Iguana iguana sanctaluciae, Breuil & Vuillaume & Schikorski & Krauss & Morton & Haynes & Daltry & Corry & Gaymes & Gaymes & Bech & Jelić & Grandjean, 2019

Breuil, Michel, Vuillaume, Barbara, Schikorski, David, Krauss, Ulrike, Morton, Matthew N., Haynes, Pius, Daltry, Jennifer C., Corry, Elizabeth, Gaymes, Glenroy, Gaymes, Joanne, Bech, Nicolas, Jelić, Mišel & Grandjean, Frédéric, 2019, A story of nasal horns: two new subspecies of Iguana Laurenti, 1768 (Squamata, Iguanidae) in Saint Lucia, St Vincent & the Grenadines, and Grenada (southern Lesser Antilles), Zootaxa 4608 (2), pp. 201-232 : 212-218

Iguana iguana sanctaluciae nov. ssp.

Saint Lucia horned iguana

Figs 7–11 .

Holotype. The holotype of Iguana iguana sanctaluciae housed in MNHN Paris under the number MNHN2362 and collected by Bonnecour (t) between 1850–1851. ( Fig. 7 )

This specimen is rigid, curved in its jar and it is nearly impossible to take accurate measurements.

Sex: Male

Age: Adult

Morphological measurements: total length: 132 cm; SVL: 38.5 cm; tail length 93.5 cm; height and width of left subtympanic plate: 16.7/14.6; height and width of right subtympanic plate: 16.4/15.5, height of 4 th dorsal spike: 47.5 mm.

Meristic characteristics: Number of gular spikes 7; Number of horns 2 median with very enlarged base + 3 small lateral on each side; Number of dorsal spikes to cloacae: 54

Colouration: type in alcohol with discolouration, the ground colouration is green light grey with dark banding, 6 on the body and 10 on the tail, the scale of the dewlap are dark or half dark, the dorsal spikes are ochre but seem to have lost their original colour.

Type locality: Saint Lucia, West Indies. No more information is known for this individual.

Paratype. The stuffed specimen MNHN 1996.8276 ( Fig. 7 ) from the same island ( Saint Lucia) and the same collector .

Diagnosis of Iguana iguana sanctaluciae ( Figs 7–9 ). Iguana iguana sanctaluciae resembles I. iguana insularis , but differs by the following association of characters:

– the scales of the jowls sometimes overlap;

– there are 7 or fewer triangular gular spikes of moderate size (cf. 8 or 9 exceptionally 10 gular spikes in I. iguana insularis );

– the vertical bands on the body are thicker, black and remain well developed in old individuals (cf. narrow bands on the body that fade with age in I. iguana insularis );

– the dewlap is black in old individuals (cf. creamy white in I. iguana insularis );

– the subtympanic plate and the associated 2–3 anterior scales have black pigmentation on their margins;

– Only the anterior dorsal spikes are orange in males (cf. most dorsal spikes have an orange hue in I. iguana insu- laris).

Size. The largest adult male to be measured on Saint Lucia was 160 cm in length (50 cm SVL) and weighed over 5 kg ( Fig. 10 ). A sample of 30 adults in Saint Lucia had a mean total length of 110 cm (30 cm SVL) and mass of 1.3 kg.

Geographical distribution ( Fig. 11 ). The distribution of native Saint Lucia horned iguanas ( Iguana iguana sanctaluciae ) and introduced alien iguanas ( Iguana rhinolopha ) on Saint Lucia is shown in figure 16, redrawn from Morton & Krauss (2011) with minor updates, after an island-wide, systematic survey ( Morton et al. 2007).

Etymology: The subspecific name is given in reference to Saint Lucia which is the only island inhabited by this new taxon.

Comparison to other species. Because in the field there is greatest risk of confusing the new subspecies with invasive alien I. rhinolopha , which also has nasal horns, figures 8, 9 and 10 highlight the main morphological differences between the anterior parts of I. iguana sanctaluciae and I. rhinolopha . The two new subspecies are distinguished from I. iguana iguana , I. rhinolopha (considered here as a full species, see below) and I. delicatissima by the following combination of characters.

Colour hue and pattern. The head, body and tail are bright green in young individuals, becoming very pale greenish grey or creamy white with age (unlike I. iguana iguana , I. rhinolopha and I. delicatissima , which vary widely in hue but are rarely as pale). The body has 6–8 thin or thick vertical black bands (except in old adult I. iguana insularis , in which only faint traces of the vertical bands remain). These vertical black bands are present on the newborn I. i. sanctaluciae whereas they are generally absent in newborn Iguana iguana iguana and iguana rhinolopha . According to Henderson & Powell (2018), juveniles most frequently are uniform green but this point has to be checked for Iguana iguana insularis . The tail has black bands that are conspicuous at all ages (unlike I. delicatissima , which does not have vertical bands on the body or tail). The legs are not black even in old individuals (unlike the indigenous iguanas of Saba and Montserrat). Although the body of pale adults may have a pinkish hue, the body colouration of breeding males is never orange as in I. rhinolopha from Central America ( Fig. 10 ).

With age the dewlap changes from green to entirely creamy white ( I. iguana insularis ) or completely black ( I. iguana sanctaluciae ) as the indigenous iguanas of Saba and Montserrat, but never orange (cf. I. rhinolopha , Fig. 9 ). The dorsal crest is often high, especially in males (unlike I. delicatissima ), and of the same colour as the light part of the body and often pink-orange towards the tips. The iris is dark brown, not yellow to orange, and the white part of the eye is visible (unlike I. iguana iguana , I. rhinolopha and I. delicatissima ). There is no black patch between the eye and the tympanum, and no pink on the jowls, as in Saba and Montserrat ( Breuil 2013, 2016, Breuil et al. in prep.) but some breeding males have pale golden yellow on the jowls.

Scalation. Several scales between the nostrils are elongated to form horns (whereas nasal horns are absent from I. delicatissima and I. iguana iguana ). There are 2 to 5 horns (usually 3–4) on the axial plane, and 1 to 3 smaller horns and sometimes up to 6 for I. iguana insularis on each side in adults (whereas lateral horns absent in I. rhinolopha ). The horns are broad at their bases and the tallest are sometimes curved back (whereas the horns of I. rhinolopha are thin, straight and shorter). However, hatchlings and young juveniles of the two new subspecies have only very small horns.

The nostrils are prominent; their openings are from oval to circular, sometimes triangular in Iguana iguana insularis , looking from the side. There are some small to rarely medium conical scales on the occiput. There are 6–10 medium-sized gular spikes on the dewlap that extend to the half lower part. In adults, these spikes are triangular. A subtympanic plate is present (cf. absent in I. delicatissima ) but it is relatively small: even in old adults the diameter of the subtympanic plate is no more than ± 20% the height of the tympanum (cf. 2–3 times the size of the tympanum in I. rhinolopha ).

There are 2–3 scales of decreasing size anterior to the subtympanic plate, a characteristic not found in other species systematically present in I. i. sanctaluciae and sometimes in I. i. insularis. (This trait however resembles a feature of F1 hybrids between I. iguana iguana / Iguana rhinolopha and I. delicatissima: Breuil 2013, 2016 ). There are only few tubercular nape scales: fewer than 10 in I. i. sanctaluciae and up to 20 in I. i. insularis, small, not very prominent and dispersed, i.e. not arranged in more or less conspicuous rows as in I. rhinolopha ( Fig. 10 ) and the largely melanistic iguanas of Saba and Montserrat populations ( I. cf. iguana ). This distinguishing character is present in hatchlings and throughout life, unlike some of secondary sex characteristics noted above.

Head. The head is relatively short and flat, and the dewlap is of medium size (cf. the large dewlap in I. rhinolopha ). The scales anterior to the subtympanic plate overlap slightly in some individuals. The jowls do not appear swollen even in reproductively active males (cf. very well-developed jowls in breeding male I. rhinolopha ).

Figures

FIGURE 7. Holotype and paratype of Iguana iguana sanctaluciae. The holotype MNHN2362 (A, C, D, E) and the paratype MNHN1996.8276 (B) Both specimens collected by Bonnecour(t) in 1850-51 in Saint Lucia. Note the nasals (median and lateral horns), the small subtympanic plate, the low number of small nuchal tubercles, the 7 gular spikes, the prominent oval nostril, the banded body.

FIGURE 8. Ontogenetic change in colour of Iguana iguana sanctaluciae. Young male (A), old male (B). Annotations: 1. Small subtympanic plate ± 10% of the eardrum. 2. Two or three scales of decreasing size anterior to subtympanic plate. 3. Low number of sublabial scales with black margins. 4. No swelling of the jowls in breeding males. 5. Lateral and median horns. 6. Median horns with enlarged bases. 7. Oval to rounded nostril. 8. Brown eye with the white of the eye visible. 9. Triangular gular spikes. 10. 7 gular spikes. 11. Dispersed nuchal tubercles. 12. Low number of nuchal tubercles. 13. Small size of nuchal tubercles. 14. Orange in first dorsal spikes in breeding animals. 15. Entirely black dewlap in old adults. 16. Body and tail black and bright green in young individuals and very light green to almost pale greenish grey in old adults. Old individuals may look nearly “black and white”. The brilliant colouration of the young male results from the flash of the camera.

FIGURE 9. Horned iguanas from the Central American clade of the “rhinolopha” phenotype. Photographed from invasive introduced populations in the Lesser Antilles: old male caught in Saint Lucia (A). young male caught on Saint Maarten (B); Annotations: 1. Huge subtympanic plate, 2 to 3 times the size of the eardrum. 2. A half crown of sublabial scales around the subtympanic plate and the first scale anterior to subtympanic plate. 3. Mosaic of sublabial scales. 4. Swelling of the jowls in breeding male. 5. Generally 2-3 small median horns and no lateral horns. 6. Flat small horns. 7. Triangular nostril. 8. Yellow to dark orange eye with not the white visible. 9. Triangular gular spikes. 10. Number of gular spikes ± 10. 11. Nuchal tubercles appear to be organised in rows. 12. High number of nuchal tubercles. 13. Very large nuchal tubercles. 14. Yellow, orange to red dorsal scales on the whole body in breeding males. 15. Variable size and colour of the dewlap but often large and not uniform black (cf. I. iguana sanctaluciae) or creamy white (cf. I. iguana insularis). 16. Body orange to red in breeding males, green in other individuals, and not heavily banded. This phenotype is recognised in this paper as a full species, I. rhinolopha, native to Central America (see text).

FIGURE 10. Adult breeding males I. iguana sanctaluciae and I. rhinolopha. The endemic Saint Lucia horned iguana (I. iguana sanctaluciae, photo from Grand Anse, A) is clearly different from the Central America horned iguana (I. rhinolopha: this specimen was photographed from an introduced population on Sint Maarten by M. Yokoyama, B) by size, body proportion, body colour, size and form of the horns, eye colouration, scalation of the jowls, and dewlap size, colour and form.

FIGURE 11. Distribution of iguanas on Saint Lucia. Locations are mapped to the nearest 1×1 km square. Data come from Morton et al. (2007). Grey squares, Saint Lucia endemic iguana, Black squares, alien iguana from Central America clade. “False absences” were minimized by interviewing persons about iguana presence in grid squares confirmed independently, through sightings and captures by us, to have iguanas present. We rejected some reported sightings of native iguanas, shown here as open grid squares, as being iguanas captured for food or pets or reports based on misidentification (for example on the islet of Maria Major off the far south of Saint Lucia; J. Lazell, in litt. 2010). Some of the reports that were accepted from the interior of the northern half of Saint Lucia may also be suspect, though they are all below 300 m ASL. These patterns of distribution suggest that the mountainous interior of Saint Lucia may create at least a partial barrier to direct east-west movements of iguanas.