The dentition of european Speleomantes spp. (Urodela, Plethodontidae) with special regard to sexual dimorphism

ELSEVIER Ann Anat 186 (2004): 33-43

http://www.elsevier-deutschland.de

ANNALS OF ANATOMY

The dentition of European Speleomantes spp. (Urodela, Plethodontidae) with special regard

to sexual dimorphism

Hartmut Greven 1, Monika Schubert-Jung 2, and Giinter Clemen 2

llnstitut for Zoomorphologie und Zellbiologie der Universit~it DUsseldorf, Universit~itsstrage 1, D-40225 D0sseldorf, Germany, and 2Institut fur Evolution und

Okologie der Tiere der Universit~it MUnster, Htifferstral3e 1, D-48149 MOnster, Germany

Summary. Dentigerous bones and dentition of juveniles and adults of several European Speleomantes-species were investigated using scanning electron microscopy. In the juveniles examined, all dentigerous bones bore bicuspid teeth. The adult males showed the well-known dentitional sexual dimorphism, i.e. monocuspid largely conical, elongated and strongly curved premaxillary teeth. However, teeth of the anterior portion of the maxillae and some teeth of the dentary were also clearly monocuspid; the remaining teeth had differently shaped apices considered to be different grades of bicuspidity. Vomerine teeth were exclusively bicuspid. Monocuspid, but smaller teeth were also found on the premaxilla of an adult female. The conical monocuspid tooth in adults is a modified metamorphosed tooth. Monocuspids, at least on the premaxillae, may be constantly present in males and development of monocuspids probably depends on differential sensitivities of the tooth producing tissue for androgen stimuli.

Key words: European Plethodontidae - Dentition - Sex- ual dimorphism

Introduction

Dentigerous bones and teeth undergo considerable mor- phological changes during the ontogeny of Urodela. In early larvae, typically, dentigerous bones bear monocuspid, conical teeth; later a weak zone is formed dividing

Correspondence to: H. Greven E-mail: [email protected]

each tooth in the basal pedicle and the dentine crown. In most taxa the latter becomes bicuspid and bladed during or after metamorphosis. Formation of bicuspid teeth is mediated by the metamorphosing hormone thyroxine (for review and terminology see Greven 1989; Greven and Clemen 1990; Clemen and Greven 1994).

However, metamorphosed adults of New World (e. g. Noble 1931; McBride Stewart 1958, Wake 1966; Duell- man and Trueb 1986; Ehmcke and Clemen 2000 a,b) and European (Lanza et al. 1995; Lanza 1999) plethodontids show a marked sexual dimorphism in dentition and the differences appear to concern largely premaxillary teeth (Wake 1966) that become elongated and monocuspid especially in males. Appearance of this sexual dimorphism is controlled by androgens (Noble and Pope 1929) and expression of androgen receptors has been recently demonstrated in tooth forming tissues of a male plethodontid (Ehmcke et al. 2003). During courtship these modified teeth gash open the female's skin to transfer pheromones secreted by the chin gland into her blood stream (Duellman and Trueb 1985).

When we had the opportunity to examine skulls of some specimens of Speleomantes-species (see Greven et al. 2002/2003) we found a remarkable variability of tooth size and shape in the upper and lower jaw of males and females not documented as yet.

Material and methods

The following preserved specimens were used for the present study:

Speleomantes genei: 4 adults (2,2). I: male; SVL 6.2 cm, TL 11.4 cm, kept since 1997 under conditions similar to those in the field, preserved in 70% ethanol on 21.6.1999; the following specimens were

0940-9602/04/186/01-033 $30.00•0

fixed in 10% formaldehyde, date of preservation unknown. III: female; SVL 7.4, TL 11.4; IV: female; SVL 7.5, TL 11.6; V: male; SVL 7.6, TL 13.5. Site of collection: Southwestern Sardinia, Ca- gliari province (no further information on the locality). Speleomantes flavus: 4juveniles (1,3). I: male; SVL 3.8 cm, TL 6.3 cm; II: female; SVL 4A, TL 7.6; III: female; SVL 3.5, TL 5.5; IV: female; SVL 4.0 cm, TL 6.5 cm. Site of collection: Southwest of the town Siniscola, Northern part of the Monte Albo mountains, and Badde Ghiramonte. Date of preservation: 27. 03. 1997 in formaldehyde. Speleomantes supramontis: 3 juveniles (0,3). I: female; SVL 4.5; TL 6.5. II: female; SV 4.2 cm, TL 6.0 cm. III: female; SVL 3.8, TL 5.8 cm. Site of collection: Central Eastern Sardinia, province Nuoro (no further information). Date of fixation in 70% ethanol unknown. Speleomantes imperialis: 2 adult males (V and VI), 4juveniles (1,2; one specimen of unknown sex). I: female; SVL 3.5, TL 5.9; II: male; SVL 3.9 cm, TL 5.5 cm. II: ?; SVL 3.3 cm, TL 5.3 cm. IV: female; SVL 3.2 cm, TL 5.3 cm. V: male; VI male (length unknown, only heads available). Site of collection: South Eastern Sardinia, province Nuoro, Grotta di Taquisa near the village Gairo Taquisera (I-IV), Grotta Oroli near Osini in 1985 (V, VI). Date of preservation in 70% ethanol: July 1994 (I-IV); 1985 (VI); January 1998 (V). Speleomantes ambrosii: 2juveniles (1,1). I: male; SVL 3.9 cm, TL 6.1 cm; II: female; SVL 3.8 cm; 6.0 cm. Site of collection: Left bank of the river Turrite Secca near the village Garfagnana. Date of fixation in 70% formaldehyde: late October 1990. Speleomantes italicus: 2 adults (1,1, only heads were available). I: female; II: male (no further information).

Animals were dissected to judge sex and maturity by their testis and ovaries. We measured the height of dentine shafts; i.e., the distance from the midst of their base to the tip of the longest (labial) cusp, when viewed laterally. Measurements of at least three teeth of the premaxilla, of the posterior and the anterior part of the maxillae and, if available, of the dentaries were taken from SEM micrographs (magnification 150 and 300 x). Micrographs were digitalized using the program Photoshop 5.0. Then the scale bar was converted to pixel and the length of the teeth including the curvature was calculated by the total number of pixels.

Most SEM micrographs of dentigerous bones were obtained from transparencies (see Greven et al. 2002/2003). Due to this technique, the smooth superficial enamel caps of teeth were often lacking. However, the remaining shape of the apex allowed for assessment of monocuspid and bicuspid teeth. In case dentigerous bones were separated from adhering tissue either by pan- creatin or mechanically, replacement teeth were lost and not available for examination. Specimens were dehydrated in an as- cending ethanol series, critical point dried, fixed on alumininm stubs, sputtered with gold and viewed in a SEM CS-530 Hitachi.

The degree of bicuspidity was classified by a gradation ranging from 1 (monocuspid) to 5 (fully bicuspid) (Fig. 1). Grade 1: Coni- cal (in S. supramontis somewhat flattened), long and smooth apex extending in a tip without any blade (sharpe edges). Grade 2: Apex a little shorter; the blunted tip shows two small bumps; un- bladed (in S. supramontis flattened immediately above the tip). Grade 3: Apex considerably shortened similar to the fully bicuspid tooth; the small bumps of the former stage are now distinct cusps of similar size separated more clearly (in S. supramontis a secondary very short labial cusp has developed. Both the short one as well as the longer lingual one may have short blades). Grade 4: Two cusps are seen, the labial one somewhat erected and broadened basally, the lingual is pointed (in S. supramontis both cusps possess short blades). Grade 5: Fully biscuspid tooth; the labial

1 4 5

& 2 3

/2 /? I

Fig. 1. Gradation (1-5) of the tooth apex according to its degree of bicuspidity in frontal (on the top) and lateral view (in the mid- die). Below: In S. supramontis the pattern is slightly modified (for further explanation see text).

bladed cusp surrounds the lingual in a semicircle, the now larger lingual cusp may be broadened with a short blade or pointed (in S. supramontis both cusps, the lingual one is longer than the labial and have distinct blades).

R e s u l t s

In SpeIeomantes four different tooth systems are present: The upper jaw arcade consisting of the premaxillae and maxillae, the lower jaws of the dentaries, the anterior vomers, all monostichously dentated, and the posterior vomerine tooth patches as well as the accompanying dental laminae (see Greven and Clemen 1976; Clemen and Gre- yen 1994).

Height of teeth and number of tooth loci

Figures 2-4 show the height of teeth from different dentigerous bones in the seven specimens used for these measurements. Table 1 lists the tooth loci of the dentigerous bones in all specimens available.

In the two males of S. genei (Nr. I and V) premaxillary teeth were monocuspid. They measured 427,81-481.6 gm (I) and 396.72--440.28 gm (II) in length; maxillary teeth tended to become bicuspid posteriorly; anteriorly they measured 297.24-362.65 gm (I) and 315.22-335.51 ~tm (II) and posteriorly they measured 122.38-171.09 gm (I) and 165.89-232.08 gm (V). Teeth on the anterior dentary measured 135.85-259.50 gm (I) and 163.68-219.29 gm (V) and on the posterior dentary 146.14-186.79gm (I) and 145.41-200.47 gm (II).

The female (Nr. III) had bicuspids on all dentigerous bones. They measured 154.10-266.04gm (premaxilla), 224.36-227.171am (anterior maxilla); 125.06-172.37gm (posterior maxilla), 114.05-187.59 ~tm (anterior dentary), and 119.67-153.63 gm (posterior dentary).

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Table L Speleomantes specimens available for this study and number of tooth loci on each side of the paired tooth systems (dentigerous bones)

Species, nr. Stage Length Premaxillae Maxillae Anterior Posterior Dentary and sex svl (era) vomer vomer

S. genei I c? adult 6.2 2/2 20/20 16/12 53/49 25/25 II c? adult 7.4 - / - - / - - / - - / - - / - III ~ adult 7.4 3/3 21/24 26/12 56/55 33/33 IV ~? adult 7.5 6/6 28/23 18/19 73/75 39/43 V c~ adult 7.6 4/4 28/28 15/17 - / - 36/37

S. flavus I c? juvenile 3.8 2/2 19/19 10/10 45/45 19/19 II ~ juvenile 4.4 4/4 20/20 13/13 51/58 31/30 III ~ juvenile 3.5 2/2 7/6 6/7 - / - 23/19 IV ~ juvenile 4.0 3/3 18/20 8/8 - / - 20/24

S. supramontis I ~ juvenile 4.5 4/4 20/22 14/15 - / - 32/32 II $ juvenile 4.2 3/3 20/19 13/12 - / - 36/33 III ~? juvenile 3.8 4/4 17/25 10/11 66/63 23/19 IV d' adult - 3/3 25/25 21/19 - / - - / -

S. imperials I 2 juvenile 3.5 3/3 14/12 7/7 - / - 33/31 II c? juvenile 3.9 4/4 21/20 12/10 32/27 30/30 III ? juvenile 3.3 3/3 16/16 7/8 - / - 19/22 IV 2 juvenile 3.2 3/3 12/11 7/7 - / - 23/25 V c~ adult - 3/3 33/35 19/16 55/- 48/47 VI c? adult - 4/4 28/26 17/16 - / - - / -

S. ambrosii I ~" juvenile 3.9 3/3 17/22 9/ 8 - / - 28/27 II ~ juvenile 3.8 3/3 20/16 9/10 - / - 25/23

S. italicus I (~ adult - 4/4 25/25 14/14 - / - - / - II c~ adult - 2/2 34/30 17/17 - / - - / -

svl = snout-vent length; - and - / - = no data

The male of S. supramontis (IV) had monocuspids on the premaxil lae and mono- and bicuspids on the maxillae. They measured 113.82-340.63 gm (premaxilla), 215.23- 260.07 gm (anter ior maxilla), and 113.58-128.10 gm (poster ior maxilla).

The male of S. imperialis (V) had monocusp ids on the premaxi l lae and mono- and bicuspids on the maxillae. They measu red 291.91-492.94gm (premaxil la) , 204.68-263.70 gm (anter ior maxilla), and 129.2% 130.68 Ixm (poster ior maxil lae), respectively.

The juvenile male of S. flavus (I) had exclusively bicuspid teeth. They measured 129.74-131.62 tam (premaxillae), 99.30-120.14 gm (anter ior maxillae), 74.00- 107.05 gm (posterior maxillae), 69.7%102.81 gm (anterior dentary), and 69.09-75.18 gm (posterior dentary).

The juvenile female of S. ambrosii (II) had exclusively bicuspid teeth. They measured 126.46-140.52 gin (premaxillae), 90.63-117.56 ktm (anterior maxillae), 87.35-90.40 gm (posterior maxillae), and 83.14-97.89 lxm (anterior dentary).

Generally, it can be stated that the height of teeth de- creased in poster ior direction (Figs. 2-4), that the premax-

illary teeth are the largest in the adult males (Figs. 2, 3), that the dentit ional sexual d imorphism is not seen in juveniles (Fig. 4), and that all teeth in juveniles and on the adult vomer were biscuspid (grade 5, Figs. 5, 6). Only pre-

600-

400 ̧

200

Iz Z !

I - Ix I zl,

pm ] mxa I m x p l da ] dp [

Fig. 2. Range of the length of the dentine crown of teeth on the premaxilla (pm), the anterior (mxa) and the posterior portion of the maxilla (mxp), and the anterior (da) and posterior portion of the dentary (dp) in two adult males (I, squares, and V, circles) and one female (III, lines) of S. genei.

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~m 600 -:

4 0 0 -

m

200 - | •

pm I m .l m pl I I

Fig. 3. Range of the length of the dentine crown of teeth on the premaxilla (pm) as well as on the anterior (mxa) and the posterior portion of the maxilla (mxp) in an adult male of S. supramontis (IV, squares) and an adult male of S. imperialis (V, circles).

[ A m

150

140

130

120

llO

IO0

90

80

70

6O

,I

pm I mxa ] m x p ] da ] dp [

Fig. 4. Range of the length of the dentine crown in teeth on the premaxilla (pm), the anterior (mxa) and the posterior portion of the maxilla (mxp), and the anterior dentary (da) of a juvenile male of S. flavus (I, squares) and a juvenile female of S. arnbrosii (II, lines).

maxillary, maxillary and dentary teeth whose apices ran- ged f rom clearly mono- to various degrees of bicuspidity will be considered in the next paragraph.

Specific aspects

Speleomantes spp. teeth investigated herein are typical urodele teeth; i.e., they consist of the pedicle and the dentine crown covered by a smooth enamel cap (Fig. 6). The major por t ion of the surface of the dentine crown and the pedicle was rough. A collagenous zone of division separated the crown f rom the pedicle (Figs. 6, 8). Immedi - ately above and below this zone the surface of the dentine crown and the pedicel was more globular (Fig. 8). The zone of division was broader lingually than labially (premaxilla, maxilla, dentary) or posteriorly b roader (aborally) than anteriorly (orally) (vomer) (Fig. 6). Den- tine crowns were abruptly (premaxilla) or slightly curved inward and pedicles were ankylosed horizontally to the vomers and pleurally to the maxillae, premaxillae, and dentaries. Apices of fully bicuspid teeth had two cusps (Figs. 9-13). The lingual or aboral cusp respectively was pointed (Fig. 10) or b roadened (Figs. 9, 11, 12); particu- larly in the latter case a sharp edge (blade) was seen. The labial cusp surrounded the lingual one often in a semicircle having a likewise sharp edge. Apices of full monocuspids were conical or somewhat f lat tened without distinct blades (Figs. 14, 19, 20, 21, 25, 28). They were found in males and in a single female. In the latter, the few monocuspids had nearly the same size as the bicuspids. ~: Speleomantes genei. Male I: The two functional teeth

of the premaxil lae were monocuspids (grade 1) as well as the replacement teeth (Figs. 5, 14). The first tooth of the left maxilla was monocuspid (grade 1), the second had two small knobs (grade 3); the teeth afterwards were more or less bicuspid. On the right maxilla the two most anterior teeth were monocuspid (grade 1) (Fig. 16), the third tooth had a longitudinal crest (grade 2) (Fig. 15) and the teeth afterwards showed increasing bicuspidity, e.g. grade 4 ( tooth 9) (Fig. 17) and grade 5 ( tooth 10). The partes dentales of

Fig. 5. S. genei, male I. Monocuspid premaxillary teeth (arrows) and anterior vomer (arrowhead). Fig. 6. S. flavus, male I. Posterior vomer with bicuspid teeth. Teeth are curved aborally. Note the gap between the pedicle and the tooth crown, that is broader orally (arrow). Fig. 7. S. flavus, male I. Posterior vomers with their tooth patches are attached to the large parasphenoid (arrowhead). Fig. 8. S. ambrosii, male I. Zone of division between pedicle and crown of a vomerine tooth, oral aspect. Note small collagenous fibers bridging the gap (arrow). Fig. 9. S. flavus, male I. Bicuspid maxillary tooth with a broad lingual blade (arrow). Fig. 10. S. supramontis, male IV. Bicuspid maxillary tooth with a short lingual blade (arrow). Fig. U. S. genei, female (without number). Bicuspid premaxillary tooth with two distinct blades. Fig. 12. S. supramontis, female. Bicuspid premaxillary tooth with two distinct blades. Fig. 13. S. imperialis, male VI. Bicuspid teeth of the anterior vomer. Fig. 14. S. genei, male I. Monocuspid premaxillary tooth (grade 1).

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the anterior parts of the vomers as well as the posterior vomerine tooth patches had a clear bicuspid dentition. On the posterior left dentary and the entire right dentary, teeth were bicuspid (grade 4). The three most posterior teeth seemed to be monocuspid (grade 1). Male V: Dentition resembled that of male I. Both premaxillae had four tooth loci each with three functional but rather worn monocuspids. Teeth of the left maxilla were all bicuspid (grade 4-5), in the posterior region some showed grade 3. Anterior teeth of the right maxilla were bicuspid (grade 4 and 5) and appeared well worn. In the middle portion, teeth of grade 3 were seen. The two most posterior teeth were smaller, but apices were extremely elongated and curved (grade 2 to 3). On the dentary teeth, grades 3 and 4 occurred. Six monocuspid teeth were found posteriorly at the left dentary (Fig. 19). Female III had exclusively bicuspids (grade 4 and 5) on the premaxillae. This also holds for the maxillae; only some posterior teeth are grade 3-bicuspids. Den- tary teeth appeared well worn. Teeth showed a mosaic of "atypical" forms not suitable for the grading suggested above. Female IV had six teeth with an elongated monocuspid apex on each premaxilla (grade 1); replacement teeth were distinctly bicuspid (grade 5) (Fig. 18). Max- illae showed a mosaic of bicuspid teeth of varying grades interspersed with some monocuspids. Dentary teeth were bicuspid (grade 4 and 5).

~II! Speleomantes supramontis. Male IV had three tooth loci on each premaxilla. The left premaxilla was occupied by one tooth, the right premaxilla by two. All functional teeth and replacement teeth were monocuspid (grade 1) (Figs. 20, 21). The most anterior tooth on the left maxilla was bicuspid (grade 2); bicuspidity increased in posterior direction (grade 3-5) (Fig. 22, 23, 24; see also Fig. 10). The first tooth of the right maxilla was monocuspid, the following two were bicuspid (grade 2 and 3). More posteriorly, teeth showed grade 4 and 5 of bicuspidity. Speleomantes imperialis. Male V had rather damaged enamel caps. Both premaxillae had three tooth loci each; at the left premaxilla two functional monocuspids and one damaged tooth, at the right two functional monocuspids were found. The two most anterior teeth on the left maxilla were monocuspid

N

followed by teeth of grade 3 and then of grade 4 bicuspidity. The most posterior teeth were also bicuspid (grades2 and 3). On the right maxilla anterior (grade 3) and posterior teeth (grade 4) were bicuspid. Male VI had four loci on each premaxilla. Two were occupied by functional teeth and two by not yet established replacement teeth. Teeth of the left premaxilla showed some irregularities regarding monocuspidity, those of the right premaxilla, in particular the replacement teeth, were monocuspid (Figs. 25, 26). The left and right maxillae possessed exclusively bicuspid functional (grades 4 to 5) (Fig. 27) and replacement teeth (grade 4). Speleomantes italicus. Male II: Premaxillae had only two loci each. At one locus on the left side, the functional tooth was cracked (Fig. 28). At the second locus only a monocuspid replacement tooth was present. On the right premaxilla a damaged functional tooth was found; the second tooth had fallen out. The first three anterior teeth of the left maxillae as well as the replacement teeth were monocuspid (Fig. 29), the fourth, fifth and sixth had a small indentation with two small knobs (grades 2 to 3) (Fig. 30), the seventh was bicuspid (grades 3 to 4) (Fig. 31). Also the right maxilla showed the tendency to become bicuspid posteriorly. The three most anterior teeth are monocuspid, the fourth showed grades ranging from 2 to 5 in the posterior direction. In the female (II), functional teeth were broken off at the level of the dividing zone. The few established and replacement teeth available for examination possessed different grades of bicuspidity on the premaxillae and maxillae.

D i s c u s s i o n

Speleomantes spp. are directly developing plethodontids (Lanza 1999). As far as is known from other directly developing ptethodontids, hatchlings possess transformed, i. e. bicuspid teeth on the dentigerous bones developed at this time (Ehmcke and Clemen 2000 a). Also in plethodontids, the typical bicuspid tooth has a distinct dividing zone and a crown with two bladed cusps, the inner, lingual one more extended (see Greven and Clemen 1976;

Fig. 15. Fig. 16. Fig. 17. Fig. 18. Fig. 19. Fig. 20. Fig. 21. Fig. 22. Fig. 23.

S. genei, male I. Bicuspid maxillary tooth (grade 2). S. genei, male I. Premaxilla (right side) and maxilla (left side) with monocuspid teeth. S. genei, male I. Bicuspid replacement tooth (grade 4) of the maxilla. S. genei, female IV. Monocuspid premaxillary teeth and bicuspid replacement tooth (arrowhead). S. genei, male V. Monocuspid dentary tooth. S. supramontis, male IV. Monocuspid tooth of the left premaxilla, lateral view. S. supramontis, male IV. Monocuspid tooth of the left premaxilla, frontal view. S. supramontis, male IV. Anterior left maxilla with bicuspids of grade 2 (left side) and grade 3 (right side). S. supramontis, male IV. Posterior left maxilla with bicuspids of grade 4-5 (left side) and 5 (right side).

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Ehmcke and Clemen 2000 a, b; in the species investigated herein this cusp was pointed or broadened) and the labial one embracing the lingual tip often like a collar (for terminology and succession of differently shaped tooth generations in Urodela see Greven 1989; Clemen and Greven 1994). All male and female juveniles examined herein bear fully transformed teeth. Thus, a sexual dimorphism in the shape of the apex and in the length of the crown is absent in non mature specimens.

The adult males, however, and one female (S. genei) had monocuspid teeth. In the male the monocuspids were considerably elongated and were present on the upper and lower jaw. Even in the paedomorphic plethodontid Eurycea neotenes, the teeth of males, typically larval, are longer than those of females (Clemen and Greven 2000). We think that the monocuspids present in the transformed adults are modified bicuspids, i.e. metamorphosed despite a superficial similarity with late larval- monocuspids. Vomers always showed a typical bicuspid dentition in both sexes. These findings indicate, that in European plethodontids 1) metamorphosed bicuspid teeth can be replaced by conical, more or less bladed monocuspids in males and even in females, and 2) that these changes do not only concern the premaxilla, but also the maxilla and the dentaries.

Sexual dimorphism in the dentition of plethodontids is well known in New World species (e.g. Noble 1931; Duellman and Trueb 1985; Ehmcke and Clemen 2000 a, 2003). Generally the upper jaw in males protrudes be- yond the lower jaw. Thus, teeth are visible, even when the mouth is closed. McBride-Stewart (1958) has shown that in Eurycea bislineata the overall bicuspid dentition of juveniles was replaced by the longer monocuspids on the premaxillae and partly on the maxillae and dentaries when males approached the first breeding season. Further, she demonstrated a remarkable seasonal change of the dentition of these bones correlated with changes in the testes and observed the greatest tooth height during the breeding season, a nearly edentulous condition of the premaxillae at the end of the breeding season, and then a tendency to replace monocuspids by bicuspids. At no time did all teeth of the maxillae and dentaries become monocuspid.

It has been suggested that males of neotropical species constantly bear monocuspids on the premaxillae (Ehmcke and Clemen 2000 a, b), but this speculation must be sub-

stantiated by examination of more males captured throughout the year. Data on seasonality of reproduction in Speleomantes spp. are too anecdotal and scarce to be dis- cussed in the context of a possible seasonal change of dentition (see below). In addition, seasonality may be different and reproduction may even be non-seasonal in the various species and environments. Whether in adult male Speleo- mantes spp. the once established monocuspids were replaced by bicuspids and vice versa is entirely unknown as yet.

Regarding the height and number of teeth as well as the distribution of sexual dimorphic teeth in European Speleomentes spp. our findings correspond largely with data summarized by Lanza et al. (1995; see also Lanza 1999). Under the heading "Hydromanes genei" authors mentioned monocuspid teeth on the male premaxillae and the anterior portion of the maxilla and "sometimes to a lesser extent also in the females" (Lanza et al. 1995, p. 102). Maxillary monocuspids and bicuspids, the latter more posteriorly attached, were already mentioned by McBride-Stewart (1958) in Eurycea bislineata. Ehmcke and Clemen (2000b) speculated that the occurrence of monocuspids on the maxillae have something to do with the course of dental laminae in this tooth system. They described the dental lamina of the upper jaw as being separated by connective tissue between the premaxilla and maxilla in Bolitoglossa subpalmata and Oedipina unifor- mis, that both exhibit monocuspids exclusively on the premaxillae, and a continuous dental lamina, however un- productive, between the two dentigerous bones in Noto- triton abscondens, a species that showed monocuspids on the premaxillae, and not fully bicuspid, but somewhat "shape-aberrant" teeth on the maxillae. In the Speleo- mantes spp. examined herein, even fully developed monocuspids have been found on the anterior maxilla and some histological sections of the insufficiently preserved material showed a continuous premaxillary/maxillay dental lamina in S. italicus.

As transformed specimens of some Salamandridae re- tained bicuspid teeth after hypophysectomy we previously hypothesized that the thyroxine dependent development of bicuspid teeth follows on "all or nothing", pattern i.e. once initiated, the following tooth generations remain bicuspid also without further thyroxine stimuli (Greven and Clemen 1990). It may be speculated that the "aberrant" teeth of the maxilla of N. abscondens (Ehmcke and Cle-

Fig. 24. S. supramontis, male IV. Establishing bicuspid replacement tooth, left maxilla (grade 4). Fig. 25. S. imperialis, male VI. Establishing monocuspid replacement tooh, premaxilla. Fig. 26. S. imperialis, male VI. Functional monocuspid and monocuspid replacement tooth (arrowhead), left premaxilla. Fig. 27. S. imperalis, male VI. Posterior maxilla with bicuspid functional teeth (grade 5) and replacement tooth (grade 4, arrow). Fig. 28. S. italicus, male II. Monocuspid premaxillary tooth. Fig. 29. S. italicus, male II. Monocuspid replacement tooth, maxilla. Fig. 30. S. italicus, male II. Maxillary tooth (grade 2). Fig. 31. S. italicus, male II. Most posterior maxillary tooth (grade 4).

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men 2000 b), the teeth of the premaxillae of several Boli- toglossa species with different proportions of either the labial or the lingual cusp (Ehmcke et al. 2004) and the different "bicuspid" teeth on the maxillae described herein for Speleomantes spp. represent tooth generations indi- cating a gradual development of monocuspidity or bicuspidity respectively. At least replacement of larval monocuspids by fully bicuspid during metamorphosis ap- pears to take place via intermediate stages (see the "inci- pient" bicuspids in late stages of transformation of some ambystomatids and salamandrids (Clemen and Greven 1977; Beneski and Larsen 1989; Greven and Clemen 1990). In general a differential sensitivity of the different tooth system and even single tooth loci to the hormones involved in the formation of the tooth apex may be as- sumed (see below).

Appearance of sexual dimorphism is controlled by androgen receptors in the target tissue. Androgen-dependent morphogenesis of the sexual dimorphic teeth has been already demonstrated by Noble and Pope (1929). They showed that in castrated males of Desmognathus fuscus the long monocuspids of the premaxilla were replaced by short bicuspids and that testes transplanted in these males again produced monocuspids. Testes transplanted in females after spaying also produced elongated monocuspids. In addition, intermediate types of teeth were noted. Influence of androgens was also indicated by the above mentioned study of McBride-Stewart (1958) who demonstrated the seasonality of this dimorphism. More recently, expression of androgen receptors was demonstrated immunocytochemically in the mesenchymal cells adjacent to the dental lamina of the premaxillae in male Bolitoglossa schizodactyla. Males of this species have "shape-aberrant" teeth on their premaxillae (see above), whereas females have a fully bicuspid dentition (Ehmcke et al. 2004). Obviously, in males sexual dimorphic structures including monocuspid teeth as well as spermatogenesis, spermiation and sexual behaviour re- flect an elevated androgen level. Elevated levels may be present more or less permanently in non-seasonal breeders such as the neotropical plethodontids (to our knowl- edge data on plasma androgen levels of such species throughout the year do not exist) or will change in seasonal breeders such as the plethodonids Plethodon jordani and Desrnognathus ochrophaeus. The former species reproduces in autumn with maximal levels of androgen correlated with male sexual behaviour, production of mature spermatozoa, spermiation, and fully developed male secondary sexual characteristics, the latter reproduces in autumn and spring with summer mating obviously not correlated with elevated plasma androgen levels (Wood- ley 1994; Houck and Woodley 1994; see also Noble and Pope 1929; McBride-Stewart 1958). A different and differential expression of androgen receptors in the odonto- genetic mesenchyme in the various tooth systems obviously allows a selective response of the tooth forming tissue to the hormonal stimulus and leads to sex-related differences in androgen receptor distribution in the tooth

forming organs (see Ehmcke et al. 2003). Similar mecha- nisms have been suggested for the effect of thyroxine on tooth systems (Greven and Clemen 1990).

Premaxillary monocuspids although shorter than in the male were also found in a single female of S. genei; the replacement tooth was bicuspid. This observation is in agree- ment with the statement of Lanza et al. (1995; see above) and indicates a (seasonal?) change between mono- and bicuspids. Here also a correlation between androgens and the development of monocuspids may exist, as androgen levels increase also in female urodeles to trigger reproduction (e. g. Triturus carnifex: Zerani et al. 1991; see also Houck and Woodley 1994).

Acknowledgements. We are indebted to Prof: Dr. B. Lanza, Uni- versity of Florence (Italy), Prof. Dr. W. Roth, University of Bre- men, and Dipl. Biol. Th. Mutz, Mtinster, who made the preserved specimens available to us, and to Josef Lange, MUnster, for tech- nical assistance.

References

Beneski JH, Larsen JH Jr (1989) Interspecific, ontogenetic, and life history variation in the tooth morphology of mole salamanders (Amphibia, Urodela, and Ambystomatidae). J Mor- phol 199:53-69

Clemen G, Greven H (1977) Morphologische Untersuchungen an der Mundh6hle yon Urodelen. III. The teeth of the upper jaw and the palate in Arnbystoma mexicanum Cope (Ambys- tomatidae: Amphibia). Zool Jb Anat 98:95-136

Clemen G, Greven H (1994) The buccal cavity of larval and metamorphosed Salamandra salamandra: Structural and develop- mental aspects. Mertensiella 4:83-109

Clemen G, Greven H (2000) Dentigerous bones and dentition in the paedomorphic plethodontid salamander Eurycea neotenes. Alytes 18:51-61

DueUman WE, Trueb B L (1983) Biology of Amphibians. McGraw Hill, New York

Ehmcke J, Clemen G (2000 a) Development of the pattern of dentition and dental laminae of Costa Rican plethodontid salamanders (Amphibia: Urodela). Ann Anat 182:327-338

Ehmcke J, Clemen G (2000 b) Teeth and their sex-dependent dimorphic shape in three species of Costa Rican plethodontid salamanders (Amphibia: Urodela). Ann Anat 182:403-414

Ehmcke J, Wistuba J, Clemen G (2004) Separated dental laminae are present in the upper jaw of Mesoamerican lungless salamanders (Amphibia Plethodontidae). Ann Anat 186:45-53

Ehmcke J, Wistuba J, Clemen G, Schlatt S (2003) Targeted expression of androgen receptors in tooth-forming tissues of a neotropical salamander (Bolitoglossa schizodactyla) enables male-specific formation of dimorphic types of teeth. Gen Comp Endocrinol 134:26-35

Greven H (1989) Teeth of extant Amphibia: morphology and some implications. Fortschr Zool 35:451-455

Greven H, Clemen G (1976) Morphologische Untersuchungen an der Mundh6hle yon Urodelen. II. Die Gaumenzahnfelder yon Hydromantes italicus Dunn (Plethodontidae: Amphibia). Zool Beitr NF 22:489-506

Greven H, Clemen G (1990) Effect of hypophysectomy on the structure of normal and ectopically transplanted teeth in larval and adult urodeles. Acta Embryol Morph Expt NS 11:33-43

42

Greven H, Schubert-Jung M, Clemen G (2002/2003) Notes on the skull of Speleomantes spp. (Plethodontidae, Urodela). Acta Biol Benrodis 12:45-58

Houck LD, Woodley SK (1994) Field studies of steroid hormones and male reproductive behaviour in amphibians. In: Heatwole H (Ed) Amphibian Biology, vol. 1. Surry Beatty & Sons, Sydney, pp 677-710

Lanza B (1999) 2.1.3. Plethodontidae - Lungenlose Salamander. In: Grossenbacher K, Thiesmeier B (Eds) Handbuch der Rep- tilien und Amphibien Europas. Schwanzlurche I. Aula Verlag, Wiesbaden, pp 77-204

Lanza B, Caputo V, Nascetti G, Bullini L (1995) Morphologic and genetic studies of the European plethodontid salamanders: Taxonomic inferences (Genus Hydromantes). Museo Re- gionale di Scienze Naturali, Torin

McBride-Stewart M (1958) Seasonal variation in the teeth of the two-lined salamander. Copeia 1958:190-196

Noble GK (1931) The Biology of the Amphibia. Dover, New York

Noble GK, Pope SH (1929) The modification of the cloaca and teeth of the adult salamander, Desmognathus, by testicular transplants and by castration. Brit J Exp Biol 6:329-411

Wake DB (1966) Comparative osteology and evolution of the lungless salamanders, family Plethodontidae. Mem South Calif Acad Sci 4:1-111

WoodleySK (1994) Plasma androgen levels, spermatogenesis and secondary sexual characters in two species of plethodontid salamanders with dissociated reproductive patterns. Gen Comp Endocrinol 96:206-214

Zerani M, Vellano C, Amabilu F, Carnevali O, Andreoletti GE, Plzonetti-Magni A (199l) Sex-steroid profile and plasma vitel- logenin during the annual reproductive cycle of the Crested Newt (Triturus carnifex Laur.). Gen Comp Endocrinol 82: 337-344

Accepted August 12, 2003

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The dentition of european Speleomantes spp. (Urodela, Plethodontidae) with special regard to sexual dimorphism

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