The Effects of Seed Number and Prior Fruit Dominance on the Pattern of Fruit Production in Cucurbits pepo (Zucchini Squash)

Many plants, especially of species with indeterminate reproduction,show first-fruit dominance, in which the presence of developingfruit reduces future fruit maturation by increasing the abortionof later (younger) fruit and by inhibiting subsequent flowerproduction. We examined the effects of seed number on first-fruitdominance by experimentally manipulating the number of pollengrains that were deposited onto stigmas of zucchini squash andthen monitoring flower production, fruit growth, and fruit maturation.Our findings show (1) that fruits containing more seeds growfaster and achieve greater size; (2) that the presence of 6–15-d-oldfruit significantly decreases the probability of female flowerproduction while significantly increasing the probability offruit abortion; (3) that the number of seeds in the prior developingfruit has a significant effect on the probability of flowerproduction and fruit abortion, and (4) that when seed numbervaries among the fruits on a vine the fruit with the fewestseeds are the most likely to abort. It is concluded that thestrength of dominance by a developing fruit depends on the numberof seeds it contains and that this also influences the resultof fruit to fruit competition. Fruit abortion, fruit growth, Cucurbita pepo, size of pollen load, seed number, zucchini, squash     

Free Vehicles and Deep-Sea Biology

SYNOPSIS. A free vehicle is a timed and weighted device releasedfrom a ship in a free fall to the ocean bottom. Instrumentscarried on the free vehicle have been built to take biologicalsamples, sediment samples, water samples, and photographs, andto measure currents, tides, and temperature. The instrumentthen returns to the surface where it is recovered by the ship.A free vehicle system for biological sampling in the deep seais described in detail. It consists of a mast assembly, flotation,hookline and traps, and a magnesium release attached to weights.Different types of magnesium links used include a rod, a wireon pliers, and a series of diamond-shaped beads that drop througha hole after dissolving. A deck plan for launching the freevehicle and its retrieval at sea are described.     

Block of Conduction in Partially Depolarized Cardiac Purkinje Fibres induced by an α-Adrenergic Agent

IF discrete areas of the ventricular conducting system are exposed to high concentrations of K⁺, conduction through these areas is slowed so much that the impulse may re-enter the normal part of the conducting system after the end of the refractory period, thereby evoking another excitation of the heart (refs. 1 and 2 and our unpublished work). This slow conduction results from a slow response that resembles the slow component of the cardiac action potential³ and the action potential of normal fibres of the atrioventricular node⁴. Adrenaline enhances the response of Purkinje fibres, depressed by exposure to high K⁺ concentration⁵ and we now report that an α-adrenergic agent, methoxamine, depresses the slow response at concentrations that do not affect the normal action potential. This finding is of interest because very few of the actions of adrenergic agents on the heart can be attributed to the stimulation of α-receptors⁶, because selective depression of the slow response is further evidence that it differs qualitatively from the response of normal fibres (our unpublished work) and because it suggests that α-adrenergic agents may be useful in the prevention of certain cardiac arrhythmias.     

The rowing-to-flapping transition: ontogenetic changes in gill-plate kinematics in the nymphal mayfly Centroptilum triangulifer (Ephemeroptera, Baetidae)

Comparative studies encompassing a wide range of aquatic animals have shown that rowing is exclusively used at low Reynolds numbers ( Re  < 1), whereas flapping is predominantly used at Re  > 100, although few studies have been undertaken to document the transition in individual species that traverse the intermediate Re regime using a single set of appendages. Thus, it is not generally known whether a gradual increase in Re within a system results in a gradual or sudden shift between rowing and flapping. In the present study, we document ventilatory kinematics of a nymphal mayfly Centroptilum triangulifer that develops using a serial array of seven pairs of abdominal gill plates and operates at Reynolds numbers in the range 2–22 during ontogeny. We found that some kinematic variables (stroke frequency and metachronal phase lag) did not change during ontogeny but that others changed substantially. Specifically, gill kinematics in small instars used strokes with large pitch and stroke-plane deviations, whereas larger instars used strokes with minimal pitch and minimal stroke-plane deviation. Gills in larger instars also acquired an intrinsic hinge that allowed passive asymmetric movement between half strokes. Net flow in small animals was directed ventrally and essentially parallel to the stroke plane (i.e. rowing), whereas net flow in large animals was directed dorsally and essentially transverse to the stroke plane (i.e. flapping). The change in whole-gill kinematics from rowing to flapping occurred across a narrow Re range (3–8), which suggests a possible hydrodynamic demarcation between rowing and flapping.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 540–555.     

A landscape genetics approach for quantifying the relative influence of historic and contemporary habitat heterogeneity on the genetic connectivity of a rainforest bird

Landscape genetics is an important framework for investigating the influence of spatial pattern on ecological process. Nevertheless, the standard analytic frameworks in landscape genetics have difficulty evaluating hypotheses about spatial processes in dynamic landscapes. We use a predictive hypothesis-driven approach to quantify the relative contribution of historic and contemporary processes to genetic connectivity. By confronting genetic data with models of historic and contemporary landscapes, we identify dispersal processes operating in naturally heterogeneous and human-altered systems. We demonstrate the approach using a case study of microsatellite polymorphism and indirect estimates of gene flow for a rainforest bird, the logrunner ( Orthonyx temminckii ). Of particular interest was how much information in the genetic data was attributable to processes occurring in the reconstructed historic landscape and contemporary human-modified landscape. A linear mixed model was used to estimate appropriate sampling variance from nonindependent data and information-theoretic model selection provided strength of evidence for alternative hypotheses. The contemporary landscape explained slightly more information in the genetic differentiation data than the historic landscape, and there was considerable evidence for a temporal shift in dispersal pattern. In contrast, migration rates estimated from genealogical information were primarily influenced by contemporary landscape change. We discovered that landscape heterogeneity facilitated gene flow before European settlement, but contemporary deforestation is rapidly becoming the most important barrier to logrunner dispersal.