The Impact of Variation in Labial Tooth Number on the Feeding Kinematics of Tadpoles of Southern Leopard Frog (Lithobates sphenocephalus)
The keratinized mouthparts of tadpoles are complex structures that play a significant role in feeding. Recent evidence has shown that the keratinized labial teeth function in two ways: to anchor the oral disc to a substrate and to rake material from it. Reports of tadpoles with missing or deformed keratinized oral structures have increased. Yet, the impact missing teeth has on feeding remains unexplored. Here we use high speed videography (500 frames per second) of tadpoles of Southern Leopard Frog (Lithobates sphenocephalus [ = Rana sphenocephala]) to study how missing teeth affect feeding. Specifically, we test the hypothesis that the number of teeth present correlates with two metrics of the effectiveness of a tadpole to rake material from a substrate. Those are the duration of the full gape cycle (opening and closing of the jaws) and of the closing phase (closing of the jaws once attached to a substrate). We found a significant positive relationship between duration of time of the closing phase of the gape cycle and the number of labial teeth present. Thus, tadpoles with fewer teeth were in contact with a planar algal-covered substrate for a shorter duration than tadpoles with more teeth. Given the reports of tadpole mouthpart abnormalities, data relating feeding kinematics of tadpoles with missing labial teeth are relevant in assessing the impact these abnormalities have on larval performance. Our data indicate that tadpoles missing labial teeth forage less effectively than tadpoles with undamaged dentition. This may help explain the pattern of reduced growth and developmental rates commonly observed in tadpoles raised in polluted environments or infected with pathogens that attack keratinized oral structures.Abstract
The oral apparatus of a tadpole of the Southern Leopard Frog (Lithobates sphenocephalus). Abbreviations for descriptive terminology (after Altig and McDiarmid, 1999): A-1 and A-2 = first and second anterior tooth rows; UJS = upper jaw sheath; LJS = lower jaw sheath; P-1, P-2, and P-3 = first, second, and third posterior tooth rows. The posterior tooth row is the first to anchor and last to release from the surface during each gape cycle.
Tadpole of Lithobates sphenocephalus with intact labial teeth as it grazes on a glass surface covered with epiphytic algae. The nine frames shown here are from a single gape cycle. This sequence of nine frames (read from upper left to lower right) shows one complete gape cycle, which took a total of 84 milliseconds. Maximum gape is reached in 31 milliseconds (first frame of middle row). The jaws then start to close before the teeth release, which begins at 56 milliseconds and ends at 84 milliseconds (first and second frames of last row, respectively). Note that in the last two frames (at 70 and 84 milliseconds, respectively), the teeth release from the surface sequentially.
The relationship between number of labial teeth and the duration of the full gape cycle in tadpoles of the Southern Leopard Frog (Lithobates sphenocephalus). P = 0.184, F = 2.06, r2 = 0.436. Each data point represents the mean duration of the full gape cycle for an individual tadpole.
The relationship between number of labial teeth and the duration of the closing phase of the gape cycle in tadpoles of the Southern Leopard Frog (Lithobates sphenocephalus). Each data point represents the mean duration of the cycle for an individual tadpole. P = 0.022, F = 5.66, r2 = 0.679. Tadpoles with fewer teeth spent, on average, less time anchored to the substrate during the closing phase of the gape cycle.
Contributor Notes
Associate Editor: J. F. Webb.