An evaluation of parturition indices in fishers

Fishers (Martes pennanti) are important forest carnivores and furbearers that are susceptible to overharvest. Traditional indices used to monitor fisher populations typically overestimate litter size and proportion of females that give birth. We evaluated the usefulness of 2 indices of reproduction to determine proportion of female fishers that gave birth in a particular year. We used female fishers of known age and reproductive histories to compare appearance of placental scars with incidence of pregnancy and litter size. Microscopic observation of freshly removed reproductive tracts correctly identified pregnant fishers and correctly estimated litter size in 3 of 4 instances, but gross observation of placental scars failed to correctly identify pregnant fishers and litter size. Microscopic observations of reproductive tracts in carcasses that were not fresh also failed to identify pregnant animals and litter size. We evaluated mean sizes of anterior nipples to see if different reproductive classes could be distinguished. Mean anterior nipple size of captive and wild fishers correctly identified current-year breeders from nonbreeders. Former breeders were misclassified in 4 of 13 instances. Presence of placental scars accurately predicted parturition in a small sample size of fishers, but absence of placental scars did not signify that a female did not give birth. In addition to enabling the estimation of parturition rates in live animals more accurately than traditional indices, mean anterior nipple size also provided an estimate of the percentage of adult females that successfully raised young. Though using mean anterior nipple size to index reproductive success looks promising, additional data are needed to evaluate effects of using dried, stretched pelts on nipple size for management purposes.221-23

The spindle assembly checkpoint: clock or domino?

In each cell division, the newly duplicated chromosomes must be evenly distributed between the sister cells. Errors in this process during meiosis or mitosis are equally fatal: improper segregation of the chromosome 21 during human meiosis leads to Down syndrome (Conley, Aneuploidy: etiology and mechanisms, pp 35-89, 1985), whereas in somatic cells, aneuploidy has been linked to carcinogenesis, by unbalancing the ratio of oncogenes and tumor suppressors (Holland and Cleveland, Nat Rev Mol Cell Biol 10(7):478-487, 2009; Yuen et al., Curr Opin Cell Biol 17(6):576-582, 2005). Eukaryotic cells have developed a mechanism, known as the spindle assembly checkpoint, to detect erroneous attachment of chromosomes to the mitotic/meiotic spindle and delay the cell cycle to give enough time to resolve these defects. Research in the last 20 years, has demonstrated that the spindle assembly checkpoint is not only a pure checkpoint pathway, but plays a constitutive role in every cell cycle. Here, we review our current knowledge of how the spindle assembly checkpoint is integrated into the cell cycle machinery, and discuss some of the questions that have to be addressed in the future