Backyard Nature: Slender Salamanders

The legs of slender salamanders are minute, giving them a snake-like appearance.

With their skinny bodies and miniscule legs, slender salamanders (genus Batrachoseps) are often mistaken for small snakes or earthworms. These salamanders are common residents of moist, leaf-strewn ground, hiding under cover objects such as rotting logs, rocks, or planters. Their slim, elongate bodies slip easily into worm holes and termite galleries as they search for meals; slugs, millipedes, mites, roly-pollies, spiders, and various insects round out their diet. Despite the slender salamander's sluggish appearance, its tethered projectile tongue snags prey half a body length away in a fraction of a second.

Garden habitat for slender salamanders: Substantial leaf mulch with flower pots and a planter serving as cover objects.

Restricted to California, except for small areas in Oregon and Baja California, slender salamanders are a fascinating example of "cryptic species." Across their range they appear so similar that scientists originally divided the group into just three species.

However, in the 37 years between the publication of the 1966 first edition of Robert C. Stebbins' authoritative Field Guide to Western Reptiles and Amphibians and the 2003 third edition, scientists discovered that the group comprised twenty distinct species, despite their near-identical appearance.

To investigate the species puzzle, scientists examined DNA found in mitochondria, which are organelles present in complex (eucaryotic) cells, such as those in multicellular organisms like salamanders. Mitochondria house the manufacture of ATP molecules, a chemical currency used by cells for their energy requirements.

Importantly, mitochondria have their own DNA (mtDNA), a tiny set of genes separate from the main genome that is contained in the cell nucleus. Since mitochondria have limited DNA repair mechanisms, mistakes made during DNA replication may not be fixed; over successive generations, mtDNA tends to accumulate changes. If two salamander populations have been isolated from each other for a lengthy period of time, their mtDNA will differ substantially. Therefore, finding multiple mtDNA differences between two populations indicates they have been separated for some time and that speciation may have occurred.

Scientists also look for variation in enzymes, which are proteins that speed up chemical reactions within a cell. Enzymes help cells get things done in a timely manner, facilitating processes such as building cellular structures or dismantling large molecules for their components.

Proteins are composed of amino acid chains; the code for the chains is encrypted in nucleotide bases on strands of DNA. If DNA mutates, the code may specify a different amino acid, slightly changing the protein. When salamander populations are separated from each other, protein differences between them mount over time. This results in enzyme variants termed allozymes, which are coded for by alternate versions of the same gene.

But how are allozymes detected? Since some amino acids carry electrical charge, substituting one amino acid for another can affect the overall electrical charge on a protein. When two different proteins are placed on a gel with a positive electrode at one end and a negative electrode at the other (electrophoresis), the proteins will separate from each other according to charge.

Using both mtDNA and allozyme analysis, Elizabeth L Jockusch, Kay P. Yanev, and David B. Wake studied slender salamander populations in Central California and were able to clearly sort 62 populations of Central California salamanders (from Monterey Bay to Morro Bay) into four new species, work published in 2001 in Herpetological Monographs. They also used slender salamander mtDNA as a molecular clock to estimate how long ago species differentiated from each other, which ranged from several million to well over ten million years ago and generally correlated with geologic events that could have isolated populations, leading to speciation.–Anne M. Rosenthal

Jockusch, Elizabeth L., Yanev, Kay P., and David B. Wake. 2001. Molecular phylogenetic analysis of slender salamanders, genus Batrachoseps (Amphibia: Plethodontidae), from central coastal California with descriptions of four few species. Herpetological Monographs, Vol. 15: 54-99.

Lombard, Eric R. and David B. Wake. 1986. Tongue evolution in the lungless salamanders, Family Plethodontidae. IV. Phylogeny of Plethodontid salamanders and the evolution of feeding dynamics. Systematic Zoology Vol. 35(4):532-551

Stebbins, Robert C., 1966, A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Company, Boston

Stebbins, Robert C., 2003, Western Reptiles and Amphibians, Third Edition. Houghton Mifflin Company, Boston