San Francisco garter snake

Source: Wikipedia, the free encyclopedia.

San Francisco garter snake

ESA
)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Colubridae
Genus: Thamnophis
Species:
T. sirtalis
Subspecies:
T. s. tetrataenia
Trinomial name
Thamnophis sirtalis tetrataenia
(Cope, 1875)
Synonyms
  • Eutaenia sirtalis tetratænia
    Cope, 1875

The San Francisco garter snake (Thamnophis sirtalis tetrataenia) is a slender multi-colored subspecies of the common garter snake. Designated as an endangered subspecies since the year 1967,[1] it is endemic to San Mateo County and the extreme northern part of coastal Santa Cruz County in California.

Some researchers estimate that there are only 1,000 to 2,000 adult snakes of the subspecies T. s. tetrataenia remaining. However, the full extent of the snakes' habitat has not been fully documented, and many snakes may utilize creeks and other waterways that are currently unexplored. This garter snake prefers wet and marshy areas, and because of its elusive nature, it is difficult to see or capture.

Geographic range

The

U.S. Fish and Wildlife Service has stated that many locations that previously had healthy populations of garter snakes are now in decline due to land development pressure and the filling of wetlands
in San Mateo County over the last sixty years. However, in many areas where it still occurs, it is not rare, but is actually quite common and can be viewed with good success once its behavior is understood.

Description

Adult San Francisco garter snakes can grow to a total length of 18 - 55 inches (46 – 140 cm).[3] They have keeled dorsal scales of blue-green, bordered by stripes of black, red (sometimes orange), and blue-green. Their head is barely wider than the neck, and is red. Its eyes are large compared to other species of garter snakes, giving the snake good eyesight to be primarily active during the day. Studies have shown that snout length is indicative of reproductive behaviors, as great snout length is correlated with ovarian follicle growth, which increases sexual activity of the female subspecies.

Garter snakes are practically harmless to humans. Their bites are fatal to their prey, but only cause a mild irritation for humans. With mildly toxic venom in their saliva, garter snakes possess no fangs.

Habitat

A San Francisco garter snake slithers along the grass
The San Francisco garter snake is often found in wet environments

The preferred

algal or rush mats, when available. The biggest population is found in a protected tract owned by San Francisco International Airport.[5]

Diet

San Francisco garter snakes forage extensively in

toxic California newt
(Taricha torosa) without incurring sickness or death.

Taxonomy and relation to other garter snakes

For a brief period from 1996 to 2000 there was confusion over the differentiation of the San Francisco garter snake from two other subspecies from California, the California red-sided garter snake (T. s. infernalis) and the red-spotted garter snake (T. s. concinnus). Barry petitioned [6] the International Commission on Zoological Nomenclature (ICZN) to suppress the changes proposed in 1996 to merge two of these species. In 2000, the ICZN agreed and voted to retain the historical taxonomic arrangement of subspecies within this evolutionary lineage. Accordingly, the subspecies tetrataenia was reaffirmed for the San Francisco garter snake and the races concinnus and infernalis retain their historical definition.

The San Francisco garter snake cohabits ecosystems that also host a subspecies of two other garter snake species: the coastal garter snake (Thamnophis elegans terrestris), a subspecies of the western terrestrial garter snake (T. elegans), and the Santa Cruz garter snake (Thamnophis atratus atratus) a subspecies of the aquatic garter snake (T. atratus). These three subspecies are known to prey upon the same foods; however, their preferences are slightly different. Herpetologist Sean Barry notes that the three subspecies divide up the food resources as follows:

  • the San Francisco garter snake eats primarily small frogs;
  • the coastal garter snake eats principally slugs;
  • the Santa Cruz garter snake eats preferentially minute fish and amphibian larvae.

DNA analysis

While the findings of the ICZN have given the San Francisco garter snake unique taxonomic standing for now, a molecular study challenges the subspecific status of this population. Janzen

mitochondrial DNA to determine relationships within the subspecies of the common garter snake (T. sirtalis). Janzen found that molecular evidence differed, often sharply, with the territorial boundaries of subspecies named on phenotypic variation. He further deduced that local environmental forces were more significant in shaping the color patterns shown by the common garter snake subspecies than shared common ancestry, and concluded all morphologically based subspecies in the western U.S. to be subject to revision. This result strongly suggests that the color traits that are diagnostic for T. s. tetrataenia are the result of local selection, rather than long-term isolation from the other subspecies of T. sirtalis in central California. On the other hand, the article places the three nearest populations of T. s. infernalis to T. s. tetrataenia in Sonoma County, Contra Costa County, and Santa Clara County into a separate group that exhibits an "elevated rate of molecular evolution". The authors suggest that sequencing nuclear DNA
may provide a more precise analytical tool to crack some of the ultimate taxonomic quandaries of the San Francisco garter snake and its relatives.

Outlook for this subspecies

Many of the factors that led to the listing of the San Francisco garter snake in 1967 continue to affect the subspecies. These environmental elements include loss of habitat from agricultural, commercial and urban development, as well as collection by reptile fanciers and breeders.[8] Collection of these endangered animals by private citizens remains illegal.[9]

In popular culture

In 2023 the San Francisco garter snake was featured on a

National Grasslands Visitor Center in Wall, South Dakota.[10]

References

  1. ^ Federal Endangered Species Listing (Federal Register 32:4001; March 1967)
  2. ^ San Francisco garter snake: species account, U.S. Fish and Wildlife Service, Sacramento office, April 2005
  3. ^ "San Francisco Gartersnake - Thamnophis sirtalis tetrataenia". www.californiaherps.com. Retrieved 2018-11-20.
  4. ^ Stebbins RC (1985). A Field Guide to Western Reptiles and Amphibians. Boston: Houghton Mifflin Company.
  5. ^ "One airport, 1,300 snakes: San Francisco helps to save endangered species". the Guardian. 2021-08-19. Retrieved 2022-12-06.
  6. ^ Barry SJ, Jennings MR, Smith HM (1996). "Current subspecific names for western Thamnophis sirtalis ". Herpetological Review. 27: 172–173.
  7. S2CID 4851873
    .
  8. ^ Kay J (April 22, 2004). "Colorful Bay Area denizen slithering away; 'Beautiful serpent' suffering effects of urbanization". San Francisco Chronicle, San Francisco, California.
  9. ^ U.S. Fish & Wildlife Service, Sacramento Fish & Wildlife Office, Species Account, SAN FRANCISCO GARTER SNAKE Thamnophis sirtalis tetrataenia; updated October 9, 2007.
  10. ^ "Postal Service Spotlights Endangered Species". United States Postal Service. April 19, 2023. Retrieved May 11, 2023.

Further reading

Retrieved from "https://en.wikipedia.org/w/index.php?title=San_Francisco_garter_snake&oldid=1164767068"