Human species and mating systems: Neandertal-Homo sapiens reproductive isolation and the archaeological and fossil records

The present paper examined the assumption of strong reproductive isolation (RI) between Homo neanderthalensis and Homo sapiens, as well as the question of what form it might have taken, using insights from the parallel case of chimpanzee–bonobo hybridization. RI from hybrid sterility or inviability was thought unlikely based on the short separation-to-introgression timeline. The forms of RI that typically develop in primates have relatively short timelines (especially for partial implementation); they generally preclude mating or influence hybrid survival and reproduction in certain contexts, and they have the potential to skew introgression directionality. These RI barriers are also consistent with some interpretations of the archaeological and fossil records, especially when behavioral, cognitive, morphological, and genetic differences between the two human species are taken into consideration. Differences potentially influencing patterns of survival and reproduction include interspecies violence, Neandertal xenophobia, provisioning behavior, and ontogenetic, morphological, and behavioral differences affecting matters such as kin and mate recognition, infanticide, and sexual selection. These factors may have skewed the occurrence of interbreeding or the survival and reproduction of hybrids in a way that might at least partially explain the pattern of introgression.

Negative effects of agricultural intensification on energetic gain rates of a declining aerial insectivore

The historical rise of intensive agricultural practices is hypothesized to be related to declines of grassland and aerial insectivorous birds. Drivers of declines may also influence the overall abundance and spatial distribution of insects within agricultural landscapes. Subsequently, average energetic gain rates of birds breeding within more agro-intensive landscapes may be impacted. Lower energetic gain rates in agro-intensive landscapes may lead to reduced growth rate, body condition or fledging success of nestlings but also to diminished body condition of food provisioning adults. In this study, we assessed if energetic gain of nestlings and food provisioning behavior of adults varied across a gradient of agricultural intensification in a declining aerial insectivore, the Tree swallow (Tachycineta bicolor). We found that hourly gain rate was lower in agro-intensive landscapes, and yet travel distances were longest within less agro-intensive landscapes. Our results highlight that, in order to maximize long term average gain rates, Tree swallows breeding within agro-intensive landscapes must forage with greater intensity, perhaps at a cost to themselves, or else costs will transfer to growing broods. Our work provides further evidence that agricultural intensification on the breeding grounds can contribute to the declines of aerial insectivores in part through a trophic pathway.