Evidence for repeated independent evolution of migration in the largest family of bats

Abstract

Background: How migration evolved represents one of the most poignant questions in evolutionary biology. While studies on the evolution of migration in birds are well represented in the literature, migration in bats has received relatively little attention. Yet, more than 30 species of bats are known to migrate annually from breeding to non-breeding locations. Our study is the first to test hypotheses on the evolutionary history of migration in bats using a phylogenetic framework.

Methods and principal findings: In addition to providing a review of bat migration in relation to existing hypotheses on the evolution of migration in birds, we use a previously published supertree to formulate and test hypotheses on the evolutionary history of migration in bats. Our results suggest that migration in bats has evolved independently in several lineages potentially as the need arises to track resources (food, roosting site) but not through a series of steps from short- to long-distance migrants, as has been suggested for birds. Moreover, our analyses do not indicate that migration is an ancestral state but has relatively recently evolved in bats. Our results also show that migration is significantly less likely to evolve in cave roosting bats than in tree roosting species.

Conclusions and significance: This is the first study to provide evidence that migration has evolved independently in bat lineages that are not closely related. If migration evolved as a need to track seasonal resources or seek adequate roosting sites, climate change may have a pivotal impact on bat migratory habits. Our study provides a strong framework for future research on the evolution of migration in chiropterans.

Figure 1. Frequency of migrants across a distance gradient in vespertilionid bats.

This graph shows short-distance migrants generally move between 100 and 600 km and long-distance migrants moved between 1000 and 2000 km .

Figure 2. Ancestral state reconstruction of migratory behavior in vespertilionid bats.

We used an equal rates Markovian model to reconstruct the evolutionary history of migration in the family Vespertilionidae. The tree shows the probabilities for migratory behavior for the internal branches for portions of the tree. The model and the ancestral states estimates were performed on the whole phylogeny but for better visibility we show only those species which display migratory behavior including two next sister taxa, as well as all the internal nodes and descendants which have reconstructed ancestral probabilities of more than 5% either for short- or long-distance migration. All nodes that have no assignment were classified as non-migratory with probabilities of more than 95%. The common ancestor for P. nathusii, pipistrellus, and permixtus is reconstructed as long-distance migrant as is the common ancestor for Lasiurus cinereus, L. borealis, L. seminolus, L. castaneus, L. ega, and L. intermedius.