Morphological Change in the Tessellated Darter (Etheostoma olmstedi) Following the Introduction of the Banded Darter (E. zonale) to the Susquehanna River Drainage
The strong connection between ecology and morphology in fishes predicts that ecologically relevant morphological features will change in concert with changes in habitat use and feeding ecology even over relatively short timescales following species introduction. Here, this hypothesis is tested by examining the trophic morphology of specimens of the native Tessellated Darter, Etheostoma olmstedi, collected at Catatonk Creek, Candor, Tioga Co., NY, USA, between 1961 and 2002. The collections of E. olmstedi bracket a 1980 range expansion by the non-native Banded Darter, E. zonale. Examination of the E. olmstedi specimens revealed that the length of the buccal cavity relative to body size increased following the invasion of Catatonk Creek by E. zonale. An increase in buccal cavity length (BCL) is expected to result in higher suction feeding performance measured as volumetric flow rate of water through the mouth. Such an increase in BCL may enable E. olmstedi to exert greater suction forces on prey and as a result, post-invasion E. olmstedi may be able to capture more elusive prey or to take prey from habitats with smaller substrates than pre-invasion E. olmstedi. The functional and potential ecological consequences of the increase in BCL suggest that the morphological change may be linked to a shift by E. olmstedi to more marginal habitats following the invasion of E. zonale.Abstract
External morphology of (A) the Banded Darter, Etheostoma zonale, and (B) the Tessellated Darter, E. olmstedi. Scale bars = 1 cm.
Recent changes in the geographic distribution of E. olmstedi (light gray) and E. zonale (dark gray) based on Lee et al. (1980), Greenberg (1982), and Page (1983). (A) Both species' historic ranges, (B) the species' ranges in 1985, approximately 15 years after the introduction of E. zonale to Little Pine Creek, PA (indicated by arrow), a tributary of the Susquehanna River, and (C) the species' present ranges. In (C), an arrow indicates the location of the study site: Catatonk Creek, Candor, Tioga Co., NY.
Lateral view of the skull of a Banded Darter collected at Catatonk Creek in 1998. Thickened lines indicate actual distances measured for premaxilla length, out-lever length, closing in-lever length, and opening in-lever length. The coronoid process of the dentary, a landmark used to measure gape width, is also indicated. Scale bar = 1 cm.
Scatterplot of the PC scores on the first two principal component (PC) axes of all E. olmstedi and E. zonale. Individuals with higher PC 1 scores have longer hyoid and premaxilla bones and lower closing and opening lever ratios than individuals with lower scores. Individuals with higher PC 2 scores have a longer buccal cavity than individuals with lower scores.
Buccal cavity length (BCL; ±1 SE) of typical adult pre- and post-invasion E. olmstedi and E. zonale. Mean and SE for each species and time class were calculated using the mean SL of adult E. olmstedi (52.5 mm) and E. zonale (51.3 mm) and the appropriate least squares regression equation of log SL vs. log BCL. BCL was similar between pre-invasion E. olmstedi and E. zonale but differed significantly between pre- and post-invasion E. olmstedi.
Mean (±1 SE) lower jaw CLR of E. zonale specimens collected from Catatonk Creek between 1984 and 2002. The closing lever ratio of the lower jaw of E. zonale exhibited a marginally significant increase in size between 1984 and 2002 after correcting for multiple tests (linear regression, r2 = 0.196, P = 0.0088).
Contributor Notes
Associate Editor: J. F. Webb.