Morphological and Physiological Adaptations of the Marine Iguana in comparison to Land Iguanas

Morphological and Physiological Adaptations of the Marine Iguana in comparison to Land Iguanas

Taxonomy of land iguanas

The Galápagos land iguanas form the sister taxon of the Galápagos marine iguanas (Amblyrhynchus cristatus), from which they diverged 10 - 20 million years ago. Given that the present-day islands are less than 1 million to 4 million years old, the split between Galápagos land and marine iguanas either occurred on older, now submerged, islands of the Archipelago following a single colonization event from the mainland, or the two genera may have split prior to colonizing the islands. Despite their ancient divergence, marine and land iguanas are still capable of hybridizing and producing viable offspring (see picture on the right: an hybrid between land and marine iguanas).

Land iguanas comprise two recognized species: Conolophus subcristatus, which naturally inhabits five islands (Plaza Sur, Baltra, Santa Cruz, Isabela, and Fernandina), and C. pallidus, which is restricted to the island of Santa Fe (cf. map below). In addition, there are three translocated populations of C. subcristatus (Islote Caamano, Islote Venecia, and Isla Seymour Norte). Contrary to Galápagos marine iguanas, no extensive population analysis based on molecular genetics data had been published for land iguanas. However, morphological analyses challenged current classification and identified three possible distinct groups that may warrant species status: animals from the eastern island of Santa Fe, the central islands (Santa Cruz, Baltra and Plaza Sur) and the western and youngest islands (Isabela and Fernandina), respectively.

The Galápagos land iguanas (genus Conolophus) have faced significant anthropogenic disturbances since the 17th century, leading to severe reduction of some populations and the extinction of others. Conservation activities, including the repatriation of captive-bred animals to depleted areas, have been ongoing since the late 1970s, but genetic information has not been extensively incorporated. We used nine species-specific microsatellite loci of 703 land iguanas from the six islands where the species occur today to characterize the genetic diversity within, and the levels of genetic differentiation among, current populations as well as test previous hypotheses about accidental translocations associated with early conservation efforts. Our analyses indicated that:

five populations of iguanas represent distinct conservation units (one being the recently discovered rosada form) and could warrant species status,

some individuals from North Seymour previously assumed to be from the natural Baltra population appear related to both Isabela and Santa Cruz populations, and

)the five different management units exhibit considerably different levels of intra-population genetic diversity, with the Plaza Sur and Santa Fe populations particularly low.

Although the initial captive breeding programmes, coupled with intensive efforts to eradicate introduced species, saved several land iguana populations from extinction, our molecular results provide objective data for improving continuing in situ species survival plans and population management for this spectacular and emblematic reptile.

Taxonomy of land iguanas

The Galápagos land iguanas form the sister taxon of the Galápagos marine iguanas (Amblyrhynchus cristatus), from which they diverged 10 - 20 million years ago. Given that the present-day islands are less than ...