David S. Jacobs

Strong population substructure is correlated with morphology and ecology in a migratory bat.

Examining patterns of inter-population genetic diversity can provide valuable information about both historical and current evolutionary processes affecting a species. Population genetic studies of flying and migratory species such as bats and birds have traditionally shown minimal population substructure, characterized by high levels of gene flow between populations. In general, strongly substructured mammalian populations either are separated by non-traversable barriers or belong to terrestrial species with low dispersal abilities. Species with female philopatry (the tendency to remain in or consistently return to the natal territory) might show strong substructure when examined with maternally inherited mitochondrial DNA, but this substructure generally disappears when biparentally inherited markers are used, owing to male-mediated gene flow. Male-biased dispersal is considered typical for mammals, and philopatry in both sexes is rare. Here we show strong population substructure in a migratory bat species, and philopatry in both sexes, as indicated by concordance of nuclear and mtDNA findings. Furthermore, the genetic structure correlates with local biomes and differentiation in wing morphology. There is therefore a close correlation of genetic and morphological differentiation in sympatric subspecific populations of this mammalian species.

Phylogeny of African Myotis Bats (Chiroptera, Vespertilionidae) Inferred from Cytochrome b Sequences

The genus Myotis is comprised of about 100 species that are unequally distributed between the Northern (81% of the species) and the Southern hemisphere (19% of the species). Only eight species of Myotis occur in the Ethiopian region, but this is the only biogeographic region with representatives of all four classical subgenera, suggesting a diverse assemblage of morphotypes. We used sequences of a mitochondrial DNA gene (cyt b) to investigate the evolution and the phylogenetic position of seven of the eight Ethiopian species, and compared them to a broad sampling of Myotis from the World and of other vespertilionids. Phylogenetic reconstruction was based on 91 complete sequences representing 79 species of bats. The two endemic southern African species of the subgenus Cistugo were not placed within the genus Myotis, but were basal to the vespertilionid radiation, as suggested by earlier work based on karyology. The remaining Ethiopian species formed a strong monophyletic clade within Myotis, further stressing the importance of biogeography as a good predictor of phylogenetic relationships. This Ethiopian clade includes one Western Palaearctic and one Oriental species, both of which probably secondarily colonized these areas from the Ethiopian region. Molecular dating based on Bayesian inferences suggest that these faunal exchanges occurred at the end of the Miocene, while the split of the Ethiopian clade from the other Old World Myotis dates back to the middle Miocene, quite early in the Myotis radiation. Thus, the relative paucity of species in sub-Saharan Africa cannot be attributed to a late entry into this continent. Instead, these molecular results suggest that other evolutionary processes are responsible for the poor species diversity of Myotis found in Africa today.

The allometry of echolocation call frequencies of insectivorous bats: why do some species deviate from the pattern?

The peak echolocation frequency of insectivorous bats generally declines as body size increases. However, there are notable exceptions to this rule, with some species, such as Rhinolophus clivosus, having a higher than expected peak frequency for their body size. Such deviations from allometry may be associated with partitioning of foraging habitat (the foraging habitat hypothesis) or insect prey (the prey detection hypothesis). Alternatively, the deviations may be associated with the partitioning of sonar frequency bands to allow effective communication in a social context (the acoustic communication hypothesis). We tested the predictions of these hypotheses through comparisons at the family, clade and species level, using species of rhinolophids in general and R. clivosus, a species with a wide distribution, as a specific test case. We compared the wing parameters, echolocation frequency and ecology of R. clivosus to those of the sympatric R. capensis. Rhinolophus clivosus has a much higher echolocation frequency than predicted from its wing loading or body mass. Furthermore, contrary to the predictions of the foraging habitat hypothesis, we found no difference in foraging habitat between R. clivosus and R. capensis. The size range of insect prey taken by the two species also overlapped almost completely, contrary to the prey detection hypothesis. On the other hand, the variation of echolocation frequencies around the allometric relationship for rhinolophids was smaller than that for Myotis spp., supporting the prediction of the acoustic communication hypothesis. We thus propose that the relatively high peak frequency of R. clivosus is the result of partitioning of sonar frequency bands to minimize the ambiguity of echolocation calls during social interactions.

A second wave of Sonic hedgehog expression during the development of the bat limb

Sonic hedgehog (Shh) plays an integral role in both the anterior-posterior (A-P) patterning and expansion of developing vertebrate limbs through a feedback loop involving Fgfs, Bmps, and Gremlin. In bat limbs A-P patterning and the size of the digital field are unique. The posterior digits of the forelimb are elongated and joined by tissue, whereas the thumb is short. The hindlimb digits often are uniform in length. Here, we reveal novel expression patterns for Shh and its target, Patched 1 (Ptc1), during limb development in two bat species. Early Shh expression in the zone of polarizing activity is wider in the bat forelimb than in the mouse forelimb, correlating with the reported expansion of Fgf8 expression in the apical ectodermal ridge and the early loss of symmetry in the bat forelimb. Later in limb development, Shh and Ptc1 expression is reinitiated in the interdigital tissue. Shh is graded along the A-P axis in forelimb and is expressed uniformly at a lower level across the hindlimb interdigital tissue. We also show that the reported Fgf8 expression in the interdigital tissue precedes the expression of Shh. We propose that the reinitiation of Shh and Fgf8 expression in bat limbs reactivates the Shh-Fgf feedback loop in the interdigital tissue of stage 16 bat embryos. The cell survival and proliferation signals provided by the Shh-Fgf signaling loop probably contribute to the lengthening of the posterior forelimb digits, the survival of the forelimb interdigital webbing, and the extension of the hindlimb digits to a uniform length.

Individual signatures in the frequency‐modulated sweep calls of African large‐eared, free‐tailed bats Otomops martiensseni (Chiroptera: Molossidae)

Frequency-modulated sweep calls of Otomops martiensseni were recorded from individuals as they emerged from nine different building roosts near Durban, South Africa. Multiple analyses of call features, including duration (ms), lowest frequency (kHz), highest frequency (kHz) and frequency with most energy (kHz), indicated significant inter-individual variation. Discriminant function analysis of call features correctly classified the calls of individuals from four roosts > 70% on 19 of 28 times. Although other species of molossids ( Chaerephon pumilus , Tadarida aegyptiaca , and one unidentified species) produced social calls as well as frequency-modulated sweep calls, O. martiensseni produced just the latter vocalizations and they were longer and lower in frequency than those of the sympatric molossids. Other species of molossids, but not O. martiensseni , produced feeding buzzes as they attacked flying insects. The frequency-modulated sweep calls of O. martiensseni seem to serve a communication function, but they may not be used in echolocation unlike similar calls by other molossids. Individually distinct communication signals (frequency-modulated sweep calls) enhance communication in a species that lives in year-round social groups (one adult male, females and dependent young).

GENETIC AND PHENOTYPIC DIFFERENCES BETWEEN SOUTH AFRICAN LONG-FINGERED BATS, WITH A GLOBAL MINIOPTERINE PHYLOGENY

Abstract The Natal long-fingered bat (Miniopterus natalensis) and lesser long-fingered bat (M. fraterculus) are morphologically almost indistinguishable and occur sympatrically over much of their southern African range. This raises the possibility that they are sister taxa. We employed a multidisciplinary approach to examine their taxonomic relationship to one another and to other Miniopterus species, whose global phylogeny requires review. We examined echolocation, morphological, and dietary differences between M. natalensis and M. fraterculus, as well as both nuclear and mitochondrial DNA variation between them in the context of a phylogeny incorporating 13 Miniopterus species and subspecies. Despite similarities in their morphology and distribution, M. natalensis and M. fraterculus echolocate at peak frequencies separated by 12 kHz, and both nuclear and mitochondrial DNA markers confirm they are distinct species. Analysis of cytochrome-b (Cytb) sequences further indicates that M. fraterculus and M. natalensis are not sister taxa; M. fraterculus appears to be more closely related to the greater long-fingered bat (M. inflatus). Examination of the global taxonomy of Miniopterus confirms that Schreiberss long-fingered bat (M. schreibersii) forms a paraphyletic species complex. Furthermore, the miniopterine bats are divided into 2 geographically isolated monophyletic groups, one containing African and European species, and the other taxa from Australasia and Asia. Cytb sequence divergence also suggests that M. natalensis is distinct from the European M. schreibersii. These results support the elevation of M. natalensis to full species rank.

Support for the allotonic frequency hypothesis in an insectivorous bat community.

Abstract. The allotonic frequency hypothesis proposes that certain insectivorous bat species can prey upon moths that can hear bat echolocation calls by using echolocation frequencies outside the sensitivity range of moth ears. The hypothesis predicts that the peak frequencies of bat echolocation calls are correlated with the incidence of moths in the diets of these bats. The aim of this study was to test this prediction on a bat community dominated by bats using low duty cycle echolocation calls, i.e. aerial foraging, insectivorous species using frequency modulated calls. The community consisted of nine species, two molossids, Sauromys petrophillus and Tadarida aegyptiaca, five vespertilionids, Eptesicus capensis, Eptesicus hottentotus, Miniopteris schreibersii, Myotis tricolor, and Myotis lesueuri, one rhinolophid, Rhinolophus clivosus, and one nycterid, Nycteris thebaica. The insect fauna in the habitat used by the bat community was suited to the testing of the allotonic frequency hypothesis because more than 90% of the moths comprising the insect fauna were tympanate. These included Pyralidae (3.8%), Geometridae (44.9%), Notodontidae (3.8%), Arctiidae (4.6%), Lymantriidae (0.8%) and Noctuidae (32.4%). As predicted, peak echolocation frequency was correlated with the incidence of moths in the diets of these nine species (r=0.98, df=7, P<0.01). Furthermore, multivariate analysis revealed that echolocation frequency (t=9.91, n=129, P<0.001) was a better predictor of diet than forearm length (t=5.51, n=129, P<0.001) or wing area (t=–3.41, n=129, P<0.001). This suggests that the selection pressure exerted by moth hearing might have acted directly on call frequency and secondarily on body size and wing morphology, as part of the same adaptive complex. It is unlikely that dietary differences were due to temporal and spatial differences in the availability of prey because the pattern of differences in skull morphology of the nine species supported our dietary analyses. The skull morphology of a bat represents a historical record of the kind of diet it has become adapted to over its evolutionary history. These results suggest that prey defences may mediate other factors structuring bat communities, e.g. competition. Competition may be reduced for those species of bats that can circumvent prey defences.

Molecular phylogenetics and historical biogeography of Rhinolophus bats.

The phylogenetic relationships within the horseshoe bats (genus Rhinolophus) are poorly resolved, particularly at deeper levels within the tree. We present a better-resolved phylogenetic hypothesis for 30 rhinolophid species based on parsimony and Bayesian analyses of the mitochondrial cytochrome b gene and three nuclear introns (TG, THY and PRKC1). Strong support was found for the existence of two geographic clades within the monophyletic Rhinolophidae: an African group and an Oriental assemblage. The relaxed Bayesian clock method indicated that the two rhinolophid clades diverged approximately 35 million years ago and results from Dispersal Vicariance (DIVA) analysis suggest that the horseshoe bats arose in Asia and subsequently dispersed into Europe and Africa.

Auditory encoding during the last moment of a moth's life

SUMMARY The simple auditory system of noctuoid moths has long been a model for anti-predator studies in neuroethology, although these ears have rarely been experimentally stimulated by the sounds they would encounter from naturally attacking bats. We exposed the ears of five noctuoid moth species to the pre-recorded echolocation calls of an attacking bat (Eptesicus fuscus) to observe the acoustic encoding of the receptors at this critical time in their defensive behaviour. The B cell is a non-tympanal receptor common to all moths that has been suggested to respond to sound, but we found no evidence of this and suggest that its acoustic responsiveness is an artifact arising from its proprioceptive function. The A1 cell, the most sensitive tympanal receptor in noctuid and arctiid moths and the only auditory receptor in notodontid moths, encodes the attack calls with a bursting firing pattern to a point approximately 150 ms from when the bat would have captured the moth. At this point, the firing of the A1 cell reduces to a non-bursting pattern with longer inter-spike periods, suggesting that the moth may no longer express the erratic flight used to escape very close bats. This may be simply due to the absence of selection pressure on moths for auditory tracking of bat echolocation calls beyond this point. Alternatively, the reduced firing may be due to the acoustic characteristics of attack calls in the terminal phase and an acoustic maneuver used by the bat to facilitate its capture of the moth. Although the role of less sensitive A2 cell remains uncertain in the evasive flight responses of moths it may act as a trigger in eliciting sound production, a close-range anti-bat behaviour in the tiger moth, Cycnia tenera.

The relative influence of competition and prey defenses on the phenotypic structure of insectivorous bat ensembles in southern Africa

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals such as insectivorous bats that have life histories characterized by low fecundity, low predation risk, long life expectancy, and stable populations. We investigated the relative influence of these two deterministic filters on the phenotypic structure of insectivorous bat ensembles in southern Africa. We used null models to simulate the random phenotypic patterns expected in the absence of competition or prey defences and analysed the deviations of the observed phenotypic pattern from these expected random patterns. The phenotypic structure at local scales exhibited non-random patterns consistent with both competition and prey defense hypotheses. There was evidence that competition influenced body size distribution across ensembles. Competition also influenced wing and echolocation patterns in ensembles and in functional foraging groups with high species richness or abundance. At the same time, prey defense filters influenced echolocation patterns in two species-poor ensembles. Non-random patterns remained evident even after we removed the influence of body size from wing morphology and echolocation parameters taking phylogeny into account. However, abiotic filters such as geographic distribution ranges of small and large-bodied species, extinction risk, and the physics of flight and sound probably also interacted with biotic filters at local and/or regional scales to influence the community structure of sympatric bats in southern Africa. Future studies should investigate alternative parameters that define bat community structure such as diet and abundance to better determine the influence of competition and prey defences on the structure of insectivorous bat ensembles in southern Africa.