Geography 316: Biogeography
The Biogeography of the
Vernal Pool Tadpole Shrimp
(Lepidurus packardi)
|
Geography 316: Biogeography The Biogeography of the
Vernal Pool Tadpole Shrimp
|
|
| Photo courtesy: Larry Serpa (#1) |
by Vanessa Stevens, student in
Geography 316 Fall 2003
Thank you for visiting
our site. This web page was written by a student in Geography 316: Biogeography
and edited by the instructor, Barbara Holzman, PhD. All photos and maps
are posted with specific copyright permission for the express use of education
on these web pages. The students have tried to be as accurate as possible with
the information provided and sources and references are cited at the end of each
page.
Species Name: Lepidurus packardi
|
Kingdom: Animalia Phylum:_Arthropoda Subphylum: Crustacea |
Description of Species:
Lepidurus packardi is a small freshwater crustacean. It ranges in size with maturity and nutrition (Rogers, 2001). Its body can be characterized as a smooth protective concave shell or carapace which protects the head and thorax. A pair of eyes is centered atop at the anterior end of its shell. The light sensitive, nuchal organ is between the eyes (Rogers, 2001). Its segmented abdomen is visible (posterior), and the last segment produces a pair of whip-like appendages called cercopods. Vernal pool tadpole shrimp from the genus Lepidurus distinguish themselves with a single leaf shaped paddle between its cercopods (Goettle, 1997). At full maturity, Lepidurus packardi has 30-35 pairs of appendages called phyllopods (leaf-feet) which propel the creature through the water and through which it exchanges oxygen (Eder, 2003, Goettle, 1997, Rogers, 2001). The tadpole shrimp swim will swim upside down just under the surface when oxygen deficient (Eder, 2003). Other characteristics that distinguish the species from each other are: the number of body rings (L. packardi =24-29), the variation and shape of spines found on its carapace (L. packardi=large triangular spines with small spines in between), the length of anal plate called the caudal lamina, and the placement of endites that grow from the thorax (Rogers, 2001). Mature adults range 15-86mm from anterior carapace to caudal lamina (Rogers, 2001). Endites and caudal lamina are regenerated in as many as 20 days if damaged or bitten off by predators (Rogers, 2001). Lepidurus packardi is black, brown or green or a mottled combination (assists in camouflage) when found in murky water, or is transparent to beige with mottled brown and green variations when found in clear water (Rogers, 2001).
 |
 |
| Photo courtesy: Tim Curtis (#2) | Diagram by: Vanessa Stevens |
Natural History:
Habitat
These aquatic creatures have evolved and adapted to a very specific environment. They inhabit seasonal wetlands known as vernal pools. These pools form in shallow depressions or terraces, and experience various flooding and drying periods annually. They are directly associated to areas of the Earth that are classified as having a Mediterranean climate (Keeley and Zedler, 1998). These pools experience flooding, or inundation that begins with autumnal rain. The water does not easily percolate through the ground due to the impervious nature of soil layers which are directly associated with vernal pools (Holland, 1978). Soils such as: cemented hardpans, claypans, and beds of ancient volcanic flow are California vernal pool soil types (Holland, 1978). Vernal pools encounter four stages in their annual cycle: (I) a wetting phase, (II) an aquatic/ inundation phase, (III) a saturated-terrestrial phase and (IV) a drought phase (Keeley and Zedler, 1998, Barry, 1995). The water that collects in vernal pools experiences daily changes in temperature, ph, and dissolved CO2 and oxygen (Keeley and Zedler, 1998). Vernal pools range in size from small single pools 2 m square to lakes 356,253 m square and are often interconnected complex pool systems (Helm, 1998, Keeley and Zedler, 1998, Goettle, 1997). The vernal pool tadpole shrimp generally occupy pools ranging 2-15 cm in depth and a volume of 23- 9,262573 m3 (Helm, 1998).
 |
| Vernal pool Photo courtesy: Treve Johnson (#3) |
Role in the Food Chain
Lepidurus packardi is a bottom feeder; it feasts on organic debris that it funnels through a groove between its phyllopod (Goettle, 1997). It also eats other vernal pool invertebrates like: fairy shrimp, seed shrimp, earthworms, assorted larvae, as well as; amphibian eggs and other tadpole shrimp (Goettle, 1997, FWS, 2003, Barry, 1995). Vernal Pool Tadpole Shrimp are prey to other vernal pool endemics such as; invertebrates, amphibians, fish and birds (Goettle, 1997, FWS, 2003, Rogers, 2001).
Reproductive Adaptations
The vernal pool tadpole shrimp has survived this incredibly unpredictable and extreme environment by depositing its drought resistant eggs (cysts) in the soil. There they remain dormant, for as long as ten years, throughout the pool’s dry phase. Then they are activated by the onset of inundation (Goettle, 1997). Sexually mature adults are present in as few as three weeks of hatching (FWS, 2003). The Lepidurus genus is composed of three sexes; males, females and hermaphrodites (Rogers, 2001). Males typically have more body rings and bear pulvilli-lobed adhesive hairs, on their endites to grasp the female while mating (Rogers, 2001). Females and hermaphrodites carry cysts in brood pouches along the thorax (Rogers, 2001). Cysts may hatch almost immediately, while others settle in the pool sediment and are preserved until future seasonal inundation (FWS, 2003). L. packardi is able to produce more than one generation in a wet season and thousands of cysts in a lifetime (Goettle, 1997). The dispersal of these cysts among vernal pool complexes occurs through the help of birds ( Simovich, 1998).
The cysts manage to survive birds digestive tracts and are dispersed when excreted (Simovich, 1998). Helm (1998) describes the maximum longevity period of one vernal pool tadpole shrimp population as an average of 143.6 days, and a maximum of 168. The same population had an average of 38.1 days to mature sexually and minimum of 25 days, as well as; an average of 54.1 days of reproduction and a minimum of 41 days (Helm, 1998). The lifecycle ends when the pool dries up.
Distribution:
Species Distribution
Eighteen populations of Lepidurus packardi are known within the Central Valley of California (FWS, 2003). Its northern boundaries are the Stillwater and Millville Plains in Shasta County –east of Redding to Tulare County in the south (Helm, 1998, Goettle, 1997). The vernal pool tadpole shrimp is found as far east as Placer County in the Sierra Foothills, below an elevation of three thousand feet, and as far west as Warm Springs Seasonal Wetlands of the Don Edwards San Francisco Bay National Wildlife Refuge in Alameda County (Goettle, 1997). There is also a population near the Modoc Plateau in northeastern California, but there has been recent suggestion that this tadpole shrimp could be a new species altogether (Helm, 1998, Rogers, 2001). It is currently undergoing genetic analysis (Helm, 1998, Rogers, 2001).
In a 1989-1996 study, Helm (1998) concluded that 16.7% of pools within the Central Valley sustain the vernal pool tadpole shrimp.
Today, this species experiences a highly confined and fragmented distribution due to human disturbances such as; agriculture, irrigation systems development, housing developments, pollution of habitat through pesticides and fertilizers, mining, and through the use of recreational vehicles like ATV’s (Goettle, 1997, Simovich,1998, Hathaway et al.,1996).
Genus Distribution
The genus Lepidurus is composed of nine different species (one pending species), and four subspecies (Channum, 2001). The species Lepidurus apus is the only species in the genus to have a subspecies, it includes all four subspecies (Channum, 2001).
The distribution is found on all continents with the exception of Antarctica (Channum, 2001). Therefore the distribution of the Lepidurus genus qualifies as a cosmopolitan population globally.
Lepidurus species live in freshwater habitats, where some bodies of water experience short seasonal periods of drying or freezing (Channum, 2001). Their eggs can survive desiccation, but do not require it for hatching (Channum, 2001). Adapting to this form of seasonal isolation has allowed these creatures to occupy a harsh environment to which few predators survive. L. articus have managed to adapt to live in permafrost where eggs survive seasonal periods of freezing (Rogers, 2001).
Distinguishing species is not easy. There are very few obvious morphological differences between species which makes classifying tricky, but genetic examination and revisions of the Lepidurus classification system are sure to come (Rogers, 2001).
Family Distribution
These species split from their ancestors about fifteen million years ago in the Miocene epoch, during the Mesozoic Era, which is similar to the time where hominoids and chimpanzees began to evolve (Channum, 2001, Brandt, 2003).
Lepidurus species are morphologically different from its relatives of the Triops species, by a small paddle shaped flap between its cercopods (Goettle, 1997). They also differ in that Triops require their habitat to completely dry out in order to initiate their cysts to hatch, whereas Lepidurus does not require it (Channum, 2001). Triops species can only produce one generation of eggs per wet season while Lepidurus species have adapted to a life cycle with multiple generations in a season (Channum, 2001). Triops are generally found in warmer climates than Lepidurus as well (Channum, 2001).
Cladogram by: Vanessa Stevens
 |
Evolution:
Lepidurus and Triops species share the family Notostraca. A family who has adapted a niche to survive in environments that undergo an extreme range of seasonal, and at times, diurnal changes; that alter the environments abiotic factors regularly. These relict species are highly adapted to their specific environments. Ephermal (seasonal) wetlands, which vary in pH, tend to relieve the habitat of predators like fish creating an “enemy free space” for the tolerant Branchiopods (Simovich, 1998). Therefore, these creatures’ basic characteristics have remained virtually unchanged for millions of years (Goettle, 1997). Tadpole shrimp are identified as “living fossils” because they appear to be identical to their ancestors in the fossil record (Goettle, 1997). The morphology of the order Notostraca hasn’t changed since the Triassic period, 250 million years ago (Brandt, 2003, Eder, 2003). The species Triops cancriformis, is 220 million years old and believed to be the oldest living animal species on Earth (Eder, 2003). That’s roughly 165 million years before the extinction of the dinosaurs and 219 million years before man used fire (Brandt, 2003).
The distribution of Branchiopods was world wide, their evolution began 545 million years ago, 345 million years before the super continent Pangaea began to break apart (Brendt, 2003).
The Endangered Species:
Lepidurus packardi was listed as an Endangered Species on September 19, 1994 and is protected today. Its habitat continues to undergo compromise with the constant rise of development in California's Central Valley.
In 1978, Robert Holland conducted a study on “The Geographic and Edaphic Distribution of Vernal Pools in the Great Central Valley, California”. This study had determined that about one third of the original vernal pools remained, and those that remained were becoming more fragmented due to the urbanization of the California Central Valley (Holland, 1978). Current estimates are that 10-35% of the original habitat exist (Goettle, 1997). The remaining habitats were protected with the onset of section 404 of the Clean Water Act in 1972. The fragmentation of these habitats results in small isolated populations with very little genetic variability (FWS, 2003, Simovich, 1998). Ecological theory suggests that small isolated habitats with low genetic diversity will make populations susceptible to extinction through a chance events, additional environmental disturbance and inbreeding (FWS, 2003).
References
Barry, Shiela. “Rangeland Oasis”. University of California Division of Ag and Natural Resources, UC Cooperative Extension. 1995?. Redbluff, California.(leaflet no. 21531)
Brendt, Neil. November 11, 2003. “Evolutionary and Geologic Timelines”. The Talk.Origins Archive. http://www.talkorigins.org/origins/geo_timeline.htm [November 11, 2003]
Channum, Chip. August 30, 2001. “Triops-A Brief Overview of the Species”. Chip’s Page. http://filebox.vt.edu/users/channum/triops_species.htm [November 11, 2003]
Eder, Erich. June 24, 2003. “Large Branchiopods- Living Fossils!”. Everything You Always Wanted to Know About Branchiopods (but were afraid to ask)!http://mailbox.univie.ac.at/Erich.Eder/UZK/index2.htm[November 11, 2003]
Fish and Wildlife Service. October 29, 2003. “Vernal Pool Tadpole Shrimp”. Online Posting. Sacramento, California. http://sacramento.fws.gov/es/animal_spp_acct/vp_tadpole.htm [October 29, 2003]
Goettle, Bradley. 1997. "Living Fossil" in the San Francisco Bay Area?" Tideline. Vol 17 No. 1 1-3. http://desfbay.fws.gov/Archives/Tadpole/tadpole.htm [November 11, 2003]
Hathawy, S.A., D.P. Sheeham, and M.A. Simovich. “Vulnerability of Branchiopod Cysts to Crushing”. 1996. Journal of Crustacean Biology. 16(3): 448-452.
Helm, Brent P. “Biogeography of Eight Large Branchiopods Endemic to California”. 1998. C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors) Ecology, Conservation and Management of Vernal Pool Ecosystems-Proceedings from a 1996 Conference. California Native Plant Society. Sacramento, California.124-139http://www.cnps.org/vernalpools/helm.pdf [October 21, 2003]
Holland, Robert F. “The Geographic and Edaphic Distribution of Vernal Pools in the Great Central Valley, California”. No. 3. California: California Native Plant Society. 1978.
Keeley, Jon E. and Paul H. Zedler. “Characterization and Global Distribution of Vernal Pools”. 1998. C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors) Ecology, Conservation and Management of Vernal Pool Ecosystems-Proceedings from a 1996 Conference. California Native Plant Society. Sacramento, California. 1-14. http://www.werc.usgs.gov/seki/pdfs/keeley.pdf [October 1, 2003]
Rogers, Christopher D. “Revision of the Neartic Lepidurus (Notostraca)”.2001. Journal of Crustacean Biology. 21(4): 991-1006
Simovich, Marie A.1998. “Crustacean Biodiversity and Endemism in California’s Ephermal Wetlands”. C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors) Ecology, Conservation and Management of Vernal Pool Ecosystems-Proceedings from a 1996 Conference. California Native Plant Society. Sacramento, California.107-118. http://www.cnps.org/vernalpools/simovich.pdf [October 21, 2003]
Photos
#1 Serpa, Larry. Vernal Pool
Tadpole Shrimp. Google Images, Online.
www.tnccalifornia.org/our_proj/ merced/who.asp
#2 Curtis, Tim. Tadpole Shrimp, dorsal surface. Google Images, Online. http://virtual.yosemite.cc.ca.us/randerson/Great%20Valley%20Museum/tadpoleshrimp.htm
#3 Johnson, Treve. Merced Vernal Pool. Google Images, Online. www.tnccalifornia.org/ news/successes.asp
contact: www.treve.com
Diagram
Diagram design
by: Vanessa Stevens
Cladogram
Cladogram design
by: Vanessa Stevens
UC Berkeley.
Introduction to Metazoa. [November 24, 2003] UC Berkley.
http://www.ucmp.berkeley.edu/phyla/phyla.html
send comments to bholzman@sfsu.edu
Geog 316 homepage Back to Geography home page Back to SFSU homepage