Seasonal variation in growth of Mastomys natalensis (Rodentia: Muridae) in Morogoro, Tanzania

The paper describes seasonal growth variation in a free living population of Mastomys natalensis (Smith, 1834) from Morogoro, Tanzania. Growth patterns are associated with rainfall patterns. Young animals enter a growth stop at the end of the dry season (October-November) and growth is only resumed after the first heavy rains. Reproduction is more related to size than to age. If the heavy rains come early in the rainy season, animals start reproducing in the beginning of the year. The resulting young reach their maximal size without growth stop and start reproducing immediately. Possible causes for the growth stop are discussed. Growth phenomena are thought to explain at least partially the relation between rainfall and reproduction in Mastomys .

Résumé

Cet article décrit la variation de croissance saisonnière d'une population de Mastomys natalensis (Smith, 1834) vivant en libertéà Morogoro, en Tanzanie. Les graphiques de croissance sont associés à ceux des chutes de pluie. Les jeunes animaux connaissent un arrêt de la croissance à la fin de la saison sèche (octobre-novembre) et la croissance ne reprend qu'après les premières fortes pluies. La reproduction est plus liée à la taille qu'à l'âge. Si les fortes pluies surviennent tôt en saison des pluies, les animaux commencent à se reproduire au début de l'année. Les jeunes atteignent alors leur taille maximale sans avoir connu d'arrêt de croissance et commencent à se reproduire immédiatement. On pense que les phénomènes de croissance expliquent au moins partiellement la relation entre les chutes de pluie et la reproduction chez Mastomys .     

Chromosomal evolution in the African Arvicanthine rats (Murinae, Rodentia): comparative cytogenetics of Lemniscomys (L. zebra, L. rosalia, L. striatus) and Arvicanthis dembeensis

Chromosomenevolution bei den afrikanischen arvicanthinen Ratten (Murinae, Rodentia): Vergleichende Cytogenetik von Lemniscomys (L. zebra, L. rosalia, L. striatus) und Arvicanthus dembeensis
Chromosomenbänderungsanalysen (G- und C- Bänderung) wurden an zwei Arten von Lemniscomys ( L. zebra, L. rosalia ) und einer dritten Art aus Benin ( L. striatus ) durchgeführt, um den Verlauf der Chromosomenevolution in dieser Gattung zu verfolgen. Ein Mustervergleich mit der G-Bänderung macht es möglich, die Umstrukturierung der Chromosomen der Karyotypen zu erkennen. Die beiden Arten aus Tansania ( L. rosalia 2n=54, FNa=62; und L. zebra 2n=54, FNa=58) sind durch zwei perizentrische Inversionen voneinander unterschieden. Ein Polymorphismus für das X-Chromosom findet sich in beiden Arten. L. rosalia zeigt außerdem zwei verschiedene Formen des Y-Chromosoms. Das Bänderungsmuster von L. striatus (2n=44, FNa=68) aus Benin läßt im Vergleich zu L. zebra fünf Robertsonsche Fusionen erkennen. Außerdem ist der Karyotyp von L. rosalia aus Tansania verschieden von dem der für Südafrika (2n=48, FNa=62) beschrieben wurde und sollte daher als eine eigene Art betrachtet werden. Eine vergleichende Bänderungsanalyse mit einer anderen arvicanthinen Art ( Arvicanthus dembeensis, 2n=62, FNa=62) zeigt zwischen den beiden Gattungen eine vollständige Homologie in den G-Banden und die Unterschiede beruhen ausschließlich auf Tandem-Fusionen, perizentrischen Inversionen und Robertsonschen Fusionen.     

The life cycle of Amblyomma neumanni Ribaga, 1902 (Acari: Ixodidae) in the laboratory

A colony of Amblyomma neumanni was started with engorged females collected from cattle in the province of Salta (24° 51S, 65° 33W), Argentina. The larvae and nymphs were fed on rabbits and the adults on calves. The non-parasitic stages were maintained in darkness at 27 ± 1°C and 83–86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days. The mean time (days) for the different phases of the cycle were as follows: feeding of females 8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5, pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The mean recovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. The nymphs moulting to females were heavier (8.1 ± 2.34 mg) than those moulting to males (6.0 ± 2.34 mg; p < 0.01), but their range of engorgement weight showed overlap (2.3–16.2 versus 2.2–12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. A comparison of biological parameters of A. neumanni with other American Amblyomma species from mammals is presented. © Rapid Science Ltd. 1998     

Chromosomal evidence for a polytypic structure of Arvicanthis niloticus (Rodentia, Muridae)

The analysis of R- and C-banding patterns of chromosomes of Arvicanthis niloticus from five localities of Africa (Egypt, Senegal, Burkina-Faso, Mali and Central African Republic) revealed the existence of three karyotypic forms labelled in the study as ANI-1, ANI-2 and ANI-3. These forms differ from each other by 6 to 8 chromosomal rearrangements such as reciprocal and Robertsonian translocations and pericentric inversions. Moreover, they possess different quantities of C-heterochromatin. The data indicate that these three forms are distinct species, cytogenetically isolated, and that a further taxonomic analysis of the genus Arvicanthis is needed.     

Chromosomal diversity in the genus Arvicanthis (Rodentia, Muridae) from East Africa: a taxonomic and phylogenetic evaluation

In this paper we discuss the contribution of cytogenetics to the systematics of Arvicanthis in East Africa, by reviewing all the known chromosomal cytotypes of the genus in the area. We also provide G‐ and C‐banding comparisons for two recently described karyotypes, provisionally named ANI‐5 (2n = 56, NFa = 62) and ANI‐6 (2n = 60, NFa = 72). This, therefore, brings the total number of known cytotypes in this area to 10. Five of these correspond to the species recognized by the latest rodent checklist, i.e. A. nairobae (2n = 62, NFa = 78), A. neumanni (2n = 52–53, NFa = 62), A. blicki (2n = 48, NFa = 62), A. abyssinicus (2n = 62, NFa = 64) and A. niloticus (2n = 62, NFa = 60–62). The taxonomic status of the remaining five cytotypes (A. cf. somalicus, 2n = 62 NFa = 62–63; ANI‐5, 2n = 56, NFa = 62; ANI‐6/6a 2n = 60, NFa = 72/76; ANI‐7, 2n = 56, NFa = 78; and ANI‐8, 2n = 44, NF = 72) is discussed. Finally, we reconstruct the phylogenetic relationships among all the known karyotypes on the basis of banding data available for the genus in Africa and show the occurrence of two main clades, each characterized by different types of chromosomal rearrangements. The times of the cladogenetic events, inferred by a molecular clock, indicate that karyotype evolution has accomplished almost all the dichotomic events from the end of the Miocene to the present day. The discovery of a large chromosomal differentiation between populations showing low genetic distances and intrapopulation chromosomal polymorphism suggests that the process of chromosomal differentiation in Arvicanthis is still ongoing and may possibly be responsible for speciation.     

Effects of photoperiod on the reproductive condition of Nile grass rats (Arvicanthis niloticus) from an equatorial population

We evaluated the effects of photoperiod on the reproductive condition of male and female Nile grass rats (Arvicanthis niloticus) descended from members of an equatorial population trapped 2°S of the equator. Study animals housed in 12:12 light:dark (LD) cycles were transferred either to short photoperiod (9:15) or long photoperiod (15:9) for 9 weeks (males) or 11 weeks (females), and various reproductive parameters were assessed. We observed no differences between short‐ and long‐day males with respect to plasma concentration of testosterone, testicular mass, seminal vesicle mass, or spermatogenesis. Similarly, we observed no differences between short‐ and long‐day females with respect to oestrous cycles, uterine mass, follicle size, or presence of corpora lutea. Reproductive parameters of male and female A. niloticus housed in short‐ and long photoperiods were similar to those typically observed among animals descended from the same equatorial population and housed in LD 12:12. Thus, photoperiod appears not to elicit changes in reproductive condition among A. niloticus from populations whose native habitat lies within 2° of the equator. These data contrast with the results of other studies indicating that photoperiod alters reproductive condition in A. niloticus populations living >10° from the equator.     

Three-dimensional geometric morphometrics of Arvicanthis: implications for systematics and taxonomy

Arvicanthis is an African murid, found throughout sub-Saharan Africa, Sudan and Egypt. Although in the past 10 years several studies have been carried out to assess its systematics, there is still a need for a general revision of the genus. In this study the morphometric relationships between 71 populations throughout the range were investigated. A three-dimensional geometric morphometric approach was used to assess differences in the size and shape of the skull. These were related to the different biogeographical domains characterizing the range of the genus and to molecular and karyotypic phylogenies. Results agree only in part with phylogeny, and show a close relationship with the environmental backgrounds of each species. It is therefore suggested that the adaptation of Arvicanthis to local environment has played an important role in the phenotypic evolution of the skull. This leads to problems in taxonomic definitions based on morphometrics, which should not be used without comparison with other independently derived characters such as the DNA and the karyotype.     

Herding Strategies of the Datoga Pastoralists of Tanzania: Is Household Labor a Limiting Factor

Datoga herding follows a cyclical pattern depending on the availability of grazing and water. This analysis focuses on two questions: (a) Is the herding strategy followed by individual households limited by the amount of labor available to that household? and (b) does the herding strategy followed by individual households influence the dynamics of cattle herds? The results show that the availability of labor on a household level does not influence either the herding strategies used by individual households, or the dynamics of cattle herds. This suggests that once minimum labor requirements are met, livestock productivity is insensitive to additional labor inputs.     

Remnant Pachira quinata pasture trees have greater opportunities to self and suffer reduced reproductive success due to inbreeding depression

Habitat fragmentation is extensive throughout the world, converting natural ecosystems into fragments of varying size, density and connectivity. The potential value of remnant trees in agricultural landscapes as seed sources and in connecting fragments has formed a fertile area of debate. This study contrasted the mating patterns of bat-pollinated Pachira quinata trees in a continuous forest to those in pasture through microsatellite-based paternity analysis of progeny. The breeding system was determined by analysis of pollen tube growth and seed production from controlled pollinations. Fitness of selfed and outcrossed seed was compared by germination and seedling growth. There was more inbreeding within pasture trees (outcrossing=0.828±0.015) compared with forest trees (0.926±0.005). Pasture trees had fewer sires contributing to mating events, but pollen dispersal distances were greater than those in the forest. Paternity analysis showed variation in outcrossing rates among pasture trees with high proportions of external and self pollen sources detected. A leaky self-incompatibility system was found, with self pollen having reduced germination on stigmas and slower growth rate through the style. Controlled pollinations also showed a varied ability to self among trees, which was reflected in the selfing rates among pasture trees shown by the paternity analysis (0–80% selfing). Self pollination resulted in lower seed set, germination and seedling growth compared with outcrossing. While remnant trees in agricultural landscapes are involved in broader mating patterns, they show increased but varied levels of inbreeding, which result in reduced fitness.     

Digit length may reveal unusual breeding behaviour in a seabird

The hormonal environment experienced during prenatal development may affect adult phenotype and behaviour. Digit lengths may provide an estimate of steroid levels encountered during embryonic development in humans and other vertebrates. Finger patterns in humans have been shown to reveal sexual orientation or cooperative behaviour. We explored individual breeding behaviour in a monogamous seabird, the Balearic shearwater Puffinus mauretanicus and unexpectedly detected some cooperative breeders. Furthermore, we show evidence of correlation between digit lengths and cooperative breeding in this species. Additionally, we suggest that the first digit could be a possible indicator of prenatal steroid levels. These results are the starting point for further tests of the hypothesis that first digit length is an indicator of prenatal hormone levels in other vertebrate species. Moreover, these results may offer practical use in wild populations to study the implications of the changes in prenatal environment for adult social behaviour.