A New Species of Gymnotus (Gymnotiformes: Gymnotidae) from Rio Tiquie in Northern Brazil

Gymnotus tiquie, new species, is described from the Rio Tiquie, a tributary of the Uaupes (Vaupes) in the upper Negro basin, Amazonas, Brazil. The new species was collected in non-floodplain (terra firme) streams, where it occurs sympatrically and syntopically with two geographically widespread congeners, the type species of the genus, G. carapo, and G. coropinae. The new species is diagnosed by a unique combination of morphometric, meristic, and osteological traits, and by a characteristic color pattern in which the dark oblique pigment bands, diverse in shape and design, are divided into band-pairs along the length of the body, in which the band-pairs are often recurved (dorsally concave), more variable, and often reticulated in the abdominal region, and in which the pale inter-bands meet at the dorsal midline along most of the length of the body. Gymnotus tiquie is a member of the G. pantherinus species group, with which it shares the presence of one (vs. two) pore in the dorsolateral portion of the preopercle (except in G. pantanal and G. anguillaris), needle-shaped (vs. conical or arrowhead-shaped) teeth on the dentary and premaxilla, and a slender body (BD 5.6-10.6% HL vs. deep 8.7-13.5%, except G. chaviro, G. curupira, G. varzea, G. chimarrao, G. maculosus, G. henni, and G. inaequilabiatus that also have a slender body). Gymnotus tiquie is most similar in overall appearance to G. cataniapo of the upper Orinoco. These two species share three unique features within the G. pantherinus group: dark band-pairs with wavy irregular margins along the length of the body, a long body cavity with 45 or more pre-caudal vertebrae, and a darkly pigmented membrane in the caudal region of the anal fin.

Paternal Care Decreases Foraging Activity and Body Condition, but Does Not Impose Survival Costs to Caring Males in a Neotropical Arachnid

Exclusive paternal care is the rarest form of parental investment in nature and theory predicts that the maintenance of this behavior depends on the balance between costs and benefits to males. Our goal was to assess costs of paternal care in the harvestman Iporangaia pustulosa, for which the benefits of this behavior in terms of egg survival have already been demonstrated. We evaluated energetic costs and mortality risks associated to paternal egg-guarding in the field. We quantified foraging activity of males and estimated how their body condition is influenced by the duration of the caring period. Additionally, we conducted a one-year capture-mark-recapture study and estimated apparent survival probabilities of caring and non-caring males to assess potential survival costs of paternal care. Our results indicate that caring males forage less frequently than non-caring individuals (males and females) and that their body condition deteriorates over the course of the caring period. Thus, males willing to guard eggs may provide to females a fitness-enhancing gift of cost-free care of their offspring. Caring males, however, did not show lower survival probabilities when compared to both non-caring males and females. Reduction in mortality risks as a result of remaining stationary, combined with the benefits of improving egg survival, may have played an important and previously unsuspected role favoring the evolution of paternal care. Moreover, males exhibiting paternal care could also provide an honest signal of their quality as offspring defenders, and thus female preference for caring males could be responsible for maintaining the trait.

Applying many-body expansion aiming to make ab in initio molecular dynamics more efficient

In this present work we present a methodology that aims to apply the many-body expansion to decrease the computational cost of ab initio molecular dynamics, keeping acceptable accuracy on the results. We implemented this methodology in a program which we called ManBo. In the many-body expansion approach, we partitioned the total energy E of the system in contributions of one body, two bodies, three bodies, etc., until the contribution of the Nth body [1-3]: E = E1 + E2 + E3 + …EN. The E1 term is the sum of the internal energy of the molecules; the term E2 is the energy due to interaction between all pairs of molecules; E3 is the energy due to interaction between all trios of molecules; and so on. In Manbo we chose to truncate the expansion in the contribution of two or three bodies, both for the calculation of the energy and for the calculation of the atomic forces. In order to partially include the many-body interactions neglected when we truncate the expansion, we can include an electrostatic embedding in the electronic structure calculations, instead of considering the monomers, pairs and trios as isolated molecules in space. In simulations we made we chose to simulate water molecules, and use the Gaussian 09 as external program to calculate the atomic forces and energy of the system, as well as reference program for analyzing the accuracy of the results obtained with the ManBo. The results show that the use of the many-body expansion seems to be an interesting approach for reducing the still prohibitive computational cost of ab initio molecular dynamics. The errors introduced on atomic forces in applying such methodology are very small. The inclusion of an embedding electrostatic seems to be a good solution for improving the results with only a small increase in simulation time. As we increase the level of calculation, the simulation time of ManBo tends to largely decrease in relation to a conventional BOMD simulation of Gaussian, due to better scalability of the methodology presented. References [1] E. E. Dahlke and D. G. Truhlar; J. Chem. Theory Comput., 3, 46 (2007). [2] E. E. Dahlke and D. G. Truhlar; J. Chem. Theory Comput., 4, 1 (2008). [3] R. Rivelino, P. Chaudhuri and S. Canuto; J. Chem. Phys., 118, 10593 (2003).