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1

Community level support for the allotonic frequency hypothesis

100%
Jacobs D. S.
Acta Chiropterologica
|
2000
|
tom 02
|
nr 2
The allotonic frequency hypothesis proposes that some insectivorous bats increase their access to moths that can hear echolocation calls by using frequencies to which the ears of the moths are less sensitive. The hypothesis predicts that the frequencies of bat echolocation calls are positively correlated with the incidence of moths in the diet of these bats. Studies that have provided evidence in support of the allotonic frequency hypothesis have relied on data collected by a number of researchers, in a number of different ways and at different times. The aim of this study was to test the allotonic frequency hypothesis on a single African bat community so that data for the different species could be collected at more or less the same time and in the same way. This community consisted of three high duty cycle species, Cloeotis percivali, Hipposideros caffer, and Rhinolophus simulator, and two low duty cycle species, Miniopterus schreibersii and Scotophilus borbonicus. As predicted by the hypothesis, echolocation frequency was positively correlated with the proportion of moths in the diet of these bats. Echolocation frequency was also a better predictor of diet than wing morphology suggesting that the selection pressure exerted by moth hearing might have acted directly on call frequency and secondarily on wing morphology, as part of the same adaptive complex. These results suggest that structure of bat communities might be determined by prey defenses rather than by competition.
2

Intraspecific variation in wingspan and echolocation call flexibility might explain the use of different habitats by the insectivorous bat, Miniopterus schreibersii (Vespertilionidae; Miniopterinae

100%
Jacobs D. S.
Acta Chiropterologica
|
1999
|
tom 01
|
nr 1
3

Factors influencing the emergence times of sympatric insectivorous bat species

63%
Thomas A. J., Jacobs D. S.
Acta Chiropterologica
|
2013
|
tom 15
|
nr 1
The onset of activity in animals restricted to being active for only part of the day is one of the most fundamental aspects of their biology because it marks the beginning of activities that they need to do to survive and reproduce. Initiation of activity is subject to several factors including presence/absence of predators and the vagaries of environmental conditions at the time of emergence. We tested if the emergence times amongst seven species of sympatric insectivorous bats were explained by predation risk, insect activity and weather conditions. We measured bat emergence times by recording echolocation calls. Peak emergence was correlated with body size, time of sunset, foraging strategy and diet, factors associated with risk of predation. Larger, faster flying bat species emerged earlier than smaller, slower flying species suggesting the former relied on flight speed to avoid predation. Clutter foragers emerged earlier than clutter-edge and open foragers, suggesting that vegetative cover is important for bats trying to avoid predation. Bats feeding on Lepidoptera emerged earlier than bats feeding on Diptera. However, insect peak activity was highly variable and did not differ between orders or time of season. Emergence time was not correlated with any of the weather variables we measured. These results suggest that predation influences fundamental aspects of the biology and ecology of insectivorous bats by determining when it is safe to become active.
4

Evaluation of maternal features as indicators of asynchronous embryonic development in Miniopterus natalensis

51%
Mason M. K., Hockman D., Jacobs D. S., Illing N.
Acta Chiropterologica
|
2010
|
tom 12
|
nr 1
The timing of early reproductive events for the Natal long-fingered bat, Miniopterus natalensis, was examined during its breeding season (August to December) in its maternity roost at the De Hoop Nature Reserve (South Africa). This migrating species is monoestrous with copulation occurring around April in South African populations. Embryonic development is stalled during hibernation by delayed implantation of the blastocyst. As a result, limb bud stage embryos (CS13) are first noted in other South African populations in mid-September. The timing of these reproductive events for the De Hoop population is similar with bats arriving at the maternity roosts in September and embryos at the limb bud stage (CS13) being noted in this month. Pregnancy was not synchronous in the population with bats dissected on the same day exhibiting differences in the stage of development of their young (CS11 to CS21 being the largest range). Maternal features (progesterone concentration, body mass and abdominal distension) were analysed to determine if they provided a reliable estimate of embryonic stage. The progesterone concentrations of pregnant bats showed a similar profile to the Kwa-Zulu Natal and the Eastern Cape populations. Though progesterone concentration did increase as pregnancy progressed, it was not an accurate predictor of embryonic stage. Maternal body mass did not correlate with the stage of embryonic development. However, abdominal distension determined by palpation is an accurate field based predictor of the stages of pregnancy: no abdominal distension, small to medium abdominal distension and large abdominal distension distinguished between non-pregnant bats and those carrying either early (CS11–CS15) or mid-developmental stages (CS16–CS21), respectively.
5

Genetic similarity amongst phenotypically diverse little free-tailed bats, Chaerephon pumilus

51%
Jacobs D. S., Eick G. N., Richardson E. J., Taylor P. J.
Acta Chiropterologica
|
2004
|
tom 06
|
nr 1
The African molossid Chaerephon pumilus shows extensive variation in colour, size and echolocation across its wide distributional range with a light-winged form in north-eastern Africa and a dark form in southern Africa. There is also much variation in supposedly diagnostic characters (e.g., degree of palatial emargination) amongst the dark form of this species in southern Africa. These differences suggest that there may be cryptic species within C. pumilus. We used phylogenetic and phenetic analyses of sequence data from the mitochondrial cytochrome-b gene of a number of C. pumilus individuals to investigate the status of the light and dark-winged forms of this species and to evaluate the possibility of cryptic species within the dark-winged form of C. pumilus in southern Africa. We evaluated species status by comparing the level of sequence divergence amongst C. pumilus with the level of sequence divergence between known species in the genus. These included C. ansorgei, C. chapini, C. nigeriae and C. jobensis. Intrageneric sequence divergences among the Chaerephon spp. included here ranged from 6.51 to 11.18%, whereas the average sequence divergence between the light and dark forms was 0.9%. This suggests that these two forms are not distinct species. Individuals of the dark form of C. pumilus were genetically indistinguishable from each other having the same cytochrome b haplotype. We thus found no evidence of cryptic species in southern African C. pumilus.
6

Phylogeny of African Myotis bats (Chiroptera, Vespertilionidae) inferred from cytochrome b sequences

51%
Stadelmann B., Jacobs D. S., Schoeman C., Ruedi M.
Acta Chiropterologica
|
2004
|
tom 06
|
nr 2
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.
7

Foraging and roosting ecology of a rare insectivorous bat species, Laephotis wintoni (Thomas, 1901), Vespertilionidae

51%
Jacobs D. S., Barclay R. M. R., Corrie Schoeman M.
Acta Chiropterologica
|
2005
|
tom 07
|
nr 1
Laephotis wintoni is a rare bat and little is known about its biology. We studied this species at Algeria Forestry Station in the Western Cape Province, South Africa. A female caught in November 2002 was pregnant and three females caught in November 2004 were all lactating. The three lactating females were radio tagged and roosted in crevices or narrow fissures in a cliff face above the valley where they foraged. Laephotis wintoni is a small insectivorous bat (body mass, x̄ ± SD = 9.6 ± 0.5 g, n = 4) with low wing loading (7.0 ± 0.7 Nm−2, n = 4), low aspect ratio (5.7 ± 0.5, n = 4), low wingtip shape index (1.2 ± 0.2, n = 4) and long ears (20.9 ± 2.3 mm, n = 2). Its morphology suggests that it is a slow manoeuvrable flyer that can fly close to vegetation, or the ground or over water surfaces. Its relatively pointed wings suggest that it probably does not fly in dense clutter. Furthermore, it combines this wing shape with echolocation calls of relatively low intensity, short duration (2.6 ± 0.8 ms, n = 5), narrow band (13.5 ± 2.9 kHz, n = 5) and surprisingly low peak frequency (22.1 ± 0.6 kHz, n = 5). The latter two parameters make it unlikely that the calls are used to overcome masking effects associated with flying in dense clutter. Instead, we propose that its echolocation calls are adapted to be less audible to tympanate insects. This is supported by the fact its diet is dominated by moths in a habitat where tympanate moths comprise 90% of the moth population.
8

Deliberate insectivory by the fruit bat Rousettus aegyptiacus

51%
Barclay R. M. R., Barclay L. E., Jacobs D. S.
Acta Chiropterologica
|
2006
|
tom 08
|
nr 2
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