.,./ •. - ,. . .. Sm F ..," ,." C ;-c" .. .: Y~fif L~s' 4.1AK • * So:?.?~ .WO..ro ::a ,,,,• :. 'Nu ' Sg .-:... ~~...? •.' . m g . . ?;?.,np : ,•' .. .•,•,,'' '. --. - - • .1?. L c W4 5g ? • '-:'. - • ••-.•. "-=l ••':•;•":, .• - .'..• •. "-" . ,. .* ,.' -. " ... = . ,.• . ? 2 a ? • cp -S ?r " m• " • •. t"S-... • •/ c .. . See ' S9 Fig. 2. Sagittalsections through granularglands in the parotoid region of Ambystoma gracile.(A) Overview of several granular glands in a metamorphosed male, 79 mm SVL. (B) Higher magnification of same specimen used in (A), showing details of the excretory pore and surroundingstructures.(C) Neotenic female, 65 mm SVL. (D) Immature larva, 47 mm SVL. Scale bar in lower right corner-120 gm for (A), 4 4m for (B), and 6 gm for (C) and (D). Ep = epidermis; Fs = fibrous sheath surroundingeach granular gland; Lc = Leydig cells in the epidermis; Lg = large granules; Mg = mucous gland in dermis; Nu = nucleus of granular gland epithelial cell; Po = excretory pore of a granular gland; Sc = stratum compactum of the dermis; Sg = small granules; Sk = skeletal muscle; Sm = smooth muscle around neck of excretory duct; and Va = vacuoles in larval granular gland. probe by quickly swimming away. Flight was immediate and no individual appeared to twist its head or neck region nor butt or press against the probe. In contrast, 23 of 27 metamorphs bent their heads and arched the parotoid gland toward the probe (Fig. 1C); 22 individuals lifted their tails and tilted their bodies toward the probe when they were touched on the side of the head. The behavioral response shown by most postmetamorphic animals was also shown by all 12 individuals tested that were losing tail fins and gills and at the beginning of metamorphosis. DISCUSSION The parotoid gland is characteristic of the toad genus Bufo, and, in that taxon, the gland structure and secretions have been well studied (e.g., Noble, 1931; Low, 1972; Cannon and Hostetler, 1976). Among salamanders, the glands are known from species in several fam- ilies including Plethodontidae, Salamandridae, and Ambystomatidae (Anderson, 1961; Steward, 1970; Brodie, 1977). In A. gracile, the fully enlarged gland is found only in metamorphosed individuals, and gland enlargement begins at metamorphosis. Whereas other features, such as gill structure and skull morphology, remain larval in neotenic A. gracile (Reilly, 1986, 1987), the parotoid gland can be considered intermediate in development. In neotenes, the gland enlarges but not to the full extent seen in metamorphosed individuals. The skin of neotenes remains larval, retaining components such as Leydig cells (Dodd and Dodd, 1976), but the slight enlargement of the parotoid represents a tendency toward metamorphosis. Thyroxine influences the development of skin glands at metamorphosis (Dodd and Dodd, 1976), and, thus, the partial enlargement of the parotoid gland in neotenes likely indicates increase in levels of thyroxine or other hormones. In A. gracile and other neotenic am- This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions LICHT AND SEVER-PAROTOID DEVELOPMENT IN AMBYSTOMA 121 TABLE 1. COEFFICIENTS FOR LEAST-SQUARES REGRESSION OF LOG GLAND LENGTH (G)* AGAINST LOG SVL (S) FOR LARVAL, NEOTENIC,AND METAMORPHOSED Ambystomagracile.The straight line is log G = log A + b log S; log A and b are intercept and slope, respectively,with standarderror (SE). Form Larval Neotenic Metamorphosed n SVL a (mm) Gland length x (mm) b (SE) log A (SE) r P 52 54 48 29.8 68.1 69.8 5.93 14.05 12.25 1.8246 (0.0922) 0.9828 (0.0809) 0.9037 (0.1112) -1.9363 (0.1350) -0.6553 (0.1482) -0.5792 (0.2049) 0.942 0.860 0.768 <0.001 <0.001 <0.001 * G is distance from neck to eye and length of visibly enlarged gland in metamorphosed individuals, undeveloped gland site in larvae, and partially enlarged gland in neotenes. bystomatids, neotenes show increased thyroid activity at the time when metamorphosis would normally occur, but levels of thyroid hormones are lower than in metamorphs and not high enough to induce transformation (Norris and Platt, 1973; Eagleson and McKeown, 1978). The parotoid glands begin to enlarge in larvae of about 50 mm SVL, the size when metamorphosis usually occurs (Licht, 1992). Likely changes in levels of hormones in neotenes are also reflected by the full development of the cloacal glands and the synchrony of sexual maturity in neotenes and metamorphs (Licht and Sever, 1991). The distance from neck to eye represents actual length of enlarged glands in metamorphs and site of the partially developed gland in neotenes. Gland length and width vary directly with SVL, and the significantly shorter gland length in metamorphs compared to neotenes (Table 1) is a consequence of the presence of eyelids in metamorphs only (Fig lA). Height of the gland is nearly the same for all metamorphosed individuals and does not vary with SVL. The granular glands of the parotoid gland are not different in cytology from those elsewhere in the dermis of the skin (Williams, 1983), except for their relatively larger size in metamorphosed individuals. Granular glands in the dorsal tail base, however, also may be enlarged, at least in well-fed individuals, and these caudal granular glands function in nutrient storage as well as predator defense (Williams and Larsen, 1986). Williams (1983) also noted two types of granules in the granular glands of A. gracile. At the ultrastructural level, the larger granules are membrane bound and separated from the more numerous (70% of the secretion) small granules by unit membrane. As found here, he also reported that both types of granules give positive reactions to protein stains; presumably both form part of the excreted product. Viewed with transmission electron microscopy, the granular gland epithelia form a syncytium, and myoepi- thelial cells occur in the sheath surrounding each gland. These features were not observed in the parotoid gland cluster, but they may not be resolved by light microscopy. Brodie and Gibson (1969) reported that the gland first appeared about one month after metamorphosis. In contrast, we found the gland already enlarged by the completion of gill resorption (Fig. 1C). Gland appearance may depend on the size and condition of the individual at metamorphosis and subsequent growth rate. For example, in toads, the parotoid gland becomes fully formed 3-4 weeks after metamorphosis in laboratory-raised animals (Licht, 1967), but larger, wild-caught individuals show enlarged glands 7-10 days earlier (LEL, pers. obs.). Observed use of the gland in defensive behavior by metamorphosed individuals is the same as that described by Brodie and Gibson (1969). A metamorphosed individual does not flee but rather lifts its body, may raise its tail also containing skin glands, and directs the parotoid gland toward a potential threat (Fig. IC). In this way, maximal gland surface area is exposed to an attacker. This posture and positioning of the gland are exhibited only by metamorphosing animals, and such behavior is acquired at the same time as the gland is structurally enlarged. The gland may also be useful in intraspecific interactions. Metamorphosed A. gracile emit sounds that may function to reduce intraspecific aggression (Licht, 1973), and vocalization coupled with defensive positioning of the parotoid glands could function to prevent bites and wounds during agonistic encounters. Larvae and neotenes flee rapidly if provoked and show no tendency to confront a potential threat; neither makes the sounds emitted by the metamorphs (LEL, pers. obs.). The parotoid gland is probably more effective in a terrestrial setting and may not be useful for larvae or neotenes in the aquatic environment. Gland secretions are water insoluble, highly viscous and adhesive, and very effective in adhering to the mouth and eyes of potential This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions COPEIA, 1993, NO. 1 122 mammalian predators (Brodie and Gibson, 1969). On land, the metamorphs face a large variety of vertebrate predators likely sensitive to the bitter taste and toxic effects of the secretions. In contrast, neotenes face few predators except fishes: for example, large trout are reported to prey on A. gracile (Efford and Mathias, 1969). Those fishes large enough to capture neotenes may swallow them whole and are not as prone to chew their prey as do mammalian predators. Thus, the adhesive quality and distasteful properties of gland secretions may not be effective on aquatic predators, and the insolubility of secretions in water may reduce transmission of secretions. Of relevance is the fact that neotenic populations of A. gracile predominate in high altitude, permanent, typically fish-free lakes (Sprules, 1974), and, except as small larvae prone to insect predation, larger neotenes apparently face little predation. ACKNOWLEDGMENTS We thank M. Stasiuk for help with manuscript preparation. This research was supported by the Natural Sciences and Engineering Research Council of Canada Grant 3142 to LEL and National Sciences Foundation Grant BSR 87-15341 to DMS. LITERATURE CITED ANDERSON, J. D. 1961. The life history and system- atics of Ambystomarosaceum.Copeia 1961:371-377. BISHOP,S. C. 1943. Handbook of salamanders. Comstock Publishing, Ithaca, New York. BRODIE,E. D., JR. 1977. Salamander antipredator postures. Copeia 1977:523-535. ANDL. S. GIBSON. 1969. Defensive behavior --, and skin glands of the northwestern salamander, Ambystomagracile. Herpetologica 25:187-194. CANNON, M. S., AND J. R. HOSTETLER. 1976. The anatomy of the parotoid gland in Bufonidae with some histochemical findings. J. Morph. 148:137160. DENT, J. N. 1968. Survey of amphibian metamorphosis, p. 271-311. In: Metamorphosis. A problem in developmental biology. W. Etkin and L. I. Gilbert (eds.). Appleton-Century-Crofts, New York, New York. DODD,M. H. I., ANDJ. M. DODD. 1976. The biology of metamorphosis, p. 467-599. In: Physiology of the Amphibia. B. A. Lofts (ed.). Academic Press, New York, New York. DUELLMAN, W. E., AND L. TRUEB. 1986. Biology of amphibians. McGraw-Hill, New York, New York. EAGLESON,G. W., AND B. A. MCKEOWN. 1978. Changes in thyroid activity of Ambystomagracile (Baird) during larval, transforming, and postmetamorphic phases. Can. J. Zool. 56:1377-1381. 1969. A comparEFFORD, I. E., AND J. A. MATHIAS. ison of two salamander populations in Marion Lake, British Columbia. Copeia 1969:723-736. FLOYD,A. D. 1990. Morphology and the art of tissue analysis. LabLeader 5:3,6. Shandon-Lipshaw, Pittsburgh, Pennsylvania. LAUDER, G. V., ANDH. B. SHAFFER. 1986. Functional design of the feeding mechanism in lower vertebrates: unidirectional and bidirectional flow systems in the tiger salamander. Zool. J. Linn. Soc. 88:277-290. LICHT,L. E. 1967. Initial appearance of the parotoid gland in three species of toads (genus Bufo). Herpetologica 23:115-118. . 1973. Sound production and behaviour in the northwestern salamander, Ambystomagracile. Can. J. Zool. 51:1055-1056. -. 1975. Growth and food of larval Ambystoma gracile from a lowland population in southwestern British Columbia. Ibid. 53:1716-1722. . 1992. The effect of food level on growth rate and frequency of metamorphosis and paedomorphosis in Ambystomagracile. Ibid. 70:87-93. , ANDD. M. SEVER.1991. Cloacal anatomy of metamorphic and neotenic salamanders. Ibid. 69: 2230-2233. Low, B. S. 1972. Evidence from parotoid-gland secretions, p. 244-264. In: Evolution in the genus Bufo. W. F. Blair (ed.). Univ. of Texas Press, Austin. L. A., AND L. E. LICHT. 1990. Natural LOWCOCK, autotriploidy in salamanders. Genome 33:674-678. NOBLE,G. K. 1931. The biology of the Amphibia. McGraw-Hill, New York, New York. NORRIS, D. O., AND J. E. PLATT. 1973. Effects of pituitary hormones, melatonin, and thyroid inhibitors on radio-iodide uptake by the thyroid glands of larval and adult tiger salamanders, Ambystoma tigrinum (Amphibia: Caudata). Gen. Comp. Endocrinol. 25:368-376. REILLY,S. M. 1986. Ontogeny of cranial ossification in the eastern newt, Notophthalmus viridescens, and its relationship to metamorphosis and neoteny. J. Morph. 188:315-326. . 1987. Ontogeny of the hypobranchial apparatus in the salamanders Ambystomatalpoideum (Ambystomatidae) and Notophthalmus viridescens (Salamandridae): the ecological morphology of two neotenic strategies. Ibid. 191:205-214. ANDG. V. LAUDER.1988. Ontogeny of aquat-, ic feeding performance in the eastern newt, Notophthalmusviridescens(Salamandridae). Copeia 1988: 87-91. SAS INSTITUTE INC. 1985. SAS users guide: statistics, Ver. 5 ed. Statistical Analysis Systems Institute, Inc., Cary, North Carolina. SEMLITSCH, R. D. 1985. Reproductive strategy of a facultatively paedomorphic salamander Ambystoma talpoideum. Oecologia 65:305-313. W. G. 1974. Environmental factors and the SPRULES, incidence of neoteny in Ambystomagracile (Baird) (Amphibia: Caudata). Can. J. Zool. 53:1545-1552. R. C. 1951. Amphibians of western North STEBBINS, America. Univ. California Press, Berkeley. I. W. 1970. The tailed amphibians of EuSTEWARD, rope. Taplinger Publ., New York, New York. This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions LICHT AND SEVER-PAROTOID WILLIAMS, T. A. 1983. Structure and function of the granularskin glandsof the salamandersof the family Ambystomatidae(Amphibia:Urodela). Unpubl. Ph.D. diss., WashingtonState Univ., Pullman. --, AND J. H. LARSEN, JR. 1986. New function for the granular skin glands of the eastern longtoed salamander, Ambystomamacrodactylumcolum- bianum.J. Exp. Zool. 239:329-333. ZAR,J. H. 1984. Biostatisticalanalysis.Prentice Hall, Englewood Cliffs, New Jersey. DEVELOPMENT IN AMBYSTOMA 123 DEPARTMENT OF BIOLOGY, YORK (LEL) UNIVERSITY, 4700 KEELESTREET, TORONTO, ONTARIO M3J 1P3 CANADA; AND (DMS) DEPARTMENT OF BIOLOGY, SAINT MARY'S COLLEGE, NOTRE DAME, INDIANA 46556. Sub- mitted 19 Aug. 1991. Accepted 1 Feb. 1992. Section editor: D. G. Buth. Copeia, 1993(1), pp. 123-133 Phylogenetic Relationships of the Sternoptychid Argyropelecus(Teleostei: Stomiiformes) ANTONY S. HAROLD The seven valid species of Argyropelecusare the subject of a phylogenetic analysis. Selected aspects of osteological and photophore anatomy were surveyed for these taxa and the outgroups Argyripnus,Polyipnus, Sonoda, and Sternoptyx. Argyropelecusand Sternoptyxare corroborated as sister groups and Polyipnus as their sister group. Of Argyropelecusspecies, affinisand gigas form a clade which is the sister group to the remaining members of the genus. Those five species are united by eight synapomorphic aspects of pelvic girdle, anal-fin pterygiophore, pleural rib, and parasphenoid form. The three species lychnus, olfersi, and sladeni form a clade which is sister group to aculeatus and hemigymnus. These last two species are highly disparate in overall form, but that is inferred to be due mainly to paedomorphic features, including small adult body size and body shape little modified from postlarvae, in hemigymnus.Five synapomorphies, notable among them highly compressed supraneural shafts, support this relationship of aculeatus and hemigymnus. T HE Sternoptychidae, according to the phy- logenetic analysis of Weitzman (1974), comprises the 10 genera Araiophos, Thorophos, Maurolicus, Danaphos, Valenciennellus, Argyripnus, Sonoda, Polyipnus, Sternoptyx,and Argyropelecus. Among the many synapomorphies uniting these taxa are the presence of Type Alpha photophores and their occurrence in glandular clusters, only three branchiostegal rays associated with the posterior ceratohyal, parietals separated by the supraoccipital bone, lack of a basihyal, and absence of mesopterygoid teeth. The last three genera, the hatchetfishes, are deepbodied, their name referring to the apomorphic abdominal keel structure and highly compressed body. To date, there is little understanding of relationships within any sternoptychid genus nor has any explicitly been demonstrated to be monophyletic. To develop reliable classifications at higher levels the integrity of recognized genera should be probed. My research on Polyipnus, to be published separately, indicates that the genus is monophyletic. This conclusion is vital to the interpretation of characters occurring among Argyropelecus species that bear some resemblance to conditions in derived members of Polyipnus. ArgyropelecushemigymnusCocco, 1829, was the first member of the genus to be described, and it remains the smallest species, not known to exceed 40 mm standard length. Several similar nominal species have been described, A. durvilli Cuvier and Valenciennes, 1849, A. intermedius Clarke, 1877, and A. heathi Harvey, 1952; but these were justifiably synonymized by Baird (1971) with A. hemigymnus.Argyropelecusolfersi (Cuvier, 1829), originally ascribed to the genus Sternoptyx,is one of the larger, very deep-bodied ? 1993 by the American Society of Ichthyologists and Herpetologists This content downloaded from 147.174.85.132 on Tue, 30 Jun 2015 16:06:04 UTC All use subject to JSTOR Terms and Conditions