Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela

The success of a reintroduction program is determined by the ability of individuals to reproduce and thrive. Hence, an understanding of the mating system and breeding strategies of reintroduced species can be critical to the success, evaluation and effective management of reintroduction programs. As one of the most threatened crocodile species in the world, the Orinoco crocodile (Crocodylus intermedius) has been reduced to only a few wild populations in the Llanos of Venezuela and Colombia. One of these populations was founded by reintroduction at Caño Macanillal and La Ramera lagoon within the El Frío Biological Station, Venezuela. Twenty egg clutches of C. intermedius were collected at the El Frío Biological Station for incubation in the lab and release of juveniles after one year. Analyzing 17 polymorphic microsatellite loci from 335 hatchlings we found multiple paternity in C. intermedius, with half of the 20 clutches fathered by two or three males. Sixteen mothers and 14 fathers were inferred by reconstruction of multilocus parental genotypes. Our findings showed skewed paternal contributions to multiple-sired clutches in four of the clutches (40%), leading to an overall unequal contribution of offspring among fathers with six of the 14 inferred males fathering 90% of the total offspring, and three of those six males fathering more than 70% of the total offspring. Our results provide the first evidence of multiple paternity occurring in the Orinoco crocodile and confirm the success of reintroduction efforts of this critically endangered species in the El Frío Biological Station, Venezuela

Simulation of GaAs Nanowire Growth and Crystal Structure

Growing GaAs nanowires with well-defined crystal structures is a challenging task, but may be required for the fabrication of future devices. In terms of crystal phase selection, the connection between theory and experiment is limited, leaving experimentalists with a trial and error approach to achieve the desired crystal structures. In this work, we present a modeling approach designed to provide the missing connection, combining classical nucleation theory, stochastic simulation, and mass transport through the seed particle. The main input parameters for the model are the flows of the growth species and the temperature of the process, giving the simulations the same flexibility as experimental growth. The output of the model can also be directly compared to experimental observables, such as crystal structure of each bilayer throughout the length of the nanowire and the composition of the seed particle. The model thus enables for observed experimental trends to be directly explored theoretically. Here, we use the model to simulate nanowire growth with varying As flows, and our results match experimental trends with a good agreement. By analyzing the data from our simulation, we find theoretical explanations for these experimental results, providing new insights into how the crystal structure is affected by the experimental parameters available for growth

Annealing of Au, Ag and Au-Ag alloy nanoparticle arrays on GaAs (100) and (111)B

Part of developing new strategies for fabrications of nanowire structures involves in many cases the aid of metal nanoparticles (NPs). It is highly beneficial if one can define both diameter and position of the initial NPs and make well-defined nanowire arrays. This sets additional requirement on the NPs with respect to being able to withstand a pre-growth annealing process (i.e. de- oxidation of the III-V semiconductor surface) in an epitaxy system. Recently, it has been demonstrated that Ag may be an alternative to using Au NPs as seeds for particle-seeded nanowire fabrication. This work brings light onto the effect of annealing of Au, Ag and Au-Ag alloy NP arrays in two commonly used epitaxial systems, the Molecular Beam Epitaxy (MBE) and the Metalorganic Vapor Phase Epitaxy (MOVPE). The NP arrays are fabricated with the aid of Electron Beam Lithography on GaAs 100 and 111B wafers and the evolution of the NPs with respect to shape, size and position on the surfaces are studied after annealing using Scanning Electron Microscopy (SEM). We find that while the Au NP arrays are found to be stable when annealed up to 600 $^{\circ}$C in a MOVPE system, a diameter and pitch dependent splitting of the particles are seen for annealing in a MBE system. The Ag NP arrays are less stable, with smaller diameters ($\leq$ 50 nm) dissolving during annealing in both epitaxial systems. In general, the mobility of the NPs is observed to differ between the two the GaAs 100 and 111B surfaces. While the initial pattern is found be intact on the GaAs 111B surface for a particular annealing process and particle type, the increased mobility of the NP on the 100 may influence the initial pre-defined positions at higher annealing temperatures. The effect of annealing on Au-Ag alloy NP arrays suggests that these NP can withstand necessary annealing conditions for a complete de-oxidation of GaAs surfaces.Comment: 31 pages, 8 figure