Prolonged baleen hormone cycles suggest atypical reproductive endocrinology of female bowhead whales

Serial measurements of hormone concentrations along baleen plates allow for reconstructions of mysticete whale reproductive histories. We assessed gestation and calving interval in bowhead whales (Balaena mysticetus) by measuring progesterone, oestradiol, corticosterone and nitrogen stable isotope ratios (δ¹⁵N) along baleen of 10 females from the eastern Canada-west Greenland population. Three immature females (body size < 14.32 m) had uniformly low progesterone concentrations across their baleen, while seven mature females (body size ≥ 14.35 m) had repeated, sustained elevations of progesterone indicative of pregnancies. The mean duration of progesterone elevations (23.6 ± 1.50 months) was considerably longer than the approximately 14 month gestation previously estimated for this species. We consider several possible explanations for this observation, including delayed implantation or sequential ovulations prior to gestation, strategies that would allow females to maximize their fitness in variable Arctic conditions, as well as suggest modified criteria defining gestation as a shorter component of the entire progesterone peak. Calving intervals varied within and among individuals (mean = 3.7 years; range = range 2.8-5.7 years), providing population-specific reproductive estimates for growth models used in bowhead whale management and conservation.

Meiotic prophase in Prunus avium cultivar Lambert

Meiotic prophase in the sweet cherry cultivar Lambert contains a diffuse stage. It is suggested that the meiotic sequence is pachynema–schizonema–diffuse–diplonema–diakinesis.

MEIOTIC SYNCHRONY, CYTOPLASMIC CONTINUITY AND CYTOMICTIC PHENOMENA DURING MICROSPOROGENESIS OF PRUNUS AVIUM

Examination of whole anther squashes of seven cultivars of sweet cherry (Prunus avium L.) revealed meiotic synchrony within a locule, all meiocytes being at a similar stage of division.Cytoplasmic connections between neighbouring meiocytes characterized meiosis I and were most evident in diplonema. Inter-meiocyte connections were not seen in meiosis II nor between the meiocytes and the tapetum.The parallel between the presence of cytoplasmic connections during meiosis I and the degree of synchronization of the meiocytes, followed by the absence of these connections and greater asynchronization of stage during meiosis II, suggests that the two observations are related.Cytomixis, in the sense of transfer of nuclear material, was observed occasionally between inter-connected meiocytes, but was considered to be an induced artifact.