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Revue suisse de Zoologie 121 (3): 293-3 17; septembre 2014

An unexpected occurrence - a case study on an intergeneric hybrid in giant snakes

Nicole ERNSTl, Andreas SCHMITZ2, Norin CHAP, Jacques RIGOULET^,

Aude BURGEOIS3, Muriel K0HL3, Christelle HANO^ & Ivan INEICH4

1 Zoologisches Forschungsmuseum Alexander Koenig, Department of Herpetology, Adenauerallee 160, D-53113 Bonn, Germany, emst_nicole@gmx.de

2 Natural History Museum of Geneva, Department of Herpetology and Ichthyology, C.R 6434, CH-1211 Geneva 6, Switzerland. andreas.schmitz@ville-ge.ch

3 Ménagerie du Jardin des Plantes, Muséum national d'histoire naturelle,

57 me Cuvier, F-75005 Paris, France.

4 Muséum national d'histoire naturelle, Département Systématique et Evolution (Reptiles et Amphibiens), ISYEB UMR 7205 (CNRS, EPHE, MNHN, UPMC)„

CP 30, 25 me Cuvier, F-75005 Paris, France, ineich@mnhn.fr

Corresponding Author: Nicole Emst, E-mail: emst_nicole@gmx.de

An unexpected occurrence - a case study on an intergeneric hybrid in giant snakes. - In recent years an increasing number of studies have identi- fied cases of interspecific hybrids in reptiles, but intergeneric hybridisation, especially in snakes, is still only rarely known. In the current study we used several methods, SEM recordings, morphometries, and both mitochondrial and nuclear gene analyses, to identify and analyse an intergeneric hybrid as a representative case study for the challenges related to this phenomenon. We here present evidence of intergeneric hybridisation between species of two well-studied boid genera: Eunectes {E. notaeus) and Boa {B. constric- tor). For the intergeneric hybrid specimen the nuclear gene analyses result in its intermediate and separate phylogenetic position whereas morpho- logical analyses clearly show that only some characteristics are inter- mediate, while other characters can be clearly assigned to either one of the parental species. The indistinct morphological character states and the conflicting phylogenetic position based on the genetic data show that such a hybrid can be extremely difficult to identify in situ and ftirthermore, those results can lead to false assumptions about the real identity and recognition of hybrids, e.g. when modem barcoding methods are used for fast and easy taxon-identifìcation. Therefore, better recognition, identification and long term observations of both interspecific and intergeneric hybrids are needed to properly assess and preserve the current biodiversity.

Un événement inattendu - étude d’un cas d’hybridation intergénérique de serpents géants. - Récemment, un nombre croissant d’études ont permis d’identifier des hybridations interspécifiques chez les reptiles, mais les cas d’hybridation intergénériques demeurent rares, tout particulièrement chez

Manuscript accepted 03.06.2014

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les serpents. Dans notre étude, nous utilisons plusieurs méthodes modernes: microscopie SEM, morphométrie et analyses génétiques des gènes mito- chondriaux et nucléaires, afin d’identifier et d’analyser un hybride inter- générique qui permettra de soulever les problématiques scientifiques liées à ce type d’hybridation. Nous présentons ici des arguments en faveur d’un cas d’hybridation intergénérique entre deux genres néotropicaux bien connus: Eunectes (E. notaeus) et Boa {B. constrictor). Les résultats de l’analyse des gènes nucléaires placent ce spécimen hybride intergénérique dans une position intermédiaire entre ses parents mais distincte phylogénétiquement alors que l’analyse morphologique montre clairement que seuls certains caractères sont intermédiaires, alors que d’autres peuvent être clairement assignés à l’une ou l’autre des deux espèces parentales. Les caractères morphologiques non diagnostics d’un taxon connu et la position phylo- génétique conflictuelle obtenue par les données génétiques montre que ce type d’hybride intergénérique peut se révéler extrêmement difficile à iden- tifier in situ. Une identification erronée est alors fortement probable plutôt que la détection de la nature hybride du spécimen, surtout lorsque les méthodes modernes de barcoding seront utilisées pour des identifications faciles et rapides. De ce fait, une meilleure connaissance et un suivi à long terme de tous les hybrides à la fois interspécifiques et intergénériques sera nécessaire afin d’identifier correctement la biodiversité actuelle pour appré- hender sa conservation avec plus d’efficacité.

Keywords: Barcoding - BDNF - Boa constrictor - Eunectes notaeus - hybridisation - mtDNA - phylogeny - RAGl - SEM - spéciation.

INTRODUCTION

Interspecific hybrids are well known in amphibians and reptiles, but have until recently been considered as uncommon (Mertens, 1950, 1956, 1964, 1968, 1972; Murphy & Crabtree, 1988; Leaché & Cole, 2007; Mebert, 2008; Kearney et al, 2009). Such interspecific hybridisation arises not only in captivity like in zoos, but also in situ where under certain circumstances hybrid zones between two distinct species occur. Especially in recent years quite a few reptile examples have been observed, e.g. in turtles [Cuora mouhotii x C. galbinifrons (Shi et al, 2005), Mauremys reevesii x M sB nensis (Fong & Chen, 2010)], in different lizard families [Anolis polylepis x A. osa (Köhler et al., 2010), Aspidoscelis dixoni x A. tigris (Cole et ai., 2007), Podarcis sicu- lus X P. wagierianus (Capula, 1993)], in colubrids [Pantherophis bairdi x E obsoletus Undheimeri (Vandewege et al, 2012)], in vipers [Bitis gabonica x B. arietans (Broadley & Parker, 1976; Broadley, 2006)], in boids [Eunectes murinus x E. notaeus (Dirksen & Böhme, 1998)], and in pythonids [Python natalensis x P bivittatus (Branch & Erasmus, 1984)].

While interspecific hybrids now seem not too uncommon, intergeneric hybrids, as are known between snake genera like Liasis mackloti x Morelia spilota (Banks & Schwaner, 1984) and Crotalus horridus x Sistrurus catenatus (Bailey, 1942) are appa- rently still very rare occurrences. One of the most recently reported occurrences of intergeneric hybridisation are two hybrid specimens of PituopMs catenifer sayi and Pantherophis vulpinus (Ledere et al, 2012) which are of particular interest since these

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

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are true naturally occurring intergeneric hybrid snakes. In the pet trade intergeneric snake hybrids are well known and some reptile breeders attempt to hybridise specific snake genera, e.g. Pantherophis x Pituophis, Pantherophis x Lampropeltis, or Acran- tophis X Boa (Ledere et al, 2012; Branson’s Wild World, 2014; Hybrid Herps, 2014). Although several fora exist where breeders exchange their experiences, unfortunately no substantial studies exist which summarise the number of successful hybridisations in captivity and compare them to the number of known natural hybrids. Thus, one can only state that interspecific and intergeneric snakes are far better known and much more common in captivity than in nature.

Here we report on a new case of an intergeneric hybrid snake which was bom in captivity and is kept in the 'Ménagerie du Jardin des Plantes’, at the Paris Natural History Museum (MNHN). This living specimen is a boid hybrid between a female Boa constrictor and a male Eunectes notaeus. With the idea to shorten the phrase “intergeneric hybrid specimen” and to reflect the identity of this hybrid we name it “Boaconda” - a joined name between the names Boa {Boa) and Anaconda {Eunectes).

Both boid genera Eunectes and Boa have been well studied (e.g. Dirksen & Böhme, 1998; Dirksen, 2002; Bertona & Chiaraviglio, 2003; Burbrink, 2005; Aller et al, 2006; Bonny, 2007; Reed & Rodda, 2009) and the phylogenetic position of both genera among boid snakes has been clearly resolved in recent multigene (mitochon- drial and nuclear genes) phylogenetic studies (e.g. Vences et al, 2001; Burbrink, 2005; Noonan & Chippindale, 2006; Reynolds et al, 2014).

The genus Eunectes consists of five acknowledged species and the genus Boa is currently believed to harbour a single species with nine subspecies. The main habitat of Eunectes notaeus is alongside the Rio Paraguay and its tributaries, which are part of the Pantanal. These rivers cross Bolivia, Brazil, Paraguay, Argentina and partly Umguay (Stimson, 1969; Petzold, 1982; Henderson et al, 1995; Dirksen & Böhme, 1998; Dirksen, 2002) (Fig. 1, distribution range of Eunectes notaeus marked with transverse lines). E. notaeus inhabits mainly swamps and seasonal flooded areas but it can also be found in forested or deforested as well as agricultural areas (Striissmann & Sazima, 1993; Dirksen & Henderson, 2002; Reed & Rodda, 2009).

Boa constrictor is distributed in Central America and north and central regions of South America, from Mexico to Argentina and southern Brazil (Bonny, 2007; Reed & Rodda, 2009) (Fig. 1, distribution range of Boa constrictor marked with vertical lines). The species inhabits a wide range of biotopes where it is common in forests, grasslands and agricultural areas (Bonny, 2007; Reed & Rodda, 2009).

Both species Eunectes notaeus and Boa constrictor are syntopic in the northern part of the Pantanal (western Brazil) and along the upper river section of the Rio Guaporé in Bolivia (Striissmann & Sazima, 1993; Junk et al, 2006; Souza et al, 2010). They prefer dense vegetation near water (Chiaraviglio, 2006; Reed & Rodda, 2009).

The hybrid Boaconda was bom on 29th May, 2009 in the “Ménagerie” of the MNHN in Paris. This snake is the only surviving individual of a clutch comprising two individuals without the skeleton, one congenital malformation and about 20 unferti- lised eggs. It was sexed twice with a testing probe and identified as a male on 14th April, 2010 and 3rd December, 2011 respectively. Because of the young age of the hybrid individual sexual activity could not yet be observed, therefore, the question

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Fig. 1

Distribution map: vertical lines - distribution of Boa constrictor spp.; transverse lines - distri- bution of Eunectes notaeus; crossed markings - overlapping distribution range of both species [modified from figures 12 and 8.2 of Reed & Rodda (2009)].

about fertility or sterility cannot be satisfyingly answered. The Boaconda (Figs 2 E-H), its mother (Figs 2 A-B) and both potential fathers (Figs 2 C-D) are still alive and therefore electronically tagged and their respective tag numbers are:

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

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250228500004090, 250228700001763, 2502296000049768, and 00-01FO-7C39. The female B. c. constrictor arrived at the Ménagerie on 28th September, 2005 and she was previously never in contact with any male snake (1. Ineich, pers. comm.). Since the arrival day the female B. c. constrictor is kept in the same terrarium as the two male E. notaeus. Copulation was observed several times by snake keepers at the Ménagerie in 2007 and 2008.

MATERIAL AND METHODS

Genetic analyses

To determine the respective position of the hybrid in phytogenies calculated on the basis of different commonly used gene sequences (both mitochondrial and nuclear genes), we used tissue samples (obtained through biopsies) from the hybrid as well as its biological mother (B. c. constrictor) and both of the potential paternal individuals {E. notaeus). DNA was extracted from each tissue sample using peqGold Tissue DNA Mini Kit (PEQLAB). A fragment of the mitochondrial 16S rRNA gene was amplified with the primers 16sar~L (5’-CGCCTGTTTATCAAAAACAK3’) and 16sbr™H (5’-CCGGTCTGAACTCAGATCACGD3’) (Palumbi et al, 2002). Furthermore, two nuclear genes were amplified: a part of the RAGl gene using the primers RAGlMartFLl (5’-AGCTGCAGYCARTAYCAYAARATGTA-3’) and RAGIAM^ PRl (5’-^AACTCAGCTGCATTKCCAATRTCA-^3’) of Chiari et al (2004) and a frag== ment of the BNDF gene using the primers BDNF-=F (5’--GACCATCCTTTTCCTK- ACTATGGTTATTTCATACTD3’) and BDNF-R (5’^CTATCTTCCCCTTTTAATG^ GTCAGTGTACAAAC--3’) of Noonan & Chippindale (2006). We used the amplifia cation protocols described in Chiari et al (2004), Schmitz et al (2005a), and Crottini et al (2009) for 16S, RAGl and BDNF, respectively. The PCR products were purified using the High Pure PCR Product Purification Kit (Roche Diagnostics GmbH) in accordance with the manufacturer’s instructions. For quality assurance both directions of the amplified PCR product were sequenced by an external vendor (Macrogen). New sequences were generated for five Boa constrictor, one Calabaria reinhardtii, two Eunectes notaeus and the hybrid (Boaconda). Accession numbers for the newly gene- rated sequences are shown in the Appendix I.

Complementary sequence data for the completion of our datasets for the respec- tive phylogenetic analyses were obtained from GenBank (see Appendix I).

The obtained sequences were initially automatically aligned using ClustalW (Thompson et al, 1994) and manually checked using the original chromatograph data in the program BioEdit (Hall, 1999).

We used neighbour-joining (NJ), maximum likelihood (ML) and Bayesian interference methods to calculate the phylogenetic trees for the respective genes. NJ analyses was performed using PAUP* 4.0b 10 (Swofford, 2002). For the ML tree we used the PhyML 3.0 computer cluster of the Montpellier bioinformatics platform (http://www.atgc-montpellier.fr/phyml/) (Guindon et al, 2010). Bootstrap analysis (20000 [for NJ] and 2000 [for ML] pseudo-replicates) was used to estimate node support. Bayesian reconstructions were performed with MrBayes, version 3.12 (Huelsenbeck & Ronquist, 2001). Estimation of the correct parameters for the both the

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Fig. 2

(A, B) Boa c. constrictor (250228700001763). (C, D) Eunectes notaeus (2502296000049768), the specimen 0001F07C39 is similar in colouration as the other E. notaeus. (E-H) Boaconda (250228500004090), with (H) shortly after birth.

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

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Bayesian and the ML analyses were done using jModelTest (Guindon & Gascuel, 2003; Posada, 2008). The exact parameters used for the Bayesian analyses followed those described in detail by Reeder (2003) and Schmitz et al. (2005b). Node support of bootstraps >70 % (Hillis & Bull, 1993) and Bayesian posterior probabilities >0.95 were considered to be highly significantly supported.

Scale microstructure

For the SEM (Scanning Electron Microscope) recordings, dried exuviae from both parent species (3 potential species: 2 paternal Eunectes notaeus and 1 maternal Boa c. constrictor and the hybrid were used. The microstructure of snake scales is unique among different species and shows almost no variation between individuals of one species and furthermore, it is independent of the individual age (N. Ernst unpubl. data; Schmidt & Gorb, 2012). Therefore, only one of the Eunectes notaeus individuals (00-01FO“7C39) will be described in detail. The samples from each body side (dorsal and ventral) were attached to a standard pin stub mount with a double sided carbon adhesive tape. The samples were powdered with a layer of 50 nm gold-palladium composite using a Hummer VII sputtering system (Anatech LTD, Alexandria, VA) with a 120 m Torr vacuum.

The observations were done with a HITACHI S-2460N Natural Scanning Electron Microscope (Hitachi, Tokyo, Japan) at an accelerating voltage of 25 kV and pictures were electronically displayed with the Digital Image Scanning System 5 (Version 5.4.14.2, copyright 2004) and exported to the Digital Image Processing System 2.6 (Version 2.6.14.1, copyright 1997-2005) by which the pictures were saved as JPEG and TIFF files. Microstructures of the anterior, middle and posterior regions of both dorsal and ventral scales were examined. Images of the hinge region (part of skin between scales) were also taken. These were taken at a magnification of 2.000x and 6.000x. The primary microstructure can be seen in the middle region of a scale.

Pholidosis and morphometrics

We selected three body and two head scale counts, four body and seven head measurements for the morphological analysis. Additionally, the gender and the eye- colour (EYC) (only of the four living specimens) were recorded (Table 3). Ventral (VEN) and subcaudal (SUC) scale numbers were counted according to standard tech- niques, as were the dorsal scale rows at midbody (DOR) (Dowling, 1951). The numbers of the supralabial (SUL) and of the infralabial scales (IFL) were counted. Following head measurements were taken with an digital calliper (Brüder Mannesmann Werkzeuge, Remscheid, Germany): the head length, which was measured from the posterior end of the lower jaw bone to the snout end (HEL); the head width, which was measured as the distance between the mandibular joints (HWI); the distance between the eyes, measured dorsally (DSE); maximal eye diameter (EYD); the distance between the nares, measured dorsally (DNA); maximum dorso- ventral diameter (DIH); maximum lateral diameter (DIW). Additionally, the snout- vent length (SVL) and the tail length (TAL) were taken with an inextensible strap and measured with a folding meter stick. The total length (TOL) was calculated by adding up the snout-vent length (SVL) and the tail length (TAL). For the analysis we calcu-

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lated some ratios (TAL/TOL; HEW/HEL; HEL/SVL; HEL/TOL; DSE/HEW; DSE/HEL; EYD/HEL; DNA/HEW; DNA/HEL; DIW/DIH). Ail measurements were taken on the right side of the snakes. We measured the Boaconda, the mother {Boa c. constrictor), the two potential fathers (Eunectes notaeus, 2502296000049768 and 00-01FO-7C39), and seven museum specimens of E. notaeus and eight museum spe- cimens of B. c. constrictor from the Natural History Museum of Geneva, Switzerland (MHNG) (see Appendix II). Additionally the weight (WEI) was recorded, the colo- ration described and the eye colour (EYC) of the four living specimens were deter- mined. The eye colour was described with the colour catalogue for field biologists by Köhler (2012).The statistical analyses [Univariate Analysis, Principal Component Analysis (PCA), with variances and covariances of groups, and between-group calculations] were conducted using PAST version 2.16 (Hammer et al, 2001).

RESULTS Genetic analyses

Of the three computed phylogenetic gene trees (Figs 3 A-C), the mitochondrial tree shows as expected a complete sequence identity of the Boaconda with its mater- nal lineage {Boa c. constrictor) and thus both the confirmed mother and the hybrid offspring are placed in the same well supported clade. In contrast to the mitochondrial tree, the hybrid is placed in an approximately intermediate position between its paren- tal species Eunectes notaeus (2502296000049768, 00-01FO-7C39) and Boa c. cons- trictor in both computed trees for the nuclear genes, even though contrarily to ML the MrBayes package treats heterozygous (ambiguous) sites as missing data (Potts et al, 2014). The nuclear genes used do not allow us to determine which one of the male E. notaeus individuals is the actual father, but since there were absolutely no differences in both nuclear genes between the two E. notaeus specimens, we treat both specimens equally.

The two parental genera are situated on highly significantly supported distinct clades and are well separated from each other. Both the BDNF- and RAG 1 -tree (Figs 3 B-C) show that the integration of hybrids does not significantly alter the node support for the parental taxa. The intermediate position can be explained due to heterozygosity at most or all of the 12 variable sites in the BDNF gene fragment and 19 variable sites in the RAGl gene fragment. 11 of the variable sites (12) in the BNDF gene fragment between B. c. constrictor mother and E. notaeus potential fathers are identified as fixed synapomorphies (Table 1) and all 19 variable sites in the RAGl gene fragment are synapomorphies in B. c. constrictor and E. notaeus (respectively 2502296000049768 and 00-01FO-7C39) (Table 2). The hybrid shows heterozygosity at 83 % of variable sites in the BDNF-gene fragment and 100 % of variable sites in the RAGl -gene fragment.

Scale microstructure

The microstructure of the dorsal scale (Fig. 4 A) of Boa c. constrictor shows cells which are irregularly shaped and mostly longer than they are wide. The cell borders are primarily smooth and form anterior a few elongated, broad peaks. The pores of the cells are elongated, almost regularly aligned, touch the cell borders, and

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

301

AF5 12737 Loxocemus bicolor

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EU4 19841 Sanzinia m. madagascariensis —— AY336061 Acrantophis dumeriU

AY336071 Acrantophis madagascariensis GQ200595 Lichanura trivirgata AF512743 Eryx conicus

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Boa constrictor MA5251 Female E204.3 BOACONDA hybrid E204.4

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Phylogenetic tree based on the mitochondrial gene fragment 16S with calculated node support for ML analysis above the branches (only node supports over 70% are listed), and Bayesian ana- lysis (only node supports over 0.70 are listed) and calculated NJ node support under the branches (only node supports over 60 % are listed).

302

N. ERNST ETAL.

Loxocemus bicolor FJ433967

Python reticulatus FJ433969

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Eryx colubrinus FJ433976 Eryx colubrinus DQ465570 Eryx colubrinus EU402639 I Eryx johni DQ465576 0.90/9? Eryx miliaris FJ433977 ■- Candela carinata AY988031 0.99/9 iL™. Candoia carinata FJ433974

Calabaria reinhardtii FJ433972 Cala baria reinhardtii AY988041 Calabaria reinhardtii EU402631

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Sanzinia madagascariensis AY988033 J— Acrantophis dumerili AY988032 * Acrantophis madagascariensis F J4 33973 Q-^i Charina bottae AY988042 Charina bottae FJ433978

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Apodora papuana FJ43397 1 Liasis savuensis FJ433970

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Fig. 3B

Phylogenetic tree based on the nuclear gene fragment BDNF with calculated node support for ML analysis above the branches (only node supports over 70% are listed), and Bayesian analysis (only node supports over 0.70 are listed) and calculated NJ node support under the branches (only node supports over 60 % are listed).

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

303

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304

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INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

305

the distance between the pores has the same width as that of the pores. The cells of the ventral scales (Fig. 4 B) of B. c. constrictor are irregularly shaped and mostly longer than they are wide with only few short, pointed anterior peaks which are irregularly arranged. The lateral cell borders are mostly smooth. The hinge region shows hemi- spheric rises with big round pores lying closely together.

The dorsal scales (Fig. 4 C) of Eunectes notaeus (00-01FO-7C39) have a micro- structure of irregular shape, mostly broad and not longer than they are wide. The cell borders are smooth and the anterior border is shaped in few rounded peaks. The pores of the cells are elongated, asymmetrically aligned, do not touch the cell borders, and the distances between the pores are wider than the width of the pores themselves. The ventral scale (Fig. 4 D) microstructure shows short but very wide cells with serrated anterior cell borders. The peaks of the cell borders are irregularly arranged, very short and rounded. The cells have small, shallow and round pores which are irregularly aligned. The hinge region consists of hemispheric rises with small and shallow pores which are situated at greater distances from each other.

There are only comparatively slight differences in the microstracture of the dorsal and ventral scales (so-called reticulated structure sensu Price, 1982) between Boa c. constrictor and Eunectes notaeus (Figs 4 E-F). The microstructure of the hybrid shares more similarities with B. c. constrictor than with E. notaeus. The only noticeable similarity the Boaconda shares with E. notaeus (00-01FO-7C39) is that the cells of the dorsal scales are broader than they are long (Fig. 4 E). It seems that the microstructure of the hybrid is intermediate to both B. c. constrictor and E. notaeus, a classic situation for hybrids, but with distinct tendencies towards B. c. constrictor; which likely leads to the observed pattern in the hybrid since even as the patterns of E. notaeus and B. c. constrictor are rather similar, the scale microstructure of B. c. constrictor is clearly more pronounced. The microstructure of the Boaconda looks regular and distinctly sculptured.

In detail one can see a close resemblance between the hybrid and B. c. cons- trictor in the anterior and posterior regions of the dorsal scales (Fig. 4 E). Also the hinge region of the hybrid with its large round pores and the cell borders, which span over the elevations, looks more like the hinge region of B. c. constrictor. The hybrid shows serrated cell borders. These serrations are blunt and elongated which appear to be an intermediate form between E. notaeus (with almost smooth borders) and B. c. constrictor (with narrow and elongated serrations).

A similar intermediate pattern can be found in the ventral scales of the Boaconda (Fig. 4 F) comparing it to those of the parents, B. c. constrictor and E. no- taeus. In general, the ventral scales show a similar but more elementary pattern than the pattern of the dorsal scales. A remarkable similarity in the microstructure can be found between B. c. constrictor and the hybrid with elongated ridges and punctate pores in-between, whereas E. notaeus has bigger rounded pores (Fig. 4 F). The primary microstructure of the Boaconda ’s cell borders shows an intermediate pattern to B. c. constrictor and E. notaeus respectively. The cell borders of the hybrid are shaped in long and broad serrations, while the borders of B. c. constrictor are almost smooth and E. notaeus has cell borders which show short and narrow serrations.

306

N. ERNST ETAL.

Fig. 4

SEM recordings. (A) Dorsal scale of Boa c. constrictor (250228700001763). (B) Ventral scale of Boa c. constrictor (250228700001763). (C) Dorsal scale of Eunectes notaeus (0001F07C39). (D) Ventral scale of Eunectes notaeus (0001F07C39). (E) Dorsal scale of Boaconda (250228500004090). (F) Ventral scale of Boaconda (250228500004090).

Pholidosis and morphometrics

The pholidosis and morphometrics show an interesting pattern. The numbers of ventral scales (VEN), the ratio of tail length to the total length (TAL/TOL), the ratio of the distance between the eyes towards the head length (DSE/HEL), and the ratio of the

INTERGENERIC HYBRIDS AND SPECIES IDENTIFICATION

307

Table 3: Pholidosis and ratios of morphometries.

Mean

value

Minimum

value

Maximum

value

Mean

value

Minimum

value

Maximum

value

Eunectes notaeus

Boaconda

Boa c. constrictor

DOR

48

45

51

57

87.22

82

95

YEN

232.67

228

242

244

246.67

236

266

SUL

13.78

13

16

18

21.11

19

24

IFL

17.33

17

18

20

24.33

22

28

TAL/TOL

15.74

11.79

19.05

12.00

11.99

10.23

13.13

HEL/TOL

3.68

3.21

4.01

3.57

4.41

3.67

5.85

DSE/HEL

26.65

24.93

29.15

35.46

35.39

33.73

39.38

DNA/HEL

12.41

11.03

16.64

16.56

14.76

13.29

17.02

EYD/HEL

8.86

7.85

10.51

9.44

7.64

6.98

8.55

distance between the nares towards the head length (DNA/HEL) of Boaconda are in the range of the values of Boa c. constrictor (Table 3, Figs 5 A-B). In