Early acoustic experience alters genome-wide methylation in the auditory forebrain of songbird embryos.

Early exposure to salient cues can critically shape the development of social behaviors. For example, both oscine birds and humans can hear and learn to recognize familiar sounds in ovo and in utero and recognize them following hatching and birth, respectively. Here we demonstrate that different chronic acoustic playbacks alter genome-wide methylation of the auditory forebrain in late-stage zebra finch (Taeniopygia guttata) embryos. Within the same subjects, immediate early gene activation in response to acute con- or heterospecific song exposure is negatively correlated with methylation extent in response to repeated daily prior exposure to the same type of stimuli. Specifically, we report less relative global methylation following playbacks of conspecific songs and more methylation following playbacks of distantly-related heterospecific songs. These findings offer a neuroepigenomic mechanism for the ontogenetic impacts of early acoustic experiences in songbirds.

Females drive asymmetrical introgression from rare to common species in Darwin's tree finches.

The consequences of hybridization for biodiversity depend on the specific ecological and evolutionary context in which it occurs. Understanding patterns of gene flow among hybridizing species is crucial for determining the evolutionary trajectories of species assemblages. The recently discovered hybridization between two species of Darwin's tree finches (Camarhynchus parvulus and C. pauper) on Floreana Island, Galápagos, presents an exciting opportunity to investigate the mechanisms causing hybridization and its potential evolutionary consequences under conditions of recent habitat disturbance and the introduction of invasive pathogens. In this study, we combine morphological and genetic analysis with pairing observations to explore the extent, direction and drivers of hybridization and to test whether hybridization patterns are a result of asymmetrical pairing preference driven by females of the rarer species (C. pauper). We found asymmetrical introgression from the critically endangered, larger-bodied C. pauper to the common, smaller-bodied C. parvulus, which was associated with a lack of selection against heterospecific males by C. pauper females. Examination of pairing data showed that C. parvulus females paired assortatively, whereas C. pauper females showed no such pattern. This study shows how sex-specific drivers can determine the direction of gene flow in hybridizing species. Furthermore, our results suggest the existence of a hybrid swarm comprised of C. parvulus and hybrid birds. We discuss the influence of interspecific abundance differences and susceptibility to the invasive parasite Philornis downsi on the observed hybridization and recommend that the conservation of this iconic species group should be managed jointly rather than species-specific.

The life-cycle of Philornis downsi (Diptera: Muscidae) parasitizing Darwin's finches and its impacts on nestling survival.

The fly, Philornis downsi Dodge & Aitken, was first collected in 1964 on the Galápagos Islands and is now widespread across the archipelago. Virtually nothing is known about the behaviour and ecology of the fly as well as for the genus in general. Here, we describe all larval instars for the first time, and discuss infection intensity and impacts of parasitism on nestling survival of Darwin's finches. Adult P. downsi are non-parasitic free-living flies, whereas the larvae are obligate blood-feeding parasites on nestling birds. The larvae show a marked shift in their host site specificity--a novel finding for the genus Philornis: the first and early second larval instars live as agents of myiasis in finch nostrils and other tissues, while the older second and third instar larvae reside in the nest material and feed externally on the blood of nestlings, leading to blood losses in nestlings of 18-55%. Pupation occurs in the bottom layer of the nest. The combined effects of tissue damage by the endoparasitic instar larvae and anaemia by nest-dwelling haematophagous instar larvae account for the high nestling mortality (76%) due to Philornis parasitism. This represents the highest mortality by Philornis reported in the literature and emphasizes the extremely serious threat this parasite poses for the endemic passerine fauna of the Galápagos Islands.

Ageing and social rank effects on the reproductive system of free-ranging yellow baboons (Papio cynocephalus) at Mikumi National Park, Tanzania.

Ageing and social status effects on reproductive condition are examined in 106 wild female baboons from 1974 to 1997. The mean duration of each reproductive state (follicular and luteal phase components, pregnancy and lactation) was examined per female, using a repeated measures analysis of variance across each of four age classes (3-6, 7-10, 11-14, and 15-20+ year olds) and dominance rank quartiles. The sex-skin swelling portion of the follicular phase increased whereas the fully swollen portion decreased in duration with advancing age and with low dominance rank. The detumescing portion of the luteal phase increased with advancing age, being most pronounced in lowest ranking females. The number of cycles to conception decreased with age, with no dominance rank effect. However, owing to variation in lactation duration, the interbirth interval was unaffected by age but was shorter in high ranking females. The miscarriage rate was unaffected by age but increased as female rank declined. Age and rank effects became significantly more pronounced in response to a crash in the study population between 1987 and 1993. In conclusion, age- and rank-related reproductive changes in baboons, like those in humans, appear to represent attempts to compensate endocrinologically for accelerated ovarian atresia and increased environmental hardship.