Intra-Populational Variation in the Intensity of Sexual Selection in Breeding Aggregations of Woodhouse's Toad (Bufo woodhousei)

Single fast fibers were isolated from the iliofibularis muscles of three species of toad with different thermal minima for active locomotion: 8 degrees C, American toad, Bufo americanus; 15 degrees C, Rocky Mountain toad, Bufo woodhousei woodhousei; 22 degrees C, Cane toad, Bufo marinus. All experiments were carried out during the summer. Fibers were chemically skinned and maximum isometric tension and unloaded contraction velocity were determined at a series of temperatures between 0 and 35 degrees C. At 25-30 degrees C, isometric tension development has a low temperature dependence (R10 = 1.1-1.3) and is in the range of 210-260 kN X m-2 for each of the three toads. However, at 0-10 degrees C, absolute values of tension increase in the series (B. americanus greater than B. woodhousei greater than B. marinus; i.e., with increasing cold tolerance), while thermal sensitivity between 0 and 10 degrees C is inversely related to cold tolerance. For example, at 0 degree C, maximum isometric tension (Po) for the most northerly distributed species is three times higher than for the subtropical to tropical species (P less than 0.001). R10 for Po (0-10 degrees C) is 1.7 for B. marinus, 1.3 for B. w. woodhousei, and 1.0 for B. americanus. In contrast, unloaded shortening speeds were similar at any given temperature for the three species. It is concluded that adaptations in Bufo myosin for activity at low temperatures largely involves changes in force production.

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Lymphatic regulation of hematocrit during hypoxia in the toad Bufo woodhousei

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1995.269.4.r814 ◽

1995 ◽

Vol 269 (4) ◽

pp. R814-R821 ◽

Cited By ~ 9

Author(s):

G. M. Malvin ◽

S. Macias ◽

M. Sanchez ◽

R. Dasalla ◽

A. Park ◽

...

Keyword(s):

Plasma Volume ◽

Lymph Flow ◽

Cholinergic Nerves ◽

Arterial Blood ◽

Rate Of Increase ◽

Lymph Heart ◽

Flow Through ◽

Bufo Woodhousei ◽

Induced Changes ◽

Toad Bufo

Hypoxia rapidly increases hematocrit (Hct) in anuran amphibians by reducing plasma volume, but the mechanism(s) mediating this response is unknown. We tested the hypothesis that, during hypoxia, plasma volume is reduced by impaired lymph heart (LH) function, decreasing lymph flow into the circulation. In Bufo woodhousei, we measured the effects of hypoxia on Hct, lymph heart rate (LHR), LH pressure, the movement of dye from the dorsal lymph sac to the arterial blood, and flow through an open LH cannula. We also tested whether splenic contraction or cholinergic nerves contribute to the hypoxia-induced changes. Graded hypoxia between 21 and 4% O2 produced graded increases in Hct (P < 0.0001) and decreases in LHR (P = 0.01). Hypoxia reduced the rate of increase in arterial Evans blue concentration after injection into the dorsal lymph sac (P = 0.041) and decreased flow through an open LH cannula (P < 0.012). Hypoxia increased Hct and reduced LHR similarly in control, splenectomized, and sham-splenectomized toads. Atropine had no significant effect on Hct and LHR. These results indicate that the LHs play a regulatory role in hypoxia-induced hemoconcentration.

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