Learn More
Since Darwin published the "Origin," great progress has been made in our understanding of speciation mechanisms. The early investigations by Mayr and Dobzhansky linked Darwin's view of speciation by adaptive divergence to the evolution of reproductive isolation, and thus provided a framework for studying the origin of species. However, major controversies(More)
Understanding the evolution of reproductive isolation is tantamount to describing the origin of species. Therefore, a primary goal in evolutionary biology is to identify which reproductive barriers are most important to the process. To achieve this goal, the strength of multiple forms of isolation must be compared in an equivalent manner. However, a(More)
1. In smooth muscle cells of the rabbit carotid artery, ACh (greater than 10(-8) M) generated a hyperpolarization with two components (transient followed by sustained), only in the tissues with an intact endothelium. There were no detectable changes in the membrane potential, as elicited by ACh (up to 10(-5) M) in tissues with no endothelium or in the(More)
The effects of ACh and histamine on electrical and mechanical properties of intrapulmonary artery and vein muscles were studied in rats. In the artery, ACh and histamine indirectly relaxed the precontracted muscles in high-[K]o solution via the release of endothelium-derived relaxing factor (EDRF) from the endothelial cells, and also produced contractions(More)
Effects of high K+, acetylcholine (ACh), 9,11-epithio-11,12-methanothromboxane A2 (STA2), thrombin and endothelin were investigated on smooth muscles of the guinea pig coronary artery in intact and endothelium-denuded tissues. In intact tissues, ACh transiently inhibited but ATP produced maintained inhibition of the STA2-induced contraction. However, in the(More)
In isolated buccal segment of the rabbit facial vein, electrical responses produced by perivascular nerve stimulation and exogenously applied noradrenaline (NA) were recorded from the smooth muscle cells using microelectrode. Perivascular nerve stimulation hyperpolarized the smooth muscle cell membrane. The hyperpolarization was converted to depolarization(More)
In ring preparations of the rabbit mesenteric artery, the Ca-contraction, but not the noradrenaline (NA)-contraction, was inhibited by FRC-8653 (10(-9)-10(-5) M) in a concentration-dependent manner, although with a potency 50-100 times weaker than that of nicardipine. The actions of FRC-8653 on Ca-contraction appeared more slowly (over 1 hr) than those of(More)
Reciprocal transplant experiments have often provided evidence of local adaptation in temperate plants, but few such studies have been conducted in the tropics. To enhance our knowledge of local adaptation in tropical plants, we studied natural populations of two recently diverged Neotropical plant species, Costus allenii and C. villosissimus, in central(More)
Examining reproductive isolating barriers is essential for understanding processes of speciation. Sexual isolation has been shown to contribute to speciation in many sympatric taxa; however, its role in parapatric taxa with reduced interspecific gene flow is poorly understood. I investigated the extent of sexual isolation in two closely related Neotropical(More)