Ontogenetic shifts of heart position in snakes

Abstract

Heart position relative to total body length (TL) varies among snakes, with anterior hearts in arboreal species and more centrally located hearts in aquatic or ground-dwelling species. Anterior hearts decrease the cardiac work associated with cranial blood flow and minimize drops in cranial pressure and flow during head-up climbing. Here, we investigate whether heart position shifts intraspecifically during ontogenetic increases in TL. Insular Florida cottonmouth snakes, Agkistrodon conanti, are entirely ground-dwelling and have a mean heart position that is 33.32% TL from the head. In contrast, arboreal rat snakes, Pantherophis obsoleta, of similar lengths have a mean heart position that is 17.35% TL from the head. In both species, relative heart position shifts craniad during ontogeny, with negative slopes = −.035 and −.021% TL/cm TL in Agkistrodon and Pantherophis, respectively. Using a large morphometric data set available for Agkistrodon (N = 192 individuals, 23–140 cm TL), we demonstrate there is an anterior ontogenetic shift of the heart position within the trunk (= 4.56% trunk length from base of head to cloacal vent), independent of head and tail allometry which are both negative. However, in longer snakes > 100 cm, the heart position reverses and shifts caudally in longer Agkistrodon but continues toward the head in longer individuals of Pantherophis. Examination of data sets for two independent lineages of fully marine snakes (Acrochordus granulatus and Hydrophis platurus), which do not naturally experience postural gravity stress, demonstrate both ontogenetic patterns for heart position that are seen in the terrestrial snakes. The anterior migration of the heart is greater in the terrestrial species, even if TL is standardized to that of the longer P. obsoleta, and compensates for about 5 mmHg gravitational pressure head if they are fully upright.

Variation of organ position in snakes

“…In recent analyses involving species of snakes for which large samples of individuals were available, the position of the heart was not different between males and females (Anderson & Secor, ; Lillywhite & Lillywhite, ). We did not consider sex as a variable in analyses that we discuss here because other organs generally show less variation than the heart (see Section 3), intraspecific differences are generally less than interspecific variation, intraspecific samples were sometimes small, and sex was difficult or impossible to determine in some dehydrated specimens.…”

“…The span of data for the vascular lung is certainly representative because it corresponds with other much larger data sets for measurements of this organ (Lillywhite et al, ; Wallach, ). Although we did not consider sex as a possible correlate of organ position, it is not a factor for some organs and species, and the influence on position is either absent or very small relative to the influence of gravity (Anderson & Secor, ; Lillywhite & Lillywhite, ). Finally, both sexes are represented across the total span of data being considered here.…”

“…With exception of museum specimens, all snakes were previously part of other investigations. Because ontogeny influences the relative position of internal organs (Anderson & Secor, , ; Lillywhite & Lillywhite, ), we limited the snakes we examined to adult specimens.…”

The Correlation Between Body Mass Index and Computed Tomography Angiography on Vascular Positioning in Anterolateral Thigh Flap Transplantation

“…great development of perforator angiography technology [8,9]. With the continuous development of imaging technology, perforator flap transplantation technology has also been improved incessantly [10].…”

“…Since the late 1990s, major developments have been made in the design of skin flaps and the types of skin flaps have become more abundant. This is mainly due to the great development of perforator angiography technology [ 8 9 ]. With the continuous development of imaging technology, perforator flap transplantation technology has also been improved incessantly [ 10 ].…”