It has been argued that demographic and environmental factors will cause small, isolated populations to become extinct before genetic factors have a significant negative impact. Islands provide an ideal opportunity to test this hypothesis because they often support small, isolated populations that are highly vulnerable to extinction. To assess the potential negative impact of isolation and small population size, we compared levels of genetic variation and fitness in island and mainland populations of the black‐footed rock‐wallaby (Petrogale lateralis[Marsupialia: Macropodidae]). Our results indicate that the Barrow Island population of P. lateralis has unprecedented low levels of genetic variation ( He= 0.053, from 10 microsatellite loci) and suffers from inbreeding depression (reduced female fecundity, skewed sex ratio, increased levels of fluctuating asymmetry). Despite a long period of isolation (∼1600 generations) and small effective population size ( Ne∼15), demographic and environmental factors have not yet driven this population to extinction. Nevertheless, it has been affected significantly by genetic factors. It has lost most of its genetic variation and become highly inbred ( Fe= 0.91), and it exhibits reduced fitness. Because several other island populations of P. lateralis also exhibit exceptionally low levels of genetic variation, this phenomenon may be widespread. Inbreeding in these populations is at a level associated with high rates of extinction in populations of domestic and laboratory species. Genetic factors cannot then be excluded as contributing to the extinction proneness of small, isolated populations.

Models for studying prenatal drug-induced intrauterine growth retardation (IUGR) have, without exception, measured growth-related factors in the postimplantation embryo, fetus or neonate. Therefore, it is not known whether effects of drug exposure on growth and metabolism begin early in the preimplantation embryo, or whether IUGR is exclusively a postimplantation phenomenon. The present study investigates whether caffeine, a drug known to induce a dose-dependent fetal IUGR, affects embryo development before and/or after implantation or is exclusively a fetal phenomenon. Preimplantation embryo assessment (with treatment from Days 2 to 4 of pregnancy) included glucose utilization, cell number evaluation and stage of development (morula to hatched blastocyst); whereas, postimplantation embryo assessment (treatment from Days 2 to 10, 10.5 or 11 of pregnancy) included somite number evaluation and extent of neural tube closure, as seen using scanning electron microscopy. Comparing control preimplantation embryos with those exposed to 30 and 60 mg kg –1 caffeine did not reveal any effects of caffeine exposure, as assessed on Day 5 of gestation. However, postimplantation embryo development assessed on Day 12 of gestation revealed that caffeine exposure of 15 and 30 mg kg –1 significantly reduced, at both dosage levels, somite number and the extent of neural tube closure. In addition, comparisons of control and experimental groups revealed that in the high-dose caffeine group the forebrain cavity was significantly enlarged and bounded by a reduced, irregularly aligned neuroepithelium. The findings suggest that IUGR is a phenomenon first identifiable during late postimplantation embryogenesis and continues in fetal life.

Many rock-wallaby (Petrogale) species within the lateralis–penicillata complex are morphologically similar and can be distinguished only by their unique karyotypes, frustrating attempts to identify specimens in the field and in museums. As chromosome preparations are not always obtainable from specimens, additional diagnostic molecular markers are required. In this study, restriction fragment length polymorphism (RFLP) analysis of three nuclear genes was undertaken using 100 Petrogale specimens, including representatives of 12 taxa. Eleven novel diagnostic nuclear DNA markers were identified, which enabled the identification of four taxa (P. penicillata, P. purpureicollis, P. lateralis and P. inornata). No markers were found that could reliably distinguish amongst five north-east Queensland species (P. assimilis, P. sharmani, P. mareeba, P. godmani and P. coenensis) or the sampled intraspecific taxa of P. lateralis (P. l . lateralis, P. l. pearsoni, MacDonnell Ranges race). These results are consistent with previous studies in demonstrating that P. penicillata, P. purpureicollis, P. lateralis and P. inornata are genically distinct and that the north-east Queensland species and subspecies/races of P. lateralis form two groups of very closely related taxa. Future research should target more rapidly evolving DNA regions, in order to identify specific molecular markers that distinguish amongst taxa within these two groups. Meanwhile, karyotypic analysis remains the only definitive technique currently available to unambiguously identify all taxa within the lateralis–penicillata group.

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The present study was designed to investigate whether caffeine administered daily throughout the estrous cycle prior to fertilization affected the development of the subsequent preimplantation day 5 rat embryo. The viability parameters chosen for assessment were glucose utilization, cell number, and stage of embryonic development (morula to hatched blastocyst). Two independently replicated experiments were conducted. Together these experiments demonstrated that after fertilization, a proportion of affected oocytes maturing in a caffeine‐perfused ovarian environment used and oxidised glucose at a significantly higher rate and were significantly more advanced developmentally compared with their litter mates or with the control counterparts. Cell number per embryo and the number of embryos recovered (litter size) remained constant, suggesting that caffeine, at the doses used, is unlikely to affect the ovulation rate or prevent fertilization. This study is significant because it demonstrates for the first time that a drug such as caffeine, when administered prior to ovulation and genomic activation, causes a quantitative difference in growth promoting energy utilization in a proportion of susceptible embryos after a genome activation. A link between genomic imprinting and changed developmental program in the preimplantation embryos was suggested. © 1996 Wiley‐Liss, Inc.