Wednesday, April 27, 2011

Michigan's Curious Caudates

Michigan's salamander diversity is pretty low given its northern latitude and general uninteresting topography. We've got four Ambystoma species, Four-toed Salamanders, Mudpuppies, Redbacks, and Newts. But there's two species here that are relatively unique and somewhat under the radar. One was discovered back in the early 2000s and the other wasn't found until a few years ago. The presence of these two species is so unknown, that neither are listed on the DNR's website for Michigan reptiles and amphibians. The two species of interest are the Northern Dusky Salamander & Two-lined Salamander. Both species are widespread throughout eastern North America and  are denizens of woodland creeks, brooks, springs, and seepages. But both are several hundred miles out of their recognized ranges here in Michigan. This has sparked debate as to whether or not these salamanders are a relict native population or if they were introduced here.

Northern Dusky Salamander - Desmognathus fuscus

Northern Dusky Salamanders are denizens of creeks, brooks, and seepages in forested areas and are never far from a trickling source of water. They are a robust species with a knife-like trail and the hind limbs are generally larger than the forelimbs. The genus Desmognathus, comes from the Greek word desmos, meaning ligament, and the Latin word gnathos, meaning jaw. The genus name is in reference to the large, strong bundle of ligaments in the jaws of members of the genus that gives Dusky salamanders a large, bulging jaw. The Northern Dusky is extremely variable in coloration. Michigan individuals may be brown, red-brown, or olive in coloration with lighter or darker coloration on the heads and dorsal surface. Some Michigan individuals have bold red coloration on the head and dorsal surface as the first animal pictured above. Although the coloration is extremely variable, all Northern Dusky Salamanders have a light diagonal line running from the eye toward the jaw.

Juvenile Duskies usually have have 6-8 yellow or red blotches along the dorsal surface which can often be obscure.  Females lay eggs in the summer under rocks, logs, and other forms of cover in the stream or in nearby wet habitats such as seepages and springs. The larvae are completely aquatic have small, but functional gills. The gills of larval stream salamander species are generally reduced in comparison to those of larval Ambystoma species as there is a great availability of oxygen in clear, moving streams in comparison to stagnant, vernal pools.

This rocky stream amid a beautiful Eastern Hemlock forest harbors Michigan's only population of Northern Dusky Salamanders. In terms of habitat, this area is extremely unique to Michigan as it lies in a deep ravine and filled with Eastern Hemlock, a generally uncommon tree species in the state. There are several springs and seepages are adjacent to the stream and flow into it. Duskies are extremely abundant at this site and utilize all types of cover around the edges of the stream including rocks, rotting locks, and leaf packs. 

Southern Two-lined Salamander - Eurycea cirrigera

The other unique salamander species is the Southern Two-lined Salamander. It is a small, boldy colored species which inhabits brooks, streams, springs, and seepages in eastern North America. Like the Northern Dusky Salamander, this salamander is several hundred miles out of its recognized range here in Michigan. Beyond genetic research which has determined that Michigan's population is E. cirrigera as opposed to E. bislineata, very little is known about them here. A limited number of specimens have been found, but the good news is that Michigan's population is reproducing as larva, eggs, and females guarding nests have been documented. The individual above is a gravid female which was found under a rotting log near a stream bank. Further research is needed in order to better understand the Two-lined Salamander's ecology here in Michigan. That's all for now. Until then, happy herping!

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