P2.202 Thursday, Jan. 5 The effects of branch structure on the locomotion of a specialized arboreal snake (Boiga irregularis) BYRNES, Greg*; JAYNE, Bruce C; University of Cincinnati; University of Cincinnati email@example.com
The surfaces in arboreal habitats have variation in diameter, incline, and branching structure that pose functional challenges for animal locomotion, but many lineages of snakes have independently evolved arboreality. We tested the effects of arboreal habitat structure on the locomotor performance of a highly arboreal snake, the brown tree snake (Boiga irregularis). We used 7 diameters of cylindrical perches (0.6 – 21 cm), 3 inclines (0, 45, 90 degrees) and 2 branching conditions (with and without pegs). For horizontal perches speed was maximized for an intermediate diameter approximating the diameter of the snake’s body, and for a wide range of diameters for cylinders lacking pegs, speed decreased with increasing diameter. With increased inclines performance decreased, and the snakes shifted from lateral undulation, which relied on balancing, to concertina locomotion, which involved periodic gripping when crawling uphill. For both of the uphill inclines some large diameters were impassable, and several snakes were not even able to maintain a grip on the largest diameter. When pegs were present the brown tree snakes exclusively used lateral undulation on all diameters and inclines, and the snakes had up to 5-fold improvements in maximum speed. The locomotion of brown tree snakes differed in two major ways from that of rat snakes and boa constrictors. First, brown tree snakes were much faster than the other species on all combinations of perch tested. Second, brown tree snakes relied more on lateral undulation rather than concertina locomotion on horizontal substrates. These comparative data may provide new insights into the consequences of specializations in axial morphology for arboreal habitats that have evolved repeatedly in snakes.