Thomasomys

Abstract: Leucism is a partial hypopigmentary congenital disorder that indicates low levels of genetic diversity and is considered to be an unusual trait in wild populations. In continental America, few cases of abnormal coloration in vertebrates have been recorded. This feature can increase the selective pressure on individuals who have it, and can result from population isolation which, in turn, could act as an alarming indicator of environmental change. This condition has not been reported previously in genera of small rodent such as Akodon, Nephelomys, Thomasomys, Trasandinomys and Mesomys . Therefore, the aim of this note is to report 38 cases of leucism found in eight rodent species for the first time: Akodon mollis ( n = 7), Nephelomys albigularis ( n = 7), N. moerex ( n = 18), Transandinomys talamancae ( n = 2), Thomasomys auricularis ( n = 1), T. taczanowskii ( n = 1), T. paramorum ( n = 1) and Mesomys hispidus ( n = 1).

Abstract: Knowledge of feeding habits of small rodents is necessary for understanding food webs, trophic structure, and plant-animal interactions in Neotropical forests. Despite several studies that have investigated community structure and feeding behavior of rodents, large gaps remain in our understanding of their guild occupancy. Our objective was to investigate the diets of 7 species of small (< 100g) sympatric sigmodontine rodents in a high (3,500 m) Andean montane rainforest in Peru. We qualitatively and quantitatively assessed diet items in fecal samples from livetrapped rodents from 2009 to 2012. Frequency data for 4 diet categories indicated that all 7 species of rodents contained 4 diet categories in fecal samples: arthropods (88%), remains of leaves and fibers from plants (61%), intact seeds (with or without fruit pulp; 50%), and mycorrhizal spores (45%). Omnivory was found to be a strategy used by all species, although contingency table analysis revealed significant differences among and within species in diet categories. Cluster analysis showed 2 main groupings: that of the Thomasomys spp. plus Calomys sorellus group which included high amounts of intact seeds and plant parts in their fecal samples, and those of the genera Akodon, Microryzomys, Oligoryzomys, which included a greater proportion of arthropods in their fecal samples, but still consumed substantial amounts of fruit and plant parts. Intact seed remains from at least 17 plant species (9 families) were found in fecal samples. We concluded that this assemblage of sigmodontine rodents is omnivorous but that they likely play an important role as frugivores and in seed dispersal in tropical montane forests in Peru. El conocimiento de los habitos alimenticios de roedores pequenos es necesario para comprender cadenas alimenticias, estructura trofica, e interacciones planta-animal en los bosques neotropicales. A pesar de que numerosos estudios han investigado la estructura de comunidades y el comportamiento de forrajeo en roedores, aun existen grandes vacios en nuestra comprension de sus gremios troficos. Nuestro objetivo fue investigar las dietas de siete especies de pequenos (< 100 g) roedores sigmodontinos simpatricos en un bosque montano andino a 3.500] m en Peru. Cualitativamente y cuantitativamente evaluamos la dieta en muestras fecales de roedores capturados entre el 2009 y el 2012. Datos de frecuencia para cuatro categorias de dieta indicaron que las siete especies de roedores consumieron cuatro categorias de dieta: artropodos (88%), pedazos de hojas y fibras de plantas (61%), semillas intactas (con o sin pulpa de frutos; 50%), y esporas de micorrizas (45%). Omnivoria fue la estrategia utilizada por todas las especies, aunque el analisis con tablas de contingencia revelo diferencias significativas entre y dentro de especies en categorias de dieta. El analisis de agrupacion presento 2 grupos principales: el grupo Thomasomys spp. y Calomys sorellus, que incluye una gran proporcion de semillas intactas, y partes de plantas en las muestras fecales y el grupo que incluye los generos Akodon, Microryzomys y Oligoryzomys, el cual incluyo una proporcion mayor de artropodos en sus muestras fecales, pero con niveles altos de semillas intactas. Semillas intactas de al menos 17 especies de plantas (9 familias) fueron encontradas en las muestras fecales. Concluimos que este ensamble de roedores sigmodontinos es omnivoro y que probablemente las especies juegan un rol importante como frugivoros y en la dispersion de semillas en los bosques montanos tropicales en el Peru.