The peninsular archipelago of Baja California: A thousand kilometers of tree lizard genetics

We studied the variability of 25 isozymes among 14 populations of tree liza rds, Urosaurus, in Baja California, Mexico. Populations were distributed fr om Cabo San Lucas northward to Catavina, including both the peninsula and t he Islands of Cedros, Danzante, and San Marcos. Twenty loci were variable a nd 18 were scored for all populations examined. We detected significant sub structuring among the populations. Urosaurus sensu "nigricaudus" from the s outhern peninsular could be differentiated from more northernly distributed tree lizards by the apomorphic expression of alpha Man-A in liver and/or m uscle tissue. Two synapomorphies unite northern U. microscutatus and Ii. la htelai. They share a duplicated Pep-B locus and a silenced duplicated Pep-A locus; sAat-A is polymorphic in northern populations but monomorphic as th e apomorphic state in the south. These patterns are correlated with two anc ient trans-peninsular seaways. A southern late Tertiary transpeninsular sea way may have isolated U. nigricaudus from U. microscutatus at the Isthmus o f La Pat. Genetic differences between populations of U. microscutatus north and south of the midpeninsular Vizcamo Desert are correlated with the mid- Pleistocene seaway that further subdivided the peninsula into an archipelag o. The patterns of allelic distribution also indicate ongoing gene flow. Th us, we recommend synonymization of Urosaurus microscutatus with U. nigricau dus. We tentatively recognize U. lahtelai pending further investigation.