Liolaemus parthenos, Cristián S. Abdala, Diego Baldo, Ricardo A. Juárez & Robert E. Espinoza, 2016

Cristián S. Abdala, Diego Baldo, Ricardo A. Juárez & Robert E. Espinoza, 2016, The First Parthenogenetic Pleurodont Iguanian: A New All-female Liolaemus (Squamata: Liolaemidae) from Western Argentina, Copeia 104 (2), pp. 487-497 : 489-494

Liolaemus parthenos , new species

urn:lsid:zoobank.org:act:53CC2C59-2E4D-41AA-8804- 462B90ABAECC

Figures 1–5; Table 1

Liolaemus boulengeri Cei (1973:464, in part) .

Liolaemus boulengeri Cei and Roig (1976:71, 87, Map 5, in part) .

Liolaemus boulengeri Cei and Castro (1978:9, 21, Map 16, in part) .

Liolaemus boulengeri Cei (1986:220–221, in part) .

Liolaemus boulengeri Schulte et al. (2000 :79, 87; table 1; figs. 4–6).

Liolaemus sp. nov. Morando et al. (2004:845; table 1–3; figs. 2, 8).

Liolaemus sp. Abdala and Díaz Gómez (2006:29; fig. 3).

Liolaemus sp. 3. Abdala (2007:51, 55, 57, 60, 77; figs. 32–36).

Liolaemus cf. darwinii Pincheira-Donoso et al. (2007 :32; fig. 3).

Liolaemus cf. darwinii Schulte (2013:5; fig. 1) .

Liolaemus sp. 3 Olave et al. (2014:329, 331; figs. 4, 6).

Holotype.— FML 16221 , adult female, Argentina, Mendoza Province, San Rafael Department, collected on the dunes next to El Nihuil Dam on Provincial Route 180 , 35°2'19.77''S, 68°40'12.60''W, 1305 m, C. Abdala, J. Abdala, and E. Malovini, January 2001 ( Fig. 1 ).

Paratypes.— FML 16222–24, same data as holotype; IBAUNC 9772–73, 9775–77, Argentina, Mendoza Province, San Rafael Department, 10 to 60 km S of El Nihuil, 35°7'0.71''S, 68°41'4.28''W to 35°33'49.47'' S, 68°41'15.14''W, 1400–1600 m, 25 November 1973; IBAUNC 11431–35, Argentina, Mendoza Province, San Rafael Department, Pampa del Diamante, 34°54'44.39'' S, 68°51'38.58''W, 1400 m, 17 February 1975; MHNSR 78–82, Argentina, Mendoza Province, San Rafael Department, Club de Pescadores, El Nihuil, 35°2'10.54''S, 68°42'33.84''W, 1325 m, 1 January 1975.

Diagnosis.— Liolaemus parthenos is the only known triploid unisexual iguanian lizard with the karyotype 3n = 49 (19M + 30m). The new species is a member of the L. boulengeri group (Etheridge, 1995; Abdala, 2007), with which it shares a femoral patch of enlarged scales on the posterior thigh. The L. boulengeri group includes the following subclades ( Abdala, 2007): L. anomalus , L. darwinii , L. wiegmannii , and L. melanops (= L. telsen group + L. goetschi group), each of which includes several species as described below. Within the L. boulengeri group, L. parthenos is a member of the L. darwinii group ( Abdala, 2007), with which it shares the following eight synapomorphies: (1) 14–18 dorsal head scales; (2) 24–28 gulars; (3) tail length/SVL ratio: 1.40–1.65; (4) femur length/ SVL ratio: 0.16–0.20; (5) 1–3 differentiated scales along the lower half of the anterior border of the external auditory meatus; (6) weakly developed longitudinal fold; (7) dark line passing vertically through superciliaries, eye, and subocular; and (8) small prescapular spots. Liolaemus parthenos can be distinguished from species in the L. anomalus group ( L. acostai , L. anomalus , L. ditadai , L. lentus , L. millcayac , L. pipanaco , and L. pseudoanomalus ) because the new species has a tail that is longer than its body, a head that is longer than wide, and lacks both a palpebral ‘‘comb’’ and pterygoid teeth. Liolaemus parthenos can be distinguished from species in the L. wiegmannii group ( L. arambarensis , L. azarai , L. cuyumhue , L. lutzae , L. multimaculatus , L. occipitalis , L. rabinoi , L. riojanus , L. salinicola , L. scapularis , and L. wiegmannii ) because the new species has a single row of lorilabials between the subocular and the supralabials (2–3 rows in members of the L. wiegmannii group) and four scales around the mental (6 scales in the L. wiegmannii group species). The new species, can be distinguished from species of the L. goetschi group ( L. camarones , L. canqueli , L. casamiquelai , L. chehuachekenk , L. cuyanus , L. dumerili , L. fitzingerii , L. goetschi , L. mapuche , L. melanops , L. morenoi , L. puelche , L. rothi , L. sagei , L. shehuen , L. tromen , and L. xanthoviridis ) based on its shorter SVL (maximum SVL 63.4 mm vs. 77–106 mm for the aforementioned taxa) and considerably less ventral melanism (except L. rothi and L. sagei ). The new species also lacks the cephalic melanism typical of L. canqueli and L. melanops . With respect to L. casamiquelai , L. chehuachekenk , L. fitzingerii , L. morenoi , L. tromen , and L. xanthoviridis , the new species lacks the gular and antihumeral melanic collar that is typical of the aforementioned species. Liolaemus parthenos is distinct from L. cuyanus , L. goetschi , L. josei , L. mapuche , and L. puelche because the new species has four scales in contact with the mental, whereas L. cuyanus has six scales and L. goetschi , L. josei , L. mapuche , and L. puelche have from 4–6 scales in contact with the mental. The new species differs from L. donosobarrosi because the former has fewer scales around the midbody (mean = 57.1; range = 53–61 vs. mean = 85.4; range = 79–95, respectively). Also, the new species has a distinct dorsal pattern of quadrangular paravertebral markings, which distinguishes it from L. rothi , which has irregular markings that are not quadrangular. The new species also has pre- and postscapular spots that are not present in L. rothi .

Liolaemus parthenos can be distinguished from species in the L. telsen group ( L. boulengeri , L. hermannunezi , L. inacayali , L. loboi , L. martorii , L. purul , L. senguer , L. sitesi , and L. tehuelche ) by its lack of gular melanism and dorsolateral bands that are more well defined. The new species differs from L. telsen because the former has less gular melanism, paravertebral markings are more well defined, well-defined dorsolateral bands, and fewer middorsal scales on the trunk (counted from occiput to anterior thigh: mean = 65; range = 61–68 vs. mean = 88.8; range = 83–96, respectively). The new species also differs from L. boulengeri , L. hermannunezi , L. loboi , L. martorii , L. purul , and L. tehuelche because the former has less conspicuous scapular spots. Within the L. darwinii group, L. parthenos is the only species with strongly cuspidate coronas and distally expanded cheek teeth, as well as a unique color pattern for the group. The new species can be further distinguished from members of the L. darwinii group ( L. abaucan , L. albiceps , L. calchaqui , L. chacoensis , L. cinereus , L. crepuscularis , L. darwinii , L. diaguita , L. espinozai , L. grosseorum , L. irregularis , L. koslowskyi , L. laurenti , L. lavillai , L. montanezi , L. olongasta , L. ornatus , L. pacha , L. quilmes , and L. uspallatensis ) because L. parthenos has a unique pattern of large dark brown or black quadrangular or subquadrangular paravertebral and lateral markings, white dorsolateral stripes, and a white abdomen with small dark spots. Liolaemus parthenos can be further distinguished from L. albiceps , L. calchaqui , L. crepuscularis , L. irregularis , L. lavillai , and L. ornatus because females of the latter three species possess precloacal pores and adult L. albiceps and L. irregularis are considerably larger than L. parthenos ( L. parthenos : maximum SVL 63.4 mm vs. 82.5–86.1 mm, respectively). Finally, L. parthenos can be differentiated from L. darwinii because the new species lacks an antehumeral arch and abdominal and femoral melanism.

Description of holotype.— Adult female ( Fig. 1 ). SVL: 59.8 mm. Tail complete, not regenerated: 92.7 mm. Rostral surrounded by 6 scales. Nasal dorsolateral in orientation. Supraoculars: 8. Interparietal smaller than parietals. Lorilabials: 7. Supralabials: 8. Mental surrounded by 4 scales. Infralabials: 5. Temporals: 8, not keeled. Posterior teeth with expanded cusps. Anterior border of auditory meatus with one differentiated scale. Snout blunt in lateral view. Midbody scales: 58. Dorsal scales: 68 from occiput to anterior thigh, laminar, imbricate, and keeled. Lateral neck folds well developed. Gulars: 27. Ventrals: in 21 rows, imbricate, same size as dorsals. Infratarsals and infracarpals imbricate and trifid. Femoral patch well developed. No precloacal pores. Head light brown with two rows of quadrangular dark brown paravertebral marks with white posterior margins. Background of vertebral region dark brown with four lateral markings of same color. Anterior and posterior limbs same color as dorsum. Ventrally, throat variegated with dark brown or black spots; spot density increases posteriorly toward chest, abdomen, limbs, and tail.

Measurements of holotype.— Head 1.2 times longer (11.9 mm) than wide (9.6 mm). Head height: 8.2 mm. Eye diameter: 2.9 mm. Subocular: 3.7 mm. Auditory meatus height: 2.2 mm; width: 1.8 mm. Torso length: 26.8 mm; width: 12.9 mm. Thigh length: 9.9 mm. Upper arm length: 8.2 mm; width: 2.1 mm. Forearm length: 8.3 mm. Hand length: 9.2 mm. Tail length: 92.7 mm.

Variation.— Data from 70 females, unless otherwise noted. Mental in contact with four scales. Infralabials: 5–6. Lorilabials: 6–7, in one row. Interparietal smaller than parietal. Temporals: 8–12. Auditory meatus with 1–3 scales on anterior edge and 0–2 on posterior edge. Neck folds well developed. Gulars: 23–28. Head narrow, longer (mean = 12.1 mm) than wide (mean = 9.4 mm). Neck narrower than head and trunk. Body slender, SVL 36.1–63.4 mm (mean = 56.7 mm). Scales around midbody: 53–61 (mean = 57.1). Dorsal scales between occiput and anterior thigh: 61–68 (mean = 65.0). Dorsal scales laminar, keeled, and imbricate. Infratarsals and infracarpals with imbricate, trifid scales. Femoral patch with 23–30 cone-shaped, mucronate scales. Ventrals: 91–105 (mean = 97.6), larger than dorsals. Precloacal pores absent. Complete tail: 64.3–92.7 mm long (n = 48; mean = 83.3 mm); 1.4–1.6 times longer than SVL.

Color variation in life.— Dorsal head light brown or gray with small black, irregularly distributed scales. Background dorsal color of body usually light brown, but light gray specimens not uncommon. Paravertebral markings square or rectangular, arranged longitudinally to long axis of body and dark brown or dark gray with white posterior margins. Lateral markings same color and form as paravertebral markings, but smaller than paravertebrals in some specimens. Vertebral region dark gray or light brown. Prescapular or postscapular spots less well defined, generally darker than lateral markings, but sometimes indistinguishable from them. Throat, abdomen, and cloaca region white with small irregularly shaped black spots. Ventral spots usually most dense along sides of abdomen. Mental and shield scales usually dark brown, but occasionally dark green. Longitudinal line extending along lateral tail (25–50% total tail length) splits into small black or dark brown rectangular bars. Color becomes less vibrant, but otherwise does not change appreciably after>6 mo in preservative (70% ethanol).

Etymology.— The specific epithet parthenos is a Greek noun meaning ‘‘virgin’’ or ‘‘maiden,’’ in reference to the presumed reproductive strategy of this all-female species.

Distribution.— Liolaemus parthenos is known only from the outskirts of El Nihuil, Salinas del Diamante, and from south of El Nihuil on Provincial Route 180 near Sierra El Nevado, San Rafael Department, Mendoza Province, Argentina (1305– 1600 m; Fig. 2 ).

Natural history.— Liolaemus parthenos is apparently an allfemale parthenogenetic species. Despite 24 collecting expeditions since 1995 for a total of approximately 650 combined person hours of observing and collecting this species in nature, and after examining more than 300 specimens (note only 65 specimens were collected and preserved because of restrictions imposed by collecting permits), no males were encountered. Thus, the probability of not encountering a male, if this was a bisexual species with an equal population sex ratio, would be 0.5 65 or 2.7 20, an infinitesimally small likelihood.

Field observations of active L. parthenos were made from October through February, and again in April. During summer months (December to February), lizards were active only in the morning and afternoon. The shift to bimodal activity apparently helps them avoid the extreme heat of midday. In April (fall), only juveniles were active at midday, indicating seasonal or ontogenetic variation in diel activity. Body temperatures (T bs) from four adult L. parthenos (SVL = 51.8± 3.4 mm) collected in the late afternoon of 11 February 1995 along the sandy shore of El Nihuil reservoir averaged 34.6±3.4°C, which is similar to the field T bs reported for other low-elevation Liolaemus lizards ( Espinoza et al., 2004).

Liolaemus parthenos is oviparous and reproduces in summer. Reproductively active females (well-developed eggs in oviducts) were observed in January (n = 5), and nonreproductive females were found in December and February (n = 13). However, in a different year, we found females with oviducts full of developing eggs in December (n = 11). These observations suggest that the reproductive period begins in November and lasts until late January.

Liolaemus parthenos is sympatric with the lizards Aurivela longicauda (Teiidae) , Diplolaemus sexcinctus and Leiosaurus bellii (Leiosauridae) , and two congeneric species: L. gracilis and L. grosseorum . Several species of snakes, which are potential predators of the new species, have also been observed in the area: the dipsadine colubrid snakes Oxyrhopus rhombifer , Philodryas trilineata , and Xenodon semicinctus , as well as the viperid Bothrops ammodytoides .

Cytogenetic analysis.— Liolaemus parthenos has a triploid karyotype with 3n = 49 chromosomes (19 macrochromosomes + 30 microchromosomes): 17 of the macrochromosomes are biarmed metacentric or submetacentric and two are acrocentric. All the microchromosomes appear to be acro- or telocentric ( Fig. 3 ). Because of their size and morphology, the macrochromosomes clustered into four groups: (1) the two largest pairs almost equal in size, but differing in centromere position (the first metacentric and the second submetacentric); (2) pairs 3 and 4 almost equal in size and morphology (with a centric fission in the haploid homologue of pair 3); (3) pair 5 (submetacentric in two homologues and metacentric in the third); and (4) pair 6, the smallest of the macrochromosomes with metacentric morphology. Only two of the homologous regions of chromosome pair 2 show secondary constrictions and areas with NORs in the telomere of their long arms.

Phylogenetic analysis.— The trees based on Bayesian inference and maximum parsimony were topologically very similar, with sources of conflict occurring solely at nodes that were weakly supported in one or both analyses ( Fig. 4 ). With respect to the new species, both trees strongly supported the placement of L. parthenos in the L. grosseorum clade of the L. boulengeri group: L. boulengeri group ( L. chacoensis group ( L. laurenti group ( L. darwinii group ( L. grosseorum clade)))) ( Fig. 4 ). The L. grosseorum clade is also supported by nine morphological synapomorphies ( Abdala, 2007). Within the L. grosseorum clade, L. parthenos is in a well-supported yet unresolved clade with L. darwinii (Río Negro Province) and L. laurenti ( Fig. 4 A) or nested within a weakly supported clade containing populations of L. darwinii from the more southern provinces of Mendoza and Ŕıo Negro and those occurring farther north in La Rioja Province, with L. laurenti strongly supported as sister to these four lineages ( Fig. 4 B).

DISCUSSION

Based on previous studies ( Schulte et al., 2000; Morando et al., 2004; Pincheira-Donoso et al., 2007; Schulte, 2013) and the phylogenetic hypotheses presented here ( Fig. 4 ), L. parthenos is closely related to L. darwinii and L. laurenti , species that are morphologically typical of the L. darwinii group ( Etheridge, 1993; Abdala, 2007). The closest known locality for L. laurenti is approximately 300 km to the north of the type locality of L. parthenos , whereas L. darwinii has a much wider distribution ( Abdala, 2007) including a small population that is sympatric with L. parthenos at the type locality of the latter species. It is noteworthy that a similarly proximate distributional association has been reported for a parthenogenetic species of Leiolepis and its matrilineal ancestor ( Grismer and Grismer, 2010; Grismer et al., 2014). A close phylogenetic association between L. parthenos and L. darwinii has been reported in previous phylogenetic analyses based on mtDNA. Schulte et al. (2000) recovered L. parthenos (as ‘‘ L. boulengeri ’’) in the clade: L. grosseorum ( L. darwinii ( L. parthenos ( L. laurenti ))). A phylogeographic analysis of the L. darwinii group conducted by Morando et al. (2004) recovered L. parthenos (as ‘‘ L. sp. nov.’’) as the sister taxon to L. laurenti + L. darwinii . Finally, Pincheira-Donoso et al. (2007) recovered L. parthenos (as L. cf. darwinii ; SDSU 3469, AF099275 ) as the sister taxon to L. darwinii in the clade ( L. grosseorum ( L. darwinii ( L. parthenos + L. darwinii from Chubut))). Although L. parthenos is superficially similar to L. boulengeri , these three molecular studies each strongly support the relationships among L. parthenos , L. darwinii , L. laurenti , and L. grosseorum .

The most parsimonious interpretation of the triploid karyotype of L. parthenos ( Fig. 5 ) is that the species arose via hybridization. The karyotype of L. parthenos ( Fig. 4 ) has a clear diploid component (12M + 20m) contributed by one parental species and an additional haploid set (7M + 10m) provided by the other parental genome ( Fig. 5 ). In the haploid component the two acrocentric macrochromosomes are interpreted as homologs of the two arms (3p and 3q) of pair 3 (3a) in the 2n set. The 30 microchromosomes of L. parthenos are best interpreted as ten pairs from the diploid genome (2n = 20), and 10m from the haploid genome.

The low levels of genetic distance between L. parthenos and L. darwinii and L. laurenti ( Table 1 ; Schulte et al., 2000; Morando et al., 2004; Pincheira-Donoso et al., 2007) suggest that one or both of these two species, or one or more closely related undescribed or extinct taxa, are the maternal ancestor(s). This conclusion is further supported if we assume a hybrid origin and that the number and morphology of the chromosomes are the same as the inferred parental species, L. darwinii ( Fig. 5 ), which has the chromosomal complement 2n = 32–34 (12M + 20–22m; Aiassa et al., 2005). Unfortunately, no cytogenetic data are currently available for L. laurenti . Although analyses based on mtDNA ( Schulte et al., 2000; Morando et al., 2004; Pincheira-Donoso et al., 2007; this study) have provided clues of the identity of the maternal ancestor of L. parthenos , studies including nuclear gene sequences are needed to identify the paternal ancestor, which is likely L. grosseorum or L. laurenti based on genetic and morphological similarity and geographic proximity.

We detected structural heteromorphisms in the chromosomes of L. parthenos , which supports the hypothesis that this species is the product of a hybrid origin with two or three parental species, as is the case for most other triploid unisexual vertebrates ( Vrijenhoek et al., 1989; Kraus, 1995; Schmidt, 1996; Avise, 2008; Lamborot, 2008; Neaves and Baumann, 2011). The species of Liolaemus examined to date have gonochoristic reproduction, and the 79 species studied cytogenetically have diploid karyotypes with 28–44 chromosomes ( Aiassa et al., 2005; Lamborot, 2008). The variation in chromosome number among species of Liolaemus results from chromosomal fusions and fissions. Natural triploids have been reported in Chilean populations of L. chiliensis and L. gravenhorstii , each of which has 3n = 48 chromosomes ( Lamborot and Vásquez, 1998; Lamborot et al., 2006), and although Lamborot (2008) suspected that some populations of these species might be or eventually evolve unisexuality, to date, no such populations have been reported.

Early ecological studies of parthenogenetic whiptail lizards ( Aspidoscelis ) from southwestern North America described their niches as ‘‘weed habitats,’’ which were considered intermediate to those occupied by their parental species ( Wright and Lowe, 1968). The adaptive explanation for this shift in habitat was, although sympatric (at least initially), interspecific competition would be reduced by a lack of syntopy between the parthenogen and its ancestors. Darevsky et al. (1985) extended this idea, asserting that the habitats occupied by parthenogenetic species should exceed that of their individual parental species because parthenogens possess the genotypes of two or more parental species. In the case of L. parthenos , there appears to be little habitat segregation between the new species and its potential parental species. For example, L. parthenos occurs syntopically with L. darwinii and L. grosseorum . In fact, most lowelevation members of the L. darwinii group have the same microhabitat preferences and several have overlapping distributions ( Cei, 1986; Etheridge, 1993; Abdala, 2007). Thus, L. parthenos may not conform to the expected niche segregation with its parental species because of historical contingency.

We provide strong evidence for the first unisexual species belonging to the large lizard clade Pleurodonta, extending the occurrence of this rare cytogenetic and reproductive anomaly among vertebrates generally, and for squamate reptiles specifically. Although the mechanism of unisexual reproduction in this species remains to be determined, all known unisexual reptiles species are apparently parthenogenetic (meiotically unreduced ova developed in the absence of sperm) with no records of gynogenesis (sperm-dependent unisexuality) or hybridogenesis ( Beukeboom and Vrijenhoek, 1998). Examination of additional molecular markers, detailed field studies, high-resolution cytogenetic techniques, and studies of congeneric species will allow us to establish the type of unisexuality, mechanistic origin, and evolutionary history of unisexuality in this unique lizard species.

Figures

Fig. 1. Dorsal (A) and lateral (B) views of the holotype (FML 16221) of Liolaemus parthenos, new species, from the type locality in San Rafael Department, Mendoza Province, Argentina.

Fig. 2. Map showing known localities of Liolaemus parthenos, new species (black circles), in San Rafael Department, Mendoza Province, Argentina. Arrow indicates the type locality.

Fig. 3. Karyotype (left) and pair carrier of nucleolus organizer regions (right) for Liolaemus parthenos, new species.

Fig. 4. Phylogenetic hypotheses for 31 species of Liolaemus emphasizing species in the L. boulengeri group (stars) based on 1776 aligned base pairs of mtDNA sequence data. (A) Phylogeny based on Bayesian inference showing branch lengths proportional to evolutionary change and branch support represented as Bayesian credibility values below each node. (B) Cladogram based on a maximum parsimony analysis showing bootstrap and jackknife values above and below each clade, respectively. Retention index (RI): 0.796, consistency index (CI): 0.490. Photos show species of Liolaemus inferred by both analyses to be closely related to L. parthenos, new species.

Fig. 5. Macrochromosome idiograms for Liolaemus parthenos, new species, and its hypothetical parental species.

Tables

Table 1. Percentage of uncorrected pairwise distances between partial sequences of the mitochondrial ND 1 gene of Liolaemus parthenos, new species, and the other species belonging to the L. grosseorum clade of the more inclusive L. boulengeri group. GenBank accession numbers appear in parentheses.

	1	2	3	4	5
1 L. laurenti (AF099273.1)	—
2 L. grosseorum (AF099272.1)	4.91	—
3 L. darwinii (AF099274.1)	1.04	5.16	—
4 L. darwinii (DQ002490.1)	1.21	4.97	0.86	—
5 L. parthenos (AF099275.1)	1.39	4.97	1.27	1.44	—