Summary The effects of implantation of testosterone propionate (TP) in various sites in the hypothalamus on the photoperiodically induced vernal premigratory functions in the White-crowned Sparrows were investigated in order to assess the role of the hypothalamo-hypophysial-testicular axis in the induction of these responses.Implantation of glass capillary tubes containing TP in the basal infundibular nucleus (IN), in the median eminence, or in the pars distalis inhibited the photoperiodically induced increase in plasma levels of luteinizing hormone (LH), as measured by radioimmunoassay, and testicular growth. The effective implants significantly lowered the levels of LH in birds held on nonstimulatory short days. These TP implants apparently inhibited release from the pars distalis of both LH and follicle-stimulating hormone (FSH). It is concluded that the site of sensitivity in the negative feedback by testosterone is either the basal IN or the pars distalis, or both. The implants of TP that inhibited the increase in plasma LH and testicular growth completely did not prevent the birds from fattening.These investigations were supported, in part, by research grants from the National Institutes of Health (HD-6527) and National Science Foundation (BMS 79-13933) to Professor Donald S. Farner. This paper is based on a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy from the University of WashingtonThe author is grateful to Professor Donald S. Farner for his guidance throughout the course of these investigations. The assistance of Mr. Philip W. Mattocks, Jr. in performing radioimmunoassays is sincerely appreciated 相似文献
1. 1.|To determine the thermoregulatory prowess of altricial nestlings, we conducted both equilibrium and transient analyses of white-crowned sparrow nestings, a representative fringillid.
2. 2.|For an individual nestling at thermal equilibrium, feather development is the major factor reducing heat loss after 2 days of age; tissue- and boundary-layer resistances are of minor importance.
3. 3.|The nest substantially reduces wind speeds near the nestlings. Heat transfer through the nest material is of only moderate importance. Evaporation also appears to be a small proportion of total heat loss during hypothermia in natural environments.
4. 4.|Net long-wave radiant exchange is also minor, but short-wave radiation is potentially a major component of the nestling's energy budget, approaching the magnitude of maximal metabolic heat production.
5. 5.|When nestlings cool, their body mass and metabolic rate are also major importance in determining the rate of cooling, and (for metabolism) the equilibrium temperature as well.
6. 6.|The huddling together of nestlings is perhaps the single most important factor affecting heat transfer.
7. 7.|An older brood actually has more insulation than does an adult in the same microclimate.
Flight responses of the parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) to two phenological stages of spring host plants (crimson clover, Trifolium incarnatum L., hairy vetch, Vicia villosa Corbiere, and cutleaf geranium, Geranium dissectum L.) and summer host plants (cotton, Gossypium hirsutum L., sorghum, Sorghum bicolor L., and soybean Glycine max (L.) Merr.) of Heliothis virescens (F.), were measured in a dual choice situation in a wind tunnel. Preflowering clover was more attractive than preflowering geranium, followed by preflowering vetch. Clover was preferred over geranium in flowering stages as well. No within species differences were detected for the two phenological stages. Preflowering and flowering cotton and soybean were preferred over preflowering and flowering sorghum. The findings could be important in pre-determining release sites for M. croceipes in the field. 相似文献
Next‐generation sequencing is providing us with vast amounts of genetic data, yet we are currently struggling in our attempts to make sense of them. In particular, it has proven difficult to link phenotypic divergence and speciation to genome level divergence. In the current issue of Molecular Ecology, Ruegg et al. ( 2014 ) present new empirical results from two closely related bird taxa. They use a promising approach combining genome scan and candidate gene analysis. Their results suggest that we may have been looking in vain for candidate speciation genes by focusing only on genes found within genomic islands of divergence. This is because genes important in divergence and speciation may not be detected by genome scans and because features of the genomic architecture per se may have a large effect on the pattern of genome divergence. 相似文献
Forage brassicas, such as summer turnip (ST; Brassica rapa) and forage rape (FR; Brassica napus), are used as supplementary crops during summer. However, studies with lactating dairy cows fed these forages are limited and report inconsistent productive responses. The aim of this study was to determine dry matter intake, rumen fermentation and milk production responses of dairy cows in mid-lactation supplemented with and without summer (‘ST’ or ‘FR’) brassicas. Twelve multiparous lactating dairy cows were randomly allocated to three dietary treatments in a replicated 3 × 3 Latin square design balanced for residual effects over three 21-day periods. The control diet consisted of 16.2 kg DM of grass silage, 2.25 kg DM of commercial concentrate and 2.25 kg DM solvent-extracted soybean meal. For the other two dietary treatments, 25% of the amounts of silage and concentrates were replaced with FR or ST. The inclusion of forage brassicas had no effects on milk production (24.2 kg cow/day average) and composition (average milk fat and protein 43.2 and 33.6 g/l, respectively). Dry matter intake was 0.98 kg and 1.12 kg lower for cows supplemented with FR and ST, respectively, resulting in a greater feed conversion efficiency (1.35 kg milk/kg DM for ST and FR v. 1.27 kg milk/kg DM for the control diet). Intraruminal pH was lower for cows supplemented with ST compared to the control diet; however, it did not decrease below pH 5.8 at any time of the day. After feeding, the concentrations of total short-chain fatty acids (SCFAs) in rumen contents increased with ST supplementation compared to the control diet. Inclusion of FR in the diet increased the molar proportion of acetate (68.5 mmol/100 mmol) in total SCFA at the expense of propionate, measured 6 h after feeding of the forage. The molar proportion of butyric acid was greater with ST and FR supplementation (13.1 and 12 mmol/100 mmol, respectively) than in control cows. The estimated microbial nitrogen (N) flow was 89.1 g/day greater when supplementing FR compared to the control diet. Based on the haematological measures, the inclusion of summer brassica forages did not affect the health status of the animals. These results indicate that mid-lactation dairy cows fed brassicas are able to maintain production despite the reduced intake, probably due to improved rumen fermentation and therefore nutrient utilization. 相似文献