Variable-density thinning promotes differential recruitment and development of shade tolerant conifer species after 17 years

Promoting patchy recruitment of shade tolerant tree species into the midstory is an important step in developing structural diversity in second-growth stands. Variable-density thinning (VDT) has been proposed as a strategy for accelerating structural diversity, as its combination of within-stand treatments (harvest gaps, thinning, and non-harvested skips) should create variable overstory and understory conditions. Here we report on western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedling and sapling densities in five mixed-conifer stands and Sitka spruce (Picea sitchensis (Bong.) Carr.) seedling and sapling densities in two stands in western Washington at 3,7, 10, and 16–17 years after VDT. Additionally, we report on western hemlock advance regeneration growth and survival in two stands over 14 years. Western hemlock seedling density was highest in the thinned treatment but only significantly so in Year 10. In contrast, the gaps contained significantly more western hemlock saplings in Years 7 and 10 and significantly greater growth of western hemlock advance regeneration through Year 10. Skips embedded within the VDT did not differ significantly from unharvested reserves in terms of seedling or sapling densities of either species. Sitka spruce seedling density was highest in the gap and thinned treatments, but saplings were uncommon in all treatments. Collectively, these results indicate that our variant of VDT promoted patchy, midstory recruitment of western hemlock but failed to recruit Sitka spruce saplings in either stand where it established. Consequently, more intensive variants of VDT may be required to promote midstory recruitment of species less tolerant of shade than western hemlock.

     

Effect of Leptin on In Vivo Goat Embryo Production

The aim of this study was to evaluate the effect of leptin administration during superovulation on in vivo goat embryo production. Ten mature does were superovulated with 133 mg follicle‐stimulating hormone (FSH) i.m. in six descending doses at 12‐h intervals. The goats received 4.8 μg/kg human recombinant leptin s.c. (leptin group, n = 5) or phosphate‐buffered saline (PBS) (control group, n = 5) with the first and second FSH doses. The does were mated and subjected to embryo collection by transcervical technique 6 days later. The total number of cells per embryo and the number of cells with fragmented DNA were assessed in selected blastocysts by combining Hoechst 33342 and terminal dUTP nick‐end labelling (TUNEL) staining. Plasma concentrations of oestradiol (E₂) and progesterone (P₄) were determined by electrochemiluminescence from the day of FSH treatment, on the day of superovulatory oestrus and on the day before embryo collection. Compared with the control group, the does that received leptin had a higher number of transferable embryos (p < 0.005), fewer embryos classified as degenerated (p < 0.001) and fewer TUNEL‐positive cells/blastocyst (p < 0.001). The number of transferable embryos was positively correlated with E₂ concentrations on day of oestrus (r = 0.562; p < 0.01) and P₄ concentrations on the day of embryo collection (r = 0.912; p < 0.001). We concluded that in vivo leptin administration during FSH treatment improved embryo quality and affected ovarian steroidogenesis in superovulated goats.     

Gonadotropins I and II do not stimulate thein vitro secretion of 17α,20β-dihydroxy-4-pregnen-3-one 20-sulphate by rainbow trout gonads during final sexual maturation

Thein vitro secretion of 17,20-dihydroxy-4-pregnen-3-one 20-sulphate (17,20-P-sulphate) and the free steroid 17,20-dihydroxy-4-pregnen-3-one (17,20-P), by rainbow trout (Oncorhynchus mykiss) gonads, in response to gonadotropin (GTH) I and GTH II, were studied during the final stages of sexual maturation. Substantial amounts of 17,20-P-sulphate were produced, by both mature ovaries and testes, indicating considerable 20-hydroxysteroid sulphotransferase (20-HST) activity within these tissues. In the post-ovulatory ovary the level of 17,20-P-sulphate (36.6 ng ml^–1) greatly exceeded that of 17,20-P (8.59 ng ml^–1). The amount of 17,20-P-sulphate produced in incubations of both mature ovary and testes was unaffected by either GTH I or GTH II treatment at physiological concentrations up to 100 ng ml^–1. Similarly, incubations of maturing ovary and testes, treated with GTH I or GTH II, in the presence of added 17,20-P at 100 ng ml^–1 of medium, produced levels of 17,20-P-sulphate that were similar to those of the controls. In incubations of mature ovarian follicles at the stages of germinal vesicle breakdown and preovulation, both GTHs significantly stimulated secretion of 17,20-P, although GTH II was always more potent than GTH I. GTH II significantly elevated the levels of 17,20-P in testicular incubations from mature males more than 4-fold relative to GTH I and controls, which did not differ from one another.In conclusion, 20-HST, the enzyme responsible for the sulphate conjugation of 17,20-P, was found to be active in the ovaries and testes of rainbow troutin vitro. However, the levels of this enzyme do not appear to be regulated by either GTH I or GTH II.     

Fertility and motility of sperm from Atlantic halibut (Hippoglossus hippoglossus) in relation to dose and timing of gonadotrophin-releasing hormone agonist implant

In broodstocks of Atlantic halibut, Hippoglossus hippoglossus, male and female gamete production often becomes unsynchronised towards the end of the spawning season—milt becomes very viscous and difficult to express while the females are still producing batches of good quality eggs. Gonadotrophin-releasing hormone agonist (GnRHa) has been shown to stimulate spermiation in a number of fish species. Therefore, we conducted two experiments where male halibut were implanted intramuscularly with pellets containing GnRHa. The effect of the pellets was tested at three periods: before, at the height of and at the end of spermiation. In the middle period, GnRHa was tested at two doses (5 and 25 μg/kg bodyweight). Measurements were made of milt hydration, sperm motility and fertilisation rate. Implanted males began spermiation at least 4 weeks before control males. Both doses of GnRHa increased the fluidity of the milt. This effect lasted for at least 20 days in the low dose group and for 40 days in the high dose group. When applied at the end of the season, GnRHa reversed the normal trend for the milt to become more viscous. GnRHa treatments did not affect fertilisation rates obtained with the sperm. However, towards the end of the spawning season, sperm motility was enhanced in males treated with the high dose of GnRHa (25 μg/kg) compared to controls. As described previously, plasma concentrations of the gonadal steroids, 5β-pregnane-3β,17,20β-triol 20-sulphate and 17,20-dihydroxy-4-pregnen-3-one, were significantly enhanced by GnRHa treatment. Concentrations of testosterone on the other hand decreased when spermiating males were treated with GnRHa. Our data suggest that 17,20β-dihydroxy-4-pregnen-3-one or its metabolites are involved in milt hydration, possibly through affecting ion transport.