BackgroundDo evolutionary specializations lead to evolutionary constraint? This appears plausible, particularly when specialization leads to loss of complex adaptations. In the owl monkey lineage, nocturnality clearly arose from a diurnal ancestor. This behavioural shift was accompanied by morphological changes in the eye and orbit and complete loss of colour vision via missense mutations in the gene encoding the short-wave sensitive visual pigment (SWS opsin). Interestingly, at least one subspecies of owl monkey, Azara’s owl monkey (Aotus azarae azarae), has regained activity in daylight. Given that all primate species that are active in daylight, including primarily diurnal species and species that are active during both day and night, have at least dichromatic colour vision, it seems reasonable to propose that dichromacy would be adaptive in A. a. azarae. With a disabled SWS opsin, the main avenue available for Azara’s owl monkeys to re-evolve colour vision is via a polymorphism in the intact X-linked opsin locus, which commonly occurs in other New World monkeys. To examine this possibility we assayed variation in the X-linked opsin of A. a. azarae, focusing on the three exons (3, 4 and 5) that control spectral sensitivity.ResultsWe found low opsin genetic variation on a population level, and no differences at the three main sites that lead to variation in spectral sensitivity in the opsins of other New World monkeys. Two rare alleles with single amino acid variants are segregating in the population, but previous functional studies indicate that these are unlikely to affect spectral sensitivity.ConclusionsGenetic constraint on the re-evolution of colour vision is likely operating in Azara’s owl monkey, which may affect the niche that this subspecies is able to occupy.

In species of mammals that habitually bear single offspring, like most anthropoid primates, the occurrence of twins is expected to impose considerable energetic costs on the caretakers. The question then arises of how caregivers cope with the potentially increased costs of raising twins. These increased costs should lead to differing developmental rates in twins when compared to singletons, and/or to changes in the caregivers' behavior. Likewise, time budgets of parents of singletons are expected to differ from those of adults without offspring. Additionally, if twinning was an adaptive response to favorable ecological conditions, it should be more likely in years with high food abundance. Following the birth in 2011 of two sets of twins in a wild population of pair-living Azara's owl monkeys (Aotus azarae) in Northern Argentina, we used long-term demographic, behavioral, and phenological data to compare (a) the proportion of time that singleton and twin infants were carried by either parent; (b) adult time budgets and ranging behavior in groups with zero, one, or two infants; and (c) the availability of food in 2011 with food availability in other years. Twins, like singletons, were carried nearly exclusively by the male, and they were carried slightly more than singletons, suggesting a relatively inflexible pattern of infant care in the species. Time budgets showed that twin parents foraged more and moved less than singleton parents or groups without infants, despite the fact that phenological data indicate that fruit availability in 2011 was not substantially higher than in some of the other years. Overall, twinning thus presumably increased costs to breeders, especially males, but its effect on animals' long-term reproductive success remains unclear.

The Humid Chaco has a high mammalian biodiversity. As habitats are threatened due to exploitation and environmental degradation, protected areas can act as refuges for wild animals. In 2006, ca 1,100 ha of gallery forest were established as the "Owl Monkey Reserve" within the private cattle ranch "Estancia Guaycoléc". The mammalian species richness and composition of the reserve was determined using direct observations, camera traps, and indirect evidence. The camera traps also allowed us to determine the activity periods of 20 of the species. Forty-two species were recorded. A fourth of those species (24%) are categorized under some risk of extinction in Argentina. While most species showed usual activity periods, 2 species (Mazama americana and Tayassu pecari) were not as exclusively nocturnal as reported from other sites, possibly due to reduced hunting pressure. The presence of various endangered species highlights the importance of protected private reserves.

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En Argentina se encuentran seis especies de crácidos, de las cuales el Muitú (Crax fasciolata) es la más amenazada y la de distribución más restringida en el país. Debido a que sus principales poblaciones parecen existir a lo largo de los riachos del este formoseño, se trabajó en la selva en galería del riacho Pilagá en la Estancia Guaycolec para (1) realizar la primera evaluación sistemática y cuantitativa en Argentina de una población de Muitú, y (2) evaluar la eficacia relativa de muestreos por tierra y agua, cámaras trampa y emisión de vocalizaciones grabadas (“playback”) como técnicas para el relevamiento poblacional de la especie. Durante 20 días se realizaron 22 muestreos en transectas terrestres y 8 en transectas sobre el curso de agua que resultaron en la detección de Muitú en 22 ocasiones (39 individuos). Las 10 cámaras trampa generaron 227 fotos de Muitú entre octubre de 2010 y julio de 2012 (4007 días-cámara). Tres de las 10 pruebas de emisión de vocalizaciones resultaron en contacto con un individuo. Los individuos fueron registrados solos o en grupos pequeños de 2–5 individuos, exclusivamente durante el día, más frecuentemente con temperaturas bajas e intermedias y principalmente en sitios cercanos al riacho. Dada la ausencia de reservas nacionales y provinciales que protejan las selvas en galería del este formoseño, resulta imperativo implementar estrategias de conservación de la especie que incorporen a las estancias privadas características de la zona.