In 2006 and 2007, female mate choice experiments at one of these syntopic sites showed that females can identify conspecific males by the structure of their clicks and ignore dominant frequency information.
Publications to come.
This research is ongoing.
Conventional wisdom holds that in the southeastern U.S., the ranges of the two species of cricket frogs,
Acris crepitans and A. gryllus, meet somewhere in the upper Coastal Plain or near the Fall Zone,
the area where the lower Piedmont and upper Coastal Plain intergrade. Relatively little research of any kind
has been conducted on these two species on the Atlantic slope, and their precise geographical and ecological distributions and degree of reproductive isolation remain unclear.
For my dissertation research, I examined the acoustic signals and morphology of cricket frogs
in North Carolina to determine the degree of sympatry and reproductive isolation between the two species and to assess the role of vocalizations in species recognition.
Because the pattern within the clicks differs substantially between A. crepitans and A. gryllus, I can reliably identify cricket frogs by sound. In the field, it is actually easier to identify them by sound than by sight,
and not just because in order to look at a cricket frog you must find and catch it first. Cricket frogs
are highly variable morphologically and effective visual identification has long been a subject of debate.
The map below shows my field sites in North Carolina. Using their vocalizations to identify them, I have found that the range of A. crepitans extends from the Piedmont far east into the Coastal Plain and the range
of A. gryllus is fairly restricted within the Coastal Plain, particularly in the central and northern sections of the state. This finding supports what a few current field guides suggest about A. crepitans in the Southeast:
the species is penetrating deep into the Coastal Plain along rivers. I found the two species in syntopy
in the Coastal Plain. At these sites, A. crepitans and A. gryllus are breeding in the same wetland
and their choruses overlap spatially.
syntopic site
Eastern Cricket Frog (Acris crepitans crepitans)
Coastal Plain Cricket Frog (Acris gryllus gryllus)
In more detail:
Vocalizations are sometimes used for identifying cricket frogs, although only two research articles
have quantitatively addressed the identification of A. crepitans and A. gryllus by sound.
I used WildSpectra, a sound analysis program, to study my recordings of cricket frogs in North Carolina.
As expected, cricket frogs from the upper Piedmont and lower Coastal Plain, respectively west and east
of the putative area of sympatry near the Fall Zone, are audibly different. The figure below is an oscillogram showing the temporal structure of a representative cricket frog vocalization at Lake Norman State Park
(in the Piedmont) and along the Neuse River (in the lower Coastal Plain). Note that the clicks are very different while the larger-scale click groups and bouts are less distinct. The click differences are consistent
with the two previous acoustic studies of A. crepitans and A. gryllus.
cricket frogs in NC
