DOI: 10.5061/dryad.dz08kprwq
title: Does stress mess with rodents’ heads? Influence of habitat availability and genetic factors in mandible fluctuating asymmetry (FA) in South American water rats (Nectomys squamipes, Sigmodontinae) from Brazilian Atlantic rainforest remnants

description: Loss of developmental stability can lead to deviations from bilateral
 symmetry (i.e. Fluctuating Asymmetry -FA), and is thought to be caused by
 environmental and genetic factors associated with habitat loss and
 stress. Therefore, levels of FA might be a valuable tool to
 monitor wild populations if FA serves an indicator of exposure to stress
 due to impacts of habitat loss and fragmentation. In studies
 examining FA and habitat fragmentation, FA levels are often
 explained by loss of genetic variation, though few studies have addressed
 FA’s use as indicator of environmental impact. Here
 we investigated whether habitat loss, genetic
 variation and/or inbreeding affect the developmental
 instability in Brazilian Atlantic rainforest populations of a
 Neotropical water rat (Nectomys squamipes). We sampled
 individuals from eight forest remnants with different amounts of available
 habitat and assessed FA levels with geometric morphometric techniques
 using adult mandibles. We
 used observed heterozygosity (Ho) and
 inbreeding coefficient (Fis), from seven
 microsatellite markers, as a proxy of genetic variation at individual and
 population levels. Populations were not significantly different for shape
 or size FA levels. Furthermore inter-individual variation in both
 shape and size FA levels, as well as inter-populational differences in
 size FA levels, were best explained by chance. However, habitat
 availability was negatively associated with both inter-populational
 variance and average shape FA levels. This association
 was stronger in populations living in areas with less than 20% of
 habitat available, which presented higher variance and higher
 average of FA, suggesting that Nectomys squamipes might
 have a tolerance threshold to small availability of habitat. Our work was
 one of the first to use FA to address environmental stress caused by
 reduced habitat availability in small mammal populations from a
 Neotropical biome. We suggest that shape FA might serve as a
 conservation tool to monitor human impact on natural animal populations.
description: Loss of
 developmental stability can lead to deviations from bilateral symmetry
 (i.e. Fluctuating Asymmetry -FA), and is thought to be caused by
 environmental and genetic factors often associated with habitat loss and
 stress. Therefore, levels of FA might be a valuable tool to monitor wild
 populations if FA serves an indicator of exposure to stress due to impacts
 of habitat loss and fragmentation. In studies examining FA and habitat
 fragmentation, FA levels are often explained by loss of genetic variation,
 though few studies have addressed FA’s use as indicator of environmental
 impact. Here we investigated whether habitat loss, genetic variation
 and/or inbreeding affect the developmental instability in Brazilian
 Atlantic rainforest populations of a Neotropical forest-dwelling water rat
 (<i>Nectomys squamipes</i>). We sampled individuals from eight
 forest remnants with different amounts of available habitat and assessed
 FA levels with geometric morphometric techniques using adult mandible
 shape and size. We used observed heterozygosity and inbreeding coefficient
 (Fis), from seven microsatellite markers, as a proxy of genetic variation
 at individual and population levels. Populations were not significantly
 different for shape or size FA levels. Furthermore inter-individual
 variation in both shape and size FA levels, as well as inter-populational
 differences in size FA levels, were best explained by chance. However,
 habitat availability was negatively associated with both
 inter-populational variance and average shape FA levels. This association
 was stronger in populations living in areas with less than 20% of habitat
 available, which presented higher variance and higher average of FA,
 suggesting that <i>Nectomys squamipes</i> might have a
 tolerance threshold to small availability of habitat. Our work was one of
 the first to use FA to address environmental stress caused by reduced
 habitat availability in small mammal populations from a Neotropical biome.
 We suggest that shape FA might serve as a conservation tool to monitor
 human impact on natural animal populations.