2,3,7,8,-四氯苯噁英对NIH小鼠早期妊娠和生殖激素的影响

用不同剂量的2,3,7,8 四氯苯二英(2,3,7,8 tetrachlorodibenzopdioxin,TCDD)对小鼠胚胎附植数量和生长发育情况进行剂量反应评估,分析TCDD对假孕小鼠子宫蜕膜生长状况的影响以及比较胚胎种植前后染毒效果.所有样本采集血液,测定母体血清雌二醇和孕酮的浓度变化.结果表明,50和100ng·(kg·d)-1TCDD处理的孕鼠,胚胎附植数量明显减少(P<0 05),着床后胚胎出现发育迟缓,质量减轻(P<0 05);同等剂量TCDD处理的假孕小鼠,子宫蜕膜生长受到了极显著的抑制(P<0 01);种植前后染毒效果比较发现种植前期染毒的小鼠胚胎对TCDD更为敏感.母体血清雌二醇浓度随剂量和染毒时段有不同程度的升高,而孕酮浓度则极显著下降(P<0 01).由此表明低剂量TCDD可能通过对生殖激素的干扰,强烈影响NIH小鼠妊娠早期生殖生理状态和着床后胚胎的发育.实验同时证明小鼠也可作为早期妊娠毒物研究的供试动物,用以筛选动物和人类早期妊娠的有害化合物.     

Survival of microscopic stages of a perennial kelp (<Emphasis Type="Italic">Macrocystis pyrifera</Emphasis>) from the center and the southern extreme of its range in the Northern Hemisphere after exposure to simulated El Niño stress

Many organisms survive stressful conditions through a tolerant life history stage. The life history known as the alternation of generations is typical of temperate kelps, producing diploid macroscopic stages, and both haploid and diploid microscopic stages, with the haploid stages thought to be stress tolerant. The survival of microscopic stages of the giant kelp Macrocystispyrifera during El Niño has been suggested, yet has never been tested. This mechanism could be critical for population persistence, particularly at the southern limit of the range in the Northern Hemisphere, which is greatly impacted by El Niño conditions. The purpose of this study was to determine if microscopic stages of giant kelp could survive and recover from El Niño-type conditions and whether those from a population near its southern limit were more tolerant than a population at the center of its range. Microscopic stages were exposed to a laboratory simulation of potential El Niño conditions (high temperature, with and without light and nitrate) for 8 weeks and then allowed to recover at optimal conditions (low temperature and high nitrate) for 8 weeks, while controls were left at optimal conditions the entire 16 weeks test period. Haploid developmental stages from both populations survived and recovered from stressful conditions with no population level effect, suggesting haploid stress-tolerance may be widespread. The more advanced the developmental stage, and the presence of nitrate, resulted in significantly greater recovery for haploids. Yet, none of these stages were able to go on to produce sporophytes, whereas all controls did. There was a large population-level effect for diploids, however, with only microscopic diploid stages (embryonic sporophytes) from the southern-limit population recovering from El Niño simulated stress, suggesting ecotypic adaptation for microscopic sporophytes. Diploid recovery was significantly greater with light. We propose that the diploid stage is the most likely to survive and recover after El Niño conditions, as it would avoid obligate egg and sperm encounters after the stress period. The survivorship of the microscopic diploid in a seed bank analogue may be how the isolated southern-limit populations are able to recover after mass disappearance during El Niño.     

Food webs and fishing affect parasitism of the sea urchin Eucidaris galapagensis in the Galápagos

In the Galápagos Islands, two eulimid snails parasitize the common pencil sea urchin, Eucidaris galapagensis. Past work in the Galápagos suggests that fishing reduces lobster and fish densities and, due to this relaxation of predation pressure, indirectly increases urchin densities, creating the potential for complex indirect interactions between fishing and parasitic snails. To measure indirect effects of fishing on these parasitic snails, we investigated the spatial relationships among urchins, parasitic snails, commensal crabs, and large urchin predators (hogfish and lobsters). Parasitic snails had higher densities at sites where urchins were abundant, probably due to increased resource availability. Commensal crabs that shelter under urchin spines, particularly the endemic Mithrax nodosus, preyed on the parasitic snails in aquaria, and snails were less abundant at field sites where these crabs were common. In aquaria, hogfish and lobsters readily ate crabs, but crabs were protected from predation under urchin spines, leading to a facultative mutualism between commensal crabs and urchins. In the field, fishing appeared to indirectly increase the abundance of urchins and their commensal crabs by reducing predation pressure from fish and lobsters. Fished sites had fewer snails per urchin, probably due to increased predation from commensal crabs. However, because fished sites also tended to have more urchins, there was no significant net effect of fishing on the number of snails per square meter. These results suggest that fishing can have complex indirect effects on parasites by altering food webs.     

Egg release and settlement patterns of dioecious and hermaphroditic fucoid algae during the tidal cycle

The timing of gamete release by fucoid algae, although known to be restricted to calm days is not clearly understood within a circadian time scale. The need for externally fertilizing species to avoid gamete dilution suggests that in wave-exposed areas spawning may occur during particular tidal phases. However, this may differ between mating systems, as selfing species may be less affected by gamete dilution. In this study, two different approaches were used to determine when egg release occurs during the tidal cycle in two sister species with different mating systems. First, egg settlement of Fucus vesiculosus (dioecious) and Fucus spiralis (selfing hermaphrodite) was quantified on removable substrates (egg settlement disks) every day for 2 months and settlement patterns were used to statistically estimate the radius of a circle that would encompass 99% of each patch of settled eggs (the egg dispersal radius). Also, egg release was quantified every 2 h during the tidal cycle. A significantly larger egg dispersal radius (P < 0.02) was found for F. spiralis than F. vesiculosus, and this difference was somewhat site dependent with a greater difference between species in exposed sites. The egg dispersal radius was negatively correlated with significant wave height and positively correlated with sea surface temperature for both the species (P < 0.05), with a greater effect of both the factors for F. spiralis than for F. vesiculosus. Egg release during the tidal cycle was variable between species and experiments, with F. vesiculosus releasing more eggs, later in the day, and at a lower tide, than F. spiralis, which released fewer eggs, throughout the day and at all tides. The dioecious species, F. vesiculosus, may have developed a specific adaptation for timing the egg release to periods when emersed in exposed habitats to avoid rapid dilution of gametes that require outcrossing for fertilization. On the other hand, egg release for F. spiralis, which can self-fertilize, occurred both when emersed and immersed, suggesting this species has developed less synchrony with specific environmental factors. Site dependence also suggests local wave conditions can modulate timing of release. The data are consistent with the relaxation of the selective constraints of water motion on fertilization success in a selfing hermaphrodite, relative to an obligate outcrossing species. Results support the idea that species with different mating systems evolve different sensitivities to environmental cues for gamete release with specific implications for inbreeding and successful external fertilization in the ocean.