OpenUCT :: Browsing by Author "Jacobs, David S"

Browsing by Author "Jacobs, David S"

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Animal personality and biological markets: rise of the individual
(2009) Jacobs, David S
The last decade has seen the emergence of two new developments in behavioural ecology: the discovery of animal personalities and a new approach to the analyses of animal behaviour, biological markets. Although both regard individual differences in behaviour as adaptive in their own right, these two developments appear, at first glance, to be opposing approaches to analysing animal behaviour. Personalities consist of suites of behaviours that are correlated across situations (e.g. some animals are consistently more or less aggressive across situations than other animals) and assumes that animals are limited in their response to their environment. By contrast, the biological market approach considers organisms as traders of commodities (e.g. food or grooming) where the exchange rates of commodities changes with time and is influenced by shifts in the abundance and demand for the commodity, as happens in human markets. Biological markets thus view animal behaviour as extremely plastic whereas the putative existence of animal personalities suggests that animal behaviour may be relatively inflexible. However, the two approaches may be more similar than heretofore realized and may be complementary rather than opposing. Here I briefly review each approach and show how animal personalities can arise from a biological market situation.
Open Access
Behavioural evidence for the perception of individual identity and gender via the echolocation calls of a high duty cycle bat, Rhinolophus clivosus
(2015) Finger, Nikita Maxine; Jacobs, David S; Bastian, Anna
Different cognitive processes underlie the perception of vocalizations in many mammals, including humans. This perception now extends to a highly specialized form of sonar called echolocation. In habituation-dishabituation experiments, a high duty cycle echolocating bat, Rhinolophus clivosus, dishabituated significantly when echolocation calls of a different gender or individual were played to the habituation. Strong individual and gender signatures but weak geographic signatures were found in both the CF and FM components of their echolocation calls. In the individual discrimination trials reactions were more pronounced to an individual that was less acoustically similar to the habituation than to one that was more similar. Bats reacted to playbacks with a variety of social behaviours. Prior to the analysis of the experiment an ethogram was done on three groups of captive R. clivosus bats. This ethogram was used to categorize the behavioural responses of these bats to the acoustic stimuli in the experiments. The reactions to the habituation-dishabituation experiments show bats perceive gender and individual-specific signatures found in their conspecifics echolocation calls. This is the first study to show behavioural evidence for individual discrimination and second to show gender discrimination of echolocation calls in high duty cycle bats. This evidence supports the theory that echolocation, a system thought to have evolved solely for orientation and foraging, has been coopted for intra-specific communication and mate recognition in bats.
Open Access
Characterization of transcripts expressed from the Meis2 locus in the Natal Long-fingered bat (Miniopterus natalensis)
(2014) Curry, Lyle; Illing, Nicola; Jacobs, David S
The Myeloid ecotropic insertion site 2 (Meis2) gene is an important transcriptional regulator involved in the pattering of the limb during vertebrate development. In the forelimbs (wings) of bats the expression Meis2 was shown to be differentially expressed when compared to mice forelimbs. Meis2 was found to be present in the interdigital webbing of the autopod (hand) of the developing bat forelimb. In both the mouse and the bat, two separate transcripts were discovered to be expressed from the 3’and 5’ region of the Meis2 locus. The 3’ transcripts corresponded to annotated Meis2 mRNA transcripts, the 5’ transcript corresponded to an mRNA transcript that did not code for any known protein. The 5’ transcript was thought to be a long non-coding RNA and was termed lncMeis2. In this study Random Amplification of cDNA Ends (RACE) analysis was used to identify the RNA transcripts expressed from the Meis2 locus and to verify the presence of lncMeis2. RACE was performed on the heads and forelimbs of the Natal Long-fingered bat (Miniopterus natalensis) and the mouse (Mus musculus) and the products sequenced and aligned to the mouse genome for verification.
Open Access
Cross-species microarray analysis of limb development in the bat, Miniopterus natalensis
(2009) Mason, Mandy K; Jacobs, David S; Illing, Nicola
This study reports the first characterisation of the embryonic bat limb transcriptome, allowing the identification of novel candidate genes that were differentially expressed between the bat hand and foot plate. These genes may have played important roles in the evolution of the bat wing and hindlimb. The reproduction and development of an African bat species, Miniopterus natalensis, was characterised and three maternal features (mass, belly size and plasma progesterone levels) examined as potential predictors of embryonic stages of development. Belly palpitation was found to be a useful field method to distinguish between non-pregnancy, early development or late development in female bats. A microarray analysis between the hand and foot plates of CS 16 and CS 17 bat embryos, and the hand plates of E 13.5 mouse embryos, revealed high correlation between the transcriptomes of the bat autopods and the mouse hand plate (r > 0.88) and among all the bat autopods (r > 0.98). However, ten genes were found to be differentially expressed in both the CS 16 and the CS 17 bat hand plate as compared to the mouse hand plate while only three genes were identified as being significantly differentially expressed between bat foot plates and mouse hand plates. A comparison between the bat hand and foot plates identified fifteen genes that were differentially expressed at the stage CS 17 stage and six at the stage CS 16. Closer examination of gene families involved in limb development revealed novel expression of genes in the retinoic acid (RA) pathway, and the Hoxd family. This included the apparent co- regulation of the 5' Hoxd genes (Hoxd10, 11, 12 and 13). Of the genes characterised in bat limb development (Hoxd13, Bmp2, Fgf8 and Prrxl), higher mRNA transcript levels in the CS 17 bat hand plate relative to the mouse hand plate was found for Hoxd13 (FC = 2.6) and Prrxl (FC = 1.8). These differences were also found in a comparison to the CS 17 bat foot plate (Hoxd13: FC = 1.4; Prrxl: FC = 1.4). A potentially novel transcript of Meis2, a gene important in specifYing the proximal-distal (P-D) axis of the limb, was noted for its high fold changes in the bat hand plate as compared the foot plate (CSI7: FC = 7.0; CSI6: FC = 2.2) and the mouse hand plate (FC = 13.1).
Open Access
The defensive role of ultrasonic moth clicks against bat predation : a mathematical modeling approach
(2007) Ribeiro, Daniel De Lemos; Jacobs, David S; Govender, A
Some moths emit ultrasonic clicks in response to bat echolocation calls. These clicks are believed to serve as a defence mechanism against bat predation by means of jamming, aposematism or startle. By assessing the characteristics and variation of the ultrasonic moth clicks it was possible to define the most likely function of the ultrasonic clicks by moths from sites in South Africa. Additionally, this study used Schaefer based mathematical models informed by field data on moth diversity and abundance, moth click parameters and bat population numbers and diversity, from these same sites in South Africa, to gain insight into the conditions that are required for each of these functions to work. The Jamming hypothesis proposes that moth clicks function by interfering with the bat's perceptual system, which is believed to be most effective in the terminal phase of the bat's attack were the clicks have been shown to be the most similar to the bats echolocation calls. This would place functional constraints on the clicks, decreasing the variation in the clicks. This was shown not to be the case, as a high level of variation was found between species' clicking parameters (e.g. peak frequency, inter pulse interval and intensity). A high level of individual moth variation was also found, with numerous patterns being produced by the same moths. Clicking variation was created both by manipulation of individual tymbals (e.g. changes in modulation cycle rate and durations) and between tymbals (e.g. timing of tymbal alternation). Furthermore the moth clicks are too different to bat echolocation calls to allow them to be mistaken by the bat as echoes from its own calls. The aposematic hypothesis suggests that the clicks function as a warning signal to inform the predator of the prey's unpalatability. As in visual based aposematism, the cost of. predator learning on the prey population would exert selective pressure towards higher densities of clicking moths and convergence in warning signals. This would allow one species to benefit from the predator learning induced by another species. This strategy is thus density dependent and would require a minimum proportion of clicking moths to work. Both the data from the ultrasonic moth clicks and mathematical modelling does not support this hypothesis as there is no signs of convergence and the mathematical modelling suggests that the low proportion of clicking moths (2.3%) in the natural moth population does not allow bats to form the association between moth clicks and noxiousness of the moth. In the case of jamming, the low proportion of clicking moths also does not reflect the competitive advantage supposedly gained from jamming. The startle hypothesis proposes that moth clicks confuse the bat by altering the normal sequence of expected events during the bat's attack. However, bats will habituate to these sounds if they are encountered regularly. Both the low proportions of clicking moths and the extreme variability of the click patterns hinder habituation and are consistent with the startle hypothesis, which suggest that the most likely function of ultrasonic moth clicks in these South African sites is startle. On the other hand, the aposematic and startle models do suggest that the existence of both noxiousness and clicking create the initial conditions for the evolution of an aposematic function for moth clicks. If the clicking moth is noxious the startle effect of the clicking could allow the population to grow to high enough numbers to make the aposematic function of the clicks viable.
Open Access
Ecomorphological differences between sister species, Rhinolophus capensis and Rhinolophus swinnyi
(2008) Kelly, Elizabeth Jane; Jacobs, David S
Phenotypic analyses of sibling species provide the opportunity to examine divergence that is caused by adaptation rather than phylogenetic history. Rhinolophus capensis and Rhinolophus swinnyi diverged from a common ancestor between 15 and 20 million years ago. The Fynbos biome of the south-western Cape (South Africa) arose around the same time, and its distribution is coincident with that of R. capensis. Since this event probably influenced the speciation of these species, I examine differences in the ecomorphology of these bats in their current distributions. R. capensis is bigger than R. swinnyi, with corresponding differences in echolocation call signatures and wing morphology.
Open Access
Environmental correlates of geographic divergence in a phenotypic trait: A case study using bat echolocation
(Wiley, 2017-06-28) Maluleke, Tinyiko; Jacobs, David S; Winker, Henning
Divergence in phenotypic traits may arise from the interaction of different evolutionary forces, including different kinds of selection (e.g., ecological), genetic drift, and phenotypic plasticity. Sensory systems play an important role in survival and reproduction, and divergent selection on such systems may result in lineage diversification. Such diversification could be largely influenced by selection in different environments as a result of isolation by environment (IbE). We investigated this process using geographic variation in the resting echolocation frequency of the horseshoe bat species, Rhinolophus damarensis, as a test case. Bats were sampled along a latitudinal gradient ranging from 16°S to 32°S in the arid western half of southern Africa. We measured body size and peak resting frequencies (RF) from handheld individual bats. Three hypotheses for the divergence in RF were tested: (1) James’ Rule, (2) IbE, and (3) genetic drift through isolation by distance (IbD) to isolate the effects of body size, local climatic conditions, and geographic distance, respectively, on the resting frequency of R. damarensis. Our results did not support genetic drift because there was no correlation between RF variation and geographic distance. Our results also did not support James’ Rule because there was no significant relationship between (1) geographic distances and RF, (2) body size and RF, or (3) body size and climatic variables. Instead, we found support for IbE in the form of a correlation between RF and both region and annual mean temperature, suggesting that RF variation may be the result of environmental discontinuities. The environmental discontinuities coincided with previously reported genetic divergence. Climatic gradients in conjunction with environmental discontinuities could lead to local adaptation in sensory signals and directed dispersal such that gene flow is restricted, allowing lineages to diverge. However, our study cannot exclude the role of processes like phenotypic plasticity in phenotypic variation.
Open Access
Environmental factors influencing the distribution of bats (Chiroptera) in South Africa
(2012) Salata, Hassan Aburaida Babiker; Jacobs, David S
Environmental factors limiting the distribution of 37 of the 56 bat species in a warm temperate region (South Africa) were determined using GIS software and the Maximum Entropy modelling technique (MaxEnt). Undertaking such a study in a warm temperate region like South Africa is essential as the outcomes of this study could inform our general understanding of distributions of other animals in other parts of the world. Hypotheses related to the ecological niche-based characteristics of species were tested to identify the most important variables influencing the distribution of South African bats and to predict the probability of occurrence for bat species in South Africa. A database that included locality records for bat species from different museums in South Africa was compiled and then combined with the researcher's own data for the Northern Cape Province as there was insufficient knowledge of bat distributions in this province. A total of 23 environmental variables were considered, of which 20 were downloaded from the WorldClim database as potential environmental variables influencing the contemporary distribution of bats in South Africa based on previous studies that use environmental variables from WorldClim to predict the distribution of species. The environmental variables were grouped into broad categories, temperature, precipitation, and biophysical (i.e., vegetation biomes, land use/land cover, geology) variables. As predicted, taxonomic affiliations appear to have no bearing on which factors influenced the geographic distribution of South African bat species. The distributional limits of even closely related species within the same genus appear to be influenced by disparate environmental factors. Geology appeared to be the most important limiting factor for 15 of the 37 species, all of which are known to use roosts associated with geological features (i.e., caves, mines and rock crevices). Land use/land cover influenced the distribution of six bat species most of which are known to use human structures or domesticated crops as roosting sites. Roost availability thus appeared to be an important factor limiting the distribution of bats. The distribution of only one South African bat species, the endemic Rhinolophus capensis, was associated with a biome as being the most important predictor variable. Temperature variables appeared to be the most important factors influencing the distribution of 12 of the 37 species of bats in South Africa. This might be linked directly to the roosting ecology and thermoregulation capability of each species and their need for hibernation and/or torpor. Precipitation parameters were the most influential in the distribution of 9 of the 37 South African bat species whose distribution is centred towards the wet east of the country. This could probably be linked to its effects on the availability of food in the form of fruit or insects. However, the results of this study should be interpreted cautiously. The majority of the environmental variables employed in this study to model the distribution of bats, were correlated to some degree, which could affect the contribution of an individual environmental variable to the performance of a model. Furthermore, certain bat species included in this study have their centres of distribution ranges further north in Africa and have only marginal intrusion into South Africa's political boundary, which means that only a portion of the distribution of these species is modelled; this could yield erroneous results that might not be transferable to other parts of the ranges of these species. Finally, field verification of the occurrence of species in areas where they are predicted to have a high probability of occurrence is crucial in order to verify the reliability of the models.
Open Access
Factors affecting the activity patterns of Myotis tricolor (Chiroptera: Vespertilionidae)
(2011) Jordaan, Stacey; Jacobs, David S
Foraging behaviour is an important component of an animal’s ecology. Increases in energetic costs associated with reproduction, should have marked effects on foraging behaviour, but may be compounded by the effects of environmental factors. I investigated the activity patterns of female M. tricolor over the reproductive period using radio telemetry. Six female bats were radio-tagged during each reproductive period: early pregnancy, late pregnancy and lactation. Times at which bats entered and exited the cave were recorded, as was the temperature, moon-phase, cloud cover, wind speed, rainfall and insect abundance. These data were used to calculate emergence time, number of foraging bouts and foraging duration for each reproductive period, which were then correlated with the environmental variables.
Open Access
Factors affecting the emergence times of seven sympatric insectivorous bat species
(2011) Thomas, Alicia Jessica; Jacobs, David S
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. Onset of activity is likely subject to several factors including presence/absence of predators and the vagaries of environmental conditions at the time of emergence. The aim of my study was to test several hypotheses accounting for differing emergence times amongst sympatric insectivorous bat species.
Open Access
Geographic distribution and composition of the parasite assemblage of the insectivorous bat, Miniopterus natalensis (Chiroptera: Miniopteridae), in South Africa
(2012) Wood, Simon; Jacobs, David S
All free-living animal species have their own unique parasite assemblages. These parasites can have a significant impact on the fitness and ecology of their hosts, and through them the ecological systems in which they occur. Gaining knowledge about these parasites offers important information on the biology, systematics and phylogenies of their hosts. During this study the following were collected: flea, fly, mite, tick and helminth species from 96 Natal Long-Fingered bat (Miniopterus natalensis Smith, 1834) individuals sampled from seven localities across South Africa. This study aimed to both identify the species forming part of this parasite assemblage, and attempted to explain the distribution of the parasites and the factors influencing it.
Open Access
Geographic variation in the echolocation calls of the endemic Cape horseshoe bat, Rhinolophus capensis (Chiroptera: Rhinolophidae)
(2009) Odendaal, Lizelle Janine; Jacobs, David S
Several intrinsic (body size) and extrinsic (foraging ecology and communication) factors are suggested to influence call frequency divergence in high duty-cycle bats. Investigating these factors within the framework of established hypotheses would contribute to understanding evolutionary changes leading to speciation in bats. Here, acoustic divergence between populations of the endemic Cape horseshoe bat, Rhinolophus capensis was investigated at both inter- and intraspecific levels. No previous study has investigated geographic variation in echolocation calls of R. capensis. Body size, wing morphology and skull parameters associated with diet and echolocation call production and reception, were compared between populations. Adult R. capensis were sampled at three sites: De Hoop situated in the centre of the species distribution in the Fynbos biome; Steenkampskraal and Table Farm were ecotone populations situated in the western and eastern limits of the distribution, respectively. Interspecific analysis revealed that the two ecotone populations deviated slightly from the allometric relationship between body size and peak frequency for the African clade. In fact, the expected inverse relationship between body size and peak frequency was not evident across populations. Ecotone populations had significantly larger mean body sizes than the population at De Hoop (10.28 ± 1.08 g; 84.60 ± 0.82 kHz). However, one population in the ecotone had the highest frequency (Table Farm: 13.88 ± 0.87 g; 85.84 ± 0.73 kHz) while the other had the lowest (Steenkampskraal: 13.15 ± 0.95 g; 80.66 ± 0.50 kHz). Several hypotheses were considered to explain the patterns of echolocation and morphological variation observed. The larger body size of the ecotone populations may be explained by James' Rule or it may be an adaptation to the intrinsic habitat heterogeneity of ecotones as it affords these bats a greater niche width and possibly larger home ranges to access spatially separated resources. On the other hand, neither climatic (humidity hypothesis), habitat (foraging habitat hypothesis) nor dietary differences (prey detection hypothesis between populations were responsible for the observed peak frequency differences between populations. Nasal chamber area was the best predictor of peak frequency and there was no relationship between the area of the nasal chamber and body size. Thus, selection may have acted directly on peak frequency altering skull parameters directly involved in echolocation independently of body size. Within each population, females were larger and used higher frequencies than males, which implies a potential social role of peak frequency for R. capensis. Observed differences in peak frequency may be because R. capensis interacts with separate rhinolophid species at either end of its distribution (Steenkampskraal: R. swinnyi; Table Farm: R. darlingi) in addition to R. clivasus, which results in the evolution of local dialects to facilitate intraspecific communication. These local dialects, possibly brought about by differences in local ambient noise characteristics (e.g. chorusing insects), could be maintained via cultural transmission. However, the role of gene flow for the evolution of these local dialects between populations cannot be discounted without adequate genetic analyses.
Open Access
Geographic variation in the phenotypes of two sibling horseshoe bats Rhinolophus simulator and R.swinnyi
(2016) Mutumi, Gregory L; Jacobs, David S; Winker, Henning
The study of geographic variation and its causes in the phenotypes of animals elucidates how evolutionary processes generate biodiversity. This thesis attempts to uncouple the relative contributions of adaptive and neutral mechanisms to population divergence in African horseshoe bats (genus Rhinolophus). The two species were sampled from their distributional ranges within southern Africa and several morphometric and echolocation parameters were taken. The relative contributions of adaptation and drift were first tested (Chapter 2) using the Lande's model. It was hypothesised that adaptation would predominate in the diversification of the two horseshoe bats owing to the flight-echolocation and diet-echolocation adaptive complexes that intricately tie these two species to environmental conditions. Selection was also hypothesised to be stronger in Rhinolophus swinnyi because it uses higher frequency sound which is more sensitive to atmospheric conditions. The hypotheses were tested using a combination of soft tissue parameters (Chapter 2) and hard tissue parameters (Chapter 3), i.e., 3D scanned skulls analysed using 3D geometric morphometrics. To reconstruct the selective forces, linear mixed-effects models were used to regress climatic variables against echolocation call signals (Chapter 4) based on two hypotheses, the Sensory Drive and the James' Rule as a guide. The Lande's model (Chapter 2 and 3) showed that drift had a minimal effect to the variation of body parameters and echolocation and that selection was stronger on echolocation than on morphometric parameters. Additionally selection was differentially exerted across different localities and between the two species, making the relative roles of selection and drift context specific. Climatic variables (mean annual temperature and relative humidity) were inversely related to the variation in echolocation signals (Chapter 4) within each species. Body size was unrelated to the observed variation, which provided evidence that echolocation signals did not vary as a result of the body size/climate relationship proposed by James' Rule. Bats rely on both flight and echolocation to survive and reproduce, systems that have to track local habitats closely to perform optimally. Hence selection plays a pivotal role in their diversification.
Open Access
Habitat correlates of pulse parameters in the highly specialised acoustic system of Chiroptera
(2021) Finger, Nikita Maxine; Jacobs, David S; Holderied, Marc
High Duty Cycle echolocating bats use high frequency echolocation pulses that have limited range but are clutter resistant i.e. can detect targets in dense clutter (the number of echoes produced other than those from the target of interest). A specialised echolocation pulse design (consisting of a constant frequency and frequency modulated components) facilitates foraging for prey in habitats characterised by dense vegetation or clutter. The constant frequency component, along with an acoustic fovea and Doppler Shift Compensation, allows them to distinguish small moving targets from stationary background objects. The frequency modulated components are thought to be used for depth resolution (i.e. ranging acuity). In contrast to their clutter specialist status, these species are found in a variety of biomes including open desert. A negative correlation between level of environmental clutter and frequency has been established for some species. The Foraging Habitat Hypothesis (FHH) proposes that the evolution of echolocation frequency is linked with changes in habitat clutter. In High Duty Cycle bats, the FHH predicts areas of low clutter should select lower frequency pulses because they are less susceptible to atmospheric attenuation making them more suited to long distance prey detection. Previous research has therefore focused on the methods by which bats vary the frequency of their pulses to achieve optimal propagation distances. However, the source levels of these signal emissions are also under control of the bat and must play a major role in signal propagation and therefore in detection of prey. My study tested the FHH by combining both an observational and experimental approach to determine how habitat clutter influences echolocation pulse divergence in High Duty Cycle bats. My focal species was Rhinolophus capensis, which has previously been shown to use different pulse frequencies apparently associated with differences in habitat structure. I focused on two populations, R. capensis in the fynbos (pulse frequency: 84 kHz) and R. capensis in the desert (pulse frequency: 74 kHz). Bats were recorded using a multiple microphone array in their natural habitat and in a flight room experiment where they were exposed to both a cluttered (simulating the fynbos biome) and open (simulating the desert biome) flight room. The experiment determined whether observed differences were a result of possible selection (as proposed by the FHH) or behavioural flexibility. A congeneric species, iii R. damarensis, was used as a control and additional test of the FHH because it inhabits the same desert biome as R. capensis but echolocates at a higher frequency (equivalent to the frequency used by R. capensis in the fynbos). In accordance with this hypothesis, I also tested if there were differences in the frequency modulated components of R. capensis pulses between biomes and whether these differences were due to possible selection for optimal ranging acuity in response to the degree of clutter in each biome. My results suggest the use of lower frequency echolocation pulses in R. capensis in the desert could have evolved for increased detection distance (as proposed by the FHH) but that lower frequencies may not be a prerequisite for successful foraging in open biomes. In R. capensis the greatest differences in prey detection between biomes was a product of both frequency and source level. However, higher source levels used by R. capensis in the desert had a greater contribution to observed differences in detection distances both within (emergence versus foraging area, cluttered versus open flight room) and between biomes (desert versus fynbos) than frequency. In addition, on average R. damarensis did not compensate for higher frequencies with higher source levels resulting in lower average detection distances than R. capensis in the desert. However, a few measurements of source levels for R. damarensis were the highest recorded and resulted in the largest prey detection distances recorded in my study. These findings support recent findings that suggest that SLs are energetically costly. In both biomes, bats used lower source levels when exposed to a cluttered versus open flight room. In the desert biome, bats actively lowered their source levels (compared to the source levels they use in the field) when exposed to a level of clutter that they do not experience naturally (cluttered flight room treatment). Unlike source levels, frequency (of the constant frequency component) was conserved during the flight room treatments. Frequency differences between R. capensis in the different biomes can therefore be attributed to possible selection rather than behavioural flexibility. The conservation of frequency prompted bats to vary their source levels to achieve appropriate detection distances when exposed to different environmental stimuli. Source level flexibility may therefore be the key to the capability of specialist clutter foragers to successfully hunt and survive in harsh open environments. To the same extent that source levels facilitate foraging in open environments, the frequency modulated components of High Duty Cycle bat pulses may facilitate the orientation and foraging of these bats in cluttered biomes. In accordance with the FHH, a strong correlation was found between the frequency (i.e. number of occurrences)/bandwidth of these components and the level of environmental clutter both within iv (between the two treatments of the experiment) and between biomes. The findings in my study highlight the importance of environmental pressures, such as clutter, in shaping the echolocation pulse parameters of bats.
Open Access
The influence of foraging habitat on acoustic signal source levels in two bat species, Neoromicia capensis (Vespertilionidae) and Tadarida aegyptiaca (Molossidae)
(2018) Mutavhatsindi, Itani Victor; Jacobs, David S; Holderied, Marc W
The source level of echolocation pulses is an essential parameter because it has an impact on the range at which bats perceive their environment and, most importantly, at which they detect prey. Echolocation pulse source level is under the control of the echolocator and its operational range is likely to vary with body size and foraging habitat because these determine the operational range needed by the bat. This study thus attempted to answer the following questions; (1) is the source levels of animal acoustic signals different in different situations? (2) Does body size and foraging habitat affect the source levels of animal acoustic signals? There are only a few studies that report on the source levels of echolocation pulses of free-ranging bats because of the difficulty of measuring the distance of the bat from the recording microphone. This distance is essential in calculating source levels of echolocation pulses. I used multiple microphone array system to investigate the echolocation sound signals, three-dimensional (3-D) acoustic flight paths and source levels of echolocation pulses at 10 cm standard reference distance from the mouth of a free-flying frequency-modulated (FM) bat, Neoromicia capensis and quasi-constant frequency (QCF) bat, Tadarida aegyptiaca. The two bat species differ in body size and foraging habitat. I found as predicted, that T. aegyptiaca, the larger of the two species and an open-air aerial hawker, emitted echolocation pulses of higher source levels and therefore had greater maximum detection distances than the smaller, clutter-edge aerial hawker, N. capensis. Tadarida aegyptiaca emitted echolocation pulses with an average of 146.9±4.6 (range 137.7 - 154.8) dB peSPL during emergence from the roost and an average of 143.0±4.9 (range 136.4 - 153.3) dB peSPL during foraging, extending the known range of free-flying bats. Neoromicia capensis emitted echolocation pulses with an average of 129.3±4.0 (range 119.3 - 138.7) dB peSPL during emergence from the roost and average of 132.8±5.0 (range 117.8 - 142.9) dB peSPL during foraging. As anticipated, I found N. capensis to be emitting echolocation pulses of higher source levels during foraging than when it emerged from the roost. However, there was no significant difference in the source levels of T. aegyptiaca between emergence from the roost and foraging habitat. The estimated maximum detection distances for the three insect size categories i.e. small, medium and large was greater for T. aegyptiaca than N. capensis. My data therefore suggests that bats might adjust their echolocation pulse source levels to suit their foraging habitat and situation.
Open Access
Investigation of population abundance, distribution, and population linkage of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) on the north and south of Zanzibar using mark-recapture and acoustic methods
(2017) St Clair-Hughes, Adam James Victor; Jacobs, David S; Bastian, Anna; Gridley, T; Elwen, Simon
Previous studies, using a variety of methods such as photographic identification, fisheries observer programs, or genetic testing, on Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Zanzibar Island, Tanzania, suggest separate populations around the north and south coasts. However, most research around the island has focused on the south coast, and movement of dolphins around the coastline is poorly understood. Photographic identification data, consisting of dorsal fin images, and acoustic data from dolphin whistles, both collected in 2008, were analysed to examine linkages between north and south Zanzibar. Photographic identification data was applied in a Mark-Recapture framework, using open population models, to generate abundance estimates of 149 (95% CI 128-173) and 120 (95% CI 97-149) individuals for the north and south coasts of Zanzibar respectively. As 16 individuals had moved from the south to the north coast of Zanzibar during the two month study, a combined population estimate of 353 (95% CI 290-430) individuals for Zanzibar Island was also generated. Acoustic analysis of standard whistle parameters was used to investigate whether these learned signals shared features between the putative populations, using whistle data collected in Plettenberg Bay, South Africa as an out-group. Discriminant function analysis of whistle parameters indicated high classification success of whistles recorded from animals in the north location (86.2%), moderate classification success for the outgroup (61.8%), and zero classification success for Zanzibar's south coast population. High misclassification rates for south Zanzibar suggest that these whistles cannot be readily discriminated from those of north Zanzibar. Shared whistle features suggest that learning may take place between individuals moving between localities. Coupled with previous genetic studies, this study suggests female philopatry and male mediated gene flow between the two areas; however, more genetic markers are necessary to test this interpretation. Further work is also necessary to quantify the degree of movement of dolphins around Zanzibar Island, and potential migration into the area, which will assist in developing management plans.
Open Access
Limbs gone batty : the role of the anterior-posterior patterning signal, Sonic Hedgehog, in the development of the unique bat limb
(2007) Hockman, Dorit; Illing, Nicola; Jacobs, David S
The unique skeletal structure of the bat forelimb and hindlimb provides a new and exciting model for the field of evolutionary developmental biology, which seeks to reveal the molecular mechanisms behind vertebrate limb diversity. The digits of the bat forelimb, excluding the thumb, are considerably elongated and webbed. The hindlimb digits are free of webbing and are of uniform length, lacking the asymmetrical patterning of the forelimb. In this study, gene expression analysis has revealed that changes in the spatial and temporal expression patterns of the anteriorposterior patterning signal, Sonic hedgehog (Shh), and its downstream target, Patched 1 (PtcJ), have contributed to the development of the unique bat limb. The embryonic development of Miniopterus natalensis (Miniopteridae) is described for the first time and the expression patterns of Shh and PtcJ in the developing limbs of this species are compared to those in Carollia perspicillata (Phyllostomidae) and the mouse. Early in bat limb development (stage 14), Shh expression in the ZPA appears to be anteriorly expanded when compared to the mouse. This observation is in line with the reported expansion of Fgf8 expression in the AER (Cretekos et al. 2007) and reveals that an enhancement of the Shh-Fgf positive feedback loop may be responsible for the initial posterior expansion of the bat forelimb. Later in development (stage 16) Shh and PtcJ acquire a novel domain of expression within the interdigital tissue of both the bat forelimb and hindlimb. These expression patterns parallel the reported up-regulation of Fgf8, Gremlin and Bmp2 in the interdigital tissue of C. perspicillata (Weatherbee et al. 2006) and support the hypothesis that the Shh-Fgfpositive feedback loop is re-initiated in the interdigital tissue of the bat limbs. The cell survival and proliferation signals provided by the Shh-Fgf signalling loop most likely contribute to the lengthening of the posterior forelimb digits, the survival of the tissue between the forelimb digits and the extension of digits 1 and 5 of the hindlimb to the same length of the remaining digits. The novel Shh and PtcJ expression patterns were observed in both M natalensis and C. perspicillata, supporting the monophyly of the chiropteran sub-order, Verspertilioniformes.
Open Access
Local adaptation of Geoffroy's horseshoe bat, Rhinolophus clivosus, to the Cape floristic region of South Africa
(2006) Walker, Maryalice Harkins; Jacobs, David S
Populations of species adapt to the environment in which they live. This study investigated local adaptation in Rhinolophus clivosus (Chiroptera: Rhinolophidae) by comparing its phenotype with that of a co-occurring endemic species. R. capensis, in the Cape Floristic Region of South Africa. If R. clivosus has become locally adapted, its phenotype would be predicted to have diverged from R. clivosus populations elsewhere in the country while converging upon R. capensis. Evidence for local adaptation was found in R. c/imslls at De Hoop Nature Reserve. The population has undergone a reduction in body size with correlated allometric responses in flight morphology. The wing shape of R. clivosus at De Hoop has not changed, resulting in a reduction in wing loading with a consequent increase in manoeuvrability. Thus R. clivosus at De Hoop is simply a scaled-down version of R. clivosus elsewhere and a scaled-up version of R. capensis. Factors such as competition and gene flow may have mitigated against local adaptation, however. Furthermore. whether phenotypic plasticity rather than natural selection may have been responsible for the apparent convergence between R. capensis and R. clivosus requires future research and advances in the study of evolutionary development and population genetics.
Open Access
Molecular phylogenetics and the evolution of high-frequency echolocation in horseshoe bats (Genus Rhinolophus)
(2007) Stoffberg, Samantha; Jacobs, David S
Horseshoe bats (genus Rhinolophus) belong to the Old World family Rhinolophidae. They are high-duty cycle bats and many species use echolocation calls dominated by high frequencies (above 60 kHz). Much is known about how they use their echolocation calls, but very little is known about why these bats use echolocation calls of such high frequencies, or what has caused the divergence in echolocation call frequency between rhinolophid species. I test five hypotheses that may explain the evolution and divergence of high frequencies in the horseshoe bats: (1) The Allotonic Frequency Hypothesis - echolocation frequencies outside of moth hearing range (allotonic frequencies) have evolved in response to moth hearing; (2) The Allometry Hypothesis - highfrequency echolocation calls are simply a function of body size; (3) The Acoustic Adaptation Hypothesis - selection pressures linked to habitat structure have shaped the evolution of high-frequency echolocation calls; (4) The Foraging Habitat Hypothesis - foraging style and habitat of a bat should correspond to echolocation call frequency and wing design; and (5) The Acoustic Communication Hypothesis - echolocation frequencies evolved under selection pressure which eliminated overlap among sympatric species of rhinolophids, within the context of effective communication.
Open Access
Phenotypic convergence in genetically distinct lineages of a Rhinolophus species complex (Mammalia, Chiroptera)
(Public Library of Science, 2013) Jacobs, David S; Babiker, Hassan; Bastian, Anna; Kearney, Teresa; Eeden, Rowen van; Bishop, Jacqueline M
Phenotypes of distantly related species may converge through adaptation to similar habitats and/or because they share biological constraints that limit the phenotypic variants produced. A common theme in bats is the sympatric occurrence of cryptic species that are convergent in morphology but divergent in echolocation frequency, suggesting that echolocation may facilitate niche partitioning, reducing competition. If so, allopatric populations freed from competition, could converge in both morphology and echolocation provided they occupy similar niches or share biological constraints. We investigated the evolutionary history of a widely distributed African horseshoe bat, Rhinolophus darlingi , in the context of phenotypic convergence. We used phylogenetic inference to identify and date lineage divergence together with phenotypic comparisons and ecological niche modelling to identify morphological and geographical correlates of those lineages. Our results indicate that R. darlingi is paraphyletic, the eastern and western parts of its distribution forming two distinct non-sister lineages that diverged ~9.7 Mya. We retain R. darlingi for the eastern lineage and argue that the western lineage, currently the sub-species R . d. damarensis , should be elevated to full species status. R. damarensis comprises two lineages that diverged ~5 Mya. Our findings concur with patterns of divergence of other co-distributed taxa which are associated with increased regional aridification between 7-5 Mya suggesting possible vicariant evolution. The morphology and echolocation calls of R. darlingi and R. damarensis are convergent despite occupying different biomes. This suggests that adaptation to similar habitats is not responsible for the convergence. Furthermore, R. darlingi forms part of a clade comprising species that are bigger and echolocate at lower frequencies than R. darlingi , suggesting that biological constraints are unlikely to have influenced the convergence. Instead, the striking similarity in morphology and sensory biology are probably the result of neutral evolutionary processes, resulting in the independent evolution of similar phenotypes.