The Zoogeography of Lesser Antillean Anoilis Lizards - An Analysis Based Upon Chromosomes and Lactic Dehydrogenases

Gorman, George; Atkins, Leonard

On each island bank of the Lesser Antilles, there are one or two distinct forms of iguanid lizards of the genus Anolis. On the basis of osteology, these anoles have been placed in two species groups, which show a sharp geographic break. The southern group (termed roquet) occupies all the islands from Grenada north to Martinique. !he northern group (called bimaculatus) Is found from Dominica, the island due north of Martinique, on through all the other Lesser Antillean islands. It also occurs on several of the Greater Antillean islands and island banks. Differences in karyotype and in electrophoretic mobility of the protein lactic dehydrogenase amongst these Antillean lizards have permitted a detailed analysis of relationships, evolutionary history, and zoogeographic movement. The two species groups are distinct osteologically, chromosomally, and biochemically. The roquet group is characterized by 12 metacentric macrochromosomes, 22 or 24 microchromosomes, and the absence of sex chromosomal heteromorphism. This karyotype appears to be primitive for the family Iguanidae and characterizes many genera, including a South American anoline genus. The lactic dehydrogenases of the roquet group are characterized by very slow anodal migration in borate buffer. The himaculatus group is characterized by a reduced number of chromosomes, a less sharply marked break between macro- and microchromosomes, and male heteromorphism. Their lactic dehydrogenases migrate more rapidly towards the anode than do those of the roquet group. Three subgroups of bimaculatus may be recognized; two are strictly Lesser Antillean and are characterized by 9 or 10 pairs of macrochromosomes, with no sharp break between the sixth and seventh pair. In the first of these, the bimaculatus group sensu stricto, all members have identical LDH mobilities. The second, wattsi, has only one species; in karyotype it is identical to most bimaculatus, but has a more rapidly migrating LDH. The third subgroup is found to the west of the Lesser Antilles on St. Croix, Puerto Rico, and Hispaniola. It is termed the acutus group. The LDH of wattsi is identical to that of two members of the acutus group. In chromosomes, the acutus group appears somewhat intermediate to the karyotypically primitive roquet group in the south, and its near-neighbor wattsi and bimaculatus groups. Like the roquet group, acutus has six pairs of metacentric macrochromosomes, and the majority of the species have a sharp break between pairs six and seven. However, pair seven is not truly small enough to be called microchromosomal; it is intermediate in size. There is a sharp break between pair seven and the microchromosomes. Like the bimaculatus group, the acutus group is characterized by male chromosomal heteromorphism, and a male diploid number of 33 or less. The karyotypes of some species of Anolis on Puerto Rico and Hispaniola are identical to that of the roquet group. It is argued that there were two colonizations of the Antilles from South America, one to the southern Lesser Antilles, ultimately giving rise to the roquet group; the second to the Greater Antilles. In the Greater Antilles, one stock arose that evolved a reduced diploid number and male heteromorphism. This group gave rise to the bimaculatus group, which became established in the northern Lesser Antilles. Furthermore, it is postulated that the roquet and bimaculatus groups were colonizing the Lesser Antilles at approximately the same time from opposite directions. The non-overlap between the two groups is due to competitive exclusion.

The Zoogeography of Lesser Antillean Anoilis Lizards - An Analysis Based Upon Chromosomes and Lactic Dehydrogenases

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