Margaretha D Hofmeyr

Publications of Margaretha D Hofmeyr

• Deep genealogical lineages in the widely distributed African helmeted terrapin: evidence from mitochondrial and nuclear DNA (Testudines: Pelomedusidae: Pelomedusa subrufa).

  Authors: Mario Vargas-Ramírez, Miguel Vences, William R Branch, Savel R Daniels, Frank Glaw, Margaretha D Hofmeyr, Gerald Kuchling, Jérôme Maran, Theodore J Papenfuss, Pavel Siroký, David R Vieites, Uwe Fritz

  Molecular phylogenetics and evolution. 03/2010; 56(1):428-40.

  We investigated the phylogeographic differentiation of the widely distributed African helmeted terrapin Pelomedusa subrufa based on 1503 base pairs of mitochondrial DNA (partial cyt b and ND4 genesWe investigated the phylogeographic differentiation of the widely distributed African helmeted terrapin Pelomedusa subrufa based on 1503 base pairs of mitochondrial DNA (partial cyt b and ND4 genes with adjacent tRNAs) and 1937 bp of nuclear DNA (partial Rag1, Rag2, R35 genes). Congruent among different analyses, nine strongly divergent mitochondrial clades were found, representing three major geographical groupings: (1) A northern group which includes clades I from Cameroon, II from Ghana and Ivory Coast, III from Benin, Burkina Faso and Niger, IV from the Central African Republic, and V from Kenya, (2) a northeastern group consisting of clades VI from Somalia, and VII from Saudi Arabia and Yemen, and (3) a southern group comprising clade VIII from Botswana, the Democratic Republic of Congo, Madagascar and Malawi, and clade IX from South Africa. Malagasy and continental African populations were not clearly differentiated, indicating very recent arrival or introduction of Pelomedusa in Madagascar. The southern group was in some phylogenetic analyses sister to Pelusios, rendering Pelomedusa paraphyletic with respect to that genus. However, using partitioned Bayesian analyses and sequence data of the three nuclear genes, Pelomedusa was monophyletic, suggesting that its mitochondrial paraphyly is due to either ancient introgressive hybridization or phylogenetic noise. Otherwise, nuclear sequence data recovered a lower level of divergence, but corroborated the general differentiation pattern of Pelomedusa as revealed by mtDNA. This, and the depth of the divergences between clades, indicates ancient differentiation. The divergences observed fall within, and in part exceed considerably, the differentiation typically occurring among chelonian species. To test whether Pelomedusa is best considered a single species composed of deep genealogical lineages, or a complex of up to nine distinct species, we suggest a future taxonomic revision that should (1) extend the geographical sampling of molecular data, specifically focusing on contact zones and the possible sympatric occurrence of lineages without admixture, and (2) evaluate the morphology of the various genealogical lineages using the type specimens or topotypical material of the numerous junior synonyms of P. subrufa.

• Living with the genetic signature of Miocene induced change: evidence from the phylogeographic structure of the endemic angulate tortoise Chersina angulata.

  Authors: Savel R Daniels, Margaretha D Hofmeyr, Brian T Henen, Keith A Crandall

  Molecular phylogenetics and evolution. 01/2008; 45(3):915-26.

  The phylogeographic structure of the monotypic endemic southern African angulate tortoise Chersina angulata was investigated throughout its distribution with the use of partial sequences from threeThe phylogeographic structure of the monotypic endemic southern African angulate tortoise Chersina angulata was investigated throughout its distribution with the use of partial sequences from three mtDNA loci (COI, cyt b and ND4). Phylogeographic and phylogenetic structuring obtained for the three mtDNA markers were highly congruent and suggested the presence of two genetically distinct, reciprocally monophyletic evolutionary lineages. Group one contained two subclades with haplotypes from the north-western Cape and south-western Cape, respectively, while haplotypes from the southern Cape comprised group two. The two major clades were separated by nine and eight mutational steps for COI and ND4, respectively. Of the three mtDNA gene regions examined, the ND4 partial sequence contained the most phylogenetic signal. Haplotype diversity was generally low and we recovered 34 haplotypes for the 125 animals sequenced for the ND4 subunit. Nested clade analyses performed on the variable ND4 partial sequences suggested the presence of two major refugial areas for this species. The demographic history of the taxon was characterised by range expansion and prolonged historical fragmentation. Divergence time estimates suggest that the temporal and spatial distribution of the taxon was sculpted by changes in temperature and rainfall patterns since the late Miocene. Corroborative evidence from other reptiles is also suggestive of a late Miocene divergence, indicating that this was a major epoch for cladogenesis in southern Africa. Apart from the genetic differences between the two major clades, we also note morphometric and behavioural differences, alluding to the presence of two putative taxa nested within C. angulata.

• Growing and shrinking in the smallest tortoise, Homopus signatus signatus: the importance of rain.

  Authors: Victor J T Loehr, Margaretha D Hofmeyr, Brian T Henen

  Oecologia. 09/2007; 153(2):479-88.

  Climate change models predict that the range of the world's smallest tortoise, Homopus signatus signatus, will aridify and contract in the next decades. To evaluate the effects of annual variation inClimate change models predict that the range of the world's smallest tortoise, Homopus signatus signatus, will aridify and contract in the next decades. To evaluate the effects of annual variation in rainfall on the growth of H. s. signatus, we recorded annual growth rates of wild individuals from spring 2000 to spring 2004. Juveniles grew faster than did adults, and females grew faster than did males. Growth correlated strongly with the amount of rain that fell during the time just before and within the growth periods. Growth rates were lowest in 2002-2003, when almost no rain fell between September 2002 and August 2003. In this period, more than 54% of the tortoises had negative growth rates for their straight carapace length (SCL), shell height (SH), and shell volume (SV); maximum shrinking for SCL, SH, and SV was 4, 11, and 12%, respectively. The shell of H. s. signatus has some flexibility dorso-ventrally, so a reduction in internal matter due to starvation or dehydration may have caused SH to shrink. Because the length and width of the shell seem more rigid, reversible bone resorption may have contributed to shrinkage, particularly of the shell width and plastron length. Based on growth rates for all years, female H. s. signatus need 11-12 years to mature, approximately twice as long as would be expected allometrically for such a small species. However, if aridification lowers average growth rates to the level of 2002-2003, females would require 30 years to mature. Additionally, aridification would lower average and maximum female size, resulting in smaller eggs and hatchlings. These projected life history responses to aridification heighten the threat posed by the predicted range contraction of this red-listed species.

• Parasites of domestic and wild animals in South Africa. XLVII. Ticks of tortoises and other reptiles.

  Authors: I G Horak, I J McKay, B T Henen, Heloise Heyne, Margaretha D Hofmeyr, A L De Villiers

  The Onderstepoort journal of veterinary research. 10/2006; 73(3):215-27.

  A total of 586 reptiles, belonging to 35 species and five subspecies, were examined in surveys aimed at determining the species spectrum and geographic distribution of ticks that infest them. OfA total of 586 reptiles, belonging to 35 species and five subspecies, were examined in surveys aimed at determining the species spectrum and geographic distribution of ticks that infest them. Of these reptiles 509 were tortoises, 28 monitor or other lizards, and 49 snakes. Nine ixodid tick species, of which seven belonged to the genus Amblyomma, and one argasid tick, Ornithodoros compactus were recovered. Seven of the ten tick species are parasites of reptiles. Amongst these seven species Amblyomma marmoreum was most prevalent and numerous on leopard tortoises, Geochelone pardalis; Amblyomma nuttalliwas present only on Bell's hinged tortoises, Kinixys belliana; and most Amblyomma sylvaticum were collected from angulate tortoises, Chersina angulata. Amblyomma exornatum (formerly Aponomma exornatum) was only recovered from monitor lizards, Varanus spp.; most Amblyomma latum (formerly Aponomma latum) were from snakes; and a single nymph of Amblyomma transversale (formerly Aponomma transversale) was collected from a southern African python, Python natalensis. All 30 Namaqualand speckled padloper tortoises, Homopus signatus signatus, examined were infested with O. compactus. The seasonal occurrence of A. sylvaticum and the geographic distribution of this tick and of A. marmoreum, A. nuttalli, A. exornatum, A. latum and O. compactus are illustrated.

• Circadian rhythm of locomotor activity in the four-striped field mouse, Rhabdomys pumilio: a diurnal African rodent.

  Authors: Desiree M Schumann, Howard M Cooper, Margaretha D Hofmeyr, Nigel C Bennett

  Physiology & behavior. 07/2005; 85(3):231-9.

  Although humans are diurnal in behaviour, animal models used for the study of circadian rhythms are mainly restricted to nocturnal rodents. This study focussed on the circadian behaviour of a rodentAlthough humans are diurnal in behaviour, animal models used for the study of circadian rhythms are mainly restricted to nocturnal rodents. This study focussed on the circadian behaviour of a rodent from South Africa that has a preference for daylight, the four-striped field mouse, Rhabdomys pumilio. In order to characterise the behavioural pattern of daily activity, locomotor rhythms were studied under different light regimes using an automated data recording system. Under conditions of natural daylight, which include dawn and dusk transitions, R. pumilio exhibited activity restricted to the daytime period. Activity was concentrated around morning and evening with a decrease during mid-day. A similar diurnal preference pattern of behaviour was recorded under a light-dark cycle of artificial illumination. Under conditions of constant darkness, the four-striped field mouse exhibited a free-running circadian rhythm of locomotor activity with activity concentrated during the subjective day. Free-running rhythms varied greatly between individuals, from slightly less to slightly more than 24 h (range = 23.10 to 24.80 h). Under conditions of constant light, the mice were more active during subjective day, but the free-running rhythm in all individuals was consistently longer than 24 h (range = 24.30 to 24.79 h).

• Viewing chelonian reproductive ecology through acoustic windows: cranial and inguinal perspectives.

  Authors: Brian T Henen, Margaretha D Hofmeyr

  Journal of experimental zoology. Part A, Comparative experimental biology. 06/2003; 297(1):88-104.

  Ultrasonography is a powerful new tool in reproductive physiology and ecology but quantitative evaluations of acoustic window efficacies are necessary to assess methodological accuracy. We evaluatedUltrasonography is a powerful new tool in reproductive physiology and ecology but quantitative evaluations of acoustic window efficacies are necessary to assess methodological accuracy. We evaluated the efficacy of the left inguinal, right inguinal and cranial acoustic windows for detecting ovarian follicles and oviducal eggs in three tortoise species. Incorporating cranial results improved upon inguinal efficacies for detecting follicles in the three species, and for detecting eggs in Chersina angulata, which had small inguinal apertures for its body size. The cranial window provided the best follicle results (highest numbers detected) but the left inguinal window provided the best egg results. This asymmetry was probably due to the primarily posterior position of the oviducts (eggs) and the pliable ovarian sheets allowing follicles to move cranially. The left-right asymmetry may result from intestinal asymmetry (i.e., between the cecum and descending colon) in obscuring ultrasound transmission or displacing follicles and eggs. Seasonal influences upon efficacies varied with species, partially due to species differences in a) reproductive cycles and b) size and number of follicles and eggs. We attributed other efficacy differences among species to differences in body size and shell morphology, especially the inguinal apertures. Correlation analyses revealed strong individual influences upon window efficacy, suggesting that individuals varied in the position of follicles and eggs and the degree of obfuscation by nonreproductive structures. The paucity of correlations between efficacies and body size reflects the complex interactions of body size, shell morphology, reproductive structures and reproductive cycles on efficacies.

• Deep genealogical lineages in the widely distributed African helmeted terrapin: Evidence from mitochondrial and nuclear DNA (Testudines: Pelomedusidae: Pelomedusa subrufa)

  Authors: Mario Vargas-Ramírez, Miguel Vences, William R. Branch, Savel R. Daniels, Frank Glaw, Margaretha D. Hofmeyr, Gerald Kuchling, Jérôme Maran, Theodore J. Papenfuss, Pavel Široký, David R. Vieites, Uwe Fritz

  Molecular Phylogenetics and Evolution.

  We investigated the phylogeographic differentiation of the widely distributed African helmeted terrapin Pelomedusa subrufa based on 1503 base pairs of mitochondrial DNA (partial cyt b and ND4 genesWe investigated the phylogeographic differentiation of the widely distributed African helmeted terrapin Pelomedusa subrufa based on 1503 base pairs of mitochondrial DNA (partial cyt b and ND4 genes with adjacent tRNAs) and 1937 bp of nuclear DNA (partial Rag1, Rag2, R35 genes). Congruent among different analyses, nine strongly divergent mitochondrial clades were found, representing three major geographical groupings: (1) A northern group which includes clades I from Cameroon, II from Ghana and Ivory Coast, III from Benin, Burkina Faso and Niger, IV from the Central African Republic, and V from Kenya, (2) a northeastern group consisting of clades VI from Somalia, and VII from Saudi Arabia and Yemen, and (3) a southern group comprising clade VIII from Botswana, the Democratic Republic of Congo, Madagascar and Malawi, and clade IX from South Africa. Malagasy and continental African populations were not clearly differentiated, indicating very recent arrival or introduction of Pelomedusa in Madagascar. The southern group was in some phylogenetic analyses sister to Pelusios, rendering Pelomedusa paraphyletic with respect to that genus. However, using partitioned Bayesian analyses and sequence data of the three nuclear genes, Pelomedusa was monophyletic, suggesting that its mitochondrial paraphyly is due to either ancient introgressive hybridization or phylogenetic noise. Otherwise, nuclear sequence data recovered a lower level of divergence, but corroborated the general differentiation pattern of Pelomedusa as revealed by mtDNA. This, and the depth of the divergences between clades, indicates ancient differentiation. The divergences observed fall within, and in part exceed considerably, the differentiation typically occurring among chelonian species. To test whether Pelomedusa is best considered a single species composed of deep genealogical lineages, or a complex of up to nine distinct species, we suggest a future taxonomic revision that should (1) extend the geographical sampling of molecular data, specifically focusing on contact zones and the possible sympatric occurrence of lineages without admixture, and (2) evaluate the morphology of the various genealogical lineages using the type specimens or topotypical material of the numerous junior synonyms of P. subrufa.