Journal of Zoology

Published by Wiley

Online ISSN: 1469-7998


Print ISSN: 0952-8369


Description of a new octoploid frog species (Anura: Pipidae: Xenopus) from the Democratic Republic of the Congo, with a discussion of the biogeography of African clawed frogs in the Albertine Rift
  • Article

April 2011


214 Reads






We describe a new octoploid species of African clawed frog (Xenopus) from the Lendu Plateau in the northern Albertine Rift of eastern Democratic Republic of the Congo. This species is the sister taxon of Xenopus vestitus (another octoploid), but is distinguished by a unique morphology, vocalization and molecular divergence in mitochondrial and autosomal DNA. Using a comprehensive genetic sample, we provide new information on the species ranges and intra-specific diversity of African clawed frogs from the Albertine Rift, including the details of a small range extension for the critically endangered Xenopus itombwensis and previously uncharacterized variation in Xenopus laevis. We also detail a new method for generating cytogenetic preparations in the field that can be stored at room temperature for up to 3 weeks. While extending our understanding of the extant diversity in the Albertine Rift, this new species highlights components of species diversity in ancestral African clawed frogs that are not represented by known extant descendants.

A cognitive perspective on aggressive mimicry
  • Article
  • Full-text available

July 2013


259 Reads

We use the term 'aggressive mimic' for predators that communicate with their prey by making signals to indirectly manipulate prey behaviour. For understanding why the aggressive mimic's signals work, it is important to appreciate that these signals interface with the prey's perceptual system, and that the aggressive mimic can be envisaged as playing mind games with its prey. Examples of aggressive mimicry vary from instances in which specifying a model is straight forward to instances where a concise characterisation of the model is difficult. However, the less straightforward examples of aggressive mimicry may be the more interesting examples in the context of animal cognition. In particular, there are spiders that prey on other spiders by entering their prey's web and making signals. Web invasion brings about especially intimate contact with their prey's perceptual system because the prey spider's web is an important component of the prey spider's sensory apparatus. For the web-invading spider, often there is also a large element of risk when practising aggressive mimicry because the intended prey is also a potential predator. This element of risk, combined with exceptionally intimate interfacing with prey perceptual systems, may have favoured the web-invading aggressive mimic's strategy becoming strikingly cognitive in character. Yet a high level of flexibility may be widespread among aggressive mimics in general and, on the whole, we propose that research on aggressive mimicry holds exceptional potential for advancing our understanding of animal cognition.

Table 1 Mean hearing thresholds ( AE SEM) of the normal and the albinotic specimens in the two species studied
Figure 5 Mean ( AE SEM) hearing thresholds of normal and albino Silurus glanis.
Figure 6 Mean ( AE SEM) hearing thresholds of normal and albino Corydoras aeneus.
Normally pigmented and albinotic specimens of Silurus glanis.
Normally pigmented and albinotic specimens of Corydoras aeneus.


How albino fish hear?

March 2011


953 Reads

Pigmentation disorders such as albinism are occasionally associated with hearing impairments in mammals. Therefore, we wanted to investigate whether such a phenomenon also exists in non-mammalian vertebrates. We measured the hearing abilities of normally pigmented and albinotic specimens of two catfish species, the European wels Silurus glanis (Siluridae) and the South American bronze catfish Corydoras aeneus (Callichthyidae). The non-invasive auditory evoked potential (AEP) recording technique was utilized to determine hearing thresholds at 10 frequencies from 0.05 to 5 kHz. Neither auditory sensitivity nor shape of AEP waveforms differed between normally pigmented and albinotic specimens at any frequency tested in both species. Silurus glanis and C. aeneus showed the best hearing between 0.3 and 1 kHz; the lowest thresholds were 78.4 dB at 0.5 kHz in S. glanis (pigmented), 75 dB at 1 kHz in S. glanis (albinotic), 77.6 dB at 0.5 kHz in C. aeneus (pigmented) and 76.9 dB at 1 kHz in C. aeneus (albinotic). This study indicates no association between albinism and hearing ability. Perhaps because of the lack of melanin in the fish inner ear, hearing in fishes is less likely to be affected by albinism than in mammals.

Chemical defense of an Asian snake reflects local availability of toxic prey and hatchling diet

April 2013


2,872 Reads

Species that sequester toxins from prey for their own defense against predators may exhibit population-level variation in their chemical arsenal that reflects the availability of chemically defended prey in their habitat. Rhabdophis tigrinus is an Asian snake that possesses defensive glands in the skin of its neck ('nuchal glands'), which typically contain toxic bufadienolide steroids that the snakes sequester from consumed toads. In this study, we compared the chemistry of the nuchal gland fluid of R. tigrinus from toad-rich and toad-free islands in Japan and determined the effect of diet on the nuchal gland constituents. Our findings demonstrate that captive-hatched juveniles from toad-rich Ishima Island that had not been fed toads possess defensive bufadienolides in their nuchal glands, presumably due to maternal provisioning of these sequestered compounds. Wild-caught juveniles from Ishima possess large quantities of bufadienolides, which could result from a combination of maternal provisioning and sequestration of these defensive compounds from consumed toads. Interestingly, juvenile females from Ishima possess larger quantities of bufadienolides than do juvenile males, whereas a small sample of field-collected snakes suggests that adult males contain larger quantities of bufadienolides than do adult females. Captive-born hatchlings from Kinkasan Island lack bufadienolides in their nuchal glands, reflecting the absence of toads on that island, but they can sequester bufadienolides by feeding on toads (Bufo japonicus) in captivity. The presence of large quantities of bufadienolides in the nuchal glands of R. tigrinus from Ishima may reduce the risk of predation by providing an effective chemical defense, whereas snakes on Kinkasan may experience increased predation due to the lack of defensive compounds in their nuchal glands.

Disentangling true shape differences and experimenter bias: Are dextral and sinistral snail shells exact mirror images?

November 2010


246 Reads

IN THEORY, SNAILS CAN COME IN TWO ENANTIOMORPHS: either dextral (coiling clockwise) or sinistral (coiling counter-clockwise). In snail species where both forms are actually present, coiling direction is determined by a single gene with delayed maternal inheritance; there is no predictable relationship between a snail's own coiling genotype and its actual coiling direction. Because of this genetic decoupling, it might be expected that dextral and sinistral individuals would be exact mirror images of one another. However, indications exist that there is a subtle but detectable shape difference between dextral and sinistral individuals that derive from the same gene pool. In this paper, we attempt to detect such differences in 50 dextral and 50 sinistral individuals of Amphidromus inversus, a species of land snail that is consistently chirally dimorphic. Four out of 18 volunteers who measured the shells with Vernier calipers found that sinistrals are stouter to a significant degree. A similar result was found by one out of five volunteers who measured the shells from photographs. These results do not allow distinguishing between real shape differences and a handling bias of sinistral as compared with dextral shells. However, when the same set of shells was subjected to a geometric morphometric analysis, we were able to show that sinistrals indeed exhibit a slight but significant widening and twisting of the shell near the palatal and parietal apertural areas. This result is surprising because species of the subgenus Amphidromus s. str. share a long history of chiral dimorphism, and the species would be expected to have been purged from disadvantageous interactions between direction of coil and general shell shape. We conclude that selection on the shape differences is either very weak or constrained by the fact that the pleiotropic effects of the chirality gene are of importance very early in development only.

Effect of lactation stage and concurrent pregnancy on milk composition in the bottlenose dolphin

October 2007


161 Reads

ALTHOUGH MANY TOOTHED WHALES (CETACEA: Odontoceti) lactate for 2-3 years or more, it is not known whether milk composition is affected by lactation stage in any odontocete species. We collected 64 pooled milk samples spanning 1-30 months postpartum from three captive bottlenose dolphins Tursiops truncatus. Milks were assayed for water, fat, crude protein (TN × 6.38) and sugar; gross energy was calculated. Ovulation and pregnancy were determined via monitoring of milk progesterone. Based on analysis of changes in milk composition for each individual dolphin, there were significant increases (P<0.05) in fat (in all three dolphins) and crude protein (in two of three), and a decrease (P<0.05) in water (in two of three) over the course of lactation, but the sugar content did not change. In all three animals, the energy content was positively correlated with month of lactation, but the percentage of energy provided by crude protein declined slightly but significantly (P<0.05). At mid-lactation (7-12 months postpartum, n=17), milk averaged 73.0±1.0% water, 12.8±1.0% fat, 8.9±0.5% crude protein, 1.0±0.1% sugar, 1.76±0.09 kcal g(-1) (=7.25 kJ g(-1)) and 30.3±1.3% protein:energy per cent. This protein:energy per cent was surprisingly high compared with other cetaceans and in relation to the growth rates of calves. Milk progesterone indicated that dolphins ovulated and conceived between 413 and 673 days postpartum, following an increase in milk energy density. The significance of these observed compositional changes to calf nutrition will depend on the amounts of milk produced at different stages of lactation, and how milk composition and yield are influenced by sampling procedure, maternal diet and maternal condition, none of which are known.

Radiographic analysis of vocal tract length and its relation to overall body size in two canid species

September 2013


205 Reads

Body size is an important determinant of resource and mate competition in many species. Competition is often mediated by conspicuous vocal displays, which may help to intimidate rivals and attract mates by providing honest cues to signaler size. Fitch proposed that vocal tract resonances (or formants) should provide particularly good, or honest, acoustic cues to signaler size because they are determined by the length of the vocal tract, which in turn, is hypothesized to scale reliably with overall body size. There is some empirical support for this hypothesis, but to date, many of the effects have been either mixed for males compared with females, weaker than expected in one or the other sex, or complicated by sampling issues. In this paper, we undertake a direct test of Fitch's hypothesis in two canid species using large samples that control for age- and sex-related variation. The samples involved radiographic images of 120 Portuguese water dogs Canis lupus familiaris and 121 Russian silver foxes Vulpes vulpes. Direct measurements were made of vocal tract length from X-ray images and compared against independent measures of body size. In adults of both species, and within both sexes, overall vocal tract length was strongly and significantly correlated with body size. Effects were strongest for the oral component of the vocal tract. By contrast, the length of the pharyngeal component was not as consistently related to body size. These outcomes are some of the clearest evidence to date in support of Fitch's hypothesis. At the same time, they highlight the potential for elements of both honest and deceptive body signaling to occur simultaneously via differential acoustic cues provided by the oral versus pharyngeal components of the vocal tract.

Figure 1 Study area in the central region of the Kruger National Park, South Africa, scats located at GPS clusters, and kills located at GPS clusters. 
Figure 2 Proportion of scats ( Ϯ SE) containing remains of the same prey species (grey) or a different species (black) as the focal kill (at the kill site [KS] and each day thereafter), based on the investigation of GPS clusters in the central region of the Kruger National Park, South Africa, between April 2005 and May 2007. 
Estimating carnivoran diets using a combination of carcass observations and scats from GPS clusters

February 2012


244 Reads

Scat analysis is one of the most frequently used methods to assess carnivoran diets and Global Positioning System (GPS) cluster methods are increasingly being used to locate feeding sites for large carnivorans. However, both methods have inherent biases that limit their use. GPS methods to locate kill sites are biased towards large carcasses, while scat analysis over-estimates the biomass consumed from smaller prey. We combined carcass observations and scats collected along known movement routes, assessed using GPS data from four African lion (Panthera leo) prides in the Kruger National Park, South Africa, to determine how a combination of these two datasets change diet estimates. As expected, using carcasses alone under-estimated the number of feeding events on small species, primarily impala (Aepyceros melampus) and warthog (Phacochoerus africanus), in our case by more than 50% and thus significantly under-estimated the biomass consumed per pride per day in comparison to when the diet was assessed using carcass observations alone. We show that an approach that supplements carcass observations with scats that enables the identification of potentially missed feeding events increases the estimates of food intake rates for large carnivorans, with possible ramifications for predator-prey interaction studies dealing with biomass intake rate.

The breeding biology of equatorial vertebrates: Reproduction of the lizard Agama lionotus Boulenger at lat. O 01' N

August 2009


152 Reads

The equatorial lizard Agama agama Eionotus possesses a distinct breeding period which occurs during the peak of the seasonal harvest of protein animal food that follows the so‐called “long rains”. The males contain bunches of spermatozoa throughout the year. As the proportion of ingested animal food increases, the sexual condition of the females heightens. There is a concurrent growth of large leaf‐shaped abdominal fat bodies. Widespread egg‐laying occurs during four months of the year (June‐September inclusive), the peak being in July and early in August. During the height of reproduction three distinct phases of egg development can be seen macroscopically: 1, a layer of colourless ovarian eggs surmounted by 2, a series of yolked eggs and 3, a clutch of ten to twelve shelled oviducal eggs. This device enables quick and repeated ovulation during the period of the maximum insect harvest. During the period of study one ovulation only was recorded after the so‐called “short rains”. This occurred in February and after unusually heavy precipitation during the, previous December. Any possibility of the photoperiodic control of reproduction was eliminated by the choice of the collecting locality. It is suggested that the sexual cycle of Agama agama is timed not by rainfall but by the seasonal appearance of proteinous insect food. Vegetable food of various kinds seems to be relatively abundant throughout the year. It is not known whether widespread reproduction after the secondary “short rains” is inhibited by a relative lack of protein food or, perhaps more probably, by the comparatively low night temperatures that occur from December to February inclusive. A. agama is almost omnivorous, feeding on grass, berries, seeds, flowers, caterpillars, beetles, spiders, ants, Hymenoptera and the eggs of smaller reptiles.

A comparative scanning electron microscopic study of the cyst wall in 11 Sarcocystis species of mammals

May 2009


40 Reads

Sarcocysts found in the musculature of necropsied mammals were dried with hexamethyldisilazane and examined by scaning electron microscopy. The object of research in this morphological study was the outer surface configuration of the cyst wall. A smooth cyst wall without villar protrusions (Sarcocystic cf. sebeki European badger, Meles meles) was compared with 10 others each with its distinctly characterized villar protrusinos. In scanning electron microscopy these resembled stumpy nails with angular heads (Sarcocystis sp./serow, Capricornis crispus), tongues (S. sp./sambar, Cervus unicolor), ears (S. sp./ wapiti, Crevus elaphus canadensis), elongated cones or clubs (S. sp./domestic horse, Equus caballus), hairs (S. sp./Mongolian gazelle, Procapra gutturosa), and molar teeth (another S. sp./Mongolian gazelle). This study revealed that what appeared in light microscopy to be finger-like protrusions of Sarcocystis hofamanni in roe deer (Capreolus capreolus), of Sarcocystis hominis in bison (Bison bison), of Sarcocystis hirsuta in cattle (Bos taurus), and of Sarcocystis tenella in sheep (Ovis aries) were more similar to columns (S. hofmanni), straps (S. hominis), stalked polyhedrons (S. hirsuta), or cylinders (S. tenella).

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