Incongruence in the Pattern and timing of intra- Specific Diversification in Bronce Frogs And Bullfrogs (Ranidae)

James D. Austin & Kelly R. Zamudio

2008. Molecular Phylogenetics and Evolution 48: 1041ˆ1053

Abstract: We compare patterns of lineage divergence in mitochondrial DNA (mtDNA)
sequences of two proteinencoding mitochondrial genes (cyt b and ND2) in two ecologically
similar, co-distributed, and closely related ranid frogs (Rana clamitans and Rana
catesbeiana), that are geographically widespread, and frequently syntopic. We identified
three lineages in R. clamitans, separated by 0.5% to 2.1% net corrected
sequence divergence, comparable to two R. catesbeiana lineages separated by 0.6%. The
geographic pattern of lineage distribution differed notably between the two species. In R.
clamitans, we found a Coastal Plain-Appalachian (CPA) lineage restricted to south and east
of the Appalachian Mountains and a widespread lineage that encompassing nearly all the
sampled range. A third distinct and divergent lineage was detected in one location in the
southwest portion of the range (Louisiana). This pattern contrasts with the east-west
pattern in R. catesbeiana, and reflects possible differences in refugial dynamics and
patterns of range expansion. Although both species have undergone range expansion and
population growth, coalescent reconstruction of Ne reflects larger lineages but more
recent divergence in R. clamitans relative to R. catesbeiana, reflecting significant
differences in population history or divergent patterns of molecular evolution at mtDNA.

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CNAH Note: Using mtDNA, Austin and Zamudio (2008) identified three evolutionary
lineages of Lithobates clamitans and two evolutionary lineages of Lithobates catesbeianus
in this excellent paper, but did not name them as distinct species, presumably awaiting
future results of an analysis that includes nucleic DNA. However, based on known type
localities (as they appear in Schmidt, 1953) for already described, published, and available
names, the following distinct species might be recognized in the future:

Lithobates catesbeianus (Shaw, 1802) (Eastern lineage of Austin & Zamudio 2008)
Type locality: Charleston, South Carolina
Standard common name would become: Eastern Bullfrog
Synonyms: Lithobates mugiens (Merrem, 1820); Lithobates scapularis (Le Conte, 1825);
Lithobates conspersus (Le Conte, 1855)

Lithobates new species (Western lineage of Austin & Zamudio 2008)
Type locality: should data warrant, to be designated and published
Standard common name would become: Western Bullfrog

Lithobates clamitans (Latreille, 1801) (ACP lineage of Austin & Zamudio 2008)
Type locality: Charleston, South Carolina
Standard common name would become: Southern Bronze Frog
Synonym: none found

Lithobates melanotus (Rafinesque, 1820) (Widespread of Austin & Zamudio 2008)
Type locality: Lake Champlain and Lake George, Vermont & New York
Standard common name would become: Northern Bronze Frog
Synonyms: Lithobates fontinalis (Le Conte, 1825); Lithobates flaviviridis (Harlan, 1825);
Lithobates horiconensis (Holbrook, 1838); Lithobates nigricans (Agassiz, 1850)

Lithobates new species (Louisiana lineage of Austin & Zamudio 2008)
Type locality: should data warrant, to be designated and published
Standard common name would become: Louisiana or Cajun Bronze Frog

The above arrangement is presented here merely as advance information of possible
future changes in the taxonomy of two wide-ranging species of the North American genus
Lithobates. Under no circumstances should the above list be adopted as a taxonomy for
the group. Additional work on the systematics of these anurans is in progress.

The status of Lithobates okaloosae (Moler, 1985) remains uncertain and awaits resolution
as to whether it is a distinct species or a synonym of L. clamitans (sensu lato).

Of more immediate interest to many north American herpetologists, the authors
synonymized the subspecies Lithobates clamitans melanotus (Rafinesque, 1820) with L. c.
clamitans (Latreille, 1801). L. c. melanotus has heretofore been called the Green Frog and
the nominate subspecies has been called the Bronze Frog. CNAH will now adopt the
standard common name Bronze Frog for the species because it better reflects the skin
color of this frog ˆ- most herpetologists know that Lithobates clamitans has little if any
green skin color. While "bronze" may not be as precise as some would desire, it is better
than a color the amphibian normally doesn't possess.

References

Schmidt, Karl P. 1953. A check list of North American amphibians and reptiles. Sixth Ed.
Publ. American Soc. Ich. Herp., viii + 280 pp.

Joseph T. Collins
Director
CNAH