Morphological Variation in Gallotia Atlantica from the Volcanic Island of Lanzarote: Subspecies Designations and Recent Lava flows
Total Page：16
File Type：pdf, Size：1020Kb
Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean Society of London, 2005? 2005 85? 395406 Original Article MORPHOLOGICAL VARIATION IN GALLOTIA ATLANTICA Biological Journal of the Linnean Society, 2005, 85, 395–406. With 5 figures Morphological variation in Gallotia atlantica from the volcanic island of Lanzarote: subspecies designations and recent lava flows PAUL BLOOR and RICHARD P. BROWN* School of Biological & Earth Sciences, Liverpool John Moores University, Byrom St., Liverpool L3 3AF, UK Received 29 February 2004; accepted for publication 27 September 2004 A detailed uni- and multivariate analysis of within-island geographical variation in scalation and body dimensions of the lacertid lizard, Gallotia atlantica, from Lanzarote (and two neighbouring offshore islets) was carried out. Two main morphological groupings were detected: four populations clustered within a putative malpaís group, i.e. from relatively recent volcanic lava fields (seven populations were sampled from these areas), while the other 19 popu- lations (including the three remaining malpaís populations, and those from the offshore islets of Montaña Clara and Alegranza) also clustered together. Thus, while there is a tendency for occupation of malpaís areas to be related to morphological variation, this model does have some inconsistencies. The differentiated malpaís group comprises populations from two geographically isolated areas, one from the central-western part of the island (Timanfaya) and the other from the north (Malpaís de la Corona). The divergence of these populations is considered to have arisen recently, rather than their being relicts of an ancient, formerly widespread, lineage. The morphological variation par- tially supports the previous use of two different subspecies to describe the within-island variation. However, if such a scheme were applied then one of the subspecies would need to encompass populations from the geographically separated southern Timanfaya and Malpaís de la Corona areas, as opposed to just the latter. We reject previous observations that either malpaís individuals in general, or those corresponding to the north-eastern subspecies, are larger than individuals from other areas. The pattern of morphological variation of G. atlantica within Lanzarote is less pronounced but shows some similarities with patterns of morphological variation in lizards from neighbouring islands. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 395–406. ADDITIONAL KEYWORDS: Canary Islands – evolution – lizard – morphology – population – volcano. INTRODUCTION Lanzarote is found in the north-east of the archipel- ago and is one of the oldest islands. It has a surface The Canary Islands, an oceanic group of seven main area of 846 km2 and rises to a maximum altitude of islands and several smaller islets, have become a 670 m towards the north at Peñas de Chache. It is gen- model region for studies of both between- and within- erally arid, with an annual rainfall of less than island patterns of geographical variation, particularly 200 mm in most areas, although slightly higher in lizards (e.g. Brown, Campos-Delgado & Pestano, rainfall is found around the aforementioned peak. 2000; Gübitz, Thorpe & Malhotra, 2000; Juan et al., The most striking ecological heterogeneity within the 2000, and references therein; Pestano & Brown, 1999; island is not due to variation in rainfall and altitude, Richard & Thorpe, 2001; Thorpe & Richard, 2001). as on the nearby islands of Tenerife and Gran Canaria The islands lie between 110 and 500 km off the coast (Thorpe & Brown, 1989; Brown, Thorpe & Báez, 1991), of north-west Africa and were independently formed but rather the different habitat types produced by by volcanic eruptions from the ocean floor over the expanses of solidified lava from relatively recent erup- past 20 Myr. P. BLOOR and R. P. BROWN tions (Fig. 1). Recent lava flows have given rise to malpaís (bad- *Corresponding author. E-mail: [email protected] lands) habitats. These are found in the central-west © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 395–406 395 396 P. BLOOR and R. P. BROWN Gallotia atlantica is known to exhibit considerable S30 Alegranza morphological variation in size, body proportions and N scalation, as well as coloration and colour pattern (Bischoff, 1985a, b; Castroviejo, Mateo & Collado, 1985; Thorpe, 1985), the extent of which has re- Montaña Clara S29 sulted in the description of numerous subspecies. La Graciosa G. a. atlantica has been assigned to populations from the main island of Lanzarote and its northern S2 offshore islets (Bischoff, 1985a; Castroviejo et al., 1985), G. a. laurae to populations from north-eastern S26 Lanzarote (Castroviejo et al., 1985), and G. a. ibagnezi S9 to the northern-most islet of Alegranza (Castroviejo et al., 1985). Of these, the widespread northern Lanzarote S7 S8 S4 (G. a. atlantica) and north-eastern Lanzarote S18 (G. a. laurae) subspecies are generally accepted S14 as conventional subspecies categories, while S20 S13 S12 G. a. ibagnezi tends to be regarded as G. a. atlantica S11 S5 (López-Jurado, Mateo & Geniez, 1995). S10 S19 S6 Castroviejo et al. (1985) believed that the S17 G. a. laurae subspecies designation was justified for S1 S15 S3 populations from the lavas of Malpaís de la Corona and those found to the south-east of Haría based on morphological differentiation. However, Bischoff S16 5 km (1985a) preferred a single widespread northern (G. a. atlantica) subspecies. More recently, López- Jurado & Mateo (1992) appear to relate the distribu- Figure 1. Distribution of sampling sites of Gallotia atlan- tion of G. a. laurae to areas of malpaís, and there is tica in Lanzarote and nearby islets. Site names and sample some evidence to support the similarity of individuals details are given in the Appendix. Shaded areas represent (primarily size, coloration and markings) from El the main regions covered by relatively recent lava flows in Mojón and El Golfo in the Timanfaya area with the central-western (Timanfaya) and north-eastern Lanzarote. G. a. laurae (Malpaís de la Corona) subspecies (López- Sites are indicated using circles, except for Malpaís de la Jurado & Mateo, 1992; López-Jurado et al., 1995). Corona (squares) and Timanfaya (triangles). Sites within These studies also indicate that individuals associ- the latter, although ostensibly close in some cases (e.g. ated with recent volcanic habitats attain adult body S12-14), were all from different exclusive ‘islets’ within the sizes considerably greater than those from other parts lava fields. of Lanzarote (Castroviejo et al., 1985; López-Jurado & Mateo, 1992). Unfortunately, most of these proposals have been made on the basis of qualitative compari- (Timanfaya) and north-east of the island (Malpaís de la sons, and/or only partial sampling of the island. Thus Corona). The former was formed by lava flows from the actual pattern of geographical variation, its poten- volcanic activity in the eighteenth and nineteenth tial causes, and the validity and utility of proposed centuries and contains several isolated areas (known taxonomic designations are still difficult to assess. locally as ‘islets’) that were not covered during these This paper provides a quantitative analysis of mor- eruptions (Carracedo, Badiola & Soler, 1992). Malpaís phological variation in G. atlantica from Lanzarote de la Corona is considerably older (although still recent based on a sampling regime that encompasses the full in geological terms), with lavas being dated at about extent of morphological variation throughout the 21 ka (Carracedo et al., 2003) and is consequently in a island and associated islets. more advanced state of ecological succession. The unique biophysical conditions prevailing on the recent lava fields suggest that they represent novel MATERIAL AND METHODS and harsh environments to colonizing populations. The lacertid lizard G. atlantica (Peters & Doria, 1882), SITES AND SPECIMENS is quite abundant throughout most of the island, but is Adult lizards (N = 460) were captured and subse- rare/absent on the Timanfaya lava fields (although quently measured between August and September present on the ‘islets’ within Timanfaya). Generally 1999, and in October 2002. Only adult animals (ten lower densities are found on Malpaís de la Corona. males and ten females from each site) were retained © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 395–406 MORPHOLOGICAL VARIATION IN GALLOTIA ATLANTICA 397 for measurement due to the difficulties of sexing a ruler and HL measured to the nearest 0.1 mm using younger individuals in the field. An individual was Vernier callipers. considered adult if it had a body size (snout-vent All bilateral characters were recorded from the length) approaching or greater than the minimum size right-hand side of the individual to avoid the influence at sexual maturity documented for the northern of fluctuating asymmetry, and characters were re- (G. a. atlantica) subspecies: 59.5 mm for males and corded sequentially for each individual to minimize 57.0 mm for females (Molina-Borja, 2003). Sex was measuring error. FBW and SBW were approximated if established by hemipenal inversion, with palpation of the upper-lateral blotches had merged (males only). the abdomen used to identify gravid females. Each character was recorded twice, with a third mea- The 21 capture sites within