Correlation of skull morphology and bite force in a bird-eating bat (Ia io; Vespertilionidae)

Behavioral innovation and genomic novelty are associated with the exploitation of a challenging dietary opportunity by an avivorous bat

Foraging on nocturnally migrating birds is one of the most challenging foraging tasks in the animal kingdom. Only three bat species (e.g., Ia io) known to date can prey on migratory birds. However, how these bats have exploited this challenging dietary niche remains unknown. Here, we demonstrate that I. io hunts at the altitude of migrating birds during the bird migration season. The foraging I. io exhibited high flight altitudes (up to 4945 m above sea level) and high flight speeds (up to 143.7 km h⁻¹). I. io in flight can actively prey on birds in the night sky via echolocation cues. Genes associated with DNA damage repair, hypoxia adaptation, biting and mastication, and digestion and metabolism have evolved to adapt to this species’ avivorous habits. Our results suggest that the evolution of behavioral innovation and genomic novelty are associated with the exploitation of challenging dietary opportunities.

•

Predation on nocturnally migrating birds is rare and challenging in nature

•

Bats exhibit high flight altitude and speed associated with foraging on migrating birds

•

Bats can actively prey on birds in the night sky via echolocation cues

•

The adaptive evolution of genes enables bats to adapt to the avivorous habits

Skull Morphology, Bite Force, and Diet in Insectivorous Bats from Tropical Dry Forests in Colombia

In Neotropical bats, studies on bite force have focused mainly on differences in trophic ecology, and little is known about whether factors other than body size generate interspecific differences in bite force amongst insectivorous bats and, consequently, in their diets. We tested if bite force is related to skull morphology and also to diet in an assemblage of Neotropical insectivorous bats from tropical dry forests in the inter-Andean central valley in Colombia. It is predicted that the preference of prey types among insectivorous species is based on bite force and cranial characteristics. We also evaluated whether skull morphology varies depending on the species and sex. Cranial measurements and correlations between morphological variation and bite force were examined for 10 insectivorous bat species. We calculated the size-independent mechanical advantage for the mandibular (jaw) lever system. In all species, bite force increased with length of the skull and the jaw more than other cranial measurements. Obligate insectivorous species were morphologically different from the omnivorous Noctilio albiventris, which feeds primarily on insects, but also consumes fish and fruits. Our results show that bite force and skull morphology are closely linked to diets in Neotropical insectivorous bats and, consequently, these traits are key to the interactions within the assemblage and with their prey.

Foraging strategies, craniodental traits, and interaction in the bite force of Neotropical frugivorous bats (Phyllostomidae: Stenodermatinae)

Bats in the family Phyllostomidae exhibit great diversity in skull size and morphology that reflects the degree of resource division and ecological overlap in the group. In particular, the subfamily Stenodermatinae has high morphological diversification associated with cranial and mandibular traits that are associated with the ability to consume the full range of available fruits (soft and hard).We analyzed craniodental traits and their relationship to the bite force in 343 specimens distributed in seven species of stenodermatine bats with two foraging strategies: nomadic and sedentary frugivory. We evaluated 19 traits related to feeding and bite force in live animals by correcting bite force with body size.We used a generalized linear model (GLM) and post hoc tests to determine possible relationships and differences between cranial traits, species, and sex. We also used Blomberg's K to measure the phylogenetic signal and phylogenetic generalized least-squares (PGLS) to ensure the phylogenetic independence of the traits.We found that smaller nomadic species, A. anderseni and A. phaeotis , have a similar bite force to the large species A. planirostris and A. lituratus; furthermore, P. helleri registered a bite force similar to that of the sedentary bat, S. giannae. Our study determined that all the features of the mandible and most of the traits of the skull have a low phylogenetic signal. Through the PGLS, we found that the diet and several cranial features (mandibular toothrow length, dentary length, braincase breadth, mastoid breadth, greatest length of skull, condylo-incisive length, and condylo-canine length) determined bite force performance among Stenodermatiane.Our results reinforce that skull size is a determining factor in the bite force, but also emphasize the importance of its relationships with morphology, ecology, and phylogeny of the species, which gives us a better understanding of the evolutionary adaptions of this highly diverse Neotropical bat group.

Who's for dinner? Bird prey diversity and choice in the great evening bat, Ia io

The mysterious predator-prey interaction between bats and nocturnally migrating birds is a very rare and incredible process in natural ecosystems. So far only three avivorous bat species, including two noctule bats (Nyctalus lasiopterus and Nyctalus aviator) and the great evening bat (Ia io), are known to regularly prey on songbirds during nocturnal avian migration. The information related to the diversity and the characteristics of the birds as prey and the hunting strategy in both species of noctule bats are already clear. However, the diversity of bird prey in the diet of I. io as confirmed by molecular identification remains unknown. Moreover, like hunting insects, it remains unclear whether the avivorous bats opportunistically prey on birds. Here, we used DNA metabarcoding to investigate the bird prey composition, diversity, and choice in diets of I. io. We found I. io consumed 22 species of seven families from Passeriformes with a body mass of 6-19 g, and preferentially selected small-sized passerine birds for optimizing the benefit/risk trade-off. Moreover, most of the species preyed upon were migratory birds, while four species were local resident birds, indicating that I. io may adopt both aerial-hawking and gleaning strategies on songbirds as do the other two noctules. Further, I. io body mass did not influence in prey choice and predation richness on birds, suggesting I. io is an opportunistic avivorous predator. This study provides novel insights into the avian dietary ecology of I. io and completes the analysis of predator/prey interaction between three avivorous bats and nocturnally migrating birds. Our results also indicate bat predation on birds which occurs as an act of ecological opportunity may subject bats to intense natural selection pressure, causing them access to the new diet-defined adaptive zones.

Great Evening Bat Ia io (Vespertilionidae, Chiroptera) from the Pleistocene of Vietnam (Lang Trang Cave)

A dentary fragment of a great evening bat Ia io Thomas, 1902 found in 2020 in the Pleistocene deposits of the Lang Trang karstic cave in northern Vietnam is described. This rare species of large tropical bats now inhabits Nepal, eastern India, southern China, Thailand, Laos, and Vietnam and as a fossil is known from the Pleistocene of China. In Vietnam the fossil remains of this species have been discovered for the first time. By the total size and lower molar structure, the specimen from the Lang Trang cave is most similar to the subspecies Ia io peninsulata Soisook et al., 2017 that now occurs in southern Thailand.